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

[Bob McGraw - K4TAX]

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
>> _______________________________________________
>> TenTec mailing list
>> TenTec at contesting.com
>> http://lists.contesting.com/mailman/listinfo/tentec
>>
>>
>
>
>
>
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