Friday, 22 August 2014

Ramp Up The Amps

After much deliberation, reading and checking, a couple of things occurred to me. First was that I should try varying the emitter resistor in the Wispy LO, to try and increase the drive to the receive mixer. Germanium diodes typically turn on around 0.3V, so with a drive of barely 240mV pk-pk, I doubt they were on enough. The resistor in circuit is 2k2. So I tried tack soldering another 1k in parallel. This brought the level up to closer to 300mV pk-pk. A bit more playing here and I should be able to obtain the right level of drive. It will probably mean though that the Tx chain will need completely realigning!

The other thing that suddenly popped into my head was why my LM386 audio PA seemed to overload so badly when fed from the Wispy audio chain. I suddenly thought, perhaps I had the gain control pot wired wrong? Indeed I had! So after changing the wiper of the pot to go to the input capacitor and not the input pin of the chip, all should now be well.

My little self contained LM386 audio power amplifier
Oooh! Look, Ive just realised how to add captions to my pictures! Expect more of that!

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