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Getting the best value from the second-hand market!
A
fter a dual-band handheld transceiver, of
which I’ve covered a few types in past
columns, about the most-often purchased
transceiver for Amateur use is that of a 144/430MHz
(2m/70cm) frequency modulated (f.m.) mobile rig, for
use on simplex and repeaters, either from your car or
from home. As promised in the last column, this time
I’ll be looking at a couple of these which could well be
of interest, and which have been proven second-hand
bargains in the recent past.
I’ve deliberately chosen two sets with fairly similar
features – each has 144 and 430MHz coverage with ‘one
band at a time’ operation, i.e. without ‘dual receivers’
which keeps costs down. Each of fers a high power of
50W on 2m and 35W on 70cm, and each has an easily
detachable front panel, just like many car radios. So
you can feel reasonably safe in keeping the set in view
under the dashboard of your car while you’re away,
while you have the transceiver’s front panel safely
tucked into your jacket pocket.
I’ve used both of these sets in the past as well as
fully testing a sample of each on my laboratory radio
test equipment. In fact the TM-G707E transceiver, which
was subsequently given to me as a birthday gift many
years ago, I personally used for a number of years in
my own car.
Whatever mobile radio you buy second-hand, it
may sound obvious but ensure that you get the direct
current (d.c.) power lead, microphone, and mobile
mounting bracket hardware too. Sometimes, the seller
will leave the power lead in the vehicle rather than try
to strip it out. In this case you could use a ‘choc block’
connector with your own lead – but this doesn’t help
when you’re trying to take the radio in and out of your
car for safe keeping if it doesn’t have a detachable
head.
The most common ‘fault’, if you could call it that, is
a scratched display on radios with a detachable front
panel. This is usually because the user has repeatedly
removed it and simply slipped it in their pocket or bag
along with keys and the like.
A small cloth storage bag is a most useful accessory
here! If yours does have a scratched plastic display
then a proprietary ‘scratch remover’ paste along with a
bit of ‘elbow grease’ can often restore it to virtually new
condition. I suggest that you ‘haggle’ for a few pounds
off the asking price to cover the cost of buying this,
unless of course the asking price already reflects the
damaged condition of the radio.
Anyway, now for some information on the radios I’ve
chosen this month!
The Kenwood TM-G707E
The Kenwood TM-G707E covers 144-146 and 430-
440MHz with a transmit power output of 50W
maximum on 2m and 35W maximum on 70cm, with
switchable low power levels of 10W and 5W on either
band. Extended receive range is available, see below
for a modification.
The main body measures just 140mm x 40mm
x 189mm. The size is kept down by the use of a
controlled fan on the rear panel together with an
internal airflow-ducted heatsink.
For frequency control, a click-step rotary knob on the
front, steps you through the channels, and pressing the
knob face inwards momentarily changes the variable
frequency oscillator (v.f.o.) to 1MHz steps so you can
get from one part of the band to another more quickly.
Further buttons above the tuning knob change between
v.f.o. and memory operation, and selection of a quick
access ‘Call’ channel for each band.
There are also 180 memory channels, a ‘Priority’
channel, and 12 extra channels to store lower and upper
limits for six programmable v.f.o. scan ranges. Each of
the normal memories can be user-programmed with an
alphanumeric channel name of up to seven characters
in place of the frequency, so that you can see what
you’ve stored in each channel.
There’s a variety of scan modes, such as memory
scan, priority scan, selected limit v.f.o. scan, 1MHz
range scan, etc. Indeed, there’s enough to satisfy
virtually all listening needs!
The set has full continuous tone codes squelch
system (CTCSS) encode and decode facilities, a 1750Hz
tone-burst is also built in. A CTCSS scan can also be
enabled, to display which, if any, CTCSS tone is being
used on the channel you’re tuned to.
The radio also has the facility for 1200 or 9600baud
Buying Second-hand
Feature
Practical Wireless, July 2010
30
This month Chris Lorek G4HCL takes a look at a pair of high power dual-band
2m/70cm mobile transceivers
Editorial announcement: Both Chris and the Editorial team are delighted by your feedback on the equipment featured.
We would also encourage readers to contact us to request that particular rigs and accessories to be featured. Indeed,
this series will rely on your requests and comments, along with Chris G4HCL’s extensive experience to be the success
we intend it to be. So, let’s be hearing from you readers!
Page 2
packet operation on
either band. Removing
a small cover at the
bottom left of the set’s
front body reveals a
dedicated six-way mini-
DIN connector for a
packet TNC.
The supplied hand
microphone has the
usual push-to-talk (p.t.t.)
and Up/Down buttons
for frequency/channel
control, plus four extra
buttons labelled Call,
VFO, MR and a user-
programmable function
such as power on/off, squelch defeat, high/low power
selection etc.
