This Old Signal Generator

My radio buddy, Mike, WA5PSE, got me a "new" signal generator at a hamfest. Well, not new, exactly. I don't know how old the actual unit is, but the manual I found at BAMA is copyright 1954. A fella's got to be a few years older than his signal generator.

This is an EICO Model 324 (you can see more information here). Mike said it was in good shape...and it is. I opened the cabinet up and it looks like it was built yesterday. Mike said it was in pretty good calibration, and it is.

The 324 has 6 bands, from 150KC to 455MC (don't ask it to do anything in KHz or MHz; this thing was built when we were still using "kilocycles" instead of "kilohertz.") Anyway, to calibrate the 324, you've got to adjust some slug tuned coils, one for each band, on the back of the band switch.

I intially thought I would check calibration by simply listening to the signal generator's oscillator on my ICOM 706.

Yeah, that wasn't a good idea. I could find the 324's output on the 706, but it was quickly apparent that this was a pretty inefficient way to calibrate the 324. When I adjusted the coils on the 324, it, of course, would cause the 324's signal to disappear from "view." I then had to chase the signal back down and readjust. Each band seemed to be about 20KHz off; so setting the 706 up to receive a calibration frequency (say, 7.0 MHz), and trying to move the 324 onto that frequency, was really shooting in the dark. I wasn't sure I was headed in the right direction (up or down). I wasn't sure how far I was from the calibration frequency at any point in time. I felt like I was doing it backwards.

What I needed was something that simply gave me a read out of the 324's real current frequency. Oh...you mean like a frequency counter? Like the Norcal FCC-1 that I just built a couple months ago? Yeah, like that - dipwad. I forgot I even had the thing.

So, I got out the FCC-1; hooked it up to the 324 and lo and behold - nothing. The FCC-1 just sat there, in all of it's digitalness, looking extremely bored. But it weren't countin no frequency! Why not? I had it properly hooked up to the 324's output. What gives? I started fiddling with the 324 and, after a little coaxing, the FCC-1 finally wakes up and displays a frequency (sorry 324; the FCC-1 reads out in KHz, not KC). Anyway, it appears that the output level of the 324 was set too low for the FCC-1 to even respond to the input. When I cranked the gain controls on the 324 up to about mid range, the FCC-1 started reading frequency like a little digital champ.

Then it was a simple matter of figuring out which slug tuned inductor to adjust for each of the 324's bands. I fiddled around looking at the schematic for awhile, but quickly decided to ignore that and just look at the coils themselves. Obviously the coils with the greatest coilness (that's a technical term for the "most wire") had the most inductance and would correspond to the lowest frequency bands (the bulkiest coil would be band "A", etc.). No duh.

I started switching from band to band and calibrating the 324 like crazy. It wasn't too far off (except on Band E, which was about 2MHz off). I got it dialed in pretty close on each band. Close enough for use in Smith Labs anyway. Besides, the old analog dial, even with its vernier knob, would still only allow for a certain amount of precision. Trying to dial it in too precise was just fooling myself. If I need that much precision when I use it, I'll just sic the FCC-1 on it.

It works like a champ.

WA5PSA