 |
 |
My Home Page             PORTABLE QRM from PLT Site Map MDS975 Home
|
ANTENNAS ( AERIALS ) 4 - Notes and Queries THE QUEST FOR MULTI BAND OPERATION - In A Limited Space The aerial is arguably the most important part of any station. No matter what transceiver is being used it is the aerial that is the last and most vital link in the chain and needs to be efficient and effective to radiate the signal to best best effect. Some amateurs are quite content to operate on one or two bands while others might want to be able to operate on many or even all of the amateur HF bands. When I gained my licence I definitely fell into the latter camp! It seems, then, that the holy grail of many amateurs is the perfect multi-band aerial. Luckily N4UJW has designed a new limited space 160m through to 70cm marvel antenna the plans of which can be found here: http://www.hamuniverse.com/antwish.html Having experimented with various types of antenna I am of the opinion that, perhaps along with many other amateurs, for simplicity a resonant dipole is the most efficient and effective of aerial. A resonant dipole it is only a single band aerial of course, but it is extremely cheap and very simple to make - and it's a very efficient radiator. So one could make a dipole for every band of interest and simply swap aerials to work different individual bands. Unfortunately the aerial described by N4UJW does not exist and compromises, such as lack of bandwidth or poor radiation efficiency, have to be made. The principal of lowering a dipole cut for one band, removing it and hoisting another dipole cut for a different band in to place sounds pretty straightforward, but would the process become frustrating after a while. I think it could!  All Band HF Vertical Antennas (non resonant) So this is where the search for a multi-band antenna begins. It's a difficult task especially if space is limited. First considerations might lie with the commercially available options that are available. Commercially manufactured aerials are available at widely varying price points - perhaps from under £100 to many many £100's One of the first commercial multi-band antennas that many keen new amateurs come across is something like the Comet CHA250B, or the Diamond BB7V or Moonraker GP2500 (pictured right). These are broad-band antennas and look like large CB antennas with a matching network at the base. Such antennas claim to allow operation of all bands between 80 metres and 6 metres with acceptably low v.s.w.r. Sounds like the perfect multi band solution, especially as Comet and Moonraker are well known names that make excellent products. These multi band antennas have their critics though: Sure enough, they exhibit an acceptably low v.s.w.r. across the whole of HF, but low v.s.w.r. isn't everything. Severe critics do, in fact, just call these types of broadband antennas glorified dummy loads - a bit unfair possibly, but maybe they have a point! The only way a simple, single vertical radiator can be made to work on across such a wide range of frequencies is by having a broad band matching transformer at the base of the radiator. This will inevitably result in the absorption of some - or much of the transmitter's power - the power loss represented by the heating up of the coils/transformer rather than actually being radiated as a useful signal by the antenna's vertical element. Such antennas could present a loss of around 6 - 12 dB compared to a resonant antenna - how do do fancy putting all 100 of your precious watts in to the antenna and only getting 6.31 watts of effective power radiated? Maybe that's a bit simplistic, so Martin G8JNJ has many superb articles analyzing the CHA250B and similar antenna designs here: http://g8jnj.webs.com/cometcha250b.htm The article Anatomy Of The Comet CHA250B by VK5ZBD can be found here: http://www.vk5zdb.com/CHA250BXII.htm I admit that, due to limited space, I considered this type of antenna when first starting out - but in the end dismissed them due to the extreme inefficiency and power loss problems. They should not be entirely discounted however, because if this really is all that can be accommodated at one's QTH then at least such an aerial will at get you on the air - and on all bands - at least in some sort of fashion. Many amateurs use these aerials with success, so they do have a place. Have a look and decide for yourself. Other similar types of broad-band antenna: There are a number of very similar designs (i.e. longish vertical radiator, with a transformer / unun at the base) available from some, perhaps, less well known names: The G Pro-Whip antenna (see http://www.gwhip.co.uk/); The ProWhip Portable Antenna (see http://www.prowhipantennas.co.uk/ ); and the Snowdonia Radio Company (SRC) SRC-X80 and SRC-X65 antennas (see http://www.snowdonia-radio-company.co.uk). All these antennas appear to be based around an UNUN (typically 9:1) matching transformer at the base of the aerial. These aerials cost considerably less than those previously mentioned. The G Pro Whip and Pro Whip Portable offer particularly convenient portable operating opportunities as they are based on one of my favourite methods of antenna support - a long telescopic fibreglass (fishing) pole. Really neat! For the 'fishing pole' types, essentially there is a vertical radiating wire of about 7 to 10 meters long, a 10m long horizontal counterpoise wire and the 9:1 unun at the base. This makes for a simple and attractive installation proposition (but remember the penalty of power losses) - all these aerials will be easy to install for permanent, semi-permanent use and easily removable or portable operating. Considering the 10 meter vertical type, the performance on 40 meters (1/4 wave) should be quite reasonable, with reduced performance on other bands. Buy (or build) a 9:1 UNUN and Make Your Own: If you already have a 10m telescopic fibreglass fishing pole and some wire, then you could easily wind a 9:1 unun, or even buy one from suppliers such as G WHip Antenn products for a reasonable cost. So, you could make your own aerial with 10m vertical radiator working against the 10m counterpoise and fed to the ATU via the 9:1 unun at the aerial's base - just for fun, for experimentation, analysis or for permanent installation or portable work. (The telescopic pole must be fibreglass not carbon fibre) Martin G8JNJ, suggests that a slightly better way to home-brew a broadband HF aerial might be to cut a vertical aerial for about 8.5 MHz, i.e. not a resonant 1/4 wave on any amateur band, but optimised to present a moderate impedance on as many bands as possible. In which case the vertical wire would be about 8.8 metres long, working against the counterpoise, and fed to the a.t.u. via an unun - perhaps 6:1 or 9:1 - this is all open to further research and experimentation! See http://g8jnj.webs.com/currentprojects.htm G0KYA has also written a couple of interesting pieces about using a 9:1 unun and a length of wire. He found that a wire length of 19.8 metres offered a good compromise for a multi band aerial. Read G0KYA's blog here: http://g0kya.blogspot.com/search/label/antennas Interestingly 2W0SAK of Snowdonia Radio Company (SRC) recommends an antenna wire length of 7.13 metres with their 9:1 unun - or for better efficiency a wire that is 19.8 metres long which would be run out horizontally. Both the 7.13 m and 19.8 metre lengths should cover the 80m to 10m bands. See http://www.snowdonia-radio-company.co.uk for their X65 Multi antenna and 9:1 Unun. Link: A neat design for an "Untenna" KC8AON: http://www.angelfire.com/electronic2/qrp/unun.html For a jack of all trades a GWhip, an SRC antenna or a ProWhip antenna might provide some fun!  Resonant