All the four microphone buttons are, in fact,
programmable in this way, giving you a remote control to
suit your needs. Pressing the PM button on the front panel
brings up a sub-display of ‘1’, ‘2’, ‘3’ and ‘4’, and each
is appropriately just above the four buttons next to the
liquid crystal display (l.c.d.). All you need do is press the
appropriate button to change between ‘personalities’. This
can be useful when you’re switching between, say, shack
and mobile use of the rig.
There’s also a selectable Advanced Intercept Point
(AIP), which switches out the front-end pre-amplifier to
improve the strong-signal handling of the set, albeit with a
slight loss in sensitivity. A transmit time-out-timer is fitted,
which limits the transmission time to 10, 5, or 3 minutes.
This can’t be disabled and personally speaking, I found it a
bit of a pain to use – but others may disagree!
On The Air
Within the 77-page user manual is a one-page, seven
step, Your First QSO guide, which helps to get you on
the air quickly. Besides normal operation the transceiver
also has an ‘Easy Operation’ mode, where the first three
buttons on the front panel just select between three pre-
programmed memory channels, with the fourth button
selecting the transmit power level.
Operating the set this way was just like using a car
radio. Af ter I’d tuned into a frequency, a press of one of
the channel buttons for more than a second automatically
stored that into memory, recall being a quick press of the
same button.
The detachable front panel contains all the user
controls – and an optional ‘remote’ kit is available so that
you can mount the control/display unit wherever you
wish, the main body unit fitting elsewhere. When I tested
the set over a prolonged period, I found the receiver to
be exceptionally sensitive on 144MHz, easily capable of
receiving distant repeaters. The high transmit power level
allowing me to reciprocate in getting back to the distant
repeaters to join in.
Incidentally, I often suffer from strong-signal
breakthrough when I use a dual-band rig from home with
it connected to my rooftop antenna system, primarily with
hand-helds but it also occurs with the occasional mobile.
However, I’m pleased to say I’ve had no problems at all
with the TM-G707E here.
Out and about
operating mobile, the
set performed equally
impeccably, with good
and loud audio from the
set’s top-panel mounted
peaker. It also has
a very easily to read
display, which I certainly
appreciated. My lab tests
confirmed the good on-air
performance, and I ended
up using a TM-G707E as
y personal choice for
quite a number of years.
Extended Coverage Ranges
Let’s now look at extended receive and transmit ranges
and here, you may find that your transceiver’s already
had this modification done by a previous owner. But if
it’s restricted to just the Amateur bands on receive and
transmit and you’d like it extended, or indeed ‘reverse’ the
modification to get the radio back to original – here’s how.
First, remove the detachable front from the
transceiver, and then remove the bottom case lid. Next,
position the transceiver in front of you, upside down, with
the antenna connecter pointed towards you.
In the upper right hand corner, behind the display
adapter, you’ll see a small set of vertical printed numbers,
0, 1, 2 and 3, next to a group of four small sur face-mount
‘zero-ohm’ resistor links. For extended receive range, use
a soldering iron and carefully lift the resistor marked 0.
You’ll find it easier to heat the solder at one end of the
resistor, then quickly transfer to the other end and use
the soldering iron to lift that end. Then transfer back to
the other to remove the resistor. After this, you’ll find the
receiver will cover the following bands;
Receive band 1; 118-136MHz a.m.
Receive band 2; 136-174 MHz f.m.
Receive band 3; 300-400 MHz f.m.
Receive band 4; 400-520 MHz f.m.
Receiver band 5; 800-999 MHz f.m.
If you’d also like extended range on transmit then,
while you’ve the set open, remove resistor 3 in the same
way. After this, the transmitter will cover the following
bands;
Transmit band 2; 136-174 MHz f.m.
Transmit band 4; 400-520 MHz f.m.
If you ever want to reverse these modifications, you
can just use a short piece to wire soldered across the
original resistor positions to restore the original band
limits.
Transmit Deviation
If your set has too much deviation on 144MHz, as they
originally came set with ±5kHz peak deviation for 25kHz
channel spacing for both 2m and 70cm operation. It’s
relatively easy to adjust and you won’t need to open the
set up to do this.
You’ll first need to place the radio into ‘Service
Adjustment Mode’ by shor ting pins 3 (PKS) and 6 (SQC)
on the data connector on the front left side of the radio,
Practical Wireless, July 2010
31
There are plenty of radio goodies about and Chris will guide you to the best buys.
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Buying Second-hand
you’ll find this under the small oval-shaped removable
cover.
To locate which pin is which, while you’re looking at
the connector from the front of the transceiver with the
connector on the left hand side, pin 3 is at the 3 o’clock
position and pin 6 is at the 10 o’clock position.
