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Andrea Baldoni · August 26th 06, 08:50 PM posted to rec.radio.amateur.homebrew

wrote:

: Dual conversion for HF and triple conversion of 2m. There would
: not be RF agc on the 2m converter. In FM modes you should see
: limiting so agc is behavour is different.

By looking closer at the AGC circuits, there is RF AGC also in the 2m
and 6m converters. However, the AGC involves not all amplifiers in this
receiver, just the first and the last but one. I often see different
configurations in receivers, where every amplifier is controlled.
Maybe they thought it would suffice.

: Likely a test point that is not marked on the board. I don't have
: a print handy.

I had calibrate it for the minimum voltmeter reading, because it appears that
the signal is negative over a positive DC bias, supplied by the JFET.
Probably there is another point where the signal is positive, anyway it
should be the same.

: Having experimented with recievers since before EE school and still
: many decades later I find it challenging. Always looking for and at
: new ideas.

I have read very interesting articles on QEX (by downloading them in PDF
format from the site) following back the chain of cross references starting
from "A software defined radio for the masses" to the R1 and R2.

Every designer has his own ideas about AGC, dynamic range, et all. Often
very different. While I never (as now) tried to design a receiver, I want
to carefully understand the reasons behind every implementation. So I could
build my own opinion and in future choose what I think better for a receiver
project.

Anther interesting argument is LO: DDS, PLL or DDS+PLL?

Ciao,
AB

.... Andrea Baldoni, 2002: messaggio non protetto da copyright.