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TOPIC: Panorama Spectrum and S-meter dbm readings

Panorama Spectrum and S-meter dbm readings 09 Jun 2020 05:42 #1

From FAQ you can find:
Step 1. Let's calculate FFT bin band (single-unit filter). 156250/16384 = 9,53 Hz. This is the bandwidth of a single-unit filter.
Step 2. Let's calculate the difference between RX filter bandwidth and single-unit filter. 2900Гц/9,53 Hz = 304 (times). Filer bandwidth is approximately 304 times wider than a single-unit filter.
Step 3. Let's calculate the difference in dB between summed noise power in single-unit filter bandwidth and summed noise power in RX filter bandwidth. 10*log(304) = 24.8 dB. i.e. noise power in 2.9 kHz bandwidth will be higher than in single-unit filter on 24.8 dB.
Step 4. Let's calculate S-meter readings. -118 dBm + 24,8 dB = -93,2 dBm.

Does this also apply for the Colibri Nano?
Independent of:
Antenna input terminated with 50 Ohm, with passive mini windom or active loop connected and different FFT sizes and sample rates. According above calculation my S-meter always shows roughly 10 dbm less than calculated
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Panorama Spectrum and S-meter dbm readings 09 Jun 2020 14:04 #2

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HI,
Do you have a signal generator?
If yes, you can apply this signal to the ColibriNANO input and then adjust S-meter in the Options-> Device-> Expert-> Preamp correction.
Роман, Roman
Expert Electronics
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Panorama Spectrum and S-meter dbm readings 09 Jun 2020 17:58 #3

Hi,

thanks for prompt reply. Actually I do not have a signal generator. But I tried the mentioned option already without. When correcting the preamp settings the panorama and RX S-Meter level are changing proportional so that finally the results stay the same as mentioned.
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Panorama Spectrum and S-meter dbm readings 09 Jun 2020 18:04 #4

On the other hand the other remarks in FAQ fit very well, so this is working as described.
If there is a useful signal in the RX filter bandwidth, e.g. SSB signal, S-meter will also display the summed power of all voice components in the filter bandwidth. On panorama, each separate voice component will be displayed lower than overall S-meter readings. This statement is also valid for TX mode.
Note: If you are in CW, with filter bandwidth 20 Hz, sample rate 312 kHz and FFT size 16384, S-meter readings and panorama noise level will be approximately equal.
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Panorama Spectrum and S-meter dbm readings 10 Jun 2020 06:25 #5

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HI,
Thanks for the clarification, glad it worked out.
Роман, Roman
Expert Electronics
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Panorama Spectrum and S-meter dbm readings 10 Jun 2020 08:23 #6

Well only only for the specific condition with useful signal or similar to the example of special CW bandwidth, sample rate and FFT size it fits
The initial issue regarding discrepancy between panorama readings and RX S-meter readings, for other settings when receiving air noise, or antenna input terminated with 50 Ohm, is still not clarified. Adjusting preamp settings does not solve this as both panorama and S-Meter readings will change proportional...

Thanks anyway for response
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Panorama Spectrum and S-meter dbm readings 10 Jun 2020 10:14 #7

Sample rate 192 Khz, FFT size 16384, RX-Filter 2K
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