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Old 6-Sep-2020, 5:50 PM   #6
rabbit73
Retired A/V Tech
 
Join Date: Aug 2012
Location: S.E. VA
Posts: 2,737
Quote:
Originally Posted by eclipsme View Post
Thanks for the pointers.

Since the scanner is not real time, the only way I see to set the gain is through trial and error - try a setting, rescan, try another. Am I missing an easier way?
You are doing it just the way I do it. I don't know of an easier way. It's not possible to see a change in the scan as you change the gain because it takes time for the scan to assemble the individual separate parts of the scan that make up the total scan. The dongle isn't able to do more than 2 MHz at a time.

If you want a scanner that will show changes of gain in real time, you would have to buy the Airspy R2 SDR ($200) and use the Spectrum Spy software that comes with the SDR# software download.

Video (too long)
https://www.dropbox.com/s/ci56eknzhh...32-00.mp4?dl=0

https://www.dropbox.com/s/ci56eknzhh...32-00.mp4?dl=1
Quote:
In any event, here is the Hi-VHF and ch 30 and 31 at higher gain.

Thanks again.


What I see in the image above are the 2nd harmonics (freq x 2) of strong FM signals and the top of a weaker TV channel 10 (192-198 MHz).

http://www.fmfool.com/modeling/tmp/a...0/Radar-FM.png



WGYL FM is 93.7 MHz x 2 = 187.4 MHz



You will probably need an FM filter to keep the strong FM harmonics from causing interference to VHF-High reception.



I only see the tops of channel 30 and 31 because the gain is set a little too high. The dongle can only show a dynamic range of 50 dB because of the limitations of its inexpensive 8 bit ADC (Analog to Digital Converter).

Try reducing the gain a little to move the 50 dB "window" down to see the noise floor.

The gain setting for my dongle is usually at 25.4 dB, but when I use a preamp it's set at about 7.7 dB.



Attached Images
File Type: jpg eclipsmeTVFscan174-216MHz20.7db_2.jpg (87.5 KB, 553 views)
File Type: jpg SDR Comparisons2.jpg (126.3 KB, 558 views)
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Last edited by rabbit73; 6-Sep-2020 at 7:36 PM.
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