[ICOM] Sherwood Engineering and DSP

[Adam Farson]

Hi Julio,

That is difficult to say. A detailed analysis of the AGC will be required to
determine which loop suffers overshoot in the presence of a noise impulse,
and for what reason. Only Icom can correct this issue.

I assume that the analogue and DSP AGC inputs are compared in the DSP AGC
process. I believe that if the analogue loop detects a signal which has
passed through the roofing filter but the DSP loop does not "see" that
signal in the DSP-IF filter passband, the analogue loop will be inhibited
from pulling the AGC line. The purpose of this is to prevent swamping.

Cheers for now, 73,
Adam VA7OJ/AB4OJ


-----Original Message-----
From: icom-bounces at mailman.qth.net [mailto:icom-bounces at mailman.qth.net] On
Behalf Of Julio Peralta
Sent: Thursday, June 07, 2007 12:54
To: 'ICOM Reflector'
Subject: RE: [ICOM] Sherwood Engineering and DSP

Adam I've noticed the problem with the ticking artifact. The fix you
mentioned is that a hardware fix or can it be done in software?

Julio, W4HY

-----Original Message-----
From: icom-bounces at mailman.qth.net [mailto:icom-bounces at mailman.qth.net]
On Behalf Of Adam Farson
Sent: Thursday, June 07, 2007 2:32 PM
To: 'ICOM Reflector'
Subject: RE: [ICOM] Sherwood Engineering and DSP

Hi Ken,

Correct - the IC-756Pro-series AGC does not have this issue.

The IC-7800 AGC subsystem is unusual; there is an analogue loop which
rectifies the 36 kHz IF at the output of the 2nd mixer, and applies the
resulting DC voltage to one of the ADC's analogue inputs. There is also a
digital loop, within the DSP, which adjusts the gain prior to the IF
selectivity process and also develops a DC AGC voltage via a DAC. This
voltage controls the gain of the 1st IF amplifier. The digital loop is
similar to the one in the IC-756Pro3.

Both loops are processed within the DSP. I believe that the ticking artefact
is due to very short attack time in one of the AGC loops, and doubtless the
designers can correct it. This artefact does not exist in the 756Pro series.

Cheers for now, 73,
Adam VA7OJ/AB4OJ


-----Original Message-----
From: icom-bounces at mailman.qth.net [mailto:icom-bounces at mailman.qth.net]
On
Behalf Of Ken Kinyon
Sent: Thursday, June 07, 2007 09:28
To: ICOM Reflector
Subject: RE: [ICOM] Sherwood Engineering and DSP


"Icom756 Pro, Pro II and Pro III are fine."

This is a quote from page 10

Am I misinterpreting this?   To me, he saying that the IC-756PRo series
does
not
have this AGC problem.

Am I correct?

73,
Ken W7TS




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