rtl-sdr.com

Why did you switch away from the Hi-Z input?

The output of the SDR is a digital signal, and that should not be affected by the relatively low level electrical noise you could find in USB hubs. Only the noise that can get to the input of the SDR (presumably mostly through the antenna) is the one that can make a significant difference. But If yo...

But you also need a Pi or something equivalent which can pretty much negates the cost advantage. I don't have a Pi, but have plenty of USB cables and hubs. I'm not trying to say that one approach is better than the others (they are all different with different pros and cons) only that it should be p...

I just verified that the RTL-SDR v3 will work fine over a chain consisting of 5 USB hubs and 6 USB cables. With 15ft long cables between the various devices that could cover up to 90ft, although the total amount of cabling in mine is slightly less than 40ft at the moment. I should have at least 2 - ...

You could start by reading: https://en.wikipedia.org/wiki/Modulation

There are quite a few books and webpages for self study material.

Just use the correct search terms such as "RTL2832U, chip, for sale" ;) https://www.semiconductorstore.com/cart/pc/viewPrd.asp?idproduct=75636&utm_source=GoogleShopping&utm_medium=cpc&utm_content=Realtek&utm_campaign=RTL2832U-GR&gclid=EAIaIQobChMI3py1us_h4gIVkK_sCh1BtA1-EAQYAiABEgLg5fD_BwE https://w...

There is the Red Pitaya, but that one isn't exactly cheap either.

However, as per: https://wiki.analog.com/university/tools/pluto you should be able to program the Zynq
"normally write custom software or HDL (for the FPGA) that runs directly on the PlutoSDR"

You should be able to figure out if the transmitter is on or not. You can just use a piece of wire as an antenna and have them near the meter, and look at the spectrum. If there is a very strong signal around 900 MHz, that is probably your meter. Then move away from the meter to see if the signal le...

Why a dipole antenna? Methinks a quarter wave monopole should work just fine, too.

Yeah, I'd second the suggestion for a bandpass filter, either a switchable filter, or standalone filters for the desired band(s) based on the issues listed.