Cct to improve modulation here, please?

[Restoration73]

What is more important is that you have an additional audio limiter circuit to prevent the
modulation exceeding 100% on peaks with the average audio level slightly raised to
provide an increased s/n ratio. This is easily added.

[Al (astral highway)]

Hmmm, for example using diodes that when forward biased beyond the peak signal level conduct and using associated circuitry , attenuate the overvoltage?

[Al (astral highway)]

Originally Posted by mhennessy

...

1. You could say the gain was 4700/(25+100), which is x37.6
2. Or you could say that gm is 1/(25+100), which is 8, hence gm.Rl also gives x37.6
3. Or you could calculate the "raw" open-loop gain (40 times 4.7), then apply NFB theory (gain = Ao/(1+AoB), which also gives x37.6

All three methods are mathematically equivalent, but give 3 different paths to understanding...

This is fascinating, cheers, Mark.

I'm drawn to several aspects of practical electronics; problem solving, the aesthetic dimension of using and re-purposing materials to fabricate things (which look good, intriguing, or fantastic!), but also to the deeper mysteries, which, ultimately, do include a growing and deepening mathematical understanding. So this is a brilliant and intriguing coincidence around the convergence on 37.6 using three discrete methodologies.

[Al (astral highway)]

Quick update: job done!

I easily reconfigured the space to pop in a module I built on a tiny square of copper foil - Mark's transistor Pre-amp. I increased gain to X 10 as modulation needed to be higher on voice.

I did in the end convert the RF choke to a tank circuit with 47pF and a tiny trim-cap as well as the series 56pF already in the output transistor, and am also using a wire aerial instead of the loop for the time being. Matching inductance is provided by 1.02 mH in series with the antenna.

Quality of the broadcast signal is high, as perceived by listening on 300M medium wave. There is no noticeable noise and the sound is rather fuller when compared to the few stations left on medium wave.

Cheers, folks!!

Thanks especially to Mark, and to everyone who contributed.

[mhennessy]

Hi Al,

That's excellent news - glad it's working for you. And sorry for the delay in replying - I was away with limited access to the forum.

Cheers,

Mark

[Al (astral highway)]

Originally Posted by mhennessy

Hi Al,

That's excellent news - glad it's working for you.

Thanks again, Mark, hope you had a good weekend.