Vertical AntennasLow SWR: Having a low v.s.w.r. across the whole of HF may seem, at first glance, to be a good thing - but my dummy load has a very low v.s.w.r. from HF to UHF, it does not make it a good antenna! As far as aerial systems are concerned, having a low v.s.w.r. across the whole of HF is probably not the best way to judge an antenna - a wide band low v.s.w.r. could indicate a fault with the aerial or feeder system - or just that lossy matching transformer that is gently heated up by the power applied from the transmitter! A low v.s.w.r. is a good thing in a resonant antenna. It will help demonstrate the antenna's point of resonance - but the v.s.w.r. will rise either side of resonance. So: The next commercial option is an antenna that is truly resonant on a number, but perhaps not all, bands. The Hustler and Butternut varieties are very well known and offer well reported good performance. Some vertical antennas use traps to achieve multi-band performance and as such are essentially one half of a trap dipole, fed against ground. A consideration is that the traps themselves, particularly if multiple traps are used, will introduce losses to the antenna system. It should also be noted as an additional consequence of using traps on a ground mounted vertical antenna, is that the highest frequency element will inevitably be positioned at the lowest position on the aerial - not a good position to be, especially for local ground wave radiation where signals will more easily be screened by local structures. Ground conductivity also needs to be good for verticals to operate efficiently. The Hustler 4-BTV, 5-BTV & 6-BTV aerials are examples of multi-band verticals that use traps; many amateurs report great success with Hustler aerials - and it is very low profile too, indeed an amateur friend of mine uses a Hustler with great success and has even modified an additional top resonator so that the aerial can be used on 160 metres.. Other manufacturers of resonant vertical antennas, using varying design methods, include GAP, Cushcraft, Diamond, HyGain, and the well known British names Moonraker and Sandpiper. http://www.moonrakerukltd.com Sandpiper Aerial Technology offer an enormous range of amateur radio antennas from HF to UHF. For HF working Sandpiper offer numerous options including simple multi band resonant antennas supported on fibreglass telescopic poles using either changeable or plug-in coils for different bands to the famous V range and shorter and more compact MV range and the Portable MV antenna on its own tripod base. The V and MV ranges use a rather innovative design, seen above right. The V and MV antennas are available in versions that cover all the HF bands - or as cheaper versions that just cover the particular bands of interest. http://www.sandpiperaerials.co.uk/ Vertical antennas will be quite short when compared to the wavelengths of some of the longer wavelength bands (particularly 80m and 160m) and so will not radiate as efficiently as a full size resonant aerial. The bandwidth will also be quite narrow. Setting up a multi band antenna to be resonant at the required portion of each band can sometimes be a little time consuming, but for the convenience it might be a price worth paying. A vertical antenna will generally have a low angle of radiation which is a good thing for long distance DX but verticals can be very noisy on RX compared to a balanced dipole. Attractive options? Horizontal Resonant Wire Aerials The great advantage of a vertical antenna is that they have a very small footprint, i.e. they can be installed in the corner of many small plots and gardens. True resonant verticals can properly cover many, if not all, the HF bands. However to be reasonably effective a vertical needs a very good ground and also must be quite tall, in the order of 6 to 9 meters in many cases (about 19 to 30 feet). This may cause objections from the XYL. Another disadvantage might be that a vertical has little near vertical incidence skywave radiation (NVIS), a consideration for the lower HF bands, so after the local ground wave coverage there will be little or no signal until after about 500 miles, not good for inter G working. (ref. G8JNJ) TRAP Dipoles: The next type of antenna to consider might, then, be a horizontal or sloping wire antenna. Perhaps the most familiar multi band wire aerial is the trap dipole. The traps, in simplest terms, divide a wire dipole into two or more resonant sections so that two or more bands can be covered. FAN (a.k.a. Parallel) Dipoles: Another design of multi band wire dipole is the fan dipole, or parallel dipole. A fan (or parallel) dipole will have, perhaps, two, three or four individual resonant dipoles with the arms arranged in a fan shape. As far as commercial options go then there are quite a number: Tony Nailer of Spectrum Communications produces a great deal of fine equipment and accessories including some extremely well designed and very well made trapped dipole aerials based on the very effective W3DZZ design. In particular the Full Size G4CFY resonant on 80m and 40m and also allowing operation on 20m, 15m and 10m, also the Half Size G4CFY resonant on 40m and 20m and additionally allowing operation on 15m and 10m. Visit http://www.spectrumcomms.co.uk/G2DYM.htm for more information. Moonraker supply a whole range of wire trap dipoles covering from 2 to 5 HF bands (MTD1; MTD2; MTD3; MTD4; MTD5; MTD6). Diamond also produce trapped wire antennas, the W-721, W-728 and W735. Comet and Diamond each produce similar interesting 5 band wire dipoles that utilize both traps and a fan arrangement - the Diamond W8010 and the Comet CWA-1000. If space really is limited then look out for KZJ Communications (dongo1950 on ebay) - he produces 'Limited Space Inductive Dipoles'. These are inductively loaded and shortened dipoles so they will have reduced efficiency, of course, but are very nicely made, so might be very useful in a tight spot. Alpha Delta Communications produce a couple of substantial parallel dipole models: http://www.alphadeltacom.com To obtain good efficiency and achieve a low angle of radiation, desirable for longer distance DX, a horizontal dipole needs to be installed at a good height - over 20 feet would be desirable and it is quite common to install horizontal dipoles at around 30 to 40 feet above ground level. This might be a problem at some QTH's, it certainly is at mine! Allan Copland, GM1SXX comments: "The dipole will operate well on the band it has been sized for , if placed at a suitable height, but will also operate as a’ three-half-wave’ aerial at three times the frequency and so on, so it’s not strictly a single band aerial. An 80M dipole (132 feet typical) will work nicely on 30 metres (three halfwaves) but not on 40m (two halfwaves)… because on 40M the feed-point is at a voltage node and not at a current node, for easy feeding. Most aerials are current fed. The radiation pattern changes when a dipole is not used on its design frequency. The pattern will break up into multiple ‘petals’. This can be either a disadvantage or an advantage depending on what you expect from it. Since most of us use co-ax, an UN-BAL should really be used to connect the unbalanced feeder to the balanced aerial, but how many people actually bother? Not many I suspect. It’s possible of course to use a balanced feed-line system instead with a dipole and just have a delta match (no centre insulator… none needed). There are many choices and permutations, but in general, dipoles are centre fed at a point of current maximum (and minimum voltage). A normal dipole is current fed but of course can be voltage fed instead. This is what’s done in the EFHWA or Fuchs aerial where a resonant half wave wire is fed at one end (max voltage / min current) from an L/C tank, against a very short counterpoise wire. The End Fed Half Wave Antenna (EFHWA) is fed at a voltage node via a parallel resonant circuit against a ‘short counterpoise’, it is a favourite of backpackers and outdoor types. It can be considered as a half wave dipole that’s end-fed at a voltage node rather than the current node, as is more usual. This is a very handy arrangement for portable QRP work. EFHWA Link: http://www.aa5tb.com/efha.html I suspect that nothing new or radical has happened in the field of radio aerials in a VERY long time, like at least many tens of decades. Most of the new wonder aerials are really a con. Choke off the feed-line and then see how good they really are. Prime among the baddies is the CFA. It doesn’t really work, at least if you place a choke in the feed-line. With any real aerial, there should be minimal radiation from the feed system… so a choke should really make no difference at all, but for the CFA it does! The CFA is not alone, there are others. The popular G5RV is another design with a radiating feed, deliberately so, but