Bob
Best description of the system I've seen today. In the modern rig,
is the S meter in the agc loop, and is the agc audio derived?
Thanks
Ron
K3MIY
Quoting Bob McGraw - K4TAX <RMcGraw@Blomand.net>:
> According to Art Collins, generally credited with the adoption of the S
> meter system, it was intended to give meaningful signal strength reports.
> The old "green magic eye" on radios was a tuning indicator. Yes, the
> original value per my Collins 75A-3B manual shows S-9 = 100 uV.
>
> Sitting here this evening in front of my Omni VII listening to WWV on 10
> MHz, at 100% RF Gain the S meter indicates S-9 +6dB. Switching in the ATTN
> in 6 dB steps to 18 dB the S meter stays at S-9 +6dB. The answer is simple.
>
> Add 18 dB of attenuation to the input, which automatically adds 18 dB of
> gain to the S meter circuit. The opposite is true when the preamp is
> engaged. Add 12 dB of gain to the receiver circuit which automatically adds
>
> 12 dB of loss to the S meter circuit. I refer to this as a smart S meter
> system. SMART = Signal Measurement, Accurate, Reliable, True
>
> The Eagle, no matter what one does in terms of Attenuation or RF Gain or
> Preamp activation, the S meter reading does not change. Again, same
> concept.
>
> Think about it, if you are receiving a station at S-9 + 20 dB and you switch
>
> in 18 dB of attenuation, did you change his signal strength at the input of
> your radio? The answer is NO. You changed the signal at the input to the
> receiver first stage. Then shouldn't the S meter always reflect the signal
> strength regardless of what one did to their receiver gain system? Hence
> you can always be assured that the S meter system in the Tentec Omni VII and
>
> Eagle will reflect the correct value at the input to the radio.
>
> Even with a signal at the input of -23 dBm or 15,811 uV which is 50 dB over
> S 9, reduction of the RF Gain to 0% the S meter does not change. It still
> shows the signal at 50 dB over S 9, hence the system inversely adds gain to
> the S meter circuit to make up for the reduction in RF Gain. Therefore, the
>
> S meter is correct reading regardless of RF Gain setting. Of course once
> you remove the 50 dB over S 9 signal with RF Gain at 0% you will see the S
> meter display drop to 40 dB over S 9. The point being that the RF Gain does
>
> not affect the accuracy of the S meter reading above AGC threshold.
>
> Now what one does see with no signal applied, as one reduces the RF Gain the
>
> S meter moves upscale in 6 dB increments or 1 S unit. This reflects the
> threshold of AGC reference to S 9 being 50 uV. At 100% RF Gain, as one
> engages the ATTN function in 6 dB increments you will observe the S meter
> indication move up scale 1 S unit per 6 dB. Now once reaching 18 dB, engage
>
> the Preamp and you will see the S meter move down scale by 2 S units
> indication that 12 dB of gain has been added.
>
> All of the math works and so does the radio respond accordingly.
>
> 73
> Bob, K4TAX
>
>
> ----- Original Message -----
> From: <k3miy@csonline.net>
> To: "Discussion of Ten-Tec Equipment" <tentec@contesting.com>
> Sent: Tuesday, April 24, 2012 11:10 AM
> Subject: Re: [TenTec] 566 Orion II Firmware Version V3.029---SpectrumDisplay
>
> &Tuning...
>
>
> > You're right, Ray. In the old days, the S meter was regarded as a
> > tuning aid, and nothing else.
> >
> > Ron
> > K3MIY
> >
> >
> > Quoting Rsoifer@aol.com:
> >
> >> Not only that, but the old Collins spec was 3 S units = 10 dB, not the
> >> modern standard of 6 dB per S unit.
> >>
> >> More broadly, I'm afraid I just don't understand the continuing
> >> preoccupation with S meter and spectrum display issues. Neither has much
>
> >> to
> >> do with
> >> performance, which is where I'd like to see T-T focus their attention.
> >> Flak
> >>
> >> jacket on!
> >>
> >> 73 Ray W2RS
> >> _______________________________________________
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> >> TenTec@contesting.com
> >> http://lists.contesting.com/mailman/listinfo/tentec
> >>
> >>
> >
> >
> >
> >
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>
>
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