[DSP-10] S-Meter reading

[Bob Larkin]

Hi Courtney and Hermann,

Interesting ideas on the S-units and the RST system.  Certainly your ideas 
are in a direction that make a lot of sense!   The T of  RST has been of 
little value for a long time. Your direction is an interesting thought for 
re-vitalizing the old idea.

I wanted to toss in a couple of thoughts on the S-meter.  It is tied to the 
peak value on the spectrum display, where the  little box marker sits. It 
is usually valid, even when the display is off screen.  The quantity being 
measured is S+N rather than S alone.

Here are a couple more thoughts, parts of which may be old stuff to people:

My original thought was that the dBm reading would be more useful than S 
units, and it lends itself to good calibration. The notes in the 
instructions for the RF Gain cover it:
http://members.aceweb.com/kd7ts/v380/rfgncfig.htm
The calibration of the RF Gain is worth the effort, as well.

The CFG variable gain_adj is small dB value to adjust power displays, and 
is nominally 0.0. This allows correcting for gain differences between 
different sets of hardware.  This should be done with the radio running 
without anything ahead of it, and then any converter, or preamp gain is 
entered into the CFG file with the transverter definition..

I must confess the bars of the S-meter had no grand plan.  I could not 
remember much about it, but my notes said it was arranged so that all bars 
could come on with a full input signal, with 100 RF Gain.  This is about 
-54 dBm.  There are 15 bars, and so it shows 90 dB of range. This gives a 
first bar at -144 dBm S+N.  This makes S9 quite a bit less than 50 uV, as 
you observe. I don't know what i was thinking about the 20, 40, 60 
markings. They aren't that much. It  must have been intended to make it 
look like an S-meter ;-)

Thanks for putting the ideas together, Courtney.  It makes for good discussion.

73, Bob  W7PUA


At 07:38 PM 1/10/2008 -0800, Courtney Duncan wrote:
>That makes more sense than my explanation.  Apparently there is a
>different S-9 convention on VHF and above than on HF.  There is so
>much environmental noise on HF that the bar is "higher."
>
>For a -93 dBm S-9, my DSP-10 is right on.
>
>Courtney, n5bf/6
>
>On Jan 10, 2008, at 12:36 AM, f5vkq wrote:
>
>>
>>
>>Hello Courtney, GM and all the best for 2008 from France, F5VKQ,
>>Hermann.!!
>>
>>(ex DC9UP)
>>
>>
>>
>>
>>
>>I am one of the DSP-10 enthusiasts in Europe and in the last years I
>>have been building several DSP-10 (6) for me and my friends.
>>
>>I mainly use one of them for 10GHz EME-work.
>>
>>I also have been in good contacts with Bob and some of the features
>>(at least partly) are out of my mind, but Bob implemented them.
>>
>>
>>
>>Pse take look to the table in the appendix and that's the relation
>>what we use over here in Europe btw dBm (50 Ohm) and S-Meter steps.
>>
>>
>>
>>When I put in 50 uV  I am seeing the same as you see, but according to
>>the official table here 5,01 uV are -93 dBm and gives me a S9 meter
>>reading on the DSP-10.
>>
>>
>>
>>So, I was not aware of this when measuring around inside the DSP-10.
>>
>>
>>
>>Could it be that Bob also used the European  convention ???
>>
>>
>>
>>73 de Hermann
>>
>><S-Meter calib.jpg>
>
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