of course G5RV planned it that way. He wasn’t cheating… merely being a bit devious, to make it multi-band Lots of stuff to pass on to my fellow radio club members, most of whom are of the ‘if it’s not expensive, it can’t be any good’ school of thought when it comes to aerials. Nothing of course could be further from the truth! Aerials are one area where it makes a lot of sense to build our own." Website of GM1SXX - www.observations.biz Thanks for your email Allan. It's a good idea to point out that an antenna could be pressed into use on odd multiples of its resonant frequency, hence a 3.6MHz antenna for 80m could be useful near the 30 metre, 10.1MHz, band - near to the third harmonic of 3.5 MHz although, as you observe, the radiation pattern may be quite distorted from the traditionally expected dipole pattern and be more petal shaped. The same goes for a 7.1 MHz antenna for 40m being usable on its third harmonic of 21.3 MHz for the 15m band - a 40m dipole being three half waves an the 21 MHz band. I have not experimented with a full size 80m dipole, but I would guess that it might be useful at 5 times 3.6Mhz in the 18 MHz / 17m band? The point made about feeding a familiar dipole at the current node rather than the voltage node is obviously very important and, I imagine, sometimes overlooked. W3EDP Antenna  The Tuning capacitor in the AMU can be a 365 - 500pF broadcast type or a miniature version is OK for QRP use. Counterpoise lengths: 3.5 & 7.0Mhz - 17ft ; 14Mhz - 6.5ft ; 28Mhz - none Tuning Unit: Values for coils in the unit, based on a 2 inch former and 16 swg wire: 3.5Mhz 21 turns ; 7.0Mhz 7 turns ; 14.0Mhz - 5 turns. K3HRN Notes: "Some folks have told me the modifications below make the antenna something other than a W3EDP. I can tell you that it works very well with 5 watts. Create a "bundle" of counterpoise wires, 1/4 wave length for each band you will use. Attach the bundle to the tuner in place of the counterpoise pictured above. Be cautious, 1/4 wave length elements can have high RF voltages present, even at QRP power levels. I've been able to work 160-10, including WARC bands with this type of antenna". Sloper Aerials Alternatively a dipole can be installed as a sloper; one end fixed to a high point on the house or building, or a tall post maybe 8 to 10 metres high, with the other end attached to a lower point such as a post maybe 3 or 4 metres high. This will give the aerial some directivity.  Inverted V Aerials Another option maybe to support the dipole at its centre on a tall pole, or roof apex, with each end sloping downwards to lower fixing points. This will give the aerial an upside down V shape. As with a sloper, the Inverted V arrangement will give the aerial some directivity - a different radiation pattern compared to a straight horizontal dipole.  Spectrum
Communications
G4CFY
Trapped
Dipole
in
"Inverted
V"
configuration
Vee
Configurationhttp://www.spectrumcomms.co.uk End
Fed
Zepp
"Zepp"
The End Fed Zepp consists of a 1/2 wavelength horizontal radiator wire connected to one conductor of a length of parallel open wire feeder, 300 ohm or 450 ohm twin feeder. The feeder is often quoted as being 1/4 wavelength long.  Basic design of an end fed Zepp
G Whip Antenna Products manufacture and
supply a version of the Zepp antenna. Geoff G4ICD explains: "The end
fed Zepp shown below has no counterpoise, just a tuned circuit in the
feedpoint plus a half wave radiator. This is a most interesting antenna
and can be used on other bands with the use of an Antenna Matching
Unit."
 A high quality End Fed
Zepp style antenna: This variation uses a
tuned circuit rather than a tuned twin feeder. Supplied by G Whip Antenna Products of the UK www.gwhip.co.uk Off Centre Fed Dipole (OCFD) - Windom Antenna The "Windom Antenna" was described by Loren
G. Windom W8GZ. It could be an ideal wire aerial for use in restricted
spaces for multi-band operation. It may also be an good candidate for portable work.
It is a wire antenna, similar to a dipole, but unlike a dipole or doublet which is fed at the exact centre, a Windom or Off Centre Fed Dipole, as the name suggests, has the feed point off center. Current versions of the Windom have a balun at the feed point which is fed with coaxial cable. As with all aerials the aerial should be as high as possible. With the feed point at between 20 and 40 feet above ground the typical claimed impedance will be somewhere in the region of 200 Ohms so a 4:1 balun will typically be required. At greater heights, and depending upon the exact position of the feed point, the impedance may be higher and a 5:1 or 6:1 balun might be a better choice although balun losses will be greater. The point at which a Windom is fed in the original design, which used an open wire to feed the aerial, was 15 percent off-centre. The current designs, which are fed with coaxial cable, are typically fed about 33 percent off centre, so one leg is 67 percent of the total length and the other leg is 33 percent of the overall length of the aerial. The bands that are covered depends upon the overall length of the aerial: 11 metres long (approx) should cover 20m, 15m and 10m and the WARC bands with a tuner. 21 metres long (approx) should cover 40m, 20m, 15m and the 10m bands and WARC with a tuner. 41 metres long (approx) should cover 80m, 40m, 20m, 15m and 10m and WARC with a tuner. 80 metres long (approx) should cover 160m, 80m, 40m, 20m, 15m and 10m and WARC with a tuner. Cut the aerial for the lowest band to be used. In imperial measurements using a familiar formula: The longer leg will be 468 divided by the frequency and multiplied by .67 = length in feet The shorter leg will be 468 divided by the frequency and multiplied by .33 = length in feet According to which sources one refers, the formula can also be found as: 62.2% for one side and 37.8% for the other leg. So: The longer leg will be 468 divided by the frequency and multiplied by .622 = length in feet The shorter leg will be 468 divided by the frequency and multiplied by .378 = length in feet [Source: New Caroline Windom - http://www.hamuniverse.com/k4iwlnewwindom.html ] or even: 69 / 37 by Buxcomm who say that "One third plus two thirds will not work. Use the formula below, as is: Do not be concerned with the off-set of the feed point, as this formula takes into consideration, the correct off-set for feeding the (BUXCOMM) Windom.for the other leg." So: The longer leg will be 468 divided by the frequency and multiplied by .69 = length in feet The shorter leg will be 468 divided by the frequency and multiplied by .37 = length in feet [Source Buxcom: http://www.buxcomm.com/windom_files/WINDOM.htm ] Given the fairly simple formula it should be quite easy to make an OCFD Windom - however a Windom can be purchased at very reasonable cost commercially, for example from M0CVO at http://m0cvoantennas.webs.com and G-Whip Antennas of the UK. Geoff G4ICD / GJ4ICD highlighted the G-Whip products website to me. There are many useful antenna products produced by G Whip. Of particular interest are the comments concerning the quality and construction of balun products. This feature on the G-Whip site can be seen here: http://www.btinternet.com/~geoffrey.brown3/gwhip/baluns.htm Here is a photograph of the G-Whip OCFD antenna product:  Here is a graphic of an Off Centre Fed Dipole typical of those available in the USA:   Commercial Suppliers: G-WHIP Antennas (UK) : http://www.gwhip.co.uk/ M0CVO OCFD Antennas : http://m0cvoantennas.webs.com Bux Comm Windom Antennas : http://www.buxcomm.com Buck Master OFC Dipole Antennas : http://hamcall.net/ Alpha Delta : http://www.alphadeltacom.com Carolina Windom : http://www.radioworks.com/ccwcover.html Inverted L
A typical Inverted L antenna will be trapped for 40m/80m using a 7.1 MHz trap. It is essentially one half of a W3DZZ dipole so can be accommodated very much more easily into a small plot or garden - especially as part of the antenna is running vertically up a wooden or fibreglass (non conductive) pole. This should allow it to be fitted into quite a small garden such as mine. The Inverted L is also a very effective aerial because it has the benefit of both vertical and horizontal radiation. While Inverted L's might make good TX aerials, like ground mounted vertical aerials they can be quite noisy on RX. Spectrum Communications can supply the complete aerial as shown below:  Spectrum
