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I am working on a fully homebrew build of ubitx version 2, which is intended for use in vhf transverter application. I wish to increase maximum receive gain (so that I can saturate the audio output amp simply with receive noise), and I am looking at the audio amplifier stage Q70 (MMBT3904) which precedes the audio amplifier TDA2822.

Would substitution with a darlington device with same pin connections (and suitable bias changes) be worth trying? For example, MMBTA13L looks like a possibility.

Interested in any suggestions/comments!

73 Dave WB0GAZ wb0gaz@...

Dave

I think the receiver back end is nicely optimized, so I would instead consider how to use the 45 MHz IF. I imagine you may need a 45 MHz amplifier added on the front end side of the mixer when you add another mixer before that. Keep your net gain up to here small and it should work. You want status quo in gain to each mixer.

Curt

Hi,

Is it possible that when the uBitx is receiving through the transverter the noise level will be greatly increased.?

At VHF and higher most of the noise comes from the RF preamp stage (rather than from the atmosphere picked up by the antenna) and may already be at a significant level when feeding into the uBitx. Assuming that your transverter has RF and other IF stages, rather than being a "passive" mixer. ? ?

But, the proof in in the pudding. As I'm only speaking to the general case.?

Tom, wb6b

Thanks, Tom -- that's what I'm seeing. Through the transverter, with an old HP 8660 synthesizer providing -140 dBm, I am just barely able to hear the synthesizer (so I think noise figure is OK), however, the overall audio level is not very high (just barely adequate.) If I put the output of the ubitx through a PC amplified speaker, it works very well - plenty of audio. The TDA2822 audio output amp is able to provide adequate volume with a higher RF input to the radio, so I figure getting some additional audio gain would suffice, and perhaps be simpler than manipulating the RF line-up. Hope that helps explain my goal!

Thanks again,

Dave