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RADIO PROJECTS & KITS
One of the really fun aspects of amateur radio
is making things for yourself.
Probably the best and most important DIY project for any amateur radio
station is building an antenna of some kind. This is often a wire
antenna for use on the HF bands such as an Inverted V, Inverted L,
Dipole or Doublet Quad Loop or Windom etc. For the shorter wavelength
VHF and UHF bands it more practical to construct more complex antennas
such as Slim Jim or Yagi for example.
Other projects will be an electronic unit of some kind.
For the Intermediate Level licence it is necessary to make several
practical electrical and electronic circuits and also build a complete
and useful device related to the subject of amateur radio.
I chose to make a Morse Code Practice Oscillator from a kit of parts
bought from Waters & Stanton. You can see this project a little bit
further down this page.
More recently I built a Field Strength Meter - "FSM"shown
further
down
this
page.
FUTURE
PROJECTS: July 2010: I have been unable operate since
March 2010
due to all my equipment being packed away for a house move that has
been constantly delayed. I have been having a few ideas as to what
homebrew (d.i.y.) projects I want to construct in the near future.
The components required for the small electronic
projects have already been ordered and delivered in readiness from Bowood
Electronics and JAB
Electronic Components. ESR supplied a couple of different
uni-directional electret microphone elements which are quite difficult
to find elsewhere. I just need to find some time to start - sometime
after we've moved house! The necessary electrical conduit and aluminium
round bar or tubes for the antenna projects will probably be obtained
from B&Q.
J-Pole Antennas:
As far as antennas are concerned I want to build a J-Pole for 10 metres
and another dual band J-Pole for 2m / 70cm which has been described by
the ARRL.
Moxon Antennas:
I quite fancy having a go at building a Moxon antenna
for the SSB portions of 70cm and perhaps another for 2 metres.
Lightweight Yagi
Antennas:
However before those projects I really fancy building the ultra
lightweight Yagi antennas described by DK7ZB Of
particular interest are the 100cm long 4-Element-50Ohm-Yagi for 2
Metres with 7dBd gain; the 5-Element 50Ohm version for 2 metres which
is about 1.5 metres long with 8.48dBd gain and the 7-Element 50Ohm Yagi
for 70cms with a boom of 100 cm and gain of 10.35dBd.
I will also need to install some discrete H.F. antennas in the garden.
Once again I'm hoping to be able to use the Inverted L for 40m and 80m
and want to experiment with adding elements for 20m and 15m. 10m, I
hope, will be taken care of with the J-Pole mentioned above and I also
intend to build a trapped dipole for the 12m and 17m WARC bands.
Microphone
Preamplifier:
I would like to be able to use a separate microphone on a boom or
gooseneck, so I am bringing together some ideas for a dynamic mic'
preamp and separate 'break-out' PTT switch here>
Power Reducer and
Power Measurement for QRP Operation:
Many 100 watt rigs cannot adjust RF power output to a low enough level
for QRP
operation. What is needed is a circuit to allow control of the ALC
circuits to reduce the power of a transceiver for QRP operation with
power levels below 5 watts. I am going to make a very simple circuit
for this task - nothing more than a 9 volt battery, a switch, battery
connector, 100k resistor and 100k preset potentiometer, a suitable
connecting plug, some thing screened cable and a project case. When in
use the power output will also need to be
measured accurately, so....
The second part of this project is to produce a meter that will allow
the measurement of voltage from the RF socket to determine an accurate
indication of power into a 50Ohm dummy load.
Analog Meter for
Yaesu FT-857D and FT-897D - The Homebrew FT-Meter
Yaesu very thoughtfully
added an external meter socket to the FT-857 and FT-897 which is
excelleint since I like analog
S-Meters and connecting a meter to these radios is child's play. There
are no additional circuits required, merely a 100k preset potentiometer
and a small microameter. A meter with a sensitivity of 100µA,
500µA or 1mA should be suitable, the final calibration being done
with
the small internal preset potentiometer, setting the meter for Full
Scale Deflection using the calibration setting on the radio.
The menus of the FT-857
and FT-897 allow the radio to output indications of Signal Strength;
Power; SWR; Modulation; Voltage and Discriminator.
I looked at the Bowood
Electronics website and found a very nice little 100µA ammeter
measuring about 60mm wide by 50mm high, so I ordered one along with
some other components that were in my basket for the QRP power reducer
and power measurement
project mentioned above.
