[TenTec] 566 Orion II Firmware Version V3.029---SpectrumDisplay &Tuning...

[k3miy at csonline.net]

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 at 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 at csonline.net>
> To: "Discussion of Ten-Tec Equipment" <tentec at 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 at 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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> >>
> >>
> >
> >
> >
> >
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