Communications Inverted L -
benefits from both vertical and horizontal radiation
http://www.spectrumcomms.co.uk Comet and Diamond produce Vee antennas that can be mounted on the side of a building at roof height, or on a pole, telescopic pole or other suitable support. These are trapped dipoles in an upright V configuration, not made of wire but of aluminium tubing for solid construction. Typically covering 40m, 20m, 15m and 10m. The Comet model is H-422V. The Diamond Model is HFV5 which also covers 6m.  Comet H-422V http://www.cometantenna.com
 Diamond HFV5 Antenna http://www.diamond-ant.co.jp/english/amateur/antenna/ante_2base/ante_base7.html Omni Directional Multi-Band Horizontally Polarized Delta Loop If all that can be erected is a single pole, masts or telescopic pole, here is an option that will provide a horizontally polarized signal on 20 / 17 / 15 / 12 / 10 metres - the Sandpiper Aerial Technology GM3 (designed by GM3VLB). A similar idea, providing omni-directional horizontally polarized signals, is the G3TPW Cobwebb Antenna from Steve Webb.  G3TPW
Cobwebb Antenna from Steve Webb - photo by G3TXQ
Other similar antennas are available
from Force12 Antennas in the form
of, amongst others, the Sigma 5 and Sigma GT5. The Sigma design
utilizes T-bars at each end of the vertical dipole for loading
technique and off-center loading coils. http://www.force12inc.com
supplied in the UK by Vine Antennas http://www.vinecom.co.uk/sigma5.html Transworld Antennas
also have produce antennaa using a similar concept - the TW2010
Adventurer and Backpacker http://transworldantennas.comhttp://www.g3tpw.co.uk http://www.karinya.net/g3txq End Loaded Dipole An end loaded dipole will produce an antenna that is H shaped. There are several commercial designs available produced in designs that cover a single band and others that cover multiple bands. The version shown below is only 3 metres tall so will be suitable for very unobtrusive, low profile use. It is the ProAntennas Multi-band I-PRO: 20m 17m 15m 12m 11m & 10m which uses a capacity hat with some loading at the centre. http://www.proantennas.co.uk/ See more from K9AY further down this page here Semi-Permanent Antenna Installations If it impossible to install a permanent aerial, then another option is to use an antenna designed for portable or mobile work deploying it only as and when necessary in the back yard or garden - perhaps supported with a portable tripod and/or guy ropes. From the ideas above it should be possible to rig up a semi-permanent or removable antenna for low visual impact. There are also very many portable antennas produced commercially that might be very useful to utilize on a semi-permanent basis. Commercially bought antennas can be very expensive indeed, especially when compared to 'home brew' aerials, but examples that immediately spring to mind for consideration include: The DMV-Pro, I-Pro, G Whip or G Whip Backpacker, the TW2010 from Transworld Antennas, the Sigma5 from Force 12 and aerials from SuperAntennas. Sandpiper Aerial Technology offer a very good choice of aertials such as the MV and MV-Portable, Buttie or Walkabout mk11 at very attractive prices. http://www.sandpiperaerials.co.uk There are very many other compact and portable antenna systems that are widely available. Check out all the amateur radio dealers for more ideas.  The DMV-Pro Antenna from ProAntennas (shown
above) could
be used in a back garden whenever required as could the company's I-Pro antenna. The
DMV-Pro uses two fibreglass arms that allow the wire aerial to be
supported in a number of different configurations such a "V" shaped,
"L" shaped, "M" shaped and Delta. The aerial elements are fed to a
balun using low loss twin feeder, the balun is then connected to an
auto ATU, such as the LDG Z-11 Pro, which is connected to the
transceiver using coaxial cable. A vertatile idea that could also be
implemented on a DIY basis with a little experimentation! http://www.proantennas.co.uk
Geoff G4ICD / GJ4ICD mentions the original design, the JJ1VKL published in CQ ham radio Sep' 2000 in Japan. "This one goes back to 2000 and is now copied by several antenna manufacturers in the UK" It is an HF multi-band Delta loop antenna for 3.5-50MHz http://www.geocities.jp/yoshiki_ja/deltae.htm   An Original Delta Loop design by JJ1VKL Read more here: http://www.geocities.jp/yoshiki_ja/deltae.htm So, there we have it, a collection of
commercial antenna ideas that will allow multi-band operation, many of
which could also be used in a location that offers limited space.
Perhaps the foregoing only scratches the surface, but hopefully will
provide a good starting point and fuel the mind in a quest for a good
multi-band HF aerial. Do check out the manufacturer and supplier
websites given on this page for lots more options and details.
Moving on: It has been said that no radio amateur should ever buy an aerial - especially a wire aerial! Joe Tyburczy WB1GFH also comments about suitable antenna installing weather on his web pages: "When you put up your antenna is also crucial. I must mention here the importance of what many early hams called "antenna weather". That is, snow, sleet, freezing rain, or combination of all the above. It has been proven time and time again that any antenna installed in conditions better than abysmal will not function worth a darn. Or, put another way, it takes bad weather to put up a decent antenna. Dark and cold New England winter days are ideal for this activity. Any antenna erected on such a day will inevitably produce miracles." Ref: Joe Tyburczy WB1GFH Most of what is available commercially could be 'home-brewed' if one has the time and a few suitable mechanical skills, so here are a few clues: HOME BREW AERIALS End Fed Zepp A popular antenna often used to save space is the End Fed Zepp. The End Fed Zepp gets its name from the fact that it was used as an end fed wire trailing out from the rear of Zeppelin airships. It consists of a 1/2 wavelength horizontal radiator wire connected to one conductor of a length of parallel 300 ohm or 450 ohm twin feeder, often quoted as being 1/4 wavelength long. K4EFW notes: "...A half-wave resonant antenna can be fed from its end. When fed this way, it is also known as an end-fed zepp. An end-fed zepp will work on its fundamental frequency and on odd and even harmonic frequencies. The end of a half-wave antenna has very high impedance, and an antenna fed this way is said to be voltage fed. Feeding a half-wave resonant dipole in the center means it is current fed. The normal way of feeding the end-fed antenna is with ladder-line. One side of the ladder-line is connected to one end of the antenna and the other side of the ladder-line is connected to nothing. To secure the unconnected side of the ladder-line, it is connected to a short wire running between two insulators. Since the antenna is connected at its high impedance point, no current flows into an antenna, but there will be a large current in the center of this antenna. No current flows from the open side of the feed-line because it is at a zero current point. The end-fed zepp can be matched by cutting the ladder-line to a quarter wavelength with the bottom end of the ladder-line shorted. A certain distance above the short is a 50-ohm feet-point and it can be fed directly with coax. You will have to find the 50-ohm point by trial and error. This method of feed makes it a single band antenna". Quoted from K4EFW. Here is a commercial product made by G-Whip Antennas of the UK offering their version of a Zepp antenna design: http://www.btinternet.com/~geoffrey.brown3/gwhip/zepp.htm Martin G8JNJ highlights a very interesting antenna designed by Mike G7FEK here:- The G7FEK antenna goes several stages further than the simple single band End Fed Zepp. G7FEK has produced a design for Multi-Band operation claimed to offer much improved performance over a half sized G5RV or 'Windom' antenna while additionally providing access to the 80 Metre Band.  G7FEK Limited Space
Multi-Band Antenna
 Adding 14MHz to the G7FEK Limited Space Multi-Band Antenna The G7FEK design will allow operation on
80m / 40m / 30m / 17m / 15m / 12m with the possibility to add the 20m
band.
