MDS975 logo

AKD HF3

Communications Receiver

MDS975 logo

THE AKD HF3 Communications Receiver

AKD Products produced the HF3 receiver together with a number of other communications products such as RF filters, but have now ceased trading.  The rights to the AKD range were been aquired by Garex Electronics www.garex.co.uk who went on to market some of the former AKD products.

These days its marketed and sold as NASA TARGET HF3 SSB receiver.  The NASA TARGET HF3 receiver can be found at most online marine chandlers and on E bay where a good deal can often be had.
[Thank you to Phil at www.tasteofsailing.co.uk for this update ]

[Download the Schematic Diagram here]

Below you will find the Radio Netherlands review of the receiver's performance:


AKD Target HF3 Receiver

Click Radio Netherlands Review
Of The AKD Target HF3


Year Introduced: 1997
Power: 12 volt DC (mains power included)
Size: 18.5 by 19 by 6.5 cm
Weight: 1800 g
Coverage: 30 kHz - 30 MHz

Value Rating 3/5

Introduction

The top end of the short-wave receiver market has slowed in the last twelve months. Sets costing over US$1000 have been particularly hit, partly because many of the cheaper portable receivers have introduced a lot of new features which attract more general users, especially those experimenting with international radio listening for the first time.

In Britain, one manufacturer has taken a different approach. AKD, a company based at Stevenage in Hertfordshire has come on the market with what they call the Target HF3 communications receiver, priced at £160, including VAT. Bearing in mind that entry level communications receivers such as the Lowe HF-150 costs £419 in it basic version, or the Yaesu FRG-100 for around £470, the AKD is clearly very much cheaper. Now that the units are in production, we have been testing one for the last 8 weeks, doing quite a bit of both practical listening as well as usual standard measuring scheme.

Construction

The first thing that strikes you as you unpack the radio is that it is extremely compact. That's partly because the 12 volt power supply is not inside the set, but comes as a brick-style power pack which you plug into the wall. You plug the jack into the back of the radio, connect an external antenna, and the radio is ready to perform.

The front panel is extremely simple. There's a large liquid crystal display showing the frequency, four little pushbuttons, two rotary controls, one marked volume, the other marked clarify, and a large tuning knob. In fact the tuning system is extremely simple and handy to operate. The tuning knob has a weight inside so it has a nice feel to it.

The coverage is from 30 kHz to 30 MHz in one kHz steps. If you turn the knob slowly then you move in one kHz steps. If you turn it faster, then the steps get progressively larger -- 10, 100 or even 1000 kHz -- at a time. So if you need to, you can hop from one end of the band to the other in a very short time. One kHz steps is fine for most broadcast applications, but if you're going to use the set for listening to utility stations, then the "clarifier" control allows you to tune finer than 1 kHz. However, these slightly changes in frequency are not reflected on the Liquid Crystal Display. The receiver is dual conversion. The first intermediate frequency is at 45 MHz, the second at 455 kHz.

Modes

You can use the set for listening to broadcast stations in AM, or switch the mode to either USB or LSB. You'll need that if you want to monitor traffic on the amateur radio bands. The HF3 has just one memory channel, which also remembers the mode. When you switch the set on, this is the channel that is recalled. If you tune around a bit, you can go back to this channel again by pressing the recall button. But that's it.

We tested a version which has a built-in board to allow you to connect up a home computer for decoding weather-facsimile signals. That's quite neat, but it means that on this version you have to forfeit the output for a pair of headphones. It is present on the standard version. That's something you can live with. But we were surprised that in an effort to keep the price down, AKD has used an ordinary hi-fi phono cinch plug for an aerial socket. You find this type of plug on the back of audio equipment, but not on radio receivers.

We don't understand why AKD didn't use a conventional SO-239 socket which is much stronger. Most ready made antennas come with a plug that matches, so it's a shame that you have to solder on a phone plug instead. This is mechanically, probably the weakest point of the receiver and within a few days of use it had worked loose on our test example.

