The R4C AGC was discussed and even modified in a CQ magazine article back in the
80's by W3RJ. It took the flatness out of the AGC clamping area so that signals
that were between S7 and 30 dB over S9 would vary in volume by about 3 dB
instead of the stock 0 dB. The thought was to allow some loudness separation by
your ear.
That being said, how hard would it be to find the Orion AGC parameters that
would cause the exact same AGC characteristics as the R4C?
73,
Tim K3LR
Tom Rauch wrote:
> > Two diodes back to back in front of a receiver is'nt that a bit of a
> > simple?
>
> Two diodes back-to-back in front of all the filters would absolutely kill
> reception if the signals were limited in the diodes! The IM and general
> "crud" would be horrible.
>
> A soft limiter after the filters, if kept well out of limiting on background
> noise, is useful. I use that on my R4C's to prevent "ear blasting" because I
> have to run gain almost full open for weak signals when listening in quiet
> directions.
>
> My (totally redesigned) R4C's absolutely blow every other receiver here out
> of the water because the AGC has a slope at low end, and does not HARD clamp
> the audio level. The harder part of the AGC comes in about 10-15 dB out of
> noise floor, and the hard limiting comes in before my ears get hurt.
>
> This means no matter what direction I listen (noise changes in each
> direction) I don't have to adjust anything except volume. I haven't moved
> any control on the R4C's except volume and tuning in the past three years,
> summer, winter, fall and spring and every direction and band. Other guest
> ops, who seem to do OK here, always strongly agree. The comment is always
> "signals jump out of the noise" and are easy to copy. The reason for that is
> the AGC slopes on the low end of threshold, becomes stiff at about 15 dB out
> of noise floor, and the whole thing hard clamps AFTER all the filters to
> prevent ear damage.
>
> IMO too much limiting on signals at too low a threshold is a VERY bad thing,
> as is anything that makes me have extra knobs to fiddle with as receive
> direction changes and noise floor changes.
>
> 73 Tom
>
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