While I am very happy with my homebrew 8640jr signal generator, I’ve had this old IG-102 RF Signal Generator from Heathkit hanging around for a decade or so.  I was curious what kind of levels it was capable of, so I dragged it out and hooked it up to the scope to investigate a bit.

 

Heathkit IG-102

Heathkit IG-102

The main problem I have always had with this generator is the connectors on the front for the RF and AF out.  They are not commonplace anymore, so replacing them with BNC connectors made sense.  Prior to doing this, I always used a coax with alligator clips to connect, which wasn’t very secure.

I found a few panel mount BNC connectors in my junk box, and installed them into the same holes as the original connectors.

Back side of BNC Connector installation

Back side of BNC Connector installation

Front side BNC Connectors Installed

Front side BNC Connectors Installed

Now that I could get decent cables on the generator, I started making measurements.  I measured the volts and power into a 50 ohm load on my scope:

Band Frequency Multiplier mv pp Power dbm
1 95.00 kc 45.8 -23
1 332.00 kc 122 -14
2 302.00 kc 79 -18
2 1.10 mc 125 -14
3 951.00 kc 127 -14
3 3.20 mc 231 -9
4 3.00 mc 74 -19
4 10.99 mc 279 -7
5 9.62 mc 37.6 -24
5 33.00 mc 286 -7
6 31.10 mc 18.2 -30
6 114.00 mc 272 -7

Most of the bands have a low output at the low end, but quickly come up to a higher output as you move up the frequency dial.

The bands below 1 mc max out around -14dbm, or 125 mvpp. HF bands are generally capable of -7 dbm into a 50 ohm load.  Not bad!

The waveform is generally pretty good, although one or two bands have some distortion.  This is not too surprising, given the design of the device.

Pretty clean waveform

Pretty clean waveform

A little distorted waveform

A little distorted waveform

The modulation is usable, if a little ugly…

Internal Modulation

Internal Modulation

At this point, I decided to replace the filter cap, because it was an old electrolytic, and bound to fail at some point.

The old, 2-section 20uf 200 volt filter cap

The old, 2-section 20uf 200 volt filter cap

This piece is not destined to be a collector’s item, so rather than go through hours and hours of work to restuff the original can, I disconnected it (leaving it in place for looks), and mounted the two new caps under the chassis.

New capacitors

New capacitors

While the back was off, I took the opportunity to replace the old power cord, with a safer, 3-wire cord.

Old 2-wire cord

Old 2-wire cord

New 3-wire cord

New 3-wire cord

Overall, it was a worthwhile couple of hours to upgrade this old  generator.  It’s a good backup, especially for those times when you need two generators at the same time.