G7FEK
Plans: Download the plans for the G7FEK antenna from G7FEK's
website here or
from this website here
TheG5RV /
Doublets / Dipoles - Thoughts from Martin G8JNJ on
multiband wire antennas:
 Multiband Wire Antenna by Martin
G8JNJ
 My favourite way of experimenting with aerials is using a 10 metre long fibreglass telescopic fishing pole as the support. These fibreglass poles are lightweight and easy to carry, put up and take down, ideal for supporting lightweight v.h.f. and u.h.f. yagis, wire dipoles and doublets and also for supporting vertical wire aerials. The telescopic pole must be made from fibreglass, not carbon fibre which is electrically conductive. One great design is by Dave G4AON who writes on his web page: "There seems to be a myth among many newly licensed radio amateurs that an antenna works better if it costs a lot of money..... The antenna shown here costs around one tenth the price of a commercial vertical, yet it will perform as well as (and in many cases better than) a trapped vertical antenna. This antenna is based on a 10 Metre long fibreglass fishing pole.....the poles will collapse inside the sections unless each joint is secured with PVC tape, for more permanent installations glue could be used. ...The wire lengths are calculated from the formula L = 234/F, where F is the frequency in MHz and L is the wire length in feet. These lengths work out to around 33' 3", 23' 2" and 16' 7" for the 7, 10 and 14 MHz bands. The lengths for 7 and 10 MHz were more or less correct, however probably due to interaction between the wires the 14 MHz wire needed lengthening by around 4" for minimum SWR. Wire size is not critical, but it is probably better to avoid the thinnest "hookup" wire. Note, ground conductivity/loss and elevated/buried radials make a significant impact on both the performance and tuning of a ground mounted vertical. In the case of buried radials the vertical may resonate significantly lower in frequency than expected." The antenna shown on the right is made for triple band operation on 7 MHz, 10 MHz and 14 MHz by the use of parallel wires, but an aerial based on a fibreglass pole could be single, dual, triple or even - at a push - quadruple band. The more bands included the more difficult it will be able to trim to tune for resonance (as with a fan dipole) so to keep interaction to a minimum the wires should be quite well spaced. Like all quarter wave verticals aerials a good ground plane will be needed. See G4AON's excellent full article here: http://www.astromag.co.uk/vertical/ Dipole Antennas The dipole antenna is possibly the simplest and chepest antenna to make. It it cut for single band operation where it should make a very efficient radiator. The simple wire dipole should be quite discrete, though not entirely invisible, ut should not raise too many objections from the XYL or neighbours. For some dipole ideas see this page: http://www.qsl.net/ta1dx/amator/practical_dipole_antenna.htm How to make a basic dipole by Marshall N1FN : http://www.morsex.com/dipole/index.htm Also see this detailed and useful page: http://www.dxzone.com/cgi-bin/dir/jump2.cgi?ID=7499 Calculator: http://www.sean1226.pwp.blueyonder.co.uk/design_your_own_antennas%201.htm Link Dipoles Link Dipoles (a.k.a Jumpered Dipoles) facilitate multi band operation by simply connecting the jumpers (one on each side of the aerial) to achieve the desired resonant band. Perhaps a bit bothersome for frequent band changes, but a very simple and effective aerial.  Link Dipole - ref ARRL Doublet Aerials Check out the The All Band Doublet and the NorCal Doublet for very simple, effective and versatile antennas for multi band operation: The ALL BAND Doublet  All Band Doublet -
http://www.hamuniverse.com
The all band doublet
antenna is nothing more than a 1/2 wave dipole cut for your lowest
operating frequency and fed with twin lead, ladder line, open wire, etc
to a tuner that will accept a balanced line connection. IT IS NOT FED
WITH COAX!It can be designed for use from 160 through to 10 meters very easily using the standard 1/2 wave dipole formula: 468/freq MHz = total length (ft)
The exact length is not critical! If there is insufficient room for a lower frequency version (160m or 80m), then the double can be designed to the shorter wavelength of the 40 metre band and used up to the 10 metre band. (Do not attempt to operate on a lower frequency than 7 MHz in that case since this could damage the a.t.u.) It may be possible to connect the ends together and tune it against earth - if you have a good enough earth - and use lower frequency bands. For best results a doublet should be mounted as high as possible (as with many aerials) and can be erected as a flat top or inverted V. For more see the dedicated page: The ALL Band HF Doublet on Ham Universe: http://www.hamuniverse.com/hfdoublet.html Introducing The All Band Doublet by the late L.B. Cebik W4RNL: http://www.cebik.com/content/edu/edu6.html N.B. Create a free account at http://www.cebik.com The Norcal Doublet Antenna: http://www.norcalqrp.org/norcaldoublet.htm Joe Tyburczy, W1GFH provides some sensible insight and advice, he writes: "I am a big fan of "balanced line" (twin lead, open wire line, etc.) vs. coax. By using balanced line and a tuner you can have one, single-element antenna that works well on all bands. You can't do that as easily with coax. The basic "W1GFH $4 SPECIAL" shown below is a variation on the type of versatile skyhook I've been using for years......Now at this point, some of you may be looking at the diagram and muttering, "Jeez Joe, that's just a dipole fed with twin lead and used with a tuner". Well of course it is. Virtually all antennas are "di-poles" (i.e. "two sides") in some form or another. This one just happens to be made from low-cost materials......I won't go into the theory here, but trust me: balanced feed line, properly used, does not "leak" RF and is less lossy than coax. I've tried the commercial 450-ohm ladder line, but prefer 300-ohm TV twin lead, and the cheaper the better. Radio Shack TV twin lead is ideal. Home Depot has some good stuff, too. Forget all the obsessive junk about standing waves, impedance and velocity factor. What you really need to concentrate on is getting an interesting set of antenna insulators." Read Joe's excellent article in its entirety here: http://www.qsl.net/wb1gfh/antenna.html Coaxial Trapped Dipoles A trapped dipole for 40m and 80m offers the advantage of being somewhat shorter than a full size single band 80m resonant dipole plus it offers 40m as a resonant band plus the possibility of working on 20m, 15m and 10m. There are several designs available on the web for this type of aerial so Google W3DZZ. One of the most comprehensive sets of instructions is by Len Paget G0ONX. Fine out more here: http://www.users.icscotland.net/~len.paget/GM0ONX%20trap%20dipole.pdf This would be my choice if I had the space, though since a dipole is a balanced aerial it would make more sense to use balanced twin feeder (as in the Spectrum Communications implementation of this design) rather than coaxial cable which is an un-balanced and more lossy feeder.  The W3DZZ Trapped Dipole - a balanced aerial, so use balanced twin feeder! Here is a variation on the W3DZZ antenna by the Maidstone Amateur Radio Society that adds a dedicated 10 meter (28MHz) resonant element as a 'fan'.  W3DZZ Dipole Aerial
design by the Maidstone Amateur Radio Society
http://www.btinternet.com/~shaun.scannell/club/w3dzz.htm Sloper Configuration of a wire dipole Inverted V Aerials Using an Inverted V can help fit a dipole into a slightly restricted space. The Inverted V arrangement can be used for single band resonant dipoles, trapped dipoles and fan dipoles.  At A, details for an inverted V fed with
open-wire line for multiband HF operation. A Transmatch is shown at B,
suitable for matching the antenna to the transmitter over a wide
frequency range. The included angle between the two legs should be
greater than 90° for best performance. [ref: QSL.net]