AKD does supply a length of 10 metres of wire with a phono plug already soldered onto one end. But this is not the best solution for short-wave listening. If you put the antenna up inside the average house, it is almost guaranteed to pick up a lot of unwanted noise from apparatus inside the house, such as fluorescent lights, thermostats, computers and TV's. We used an external antenna with a Magnetic Balun, mounted 5 metres away from the building, with a coaxial cable feeding the signal into the shack. The background noise was considerably quieter this way. We also experimented with an active antenna mounted outside, well away from the house.

The radio is very well constructed. If you look inside the HF3, you'll find that it is logically laid out and built to last. The PLL synthesiser is shielded inside a separate box to keep the noise away from the sensitive input circuitry. But the outer casing is made of durable plastic which is not shielded.

Performance

So now to some of the receivers specifications, starting with sensitivity across the range between 30 and 30,000 kHz. We were measuring the point for 10 dB signal to noise at 60% modulation, which is equivalent to an AM station that is just intelligible. In practice, 20 dB signal to noise was needed for acceptable listening, using the 6 kHz filter. Between 50 kHz and 15 MHz, the sensitivity is quite constant, hovering around 2.5 microVolts. Above 15 MHz, the sensitivity drops, so that you need between 3.5 - 4.5 microVolts to get the same level of intelligibility. In the SSB modes, the receiver is roughly three times more sensitive, which is to be expected.

Those figures for sensitivity are only fair, but remember that below 10 MHz, a receiver doesn't have to be too sensitive. In this region, the antenna will provide more than sufficient signal to drive the radio. Above 15 MHz, the fair sensitivity of the set is noticeable, especially if you live in low signal strength areas like the West Coast of North America or in the Pacific

The designers of the HF3 have done this to reduce the problems of overloading. Remember that a huge number of signals are presented to the front end of the receiver, and the task of any radio is to pick out the wanted signal and reject the rest. The more sensitive you make a radio, the more you have to invest in circuitry to ensure that strong signals don't overload the front end of the radio. Once this happens, weak stations disappear into the background noise, suppressed by local powerhouse broadcasters using 500 kW or more.

Attenuator difficult to access

There is a two-position attenuator on the back of the radio. If you switch it on, signals are attenuated by a factor of 4, in other words by 12 dB. That's quite coarse, and operation is complicated by the fact that the attenuator is on the back of the radio. If you can pick up a fine step attenuator at a ham radio store, you'll find that being able to try something like 6, 12, or 18 dB of attenuation is quite handy. In practice, you're trying to find the balance between letting too little signal into the receiver and too much.

The signal strength metre is in the form of a bar graph on the liquid crystal display and in fact is only a rough guide to signal strength. There are 10 segments, one of which is always lit. We found it was easier to use your ears than use the tuning metre as a guide.

The receiver has two bandwidth filters installed. For AM broadcast use, the best results are obtained with the 6 kHz filter. We would have chosen a slightly narrower filter for AM use, since shortwave stations are spaced 5 kHz apart in practice. This results in sideband splatter if you´re listening to a weak station that is 5 kHz away from a strong station. For SSB and facsimile, a 3.8 kHz filter is installed, but you cannot use this for the AM mode. The selectivity of both filters turns out to be quite good, especially for a set of this price category.

Limited dynamic range

The selectivity of the HF3 is contrasted by the limited dynamic range of the receiver. The budget design of the HF3 shows through here. In single sideband, two signals, each of 1.3 milliVolts and spaced 50 kHz apart, produce a 1 microVolt intermodulation spurious product. This unwanted signal gives 10 dB signal to noise ratio and can thus disturb reception of a desired signal. These figures are equivalent to a third order intercept point of -9 dBm.

The limited dynamic range is also a problem with AM broadcast reception. To give an example. The receiver is tuned to a station of moderate strength (6 Signals stronger than 50 dB than the desired signal start to overload the receiver. So in practical terms the dynamic range of the HF3 is only 55 dB, 72 dB in SSB. Any reasonable antenna is capable of providing sufficient signal to overload the radio, especially here in Europe, after dark, on bands below 10 MHz. In AM, we measured a third order intercept point of around. That's about the same sort of results we measured on the Kenwood R-600 ten years ago.