The physical construction
of putting a small meter movement into a case should be very
straightforward, but there was the small problem of
replacing the 0 - 100µA
scale supplied with the standard ammeter with a suitably calibrated and printed
scale. Producing
a new scale for the meter's dial with a
professional appearance was more of a challenge for my graphics / image
editing skills! I searched Google
for some helpful images. LDG market two commercially manufactured
meters for
this job - the FT-Meter and the much larger FTL-Meter; these retail at
about £46.00 GBP and £66.00 GBP respectively - my FT-Meter
should cost about £10.00, but I digress! The photographs
of these products illustrated the layout of the graphics, but nothing
that was reproducable for this homebrew project.
I was beginning to think
that I might have to draw something by hand - then I happened across
the
website of Frank OK2FJ. Frank has produced an excellent meter scale for
his version of the
Yaesu FT-Meter. Frank obviously had the
same idea as me, to produce a homebrew FT-Meter for a fraction of the
cost of a commercial unit, but Frank has greater image
editing and graphics skills mine. I saved Frank's image file
and then made a few of my own simple modifications to the image file
using a basic image editing program. The
result is shown below and can be downloaded and saved, ready to be
re-sized and printed to match the size of the particular meter being
used:
Above:
The
image
graphic
for
the
Yaesu
FT-857
and
FT-897
meter
scale.
Save
and
print
if
required.
Printing The Scale:
The
scale
can
be
printed
on
paper
or
thin
card
and possibly laminated,
which is what I did. White paper or card might be the obvious choice,
but cream, light green, yellow or light blue card would also make a
good background colour.
When printed, the image will need to be scaled quite accurately to suit
the size of the particular meter movement being used, otherwise the
needle will not line up properly with the scale and the indication will
be inaccurate. This can be done by trial and error until the correct
size is found - a bit of a fiddly and a rather wasteful method.
Alternatively a bit of simple math's can be used.
My image editing program allows scaling of the print-out using a
sliding scale that shows the total width of the image when it's printed
and the dpi (dots per inch) output to the printer. Knowing the total
image width isn't especially helpful since what is needed in this case
is the dimension that is the distance between the left and right end
markers of the S scale - the top curve. My simple image editor does not
allow an accurate measurement of a portion of the image, so I did a
test print, estimating that the resultant image would need to be 50 mm
wide, the output in this case was 920 dpi. I then measured the width of
the top curve on the test print, from end marker to end marker - it was
40mm. The scale of the original microammeter is 34mm wide, so the print
had to be scaled down in size.
The magnitude of the size reduction can be found by dividing that
measurement, 40mm, by the required measurement - in this case 34mm.
40mm ÷ 34mm = 1.176 (the scaling factor)
The original test print produced an scale that, at 40mm, was too wide.
It needed to be 34mm wide. The original image width of the test print
was 50mm and therefore this needed to be divided by the scaling factor
of 1.176
50mm ÷ 1.176 = 42.5mm
The calculation suggests that 42.5 mm is the width required for the
whole image. The image was printed again at that width and the reulting
print measured. It was found that the width across the top curve from
end marker to end marker was, indeed, the required 34mm.
The other way of doing the scaling is to note the dpi output of the
original test print, in this case 920 dpi, and multiply (not divide)
that by the scaling factor. The original dpi figure is multiplied,
rather than divided, becuase the dots per inch will increase as the
original image size is shrunk. In this case the new, and correctly
sized print, is 1082 dpi. Whichever method is used, the second print
should produce a scale of the correct size.
Reference: http://www.radio-foto.net/radio/ftmeter2.png
This is the original meter scale image that was produced by Frank
OK2FJ, I altered this to produce the meter image that is shown above.
Above: The image
graphic for a simple analog S Meter scale.
Save
and
print
if
required.
John, G0TEV, emailed with a helpful suggestion for those who want to
produce a custom made meter scale: Meter Basic is free and will produce
a basic linear scale. Meter is a paid for program that will allow
more complex designs such as dB, vu, VSWR and S-meter scales. Both
programs are available here: http://www.tonnesoftware.com/index.html
FIELD
STRENGTH METER
It is often said that one of the most useful pieces of test
equipment in and around the shack is a Field Strength Meter. A Field
Strength Meter can be used to quickly check the presence of RF energy,
for example to check that a transmitter is transmitting, for use with
antenna experiments such as judging the radiation pattern and
efficiency of antenna and for checking RF oscillators etc.