Fan Dipoles A fan dipole is a very handy way of using a dipole that will be resonant on several bands - typically three or four. The fan dipole (a.k.a. Parallel Dipole) See M0WYM's page for a QRP Fan Dipole design: http://www.radiowymsey.org/FanDipole/fandiploe.htm See this page for construction details: http://www.hamuniverse.com/multidipole.html  Fan Dipole shown on Ham Universe ki4nrh built a really neat fan dipole shown in the photograph below: Windom - Off Centre Fed Dipole See some designs at these links: http://users.erols.com/k3mt/windom/windom.htm http://www.dxzone.com/cgi-bin/dir/jump2.cgi?ID=7478 http://www.radioelectronicschool.net/files/downloads/ocfdipole.pdf http://www.hamuniverse.com/k4iwlnewwindom.html http://www.g4nsj.co.uk/windom.shtml http://www.m0ukd.com/Carolina_Windom/index.php  M0UKD -
4:1 balun. It is 17 bifilar turns on a half inch ferrite rod. 50Ω -
200Ω, 1-30MHz
http://www.m0ukd.com/Carolina_Windom/index.php  M0UKD Line isolator - 10 turns RG8
on a half inch ferrite rod
http://www.m0ukd.com/Carolina_Windom/index.php  Windom design for 40m 20m 15m and 10m by K4IWL http://www.hamuniverse.com/k4iwlnewwindom.html More information at BucksCom: http://www.packetradio.com/windom.htm or http://www.buckscom.com/pdfzips/windom.pdf Inverted L Aerials The Inverted L for 40m/80m is shown below. It is essentially one half of a W3DZZ dipole fed against ground using one 7.1 MHz trap. The 40m / 80m Inverted L has the advantage of providing both horizontal and vertical components. It's a very compact antenna and is simple to construct. It is most efficient, of course, on 80 metres and 40 metres, but can also be used, with an a.t.u., on 20m, 15m and 10m. While Inverted L's might make good TX aerials, like ground mounted vertical aerials they can be quite noisy on RX. Find out how to make one here: http://www.users.icscotland.net/~len.paget/5%20band%20Inverted%20L.pdf  The basic layout of the Inverted L Antenna by Len Paget GM0ONX (Practical Wireless) Adding 160m / Top Band to an Inverted L The 160 metre Top Band can be added to this aerial by connecting a 3.5 MHz trap at the end of the 80 metre wire (where to monofilament joins the 6.55m section of wire below) with another length of wire on the other side, increasing the overall length of the antenna. Find out how to do it here: http://www.users.icscotland.net/~len.paget/Inverted%20L%20adding%20top%20band.pdf  Adding Top Band to
an Inverted L by Len Paget GM0ONX (Practical Wireless magazine)
160m Top Band 'Inverted L' Wire Antenna At the time of writing I am using a 40m/80m Inverted L aerial and in an attempt to get on Top Band I have also been experimenting with a shortened 160m antenna in an inverted L configuration that uses a wire about 19 metres long - about half the size of a full size inverted L for 160 Metres. A Top Band aerial of this type also needs a very good ground / counterpoise and can suffer the disadvantage, like ground mounted vertical aerials, of being rather noisy on RX . The drawing below shows the general idea. Read more here >  General layout of
Top Band Aerial with fibreglass pole retracted to a height of 2 metres
Wire lengths are approximate: Inductor 5cm dia with approx 40 turns of enamelled copper wire Linear Loading Linear loading a dipole can reduce the length to help fit a ling dipole into a shorted space by essentially folding back some of the dipole elements. Here is a design by K4VX for a 7MHz Linear Loaded Dipole: http://www.arrl.org/files/file/Technology/tis/info/pdf/0207040.pdf End Loading End loading can also help reduce the size of antennas, particularly useful for dipoles used on the 80m and 160m bands. K9AY Notes that: "I have come to the conclusion from my experiments, readings and observations, that a capacity hatted vertical dipole, a few feet over ground, is less compromised than a 1/4 w/l vertical of the same height fed against a less than perfect ground. Let's face it, most amateur's ground systems are mediocre at best. Also, the dipole is easier and cheaper to rig, and is two dimensional..Very important in my situation, as I cannot run out radials on my neighbours property. Or, to quote W4RNL.."Since only a handful of hams can ever have 160-meter antennas high enough to yield a low angle DX signal, more practical are vertical arrays such as yours. Vertical dipoles with hats (or Tees) save a plethora of wire needed by monopoles." http://www.dxzone.com/cgi-bin/dir/jump2.cgi?ID=7466  Information by K9AY  Information by K9AY
 Interesting concepts from K9AY
Delta
Loop: Using fibreglass fishing poles (Sota
Poles) again.
Two 7 metre long poles can be erected in an inverted V shape and used
to support a 20 metre delta loop which will be useable on 20m to 10m
and also adaptable for use on the 40 metre band.
The two aerial wires used are connected directly to a 4:1 balun which is, in turn, connected to an ATU such as the Z-11 Pro or Z-100 via coaxial cable. See this page which shows the W6ZO delta loop to get for the general idea of what will be achieved. The finished aerial will be very much like the commercially available DMV-Pro.  Zepp Here is a wonderful olde worlde style cartoon from WB1GFH that certainly inspires antenna experimentation with antenna designs:  Superb. I love it!
See more inpiration from Joe Tyburczy, W1GFH, here: http://www.hamuniverse.com/fourdollarspecialw1gfh.html STEALTH / COVERT / HIDDEN or DISGUISED ANTENNAS: Ideas from G4ILO - Stealth Antennas: http://www.g4ilo.com/stealth.html CONCLUSIONS? Arguably the most effective, simplest and, indeed, cheapest way to attain multi-band operation is by using a full size resonant dipole for each band of interest - perhaps having a couple suspended at any one time and swapping aerials when other bands are needed. As mentioned in the introduction this is a little inconvenient which is why the holy grail of so many amateurs is one antenna that that will do everything - perfectly. As we have seen such an aerial does not exist, and never will due to those pesky laws of physics. Compromises will always have to be made; compromises of efficiency, size, number of bands and bandwidth per band etc - nevertheless there are enough options available to be able to choose a configuration of antenna or antennas that will make the best use of precious transmitter power for a particular circumstance. My two key criteria are that the antenna should be truly resonant on the band(s) of interest and that the radiating elements should be as near to full size as possible, relative to the wavelength(s) being used, to ensure the best possible efficiency (i.e. lowest loss of power). This means full size quarter wave vertical or full size half wavelength long dipole. I don't like aerials that are shortened by using a loading coil, but accept that such an arrangement is sometimes necessary for the longer wavelength bands. Top Band is a real problem in average size gardens. Where the is a coil, a trap, or transformer there will be some loss or reduced efficiency introduced into the antenna system. I do find that using a trap is an excellent compromise - the 80m / 40m Inverted L and the 20m / 10m trapped dipole work especially well. My next favourite option might be for a fan (Parallel) dipole. All the pros and cons have to be weighed up to find the best compromise for particular operating circumstances. I hope that this page has given new operators some ideas to take away and mull over. Links G4ILO - Stealth Antennas: http://www.g4ilo.com/stealth.html M0WYM - QRP Fan Dipole: http://www.radiowymsey.org/FanDipole/fandiploe.htm See Multi Band Dipoles Compared: http://www.arrl.org/tis/info/pdf/9611073.pdf http://www.dxzone.com/cgi-bin/dir/jump2.cgi?ID=7499 See Practical Dipole Antennas Compared: http://www.qsl.net/ta1dx/amator/practical_dipole_antenna.htm See What Antenna For H.F? by Wrexham ARS: http://www.qsl.net/wars/construct/hf_ant.htm Multiband Loft Dipoles: http://www.qsl.net/g0kya/multibanddipole.pdf TRIMMING AERIALS Antenna Trimming Chart This following information below could be very useful indeed when constructing aerials an is compiled by DX Zone and from their web page at: http://www.dxzone.com/cgi-bin/dir/jump2.cgi?ID=13444 Use this chart as an aid in trimming the length of your antenna. It gives you an idea of the change in wire length needed to move antenna resonance a specific number of KHz. * Dimensions are for each leg of a half-wave dipole * For quarter-wave antennas (i.e. verticals ) use the dimensions directly from this chart * Full-wavelength antennas (loops) - multiply the chart dimensions by four (4) and change the overall length of the antenna by that amount. Lengths are estimates. Many factors will affect their exact value.