If you’re unsure of poking wires into the connector, then
you could get yourself a PC keyboard extension cable and
use this to plug into the set and link the wires on it, the
connector is exactly the same.
With the pins linked, simultaneously press the F key
and Tone key while you switch the set on. Then select
v.f.o. mode and tune to a 144MHz frequency, which you
can monitor on another receiver, or even better a radio
communications test set to measure transmit deviation if
you have access to one (or use a PC and monitor receiver,
read on in this month’s column).
Next press ‘MNU’ to select the adjustment mode, and
use the keys to select ‘DEVI’. Press the mic PTT and speak
into the mic, and use the rotary encoder knob to adjust the
transmit deviation until you get to the right level. You’ll see
the display will indicate a two-character level as you adjust
this. Once you’re at the right deviation level, ideally 2.5kHz
maximum deviation, press the ‘OK’ button to save this
adjustment level into the set’s memory.
Then press the MNU button to return the set into v.f.o.
mode. If you need to adjust the 430MHz deviation level,
you can simply tune to a 70cm channel to do the same
series of operations. The deviation level for v.h.f. and u.h.f.
i
s stored separately inside the transceiver. When you’re
finished, switch the set off and remove the wire short on
the connector.
The Icom IC-207
Next, I’m turning to the Icom IC-207, a set that provides
you a 50W 144MHz rig and a 35W 430MHz rig squeezed
into the same box, a ‘band’ button switching between the
two bands. Wide-band coverage is also available (see later
for this) the modification for this. The set’s case measures
a very small 140x40x185mm, so you should be able to fit it
in into the tiniest of available positions in a car.
The transceiver’s front panel offers a number of
operating knobs and buttons. A detachable microphone
cover reveals a fully-fledged
remote control system for the
set, with each button being
backlit for night-time use.
The microphone control
even provides Up/Down
volume and squelch controls,
as well as handy facilities
such as a reverse-repeater
monitor and transmit power
selection. There are 150
memory channels plus extra ‘call’ channels and the like
available for frequency storage and one-touch scanning.
A bright yellow back-lit liquid crystal display is used, with
the functions for the six push-buttons below the panel also
being shown on the display.
Along with the detachable front panel, a ‘separation
kit’ is also available, so the transceiver itself can be
mounted remotely with just the small display fitted in a
more easily-viewed position on your dashboard. Together
with a 1750Hz tone-burst facility from the microphone for
repeater access, the IC-207H also has full CTCSS (sub-
audible
tone) encode and decode built in, and ‘tone scan’
l
ets you check which, if any, sub-tone is being used on an
active channel.
For packet radio use, a 6 pin mini-DIN connector is fitted
to the rear panel, the transceiver accommodating both
1200 and 9600baud speeds.
On The Air
When I used the set, I found it was very easy to operate
and within a few minutes of switching on I was enjoying
a QSO on my local repeater. I found the set’s front panel
controls were intuitively very simple to use.
With the plastic cover in place on the supplied
microphone, it of fers a smaller number of controls, such
as you’d typically use for ‘normal’ operation, like Up/Down
frequency or channel change, VFO/memory switching,
band switching, and so on.
About the only awkward operation mode I found with
the set was that of generating a 1750Hz tone for initial
repeater access – this needed the microphone’s plastic
cover removed, with a sequential press of two different
buttons beneath the cover. I found this rather awkward in
practice, although if you know the CTCSS access tone for
the area you’re using the set in and pre-program it, this
isn’t too much of a problem.
This rig also includes a handy facility, which consists of
five ‘scratch pad memories’ for each band. Here, the set
automatically memorises the operating frequency every
time the p.t.t. is pressed, storing the last five frequencies
(including repeater shifts) on each band into separate
memory channels. Recalling these just needs a quick
press of the ‘M/Call’ button, the tuning knob then selecting
between them – very useful and especially handy when on
the move.
Operating from home, with the set connected to my
rooftop collinear, it showed a good level of performance
without a trace of the ‘typical’ intermodulation problems
I’ve learned to expect on 144MHz in my r.f. congested
location. Icom have also usefully incorporated an
automatic attenuator in with the squelch control – turning
this beyond around
the mid-way point
gradually adds
up to around
10dB of front end
attenuation, to
help guard against
strong signal
problems without
a lot of button-
pushing.
I found operating with the transmitter on high power for
long ‘ragchew’ periods did cause the heat-sink panel to get
very hot and I usually found I needed to drop down to the
‘next lower’ power level for this. However, programming
the set to keep the rear panel fan on continually helped, as
long as I didn’t mind the fan’s constant low-level ‘whirring’
noise on receive.
