The mauldulator looks really cool, I love the videos of those 300% type envelopes. I really want to do that but buying a new radio, power supply, and other supporting equipment seem like an expensive road to take nor do I have that kind of liquidity in cash flow.
So I set off to discover how to make my 2000 do this. Looking at the waveforms many have posted it appeared to be DSB-RC. To generate the that type of signal I simply injected mic audio and the carrier oscillator in to a balanced modulator that is running unbalanced. The result is a DSB-RC signal that moves on the to the final mixer where the PLL signal is injected and 27 MHZ signal generated. The hardest part of this project was in switching of circuits that are not usually on when running in in AM mode.
So the real question is "How does it sound?, 'scope readings are meaningless." It sounds fantastic. I'm using a lightly modified D104 and the stock audio preamp on the 2000 with a few input and output cap changes. I can see how one could benefit from external audio processing but to sound great it's really not necessary. I set it up so I was able to switch between the stock modulator and the DSB-RC modulator, the difference is night and day. I believe that the increase in audio fidelity is combination of the way the DSB-RC modulator runs and the fact that audio goes though way less fidelity mangling filters, amps and transformers (electronic or iron based).
The carrier level is adjustable, as is the modulation % from 0% to 300 % or so. I measured the modulation percentage using the MMM 'scope method. My waveforms appear to be exactly the same as the MMM board.
A Cobra 148 and a Cobra 29 were used for an A/B test. The Cobra 29 has the schottkey diode mod while the 148 uses an active detector, a super diode. On either radio the audio sounds great however the 29 is only able to demodulate cleanly to about 130%, on the other hand the 148 demodulates signals to about 200% (A function of the superdiode).
This was an interesting project, I enjoyed it and I feel if others want to walk down this road the reward waiting is really good warm audio even using just a modest audio setup. The result is so dramatic that I will never use the stock modulator from a high-level AM C.B. Radio again, instead opting to use this modulation technique not only for the enhanced performance but the low cost.
I don't have enough post's to upload pictures/video - sux
73's
-- Wednesday, 26 November 2014, 11:06 AM --
Here is a picture of the the 'scope adjusted to 0% modulation consuming two divisions.
This is me saying 10-FOOOOUUUURRRR - About 200% or so.
Conditions:
14 Volts on the Collectors of the Final Amp in linear mode
Balanced Modulator - Unbalanced and modded for more carrier
Power Supply: Stock in the Cobra 2000 GTL
O''scope Pick up - A wire with multiple wraps around the coax
Let me know what you think. Is this close? It sounds great.
73's