Example: You have measured the SWR of your 40 meter dipole at various frequencies across the band. You have determined that the SWR is lowest at 7.00 MHz. You actually want the lowest SWR to occur up in the sideband portion of the band, so you need to move resonance up in frequency about 200 KHz. According to the chart, to move +200 KHz on 40 meters, you will have to shorten each leg of the dipole 10" (-10"). The overall length of the antenna is shortened a total of 20 inches. Lengthening or shortening the antenna is done at the end insulators. To shorten the antenna, unwind the antenna wire as it wraps around itself at the end insulator. Move the insulator several inches toward the center of the antenna. Re wrap the antenna wire to secure the end insulator. Do not cut the wire. Wrap it back around the antenna wire. You may need to increase the antenna later. [From DXZone] More Links Fibreglass Telescopic Fishing Poles http://www.sotabeams.co.uk http://www.skyblueleisure.co.uk/acatalog/Telescopic_Poles.html see: Bowmanarcher on ebay Line-Lok guy runners for support pole guy ropes by ClamCleats: http://www.clamcleat.com/cleats/cleats.asp?menuid=7 Other Aerial Supports http://www.tecadi.de/ Commercial Antennas Spectrum Communications: http://www.spectrumcomms.co.uk Sandpiper Aerial Technology: http://www.sandpiperaerials.co.uk Moonraker: http://www.moonrakerukltd.com GWhip Antennas: http://www.gwhip.co.uk/ ProAntennas: http://www.proantennas.co.uk Cobwebb Antenna: http://www.g3tpw.co.uk SRC - Snowdonia Radio Company: http://www.snowdonia-radio-company.co.uk ProWhip Antennas: http://www.prowhipantennas.co.uk/ W.H. Westlake - for wire, cable, feeder, connectors & components: http://www.whwestlake.co.uk/ Hustler Antennas from DX Engineering. 4-BTV, 5-BTV & 6-BTV compact antennas: http://www.dxengineering.com Butternut Antennas from Bencher Inc: http://www.bencher.com/ham/ Cushcraft Antennas from MFJ: http://www.cushcraftamateur.com Comet Antenna: http://www.cometantenna.com Diamond Antenna: http://www.diamond-ant.co.jp/english/amateur/antenna/ama_antennas.html Hygain Antennas from MFJ: http://www.hy-gain.com Alpha Delta Communications - Dipole and Parallel (Fan) Dipole Multi-Band Antenna Designs http://www.alphadeltacom.com/ WIMO Antennas and Accessories: http://www.wimo.com/cgi-bin/verteiler.pl?url=wireantennas_e.html GAP Antennas: http://www.gapantenna.com True Ladder Lines and Wire Antennas: http://www.trueladderline.com/index.html Radio Wavz - wide range of amateur radio antennas: http://www.radiowavz.com Radio Works - amateur radio antenna manufacturer and supplier: http://www.radioworks.com/ Force 12 Antennas (Sigma5) : http://www.force12inc.com Transworld Antennas (TW2010 Adventurer) : http://transworldantennas.com Superantennas: http://www.superantennas.com SOTA Beams: http://www.sotabeams.co.uk/ Amateur Radio Suppliers RADIOWORLD http://www.radioworld.co.uk/ ROCKET RADIO http://www.rocketradio.co.uk/ SPECTRUM COMMUNICATIONS http://www.spectrumcomms.co.uk/ MOONRAKER http://www.moonrakerukltd.com/ HAYDON COMMUNICATIONS http://www.haydon.info/ KZJ Communications (DeeComm) (Haydon West Midlands) http://www.kzjcommunications.com/ WATERS & STANTON http://www.wsplc.com/ MARTIN LYNCH & SON http://www.hamradio.co.uk/ DIODE COMMS http://www.diodecomms.co.uk NEVADA RADIO http://www.nevadaradio.co.uk/ HAM RADIO SUPPLIES http://www.hamradiosupplies.eu/ LAM COMMUNICATIONS http://www.lamcommunications.net ANCHOR SUPPLIES http://www.anchorsupplies.com VINE ANTENNAS: http://www.vinecom.co.uk/ Projects and Information G4ILO - Stealth Antennas: http://www.g4ilo.com/stealth.html M0WYM - QRP Fan Dipole: http://www.radiowymsey.org/FanDipole/fandiploe.htm See Multi Band Dipoles Compared: http://www.dxzone.com/cgi-bin/dir/jump2.cgi?ID=7499 See Practical Dipole Antennas Compared: http://www.qsl.net/ta1dx/amator/practical_dipole_antenna.htm The ALL Band HF Doublet on Ham Universe: http://www.hamuniverse.com/hfdoublet.html Multi-band Inverted V $4 Special by Joe Tyburczy, W1GFH: http://www.qsl.net/wb1gfh/antenna.html http://www.hamuniverse.com/fourdollarspecialw1gfh.html The Norcal Doublet Antenna: http://www.norcalqrp.org/norcaldoublet.htm N4JTE - 6 Band Ribbon Dipole by N4JTE http://n4jte.blogspot.com/2009/04/n4jte-6-band-ribbon-antenna-35.html http://g8jnj.webs.com/ http://www.astromag.co.uk/vertical/ http://www.hamuniverse.com/multidipole.html http://www.hamuniverse.com/fourdollarspecialw1gfh.html http://n4jte.blogspot.com/2009/04/n4jte-6-band-ribbon-antenna-35.html http://www.dxzone.com/cgi-bin/dir/jump2.cgi?ID=20420 http://www.tc006a8364.pwp.blueyonder.co.uk/brats/radio_07/advanced/mathequat_1.htm http://www.tdars.org/library/TechTopics/tech22.html http://www.rsgb.org/tutors/advanced/pdf/maths_primer.pdf http://www.users.icscotland.net/~len.paget/Mini%20quad.pdf http://www.users.icscotland.net/~len.paget/5%20band%20Inverted%20L.pdf http://www.users.icscotland.net/~len.paget/Inverted%20L%20adding%20top%20band.pdf http://www.btinternet.com/~shaun.scannell/club/w3dzz.htm http://homepage.ntlworld.com/lapthorn/70cms.htm http://mw0idx.co.uk/2mPortPockBeamGW0VMW.html http://www.dxzone.com http://www.arrl.org/tis/info/pdf/0207040.pdf http://www.dxzone.com/cgi-bin/dir/jump2.cgi?ID=7466 W2BLC - Amateur Radio Antenna Ideas: http://www.w2blc.us/linkant.htm Back to Aerial Types More "thinking out loud" notes and queries which I intend to edit and condense (honestly!): Multi Band HF Antennas Covering ALL the HF bands with separate antennas dedicated to each band would take up a large amount of space which many of us don't have. Either we must decide on a limited number of favourite bands and put up a specific antenna for these or try to find a multi band antenna that covers all the bands of interest. The perfect HF multi band is many an amateur radio operator's holy grail.You can read more about an All Band Antenna Marvel covering 160m to 70cms on this external link: Hamuniverse ALL BAND N4UJW Antenna So, multi-band antennas necessarily involve compromises which usually translate into lower efficiency i.e. the antenna will not effectively radiate all the power that is fed to it. There will be losses, some large and some not so large depending on the design and the number of bands that the antenna is attempting to cover. The 80m / 40m Inverted L, mentioned above, is down by about 2dB on 80m when compared to a full size 80m inverted L. That's not too bad, but it does still mean a theoretical best case scenario of about a 40% loss of power! So if 100 watts of power arrives at the antenna (disregarding additional feeder losses) then only 63 watts will be radiated - actually less due to any feeder and other losses. If these compromises are accepted then there are a number of different multi-band antennas that can be considered. Having a small plot I have had to consider many such designs, some are vertical antennas some are horizontal wires, some are commercial products and some can be 'home brewed'. Home brewing a wire antenna is relatively straightforward since wire is easy to obtain and work with. A wire antenna is typically installed horizontally above the ground, although it may also be installed as an Inverted V or as a Sloper. A wire antenna is easy to adjust for resonance and often reasonably straightforward to suspend in the air using existing structures, buildings, trees or simple wooden posts. Home brewing a vertical antenna might present slightly more difficult mechanical and engineering