[TenTec] IRF gain, IF gain or AF gain?

[Martin Sole]

Since we  now have selectable notch or peak (SAF), selectable AF/RF gain
doesn't sound impossible (hi hi!).

With the S meter I think some of it is the change from AF to RF derived AGC
(or the other way around). Annoying as S meters can be, almost pointless
some might say the real story is that pretty much every communications grade
receiver has a meter that shows at least some sort of relative strength and
we do make use of them.  The older approach of riding the RF gain was
generally to stop detector overload before we had product detectors (today
of course it's to stop AtoD overflow) and for this the AGC would be turned
off. Even with Orion I find that riding the RF gain control diminishes the
rather excellent AGC and indeed it seems you can get a similar effect by
increasing the AGC threshold, I usually run mine between 3 and 6 uV with the
slope at 2:10 for the smoothest audio and minimal band noise, but this with
the RF gain up. AGC threshold clearly works in the same area as it also
drives the S meter upscale. The attenuator of course does not affect the S
meter but can stop AtoD overload.

Didn't know about the K3, have played with a couple but not that in depth.
Might need to borrow one again.


Regards
Martin


-----Original Message-----
From: tentec-bounces at contesting.com [mailto:tentec-bounces at contesting.com]
On Behalf Of Barry N1EU
Sent: 23 February 2012 08:54
To: Discussion of Ten-Tec Equipment
Subject: Re: [TenTec] IRF gain, IF gain or AF gain?

On Thu, Feb 23, 2012 at 12:21 AM, Martin Sole <hs0zed at csloxinfo.com> wrote:

> I find the use of RF gain as an audio level control rather counter 
> intuitive, but workable however it renders the Orion as a radio with 
> essentially no S meter and ties up the multi knob that is used for 
> everything else leaving the AF gain virtually unused.
>
> If this is really the best way to extract maximum weak signal 
> performance from the Orion, and enough people do seem to think it 
> does, then it also seems reasonable to look at a way to either reverse 
> the controls, having the AF control operate RF gain full time and 
> change the soft key RF gain to AF gain and further, to remove the S 
> meter from the loop that is affected by the RF gain control.
>

I think that's a brilliant suggestion - to reverse the AF and RF Gain
controls.



In terms of the s-meter, v1.373 managed to preserve full scale s-meter
action at reduced RF Gain.  It's unfortunate that ability was lost later in
the firmware development cycle.  I sorely miss it.



> Whilst I think I understand that the Orion RF gain is acting to reduce 
> overload of the succeeding analog to digital conversion process there 
> seems to be a difference between how Orion achieves this and how 
> almost every other design does it, I've not heard mention of the need 
> for this approach on other IF dsp radios.
>

The Elecraft K3 must be approached in an identical fashion.

73,
Barry N1EU
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