To buy a simple ready made FSM would cost around £30.00 and
£50.00. Since such a device is simply a form of 'crystal set'
without a tuned circuit I set about looking through the junk box to see
what electronic components I had that I could use to make a suitable
circuit.
I found a nice aluminium case, a good telescopic aerial, a couple of
germanium diodes, a potentiometer, some suitable ceramic
capacitors, a nice 250µA signal meter (minus the scale which I
had somehow lost) and some other useful bits and bobs. All I needed to
assemble a simple yet perfectly effective Field Strength Meter that I
am sure is as good as anything that could be purchased ready made - and
all made from junk box componets!
Photograph
showing
the
simple
construction
of
the
Field
Strength
Meter

Circuit Diagram of the Field Strength Meter
All the Field Strength Meter has to do is convert the radio frequency
signal into a DC current that can drive a meter movement or digital
multimeter (DMM). As can be seen from the above circuit diagram the
field strength meter bears a great resemlence to a simple crystal set.
The differences being that since the field strength meter needs to be
sensitive to a wide range of frequencies the tuned circuit (inductor
and variable capacitor usually found in a crystal set) is omitted, and
rather than headphones or an earphone the output is fed as DC to a
signal meter or to a digital multi-meter so that comparative (rather
than absolute) measurements can be made.
The telescopic aerial picks up the radio frequency signal and
the germanium diode converts the signal to DC. It is important
that germanium diodes are used as they exhibit a very small forward
bias which is needed to make the meter sufficiently sensitive. |Silicon
diodes have a substantially higher forward bias which would
substantially reduce the sensitivity, so for this reason it is
important to use germnium diodes.
On the same theme it is important to use a sufficiently sensitive
meter, so a microammeter will be required. I was lucky to have an old
Maplin signal meter with a sensitivity of about 250µA
for full scale deflecton (FSD) in the junk box, although I would
imagine that it would still be worth experimenting with any meter
between 50µA to 1000µA. Alternatively a digital multi meter
can be used to measure the output.
The field strength meter that I built has both options selectable with
the miniature DPDT switch. The meter is connected to the digital
multimeter with a short fly-lead terminated with a red and black banana
plug to identify the positive and negative wires.
The 47K
potentiometer allows for the adjustment of the overall sensitivity of
the meter.
The advantage of using a DMM is that
it has a very high input impedance a therefore will not load the
circuit to any great extent,
it also enables the meter to be much more sensitive to weaker RF fields
if required and also it will be easier to make more precise
measurements from the digital readout, particularly small differences.I
find that th e DMM is usually
set to the 200mV range, or perhaps to 2000mV range if the RF field is
especially strong.
The value of the various components is not particularly critical, but
as mentioned, the diodes must be germanium rather than silicon and any
diodes such as OA90,OA91, OA80, OA81, OA47 could be used.
Field
Strength
Meter
Parts
List:
2 off OA91 or any similar Germanium Diodes
1 off 470 pF ceramic capacitor (code 471)
1 off 0.01 µF ceramic
capacitor (code 103)
1 off 0.047 µF ceramic
capacior (code 473)
1 off 47 K Ohm linear track potentiometer
1 off 250 µA signal Meter
1 off Telecopic Aerial about 20 inches long
1 off Red Banana Plug
1 off Black Banana Plug
Small Aluminium or Plastic Case
2 off Rubber Grommets
Hook Up Wire |

Photograph of
completed Field Strength Meter |
SHORT LOADED TOP BAND ANTENNA FOR
160
Metres
/
1.810
to
2.0
MHz
My experimental project
during 2009 was trying to accommodate a small top band antenna in the
restricted space at my QTH.
A full size aerial for Top Band is going to be far too big for most
back gardens, but the basic requirement really is to get as much aerial
wire in the air as possible - the longer the better - and then load the
antenna to bring it to resonance on the band. I used a small inductor
wound on a 50mm diameter plastic tube. A top band aerial like this also
needs the very best earth possible - i.e. as many ground wires as can
be accommodated.
