Re: G8 signal strength meter


Tony Germanotta
 

So would you avoid the soft mute or the zero reading by merely keying in 1209 instead of 1210, for instance? Or by setting the step to 9Khz rather than 10 for transatlantic stations? It doesn't seem to do anything for me, but that would be a rather simple way to eliminate the soft mute, which doesn't seem to bother me nearly as much as most folks here. I am still amazed at what this little chip can do.


On Jan 27, 2010, at 12:51 PM, sdwillingham wrote:

 



Hi Tony,

I am glad you find the discussion interesting. Sometimes I
worry about alienating the non-tech group members with too
much technical stuff vs dxing strategies, techniques, and
results.

>> "Does the radio somehow know the center of the signal I
>> am shooting for?"

Actually, the problem is that it doesn't know the center you
are shooting for when you tune to a different one!

Your question is a very good one and the answer is non-obvious
to anyone without inside information on the chip's design.
Essentially, the chip needs to know the desired carrier frequency
in order to do its 'smart' SNR signal processing and calculation.
When you off-tune, the chip no longer 'sees' the carrier where
you told it to 'look'. Under this condition, the processor
considers the SNR calculation to be invalid and returns a 0 dB
result.

By the way, this is part of the issue dxer's have with soft-mute.
The soft-mute calculation is based on the measured SNR. So when
you off-tune, the SNR goes to zero and soft-mute (if enabled)
kicks in.

Cheers,
Scott

--- In ultralightdx@yahoogroups.com, Tony Germanotta tony@...> wrote:
>
> Thanks Jim and Scott for the info. This is fascinating stuff for a non-techie like me. I have a question, though. When I offtune my PL-310 to one side or another of a frequency, not only does the signal strength drop a few notches on the volume knob, I always get a 0 SNR reading, no matter how well the station is coming through, no matter how tight the bandwidth. Does the radio somehow know the center of the signal I am shooting for? Of course, it really doesn't matter, the important thing is intelligibility. But it has me wondering just how smart this chip really is. Is it reading my mind, or just my WRTV Handbook?
>
> On Jan 26, 2010, at 11:17 PM, sdwillingham wrote:
>
> >
> > Jim gives an excellent explanation of the RSSI and SNR indicators.
> > Here are some further comments for more technical readers.
> >
> > 1) The abbreviation RSSI stands for "Received Signal Strength
> > Indicator", not "Relative . . ." Jim correctly emphasizes
> > that this strength refers to the LNA input voltage, not
> > electromagnetic field strength.
> >
> > 2) The signal-to-noise ratio Jim describes refers to signal strength
> > compared to the noise generated by the radio circuitry. The SNR
> > metric from the Si4734 is more sophisticated than that. If one
> > substitutes a short-circuit across the AM antenna terminals, he
> > will see the RSSI drop to 2-5 dBuV. With an antenna connected
> > and "between stations", the RSSI can be 30 or more dBuV. Yet the
> > Si4734 does not report the SNR as 25 dB, i.e. the signal strength
> > above the receiver noise floor. Instead, the chip reports a
> > metric measuring the signal strength relative to atmospheric
> > noise and interference. Of course, if the atmospheric noise is
> > low enough (or antenna gain is inadaquate), the SNR calculation
> > will reflect the receiver circuit's noise floor. I wish I
> > could give more detail about the calculation, but I believe that
> > is proprietary information.
> >
> > Cheers,
> > Scott
> >
> >
>


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