Cunningham CM 3050 Transmitter

It is great to see old gear get a second chance.
Looks like a carrier current rig to me too, but i don't think you would have a whole lot of trouble getting it to work for leaky coax.

Let us know how things turn out and don't forget to have fun.

i have one of these. it belonged to alan mccall. was going to run neutral loaded carrier current with this tx, a be ax10 cquam exciter and cunninghams universal tuner.

"cunninghams universal tuner."

Very Cool!

What is cunningham's universal tuner?

I'm trying to figure out if I should Leaky Coax it, or try carrier current...

As Robert said, I used to have a Cunningham xmitter. The "tuner box" was mounted outside on a pole, and featured a tuning coil inside that was adjustable for peak range. There was a small light bulb inside the box that would glow when you had an optimim match.

I ran it on 1160 as a daytimer. Included with the xmitter was what I would call the equivalent of a long-wire antenna. The station averaged a 3-mile range, with the power kept low. Clear Channel once bought an ad flight on the station with that set-up. It reached an audience segment their cluster didn't.

Rev. Cunningham has passed away now but was quite knowledgeable as an engineer and built transmitters for missionary stations.

I have a Rangemaster now, and recently acquited a Radio Systems 2-20, that is a 20-watt model intended for use as a carrier-current model.

My station is getting its own building very soon, and I'm thinking of adding the RS unit in to the new set-up at some point.

Bow,

Your scope pictures are excellent quality.

The modulation picture shows significant distortion. Even though you see some RF wiggling the trace at zero modulation, that is not the same as "I was able to get above 100% positive peak modulation, without over-modulating the negative peak."

Look at the modulation waveform carefully, it is distorted. The easiest way to look for symmetry is to look a the bright trace above the zero point and compare it to the dark area below the zero point. The bright area above the zero point looks very good, but the dark area below the zero point is rounded significantly as it goes up to the zero point. The shape of the negative going modulation is quite different from the shape of the positive going modulation.

For some reason, your transmitter is softening the negative peak rather than showing a flat line during negative peaks, but you are still getting negative peak distortion. You should adjust for symmetry in the positive and negative regions.

An audio processor, such as the Innovonics 222, will allow asymmetric modulation for voice (not music). First adjust the TX for symmetry. Then connect the 222 to enable asymmetric modulation. Once you are in the 222 asymmetric mode, you can't really use the scope to determine what is happening to the waveform because the 222 only works on the asymmetric nature of voice (not a sine wave). You will just need to judge it by audio quality. You can supplement the judgement by looking at the scope and watching that the positive peaks don't go too far above what you saw with a symmetric sine wave display. The voice peaks shouldn't go much above about 130%.