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Old 26-Oct-2020, 3:42 PM   #64
Retired A/V Tech
Join Date: Aug 2012
Location: S.E. VA
Posts: 2,683
Originally Posted by tripelo View Post
Have noticed that (spurs) in the low cost RTL devices. Most of the time not a problem if one is aware of their presence.
I found another scanner that can be used with the RTL-SDR.COM V3 dongle.

The resolution isn't too good and there is no way to adjust the gain of the dongle. It is necessary to insert an attenuator before the dongle to obtain the correct representation of SNR.

But, the Touchstone software does cover more than one channel and you can see changes in real time. With the RTLSDR Scanner, you don't see the scan until it is completed.

The amount of attenuation must be found by trial-and-error. It helps if you have a TV that will tell you the SNR of a known signal.

The Toner attenuator shown above could be used.

My amateur Videos

I didn't use a preamp for this scan. The channel 16 signal (first strong signal on the left) measured -6.3 dBmV (-55.1 dBm) with my Sadelco DisplayMax 800 signal level meter:

When I used a 17 dB preamp (CM7777HD Amplify, low gain setting), more attenuation before the dongle was needed.

I use VLC Media Player.

If you want to be able to adjust the gain, you would need to purchase the Rational Waves RF SPECTRUM ANALYZER SOFTWARE:

But, I think it would be better to buy an SDRplay RSP1A and use the RSP Spectrum Analyser software.

When I used the 17 dB preamp with the SDRplay RSP1A and the RSP Spectrum Analyser software, I was able to adjust the Display Scale settings for a proper display:

The ADC is the Analog to Digital Converter in the SDR.

The channel 16 signal input to the RSP1A with the 17 dB preamp measured -35 dBm. I don't usually use the preamp; just wanted to see how the RSP Spectrum Analyser software would handle the stronger signal.

When the RSP1A is used with the SDRuno software, there is an overload warning if the gain is set too high. It did flash when the gain was set to MAX when using the 17 dB preamp. To avoid damage to the RSP1A, the input signal should be kept below 0 dBm (49 dBmV).

Attached Images
File Type: jpg Touchstone 10-25-2020 VHF-High_1.jpg (98.0 KB, 223 views)
File Type: jpg Touchstone 10-26-2020 UHF 10dBAttn_1.jpg (108.2 KB, 222 views)
File Type: jpg 11-1-2020 RSP SpecAnal-17dBamp_4.jpg (152.4 KB, 186 views)
File Type: jpg 11-1-2020 RSP SpecAnal-17dBampUHF_2.jpg (115.7 KB, 186 views)
File Type: jpg RSP1A Overload2.jpg (70.5 KB, 185 views)
File Type: jpg TV Minimum Signal3.jpg (111.7 KB, 91 views)
If you can not measure it, you can not improve it.
Lord Kelvin, 1883

Last edited by rabbit73; 7-Nov-2020 at 8:27 PM.
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