AKD have put a decent audio amplifier inside the HF3. It sounds quite pleasant. It delivers half a watt RMS into a loudspeaker, with less than 1% distortion, which is more than sufficient for more listening purposes. Remember that only the standard model has an output for headphones.

If you plan to use to set for unattended monitoring, try to pick a place with a fairly constant temperature. We found that at a stable room temperature our example wandered about plus or minus 30 Hz during a listening period of a few hours. That's not a problem with AM reception, but it's a bit more critical for telex reception. If you use the set in an outside shack where temperatures are more variable, then the receiver wanders by as much as 200/300 Hz over a period of few hours.

The Bottom Line

In conclusion, we did quite a bit of listening with this receiver. During the day, using a good 15 metre long external antenna**, we found the set pleasant to use. It was great for general broadcast reception and was able to decipher at least some of the stronger amateur radio transmissions on 40 and 20 metres. In the evening though, listening around 14 MHz, we had severe problems with broadcast interference from 15 and 11 MHz. Attenuation helped a bit, but not that much.

The bottom line is that this set is a great entry-level receiver for the shortwave broadcast listener. You get what you pay for. If you pay three times the price for a communications receiver, you will get noticeably better results. Remember too that some of the portable sets like the Grundig Satelliet 700 will give similar, if not better short-wave performance and they have FM reception and more memories. On the other hand, the HF3 from AKD in the UK is easier to tune, well built and sounds better than many portables. It fulfils a need in the European market place.

In the UK, the set costs £160 including VAT. Outside the UK, the set is more expensive, costing around €250 here in The Netherlands. That's of course because of import duty and transportation costs. The HF3 is made by AKD, Unit 5, Parsons Green Estate, Boulton Road, Stevenage, Hertfordshire, SG1 4QG, UK. AKD can also be contacted by fax. The number is 44 for the UK, then 1438 357591.

The Lowe-badged version - the SRX-100 - is sold in overseas markets where AKD does not have any presence.


The AKD HF3 Receiver was also marketed as the NASA TARGET HF3 and as the SRX100 by Lowe Electronics


** Antennas:

Although any reasonable length of lightweight, PVC insulated wire wire can be used as an antenna connected to the antenna terminal, with the ground terminal connected to an earthing point or a counterpoise wire of equal length, I generally connect an antenna via an antenna tuning unit which is connected to the antennas and earth terminals on the receiver.

An antenna  tuning unit "ATU" (or more correctly and antenna matching unit "AMU") helps match, or 'transform', the wildly varying impedances presented to the radio by a random length of aerial wire, when used on a wide range of frequencies, to the (approx) 50 Ohms required by a radio receiver. This helps ensure the efficient transfer of radio energy (the signals).

An ATU is a good DIY ("home brew") constructional project that can be made simply and cheaply. I even have a couple of ideas on these web pages. There are also commercially available ATU's available of course.

Even without an ATU I would use a simple variable attenuator (made from a potentiometer) to reduce the effects of strong signals that can otherwise tend to overload such a receiver causing unwanted noise and spurious signals that manifest as interference.

An antenna has to be of the correct size to work efficiently for a given frequency (wavelength). Two examples are a Quarter Wave Vertical fed against earth (ground) or a 1/4 wave 'counterpoise' or several 1/4 wavelength radial wires . Another type is a Half Wave Dipole - which is essentially two 1/4 'arms' fed at the centre to create an antenna that is a half wavelength long.

So: If your required station is  transmitted on, say, 8MHz  (8,000 kHz), you would make two wires each a 1/4 wavelength long: 8 MHz has a wavelength of 37.5 metres, so 37.5 ÷ 4 = 9.37 metres long (less about 5%) = 8.9 metres. So if using on a boat, for example you may be able to run an 8.9 metre long vertical wire up the mast as the antenna wire connected to the antenna terminal, with a wire of equal length connected to the ground terminal as the 'counterpoise' run out along the hull.





^Top Of Page



Home  |  Contact  |  Site Map  |  Reciprocal Links & Credits  Thank You

www.mds975.co.uk © 2004 - 2013