Dan Schaaf wrote:
> My take on this has always been, if the atmospheric noise can be heard in
> the radio, above the inherent radio noise ( with no antenna connected )
> then you don't need a preamp. The preamp will amplify the noise as well as
> the signal.
The problem with this concept is that you end up with no AGC,
because of inadequate IF gain in nearly all receivers, especially
when using 200 Hz CW bandwidth. The correct fix is to add about
20 dB more IF gain. I actually did this to my FT-757. It worked
great, I got AGC on the weakest signals. You can also add
enough preamp gain to get the AGC at the threshold on atmospheric noise.
The problem with this is that your preamp is subject to overload.
A third idea I have been thinking about is to build a audio AGC,
which has the advantage that no receiver modification is necessary.
It would likely be necessary to have an audio roofing filter to
get rid of out of band audio hiss and hum. It might be possible
to find some off the shelf audio processing box with AGC to do this.
Equipment for DJ's, radio stations and/or recording studios would
be likely to have an AGC function.
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