Does this mean that on Sunday I should NOT have been one of the few on the
east coast to not only copy, but also work the 9M2 on the low end of 80m CW
because I had my Orion's gain set at 100 and my PROG threshold set for 95uv?
Sorry I can't relate the S-meter reading because I very seldom watch that
when operating CW. Maybe I just have a super-gain plain old 80m dipole? Or
maybe I, being a full-flegged memeber of the TT CULT, just enjoy operating
my gear more than trying to technically analyze faults into a design teams
efforts. Perhaps your efforts would have been more fruitful IF you had been
a member of that design team.
I'm curious as to why you think (not really though) if I'm copying a very
weak signal in low band noise and I have a BW set to about 300Hz, why is it
that the very weak signal seems to pop right out of the noise when I set L
CUT to about -100?
Tom-W4BQF
----- Original Message -----
From: "Sinisa Hristov" <shristov@ptt.yu>
To: <tentec@contesting.com>
Cc: <orion@contesting.com>
Sent: Wednesday, February 11, 2004 1:34 PM
Subject: [TenTec] Orion's AGC THRESHOLD is in error by 21 (9) dB
> Orion's AGC Threshold control is useful for
> avoiding AGC action on noise peaks.
> Such an action tends to intermodulate a weak signal with noise,
> significantly reducing readability.
>
> The same benefit was available to receiver users for decades.
> One simply turns RF GAIN counterclockwise
> until the S meter stops responding to noise peaks.
> Contrary to popular belief, no sensitivity is lost
> by reducing RF GAIN control this way, because the actual
> gain would have been reduced by AGC anyway.
>
> I've already written that Orion's AGC Threshold control
> is less adequate for the purpose than an ordinary RF GAIN
> (not Orion's) because of:
> * lack of correlation between AGC THRESHOLD values and S meter readings;
> * lack of dedicated knob.
>
> Both disadvantages can be overcome,
> but not without substantial price in time and effort,
> which is important in contests.
>
> Particularly cumbersome is to know "how much of it" to apply
> (vs. RF GAIN method where one simply looks for a non-moving S meter).
>
> Menu readings are given in microvolts. The manual is not explicit
> where are these microvolts measured. One is tempted to assume
> that they are measured at antenna connector and can therefore
> be correlated with S meter indication on the basis of S9 = 50 uV
> and +1 S unit = doubling the voltage.
>
> However, such an assumption is wrong.
> The measured AGC threshold occurs at signal levels
> ~21 dB below set values with preamp on,
> and ~9 dB below set values with preamp off.
>
> Correlation with S meter indication was found to be as follows:
>
> AGC THRESHOLD S meter
> 191.48 8.8
> 95.74 7.9
> 47.87 6.8
> 23.94 5.6
> 11.97 4.3
> 5.98 2.9
>
> The table above is valid independent of preamp and attenuator settings.
>
> The moral from this is twofold:
>
> * adjust preamp, attenuator and RF GAIN controls (in this order)
> to avoid noise peaks going above approx. S 8
> (don't be afraid, no sensitivity will be lost);
>
> * adjust AGC THRESHOLD slightly above S meter noise peak readings,
> according to the above table.
>
> TenTec would have done a much better job by displaying AGC THRESHOLD
> values in S meter units, with some care taken to ensure good tracking
> between them, which I guess is easy, as both S meter and AGC are
> DSP functions.
>
>
> 73,
>
> Sinisa YT1NT, VA3TTN
>
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> TenTec@contesting.com
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