NC40 Output


From: Doug Hendricks (
Date: Tue Feb 22 1994 - 01:04:27 EST

I spent the day today with ham radio and I had a blast. Bob Warmke, W6CYX
and I are building beta rigs of the Sierra, the NorCal QRP Club's next club
project, which is an all band cw transceiver using plug in band modules
designed by Wayne Burdick, N6KR. I had several parts that Bob needed, and he
had the bottom to my case, so I drove over to San Jose and visited Bob.
     We exchanged parts, and while I was there, I watched as Bob did 3 simple
mods to my NorCal 40. He increased the coverage of the VFO from 38 KHz to
144 KHz by putting in a 10 turn pot and a capacitor, he improved the keying
shape by changing two capacitors, and he increased the power by changing yet
another capacitor. The unique part of all this was that Bob did the mods
with a soldering iron, solder wick, and a general coverage digital receiver,
I think it was a Kenwood 850. That is it.
     He calibrated the rig by hooking the NorCal to an antenna, and unpluging
the antenna to the Kenwood. Then, he keyed the NorCal and found it on the
receiver of the Kenwood. He adjusted the variable capacitor on the vfo set,
and put it right on 7.000 MHz. Then, he tuned to the top of the vfo range
and found it on the receiver. It was at 7.144, which was good enough for me.
He then put the rig in the mid range of its tuning range, 7.072 KHz, and
adjusted the trim caps for the receiver and the trim pot for the transmitter.
     That was it, no test equipment, just a wattmeter and receiver, and Bob
had my NorCal up to snuff. His watt meter said 4 watts, and I didn't believe
it, so when I got home, I decided to measure it myself.
     I recently bought a good used Tektronics 465 Scope (Don't mention it to
my wife), and now this was the way to use it. Bob told me that I could use
the scope to measure the peak to peak voltage, and then figure out the RMS
voltage and the power. I bought four 200 ohm 2 watt resistors and made a
dummy load by soldering them together in parallel. You do remember that part
of your Novice theory? This made a dummy load capable of handling 8 watts,
with a measured resistance of 51 ohms. I used carbon resistors, and not the
new type. Now that I have a dummy load, I was ready to go. Hooked up the
NorCal to 12 volts, and took the 10X probe and the ground went to the sleeve
of the SO239, and the probe tip went to the center conductor. Then I keyed
the rig and looked at the scope. Ooops, should have been a sine wave, and it
was a wide solid line. Hmn, call Wayne, and ask for help. Wayne told me
that I had the scope display set wrong. These are the settings that worked.
Time/division was set at .05 microseconds, and volts per division was set at
1. Tried it again! Success, beautiful sine wave, and the peak to peak
measurement was 3.7. Wayne was on the phone with me, and said that means
that it was 37 volts peak to peak, since I was using a 10X probe. I then
divided 37 by 2.8 to get the RMS voltage, which was 13.21 volts. I then
squared the RMS voltage, 13.21 and got 174.5. Since my resistance was 51
ohms, I divided 174.5 by 51 and discovered that my NorCal 40 is putting out
3.42 watts. I am excited! I learned something today. Thankyou to Bob
and Wayne, but I learned!!! None of this would have happened if I was not
working with building my own gear. Ham radio is great!! Now all of those
formulas that I "learned" are starting to mean something. Jeff Gold is
absolutely right. Build and you will learn. Get a scope, and you will
really learn. Have a good day, and 72. Doug, KI6DS

By the way, full details of Bob's mods and others are in the next issue of
QRPp, to be mailed before March 1.

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