[TenTec] Omni VII - S-meter reading lower in 6k/2600 than 2.5k/2500

[Jay Lyle]

Dr. Johnson,

Thank you for the explainiation.  I know very little about DSP filtering but 
I can picture the "granularity" of the readings.  If I'm understanding 
correctly, due to digital bit "quantization", and the order of how many bits 
are used, this may affect the compensation of the filter loss.

S-unit difference might not actually be 6 db; I could below the point where 
the s-unit is changing to the next bar.  This means that there might 
actually be a 2 db difference which is probably whithin spec.  My measuring 
device, the s-meter, just doesn't have the precision to measure properly.

Am I understanding this?

I ran a test under a more controlled environment by using another 
transmitter into a dummy load.

There is a repeatable 1 S-Unit difference at the lower s-unit range (like 
s-5)... but at a higher level the effect is not seen.

I'll call TT on Monday anyways to see if they think something is wrong.

What makes me wonder is that I hadn't seen this effect in the 1.5 years of 
ownership.

73,

Jay
----- Original Message ----- 
From: "Dr. Gerald N. Johnson" <geraldj at weather.net>
To: <tentec at contesting.com>
Sent: Saturday, July 17, 2010 7:03 PM
Subject: Re: [TenTec] S-meter reading lower in 6k/2600 than 2.5k/2500


> Since those are digital filters there could be gain compensating
> factors, that are over compensating, or different styles of filters and
> the filter coefficients don't match the gain from one bandwidth and
> shape factor to another. One of the nagging details of DSP filters is
> that you have to keep track of levels in accumulators so as to not go
> over the range of available numbers, that's most critical in a 16 bit
> integer DSP, fairly critical in 32 bit integer DSP and hardly a problem
> in a 32 bit floating point DSP. Trouble is the 16 bit integer DSP is
> cheapest and fastest, the 32 bit integer DSP can be low cost and very
> fast, while the 32 bit floating point DSP is inherently most expensive
> and slowest.
>
> 73, Jerry, K0CQ
>
> On 7/17/2010 12:41 PM, Jay Lyle wrote:
>> This seems strange to me:
>>
>> 1) Right now, noise level with 6k/2600 is 3-4 s-units
>> 2) If I go down a notch to 2.5k/2500 noise GOES UP to 4-5
>>
>> Is this observation is consistent across all bands (blankers/notch and 
>> such are
>> off).
>>
>> You'd think it would GO DOWN with a narrower filter combo.
>>
>> Going down to narrower settings, I get the expected results.
>>
>> 2.5k/600 shows 4 s units
>> 500/500 GOES DOWN to 2
>>
>> I believe radios will have different gain settings depending on different
>> filters to make up for the insertion loss.
>>
>> Anyone else see this effect?
>>
>> 73!
>>
>> Jay
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