GM20 alive and well!


From: Carol N. Wright (
Date: Sat Apr 19 1997 - 22:58:34 EDT

Hey Gang,
I recently wrote a post to the list about getting either a GM20 by NN1G or
a NW8020 for 20 meters by Emtech. I was asking about comments or
suggestions or likes and dislikes of both of the rigs.

Well I got quite a few great posts on both of the rigs. I decided on the
GM20, even though it doesn't come with a case enclosure which I am usually
accustomed to.

Everything in the kit was their and well packaged except one diode, no
sweat though, I had the diode in my junk box. I really like the headers
that the kit comes with, it makes wiring easy and makes runs from the main
circuit board to the case a lot neater and nicer looking.

I got started with the construction of the rig, first you build the
Heterodyne LO section of the board. I built the LO very carefully and
then tested it to specifications. I really like how Dave has the manual
setup so that if you don't have a great test bench--like me :^)--you can
still align and test the rig using a general coverage receiver, a VOM, and
a small circuit which is included with the kit. You use a VOM and the
small circuit to align the LO.

I got the LO aligned to specifications and then started with the rest of
the rig. I installed the resistors, capacitors, IC sockets, etc., and
installed the IC's, toroids, and header pins last.

I then hooked up the headers to pots and connectors and got all the
headers wired up except for the RIT pot, which I decided to wait until
later to wire up.

I then connected up 13.8 volts and a dummy load. Then I connected up
phones, a key, and a antenna and dummy load. I set my frequency to where
I wanted it by listening to the 22 mhz signal on a general coverage
receiver and adjusting some caps.

Next I aligned my receiver. I adjusted it to have the most atmospheric
noise in the head phones. At first I couldn't really hear any signals on
my GM20 receiver, I just figured that the band was dead because I could
hear my big rig signal on the GM20.

Then I aligned the transmitter section on my GM20. I tuned up C40 and C45
for maximum signal on the s-meter of the general coverage receiver and
then turned up R1 all the way up.

This is where the bad news starts. I couldn't get any output from my
transmitter. I tried numerous things, rewoud T2, adjusted the trimmer
caps again, and even installed a new driver. All of these steps still
didn't bring any life to the receiver.

So because of Dave's great service, he has an email address so that he can
give troubleshooting advice online or over the phone line, even via snail

So I sent Dave a email message and he replied quickly. After a few email
messages from Dave I started testing the voltage check points. One of the
voltages that I measured was wrong so we solved it by installing a new
resistor. Now the voltage was up to par. Ok now let's hook up the rig
up again to the dummy load and see if I can get any ouput from the
transmitter. No, still no ouput.

Well I know Dave had to be getting tired of me after about four or five
email messages. Dave was being patient with me though and was trying
really hard to get my rig going over email messages so I wouldn't have to
send the rig back to him.

After I readjusted C30 and C34 I started seeing the s-meter on my big rig
go up. That is strange. I happened to look up at my watt meter on my
dummy load. Wow! There is a small output. Knowing my I went ahead and
tried to make a QSO at about 500mW, no comebacks on my CQ. I looked at my
GM20 laying on the bench haywired together and lookie what I found. R1,
which is the variable power output pot was turned all the way counter
clockwise. Doesn't that mean the least power output at the most counter
clockwise position? Yes, it sure does.

I grabbed an insulated tool and rotated R1, the variable output power pot,
clockwise and the power started going up, 1 watt, 1 and a half watt, then
the finally about 2 watts.

I then realigned the LO, frequency, receiver, and transmitter. It works
like a charm. The GM20 has a great receiver and as far as I know a great
transmitter. The sidetone is nice and no really signs of thumps.

Where as I was hearing no signals, except for my big rig, I now hear a
great deal of signals from everywhere. So now I have a perfectly working
rig and just need to put it in a case and get the case looking nicely.

Has anyone had similar problems with their GM-XX series rig(s) I would
like to hear from you. I would also like to hear from you if you have
any mods and how you went about putting the GM-XX series in a
case/enclosure. Are their any mods to the GM-XX series?

Now I just got to add my RIT pot and put the GM-20 in a case. So thanks
a lot to everyone for helping out with my choice of the GM-20 and also
the comments that I got for case ideas for my rig. Any comments are more
than welcomed, even ones that I might not like. Hee Hee!

Best 72/73 DE Matt, AE4JM
JCARC--ARCI 9178--ARRL--ARRL ORS--Ten Ten 66932--VP 2855--WAS
Matt Wright, ph. (205)228-6547, packet: AE4JM@K4BFT.#HSV.AL.USA.NA
email: snail mail:8679 Co. Rd. 19, Section, AL 35771
Rigs built: Ramsey mini rcvr-40mtrs, NC38S, SW30-40, NC49'er, NC40A with
KC1, SWL GM-20.

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