challenges to produce a stable and, perhaps, visually acceptable device. Standard Wire Dipole In my own circumstances I could probably fit in a couple of dipoles up to about 15 metres (45 feet) in length. For a straight dipole, such a short length would preclude 160m, 80m and even 40m. So dipoles that could fit in a fairly small space would give two of the bands between 30m and 10m. Loaded Dipole Loading a dipole with a centre or end inductor on each arm would maintain its electrical length while reducing the antenna's physical length. This would allow the antenna to be resonant on the required band and enable the longer wavelength bands to be used even though efficiency will be less than a full size, un loaded, dipole. A loaded dipole will be relatively easy to construct, the most time consuming part being the winding of the inductor coils and their subsequent adjustment to obtain the desired physical length at the correct resonance. An antenna analyzer is a very useful piece of test equipment for speeding up these adjustments. Trapped Dipole The use of traps can effectively split the antenna into two or more resonant sections. Using one trap on each arm of a dipole will transform a single band dipole into a dual band dipole. Using two traps on each arm will enable the dipole to be resonant on three bands. A four band trapped dipole would use three traps etc. Traps also shorten the overall physical length of the dipole which might be seen as an advantage, however traps tend to be lossy and short antennas obviously do not radiate as efficiently as their full size counterparts. Once again the compromise for covering more bands, and in less space is effective radiated power loss. Traps can be quite tricky to home brew, though it is entirely possible. As an alternative traps can be purchased pre-made from some amateur radio suppliers such as Spectrum Communications. The other time consuming part of d.i.y. construction a trapped dipole will be adjusting the antenna wires so that the aerial is at resonance on each band. Again an antenna analyzer is a very useful piece of test equipment for speeding up these adjustments. Fan or Parallel Dipole An alternative to using traps is to use the fan dipole (parallel dipole) method. This essentially connects two or more full size dipoles together at the centre feeder point. For example, whereas a single band dipole would have one pair of 'arms' a four band fan dipole will have four pairs of 'arms' arranged in a fan like pattern. The fan dipole will be very straightforward to physically construct although it will be quite tricky to get each dipole to the correct resonance for each band since each arm will interact with its close neighbour. Again an antenna analyzer is a very useful piece of test equipment for speeding up these adjustments. The Fan / Parallel dipole should be a very efficient and effective radiator since all the dipole elements are full size, however its bandwidth on each band might be be narrower than a trapped dipole, though it should be less lossy. Most designs of Fan / Parallel Dipole (even commercial ones) seem to opt for coaxial feeder. Personally I don't think that this is a good idea. I would use twin feeder to feed this type of design (probably 72 ohm twin or similar) for three reasons. 1. Twin feeder is far and away less lossy than coax, so when an antenna has reduced bandwidth and one is forced to operate with a higher vswr than might be considered ideal, the subsequent feeder losses in coax will be very high indeed compared to to losses in twin feeder which will be much lower. 2. A dipole is a balanced antenna, and coaxial cable is an un-balanced feeder - not a good match... 3. Using un balanced coax with a balanced antenna would customarily demand the use of a balun at the centre of the dipole which is another point that could induce power loss. For all those three reasons twin feeder seems to be the better, more efficient option. Combination of Trap, Inductive Loading and Fan arrangement There is no reason why a combination of a techniques might not be employed to produce a multi band dipole. Just as one example, a fan dipole with two pairs of arms could be made to cover four bands by using a pair of 7.1MHz traps in one pair of arms to create a 80m / 40m dipole and load the end of the dipole with an inductor to shorten its physical length. A second trapped dipole could be added to cover 20m and 10m using a 28MHz thereby making a fan dipole with two pairs of 'arms'. Commercially Manufactured Options: Designs that are most attractive for use on my small plot. Wire Dipoles: Interesting parallel dipole with end loading: Alpha Delta Model DX-EE Parallel Dipole (40-20-15-10) - A Fan Dipole only 12 metres long. Reasonable design, though fed with coax. (I'd build one and use twin feeder.) Similar design from Alpha Delta, but too big for my plot: Alpha Delta Model DX-CC Parallel Dipole (80-40-20-15-10) - Fan Dipole design, 25 metres long. Some interesting trap dipole designs: Diamond W8010 - Trapped Fan Dipole for 80m, 40m, 20m, 15m and 10m only 19.2 metres long. Comet CWA-1000 - Trapped Fan Dipole for 80m, 40m, 20m, 15m and 10m Similar to Diamond W8010 19.8 m long. [ Thinking out-loud: Could take the 80m segments and 7MHz traps off the ends of both the W8010 or CWA-1000 to produce a shorter antenna covering 40m, 20m, 15m and 10m that would only be about 13.6 metres long? ] KZJ - Restricted Space Inductive Dipole (trapped?) Straight - For 80m, 40m, 20m and 10m only 16.5 metres long. KZJ - Restricted Space Inductive Dipole (trapped?) Straight - For 160m 80m, 40m, 20m and 10m 22.3 metres long. Top quality designs: Spectrum Communications 80m + 40m Dipole fed with twin feeder and will cover other bands up to 10 meters. Spectrum Communications 40m + 20m Dipole fed with twin feeder and will cover other bands up to 10 meters. Spectrum Communications 80m + 40m Inverted L. Will cover other bands up to 10 meters. Verticals: Usually very short when compared to the wavelength being used so power loss may well be very high. Might be useful in very restricted spaces where nothing else really will fit in. A vertical antenna can provide better low angle radiation which can provide better long distance DX. Sandpiper V10 and derivatives. Depending on bands covered, between 4.2 m and 6 metres tall. Sandpiper MV10 and derivatives. Depending on bands covered, between 2.5 m and 4.2 metres tall. Butternut HF9-V covers 80m, 40m, 30m, 20m, 17m, 15m, 12m and 10m. - 7.9 metres tall Diamond CP6 covers 80m, 40m, 20m, 15m, 10m and 6m. - 4.6 metres tall. Diamond CP5-H covers 40m, 20m, 15m, 10m and 6m. - a mere 3.6 metres tall. Comet / Maldol HVU-8 80m, 40m, 20m, 15m, 10m, 6m, 2m, 70cms. - tiny at only 2.6 metres tall. GAP Eagle DX 40m, 20m, 17m, 15m, 12m, 10m. - 6.4 metres tall. |
|||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
Amateur Radio Page | My Station | Antennas
/ Aerials | Accessories
| Projects
& Kits | Data
Modes | Information |
QSL
| RSGB
|
||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
Mike Smith - MDS975.co.uk © 2003 - 2010
M0MTJ
Amateur Radio; Ham Radio; Radio; Transceivers; HF; VHF; UHF; Data Modes; Morse Code; RTTY; PSK31; SSTV; FSTV; Amtor; Sitor
Antennas; Aerials; Cable; Coaxial Cable; Twin Lead; Masts; Poles; Propagation; Computer; PC; USB Computer Interface; Microphone
Loudspeaker; Filters; Noise Reduction; DSP; Digital Signal Processing; Morse Key; SWR ; Inverted L; Inverted V; Dipole; Doublet;