Topband: BDR redux

[Oleg Skydan]

Hi, Bob,

I have made a lot of experiments with my AGC design in my T03DSP transceiver
(http://users.ints.net/skidan/T03DSP/ ).

The latest experiment was with the AGC static response. I tryed a system
where
weak signal (below S7) are less compressed by AGC then the strong one.
(4dB:1dB below S7 and 25dB:1dB above S7).

I have found no much difference in the performance compared to the system
where
all signals are compressed equally (10dB:1dB). I found that compression of
about 10 dB:1dB
works fine.

I would suggest to pay more attention to the AGC dynamic characteristics. I
have less
problems with it since my AGC system is all digital and forward type. In the
closed loop
system the system with less gain can benefit not from the "slope at the low
end", but from the
better dynamic characteristics.

All the best,
Oleg
73 de UR3IQO

>
> Tom:
>
> I am attempting to capture good AGC action in the next release of
> the SDR-1000 software (which is a major rework, using different tools,
> libraries, programming style and VB is gone forever and utilizing the
> much improved front end).
>
> I do not understand what you mean by "slope at the low end".  Can you
> also elaborate on what you mean by "harder part of the AGC".
>
> Thanks for the constant stream of good stuff.
>
> Bob
> N4HY
>
> -----Original Message-----
> From: topband-bounces at contesting.com
> [mailto:topband-bounces at contesting.com]On Behalf Of Tom Rauch
> Sent: Friday, February 06, 2004 11:57 AM
> To: on4kj; Doug Waller; topband at contesting.com; Bill Tippett
> Subject: Re: Topband: BDR redux
>
>
>
> >   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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