The Cranky Sysadmin A world of technology, fun, and ignorant rants.

December 11, 2011

Now that I’m a Ham…

Filed under: ham radio — Cranky Sysadmin @ 9:07 pm

One of the things I want to do, now that I have an amateur radio license, is build a transceiver. I’m probably going to settle on the Bitx 20 since I can hold the whole design in my head. I’ve actually built the VFO on a breadboard as a learning exercise.

Yes, I know. The stray capacitance of the breadboard probably impacts the VFO output. That’s ok though because I used several approximate valued components since I didn’t have exact values.It’s all good. Since I don’t have a frequency counter, I can’t see how far the frequencies are off! Clearly, I was in need of a frequency counter.

While I waited on the weekend to visit my favorite electronics surplus store, I took another crack at fixing up my grandpa’s old short-wave radio, a Heathkit Mohican. It turns out that its main problem was a cracked trace on the ancient (and poor quality) pc board. After soldering in a jumper, the radio came to life. I found it while nosing around with an o’scope trying to figure out why the BFO (an oscillator) wasn’t working. It had no power, so I traced the power (or lack thereof) back to the audio amplifier. Now I have a short-wave to listen to while I build a transceiver.

Well, it turns out that the surplus store had an ancient but still nice fluke 1953a frequency counter. When I plugged it in at the store, it had a nasty hum and the display was a little flaky. Well, I took a chance and took it home. In my past, a “nasty hum” usually means a cap is bad. When I got home, I downloaded a manual and started on the troubleshooting procedures since it wouldn’t count a signal. I got to the “test the 12V regulated supply” portion. The supply was running at 9.5V according to my volt meter. Also, by ear, I had a hard time pinning down where the hum was coming from. I came back later and started poking around with  an o’scope. The reference oscillator was pulsing on and off with a period of 16ms. That seemed odd. Then I happened to check the +12 volts and the light went on in my head. The volt meter was measuring rms voltage. The supply voltage was pulsing on and off. I checked each of the big smoothing capacitors and two of them were bad. I replaced them with scavenged parts and the frequency counter started working again.

This counter has the 10mhz oven stabilised crystal oscillator and an “IEEE 488 interface” which I don’t anticipate ever using. Now I have a counter I can use so I can be more critical of my oscillators. It’s about time to start building that 20 meter transceiver now.

No Comments »

No comments yet.

RSS feed for comments on this post. TrackBack URL

Leave a comment

Powered by WordPress