Bob,
let me see if I can help, having written appendix C of the F5K manual. I
remember struggling, just like you seem to be, when dealing in my mind with
AGC-T (or Max Gain as it is called on the Setup Form->DSP->AGC/ALC. Why the
same control has two names is beyond me, but so be it).
Fig 186 on page 215 of the F5K v 1.14 manual shows the signal level post AGC
in relation to the signal level pre AGC. Each slanted line corresponds to a
certain setting of the "Max Gain". The maximum output from the AGC
equals -13dBm (I cannot remember where this came from - I probably measured
it. However, the actual level is not relevant, what is relevant is that
there is a maximum output level). Assuming the Slope setting of the AGC is
set to zero, the line across the top of the graph corresponding to maximum
output level is horizontal and shown fixed at -13dBm.
Therefore, at a MaxGain of 60dB, an input signal of -73dBm just equals the
maximum output of -13dBm. Any higher input level will result in -13dBm
output level. For Max Gain = 60dB then the "AGC Threshold" (NOT EQUAL to
AGC-T - more on this later) equals -73dBm. It is obvious that as the Max
Gain setting is adjusted, the "AGC Threshold" value changes as well such
that "AGC-Threshold" + "Max Gain" = Maximum AGC Output Level.
Now here's the really confusing thing. The control labeled "AGC-T" on the
front console is in fact not at all the "AGC Threshold", but is in fact the
Gain setting of the AGC. (A long time ago there was a huge discussion on
this reflector as to what to call the front console control and it
eventually settled on AGC-T). If you open Setup->DSP->AGC/ALC you will
notice that the Max Gain value is exactly the same as the AGC-T value.
Change one and the other will follow. As I said, they are the same control.
I hope this helps somewhat,
73 de Joe - AB1DO
----- Original Message -----
From: "Robert Jefferis" <jeffe...@antelecom.net>
To: "Bob McGwier" <rwmcgw...@gmail.com>
Cc: <flexradio@flex-radio.biz>
Sent: Monday, June 29, 2009 10:11
Subject: Re: [Flexradio] Automatic Gain Control Threshold "AGC-T" versus
reality
Bob,
Continuing, I just looked at the AGC discussion on p. 109 of the F5K
manual. The bullet describing the "Slope (dB)" parameter clearly states
that there is an AGC threshold. Does the operating control panel "AGC-T"
control actually adjust the threshold? Or, is the threshold hard coded? I
do not really care about twiddling the threshold, I would like to
understand just what the AGC-T is adjusting. Thanks.
Bob
On Jun 29, 2009, at 1:11 AM, Bob McGwier wrote:
This one does conform and should function like legacy, out of touch,
radios. Since this radio is calibrated to a 50 Ohm load with the
internal generator producing a known voltage, AGC-T is calculated to dBm
or as close to it as we could get.
Bob
N4HY
Tim Ellison wrote:
Read this article. It should clear up a few misconceptions regarding
AGC-T. Remember this is a software defined radio and not everything
works like it did on a traditional analog/dsp radio.
http://kc.flex-radio.com/KnowledgebaseArticle50153.aspx
-Tim
-----Original Message-----
From: flexradio-boun...@flex-radio.biz
[mailto:flexradio-boun...@flex-radio.biz ] On Behalf Of Robert Jefferis
Sent: Sunday, June 28, 2009 8:57 PM
To: flexradio@flex-radio.biz reflector
Subject: [Flexradio] Automatic Gain Control Threshold "AGC-T" versus
reality
Greetings all,
I am wondering if anyone in "FLEX LAND" can tell me whether or not
there is a known functional relationship between the "AGC-T" setting
and receiver input signal to noise ratio (SNR). I have read several
postings related to adjustment of AGT-T for good, or desirable
performance. My experience with traditional receivers tells me that
this parameter should, in principle, be a "set and forget" parameter.
Pick the number of choice, typically between 0.5 and 2 micro Volts
into 50 Ohms. Not that it matters, but I am using an F5K.
Bob, KF6BC
--
(Co)Author: DttSP, Quiktrak, PowerSDR, GnuRadio Member: ARRL, AMSAT,
AMSAT-DL, TAPR, Packrats,
NJQRP, QRP ARCI, QCWA, FRC.
"You don't need to see the whole staircase, just
take the first step.", MLK.
Twitter:rwmcgwier
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