I gradually refined my ideas and have now put the results on the
antennas
page
here
MORSE CODE
PRACTICE OSCILLATOR

Internal view showing
PCB and other components

The
completed
CW
Practice
Oscillator
with
Morse
Key
WIRING A CABLE FOR A
DIFFERENT MICROPHONE
I
decided
to
use
my
existing
Leson
(Altai)
TW-232
Desk
Microphone
as
an
alternative
to
the Icom
HM-103
hand mic that is supplied with
the
Icom IC-706MK2G transceiver.
The TW-232 desk mic is fitted with a standard type 6 pin mic plug wired
for my Midland 48 Excel CB radio. The Icom 706 has a completely
different RJ45 type mic
socket. I needed to make a 'cross-over cable' to fit between
the
mic plug on the TW-232 and the Icom 706 transciever.
Looking at the circuit diagram for the Icom IC706, the basic wiring
only needs four wires: PTT (Push To Talk transmit switch), PTT Ground,
Microphone Audio and Microphone Audio Ground.
This is slightly different to CB wiring which does not have separate
grounds for PTT and Mic, inside the plug on the TW-232 microphone these
two ground wires were connected together. I therefore
I separated
the MIC Ground and PTT Ground within that plug.
This would require two Cross-over cables; one for the CB that
re-combined the two grounds together to match the wiring scheme
required for CB and the second cross-over cable for the connection to
the IC706Mk2G.
Here
is the wiring scheme for the TW-232 mic and the Icom transceiver:
The Leson (Altai) TW-232 desk microphone wiring is as follows:
White = PTT
Black
= PTT
/ Receive Ground
Blue
= Receive
Red = Mic audio
Shield = Shield (mic audio shield)
Icom
IC706Mk2G
microphone
plug
wiring
for
RJ45
plug:
1 = +8 volts d.c. *** Do not connect &
be careful NOT to short out otherwise the radio will be
damaged ***
2 = Frequency up/down buttons
3 = Audio output
4 = PTT
>>>>>>>>>>>>>>>>>>>>
Connects
to
the
White
wire
of
the
TW-232
Mic
5
= GND - Microphone Ground
>>>>>> Connects to
the Shield wire of the TW-232 Mic
6
= Microphone audio input
>>>>>>>> Connects to
the Red wire of the TW-232 Mic
7
=
GND - PTT Ground
>>>>>>>>>>
Connects to the
Black wire of the TW-232 Mic
8 = Squelch control
Above:
Leson
/
Altai
TW-232
wiring
diagram
*Important: Please
check that the colour coding of the wiring of your TW-232 microphone
is the same as that
shown above - if not note the differences and proceed accordingly
Wiring
diagram
for
Icom
HM-103
microphone
shows
the
microphone
socket
as
seen
from
the
front
of
the
radio
(Icom Corporation)
Icom
IC-7000 The wiring for the IC-7000 would be similar
for the TW-232 microphone (see TW-232 diagram above)
1
= +8 volts d.c. *** Do not connect &
be careful NOT to short out otherwise the radio will be
damaged ***
2 = Frequency up/down buttons
3 = HM-151 connection
4 = PTT
>>>>>>>>>>>>>>>>>>>>
Connects
to
the
White
wire
of
the
TW-232
Mic
5
= GND - Microphone Ground
>>>>>> Connects to
the Shield wire of the TW-232 Mic
6
= Microphone audio input
>>>>>>>> Connects to
the Red wire of the TW-232 Mic
7
=
GND - PTT Ground
>>>>>>>>>>
Connects to the
Black wire of the TW-232 Mic
8 = Squelch control
(HM-103) or Data in (HM-151)
Above
-
Microphone
wiring
for
HM-103
and
HM-151
pertaining
to
the
Icom
IC-7000
transceiver
(Icom Corporation)
The
Up / Down frequency buttons are not wired in my cross-over cable, but
could be used if required if additional switches were fitted into the
desk mic. The basic wiring only requires four wires to pins
4,5,6
& 7 in the RJ45 plug - as seen below:

The RJ45
plug fitted to a short piece of mic cable

Fitting
the
RJ45
plug
to
the
mic
cable

Fitting the mic socket
on the other end of the cable

The completed
cross-over cable
Thanks to Alex and
Dave at the Charlie Delta ARC for the necessary plugs that enabled me
to make this cross-over lead. Cheers guys!!