My lab tests back in the days when the set was
Practical Wireless, July 2010
32
Page 4
launched showed the
transceiver worked
well, especially the
strong signal rejection
performance,
although the 12.5kHz
adjacent channel
rejection wasn’t quite
up to the mark of the
TM-G707E. But even
so it offers very good performance for a dual-band set
which was originally sold at a quite reasonable price when
new, so second-hand models should (hopefully also they
shouldn’t
be expensive either).
Extended Ranges
As with the TM-G707E, you may find that one of the
previous owners has extended the receive and transmit
coverage range. But if not and you’d like extended
coverage, or in fact if you’d like to reverse the mod – here’s
how you do it.
First, remove the four screws securing the bottom cover
of the set and remove this cover, you might find it’s quite a
tight fit. Then position the set with the front panel towards
you and the opened-up side facing you.
You’ll then see a row of three surface-mount diodes at
the extreme top right, these will be in a neat row from top
to bottom as you look at them. Let’s call these diodes 1, 2
and 3 from top to bottom. Next, using a hot soldering iron,
lift off diodes 2 and 3.
Then, follow the line of the diodes downwards and
you’ll see a normal discrete type resistor, vertically
mounted (i.e. sticking up), this is ‘W14’. Use a pair of wire
cutters and make a cut in the lead of this, moving the lead
ends away from each other away so they don’t connect.
Finally, replace the radio’s lid and switch the power on
while you’re simultaneously holding the Set and SMW
buttons down.
This will perform a reset of the radio – you’ll lose stored
memory information (take a look at page 69 of the user
manual for more information on this). So make a prior note
of anything important to you which you’ve programmed
into the set so that you can re-program it if needed.
After the reset you’ll now have;
118-135MHz receive.
136-174MHz transmit and receive.
320-399MHz receive.
400-479MHz transmit and receive.
849-950MHz receive.
Deviation Adjustment
The IC-207 came supplied from the factory with 144
and 430MHz both set with ±5kHz transmit deviation, for
25kHz channel spacing. If you find you need to reduce
the 144MHz deviation down to ±2.5kHz, then with the
bottom cover removed and with the controls of the set
towards you, you’ll
see a screened
rectangular section
at the middle
front of the set,
this housing
the transmit
synthesiser.
At the bottom
left hand corner
of the synthesiser and a little towards you, you’ll see a
pre-set trimmer potentiometer, R158 – the v.h.f. transmit
deviation adjustment. Carefully turn this until you get the
required ±2.5kHz 144MHz transmit deviation while you’re
monitoring on an adjacent receiver, or using a radio test
set (or a PC and monitor receiver, see below).
If you need to alter the 430MHz deviation, this is
achieved with a further pre-set trimmer potentiometer,
R161. This is at the lower right corner of this metal
screened rectangular section, again a little towards you.
Easy Deviation Adjustment
Here’s an easy way of deviation adjustment without
expensive test equipment! This technique applies to
any transmit deviation adjustment you may need to do,
either now or in the future. Your aim is to get your early
production second-hand transceiver’s peak transmit
deviation to that of ±2.5kHz on 144MHz, typically reduced
from the ±5kHz it was supplied with from new. You’ll need
a monitor receiver for this, and a PC with a sound card
input.
First, locate and install one of the many ‘PC
Oscilloscope’ or ‘Software Oscilloscope’ freeware
programs that are readily available. Note: PW’s sister
magazine, Radio User (for example) had a massive 4-DVD
collection of all known Amateur Radio public domain,
freeware, and shareware software available worldwide,
in their December 2009 and January 2010 issues – the
collection’s still available (an E-mail to software@qsp73.
co.uk will bring you information).
Then, link up your monitor receiver’s external speaker
audio jack to the ‘virtual oscilloscope’ with a 3.5–3.5mm
connector audio lead, tune your receiver to your local
144MHz repeater (which will typically be very accurately
set to ±2.5kHz peak) and note the levels of the upper and
lower peaks of the displayed audio waveforms on your PC
screen. (You might use a couple of pieces of sticky tape on
your PC screen to mark these levels).
Leave your monitor receiver volume at the same setting
and re-tune the receiver to a nearby unused 2m frequency,
key up your 2nd hand 2m transceiver on this, and with
a loud shout into the microphone (a ‘long ‘four’ works
well) adjust the deviation until your displayed audio peak
level exactly matches that which you’ve monitored off-air.
That’s it, you’re up and ready, simple eh?
●
Practical Wireless, July 2010
33
Next Column
Again, as promised, in the next of these bi-monthly columns (in the Sept 2010 cover-dated issue of PW) I’ll be featuring
a selection of ‘get you going’ h.f. transceivers available at low cost together with a number of tips on how to get the very
best out of them. See you then!
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