[TenTec] AGC Threshold, RF Gain, Volume

[John Huffman]

Thanks Merle!

That was a good explanation of what I was experiencing.  I like version 2 
firmware, but will try v1.373b5.  I've tried it before, but never for long 
enough to get used to it.

73 de K1ESE
John


----- Original Message ----- 
From: "Merle Bone" <merlebone at charter.net>
To: <tentec at contesting.com>
Sent: Sunday, May 11, 2008 3:15 PM
Subject: [TenTec] AGC Threshold, RF Gain, Volume


> John,
> Yes the RF gain control changes the AGC threshold level - just like 
> setting
> it in the AGC menu. One of the original Orion firmware developers, Doug
> Smith, wrote in a paper describing the Orion Digital AGC System:
> -----------------------------------------------------------------------
>
> "In digital AGC systems, it is relatively easy to provide a variable
> threshold or "knee." Input signals below the threshold do not actuate the
> digital AGC and are not compressed. At thresholds well above the receiver
> noise floor, a receiver therefore gets quiet when only puny input signals
> are present in the passband. At thresholds near the noise floor, all 
> signals
> are boosted to meet the output-level criterion. The net effect of a 
> variable
> threshold is very much like that of an IF gain control."
> ------------------------------------------------------------------------
>
> Consequently, if you "ride the RF gain" and set it for a good audio level 
> on
> a stronger signal, weaker signals will not activate the AGC and they will 
> be
> too low in volume. I've never been fond of this process. I think it was a
> "crutch" to offset the gain distribution issues in the new Orion V2
> firmware. There was an AVC loop in the V1 code that prevented the audio
> stages from being overdriven and distorting. That code was taken out of 
> the
> V2 firmware and there have been peak signal distortion issues since. That
> started some people doing what you described with the audio and RF gain
> controls. Unfortunately you are seeing some of the unintended consequences
> of operating the radio like that. Hopefully Ten-Tec will address the
> distributed gain level issues in the next Orion V2 firmware release - 
> maybe
> they will put the ALC code back.
> 73, Merle - W0EWM
>
>
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