Microphone
preamplifier
ideas
Rather than always using a
hand held microphone I would like to experiment with a different
microphone that can be suspended from a boom or gooseneck. I have a
good quality dynamic microphone and a couple of different
unidirectional electret condenser elements to experiment with. The Icom
IC-706MK2G is not best suited to dynamic microphones due to their low
output, so I decided to look at building a simple external microphone
preamplifier to compensate.
Building an external
amplifier would also allow experiments with some simple audio
filtering, particularly useful could be a low pass filter to roll off
audio frequencies below a certain point, say below 200 Hz or below 300
hertz, for example.
Basic Microphone preamplifier
using simple inverting op-amp arrangement:
A
Typical Inverting Operational Amplifier configuration
The gain is set by R1 and
R2. In this case 220,000 Ohms ÷ 2,200 Ohms = gain of 100 x
C2 and R1 form a simple
first order high pass input filter that would have a gentle filter
slope from a cut off frequency of 72 Hertz
fc = 1/(2πRC) Where
f is cut-off frequency in Hertz, R is resistance in Ohms and C
capacitance is
in Farads. (1µF = 0.000001F)
1 ÷
2 x 3.14 x 2200 Ohms x 0.000001 Farads =
72 Hertz
A first order filter will
reduce the amplitude of the signal by 6db (power reduces by half) every
octave (halving or doubling of frequency) - that is -20dB per decade
(factor of 10 of frequency).
For SSB communications use
a high pass filter with a cut-off frequency of somewhere around 300 Hz
might
be more appropriate. Changing the resistor R1 to a 5.6k Ohm device and
the capacitor C2 to 0.1µF (0.0000001F) would produce an fc of 284
Hertz. Since most capacitors have a tolerance of +/- 20% the
0.1µF capacitor could, in reality, have a value of anywhere
between 0.08 and 0.12 µF which would affect the fc quite
significantly to between 236 Hertz and 355 Hertz.
Switching C2 to
0.22µF would change the fc to 129Hz and switching to 0.47µF
would give an fc of 60Hz.
Since R1 has been changed,
the gain of the amplifier will have also changed. To retain a gain of
100x R2 will need to be adjusted accordingly to 560k Ohms. However a
gain of somewhere between 10 and 20 might be more appropriate for
connecting a microphone to a transceiver so a value of 100k Ohms could
be used for R2 giving a gain of 17 x. The final output level being set
by the 1k preset potentiometer being careful not to overdrive the
microphone preamplifier in the transceiver.
Alternatively, by
retaining the 2.2 k Ohm resistor in the above circuit the gain could be set at 21 by changing R2
to 47k Ohms, for example, and
the cut off point (fc) could be set to various other values by swapping
the capacitor C2 according to fc
=
1/(2πRC) :
2.2µF
-
fc = 33Hz
1.0µF - fc = 72Hz
0.47µF - fc = 154Hz
0.22µF - fc = 329Hz
+ / - tolerance of
capacitor and resistor
Non-Inverting Operational
Amplifier example:
Non-Inverting
Operational
Amplifier
configuration
for
dynamic and electret microphones
www.zen22142.zen.co.uk/Circuits/Audio/lf071_mic.htm
Above, a
circuit
design by Andy Collinson for microphone preamplifier of high
quality. The circuit uses a single power supply and is particularly
suitable for dynamic microphones, although electret microphones can
also be used.
The design is a typical non-inverting configuration with input
impedance is 23.5k Ohms. The op-amp should be of high quality for best
performance with high signal o noise ratio. e.g.TL071, NE5534 or OPA 371
Voltage gain is set by R2 and R1 - use the formula: Vo = ( R2 / R1) + 1
It could also be possible to power the electret element remotely by the
addition of a resistor of 1k or 2k from the power supply line to the
audio input, but this arrangement needs a DC blocking capacitor at the
input - as shown in the above diagram the capacitor is of the incorrect
polarity for this function so this would need to be slightly redesigned
- a second electret capacitor before the 10µF shown but with
reversed polarity should do the job. Care should be taken with values
as this will affect the input filtering - a non polarised capacitor
might also be considered for this position.
Audio Filtering: Rod
Elliott of ESP (Elliott Sound Products) provides information in the
diagram below for a simple first order input filter when using an
operational amplifier in a non inverting configuration. As with the
previous example, the cut off frequency, fc, is determined by the
formula fc = 1/(2πRC)
Filtering with a
non-inverting operational amplifier arrangement - fc =
1/(2πRC)
Microphone
Preamplifier
with
compressor
using
the Analog Devices SSM2165-1
integrated circuit:

SSM2165-1 Microphone
Preamplifier and Compressor
A building
block idea that can be modified as explained below
The preamp that I intend to construct will
be based around the Analog
Devices SSM2165-1 integrated
circuit along the lines of the circuit diagram sown above which is
based on the DYC817 implementation.
The BC549 transistor is a simple input preamplifier stage. The input
level to the SSM2165 integrated circuit being adjusted by the 1k Ohm
preset potentiometer. Some
designs omit the transistor stage when using electret condenser
microphones since these have higher output, however if connecting a
dynamic microphone directly to the SSM2165 the internal noise gate may
not be successfully opened - causing obvious operational problems!
The BC549 stage is
therefore included in this design for use with lower output dynamic
microphones so that the noise gate within the SSM2165-1 will be opened
successfully. The 1k preset potentiometer can be carefully adjusted for
proper noise gate operation with both dynamic and electret microphones.
The capacitor across pins 3 and 2 couples the internal buffer amplifier
to the internal output VCA. The value of this capacitor determines the
low frequency response of the unit because it forms a simple high pass
filter in conjunction with two 500 Ohm internal resistors - a total of
1000 Ohms; so fc = 1/(2πRC)
so; fc = 1 ÷ 6.28 x 1000 x 0.0000033F = 48 Hertz. For voice
communications a value of 1µF
would
provide
a
roll
off below 160 Hertz. A
0.47µF capacitor would
produce an fc of
339 Hertz.
The compression ratio can be adjusted from 1:1 up to 15:1. The resistor
or variable preset potentiometer between pin 6 and ground sets the e
compression level. The diagram above allows the resistance to be varied
between 47k and 147k which adjusts the compression ratio between 4:1
and 9:1. A value of 5k Ohm or less will produce a compression ratio of
1:1 while using a 200k Ohm variable potentiometer will allow the
compression ratio to be adjusted up to 15:1
The capacitors at
the input pin 4 and
output pin 7 should be non polarised, this helps prevent a 'pop' as the
noise gate opens and closes.
Adding a 47k Ohm resistor
in parallel with a 22µF capacitor from pin 5 to ground will also
help to eliminate the 'pop' from the noise gate as it opens and closes
by smoothing the attack and release curve, reducing the attack and
release time constant. The SSM2165 datasheet suggests that a 22µF
would be suitable for music use, but during speech communications one
would always hear a noticeable rise in audio level during a pause in
speech for an additional one or two seconds before the noisegate closes
- a very annoying effect for the receiving station. The use of a
22µF in conjunction with a parallel 47k Ohm resistor will cause
the noisegate to close immediately after the speech stops of during a
short break in speech. (Tip by DG2IAQ )
The capacitor from pin 5 to ground controls the time constant of the
internal level detector, values of between 2.2µF and 22µF can be used and will change the response
to low frequency sounds. According to the data sheet 'Capacitor values
from 18µF to 22µF have been found to be more appropriate in
voice band applications, where capacitors on the low end of the range
seem more appropriate for music program material. For optimal low
frequency operation of the level detector down to 10 Hz, the value of
the capacitor should be around 22µF. Some experimentation with larger values
for this AVG CAP may be necessary to reduce the effects of excessive
low frequency ambient background noise. The value of the averaging
capacitor affects sound quality: too small a value for this capacitor
may cause a “pumping effect” for some signals, while too large a value
can result in slow response times to signal dynamics'.
OTHER PROJECTS
There are
many other
useful devices that can be made, such as an ATU for portable QRP use,
various types of receivers, pocket sized QRP CW transmitters, complex
transceivers - the list is endless. Some projects have to be built from
scratch which involves making the necessary PCB, other designs provide
a pre-etched PCB while many are available in complete kit form.
Another project that I wish to make in the future is a Noise Bridge. I
even fancy having a go at a Crystal Calibrator - and more experimental
antennas - of course!
Looks like my soldering iron may
be busy!
"One person's junk is another
person's treasure"
|