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need to relocate RTL-SDR away from computer

Posted: Sun Jul 08, 2018 11:49 pm
by W1ABA
Hi All,

I discovered, the hard way, that having a quarter wave antenna on the RTL-SDR doesn't work-the computer makes to much rf noise.

So, I need to relocate the RTL-SDR away from the computer....actually I could relocate the antenna-but coax is expensive and lossy in terms of being able to copy weak-ish signals.

So, I bought a high end USB cable and expected the RTL-SDR to run when connected via the cable. It didn't::> Not only did the RTL-SDR not run, my 1GB USN HDD also didn't run. Both run perfectly when plugged directly into the computer USB port though.

The cable I bought is rated for USB 2 at full bandwidth, double shielded, and has 2 ferrite bead on the cable to knock down the noise on the shielding shell (one on each end of the cable).

The symptom is that neither device is recognized. It's as if the new USB cable was an open switch.

I'd actually like to move my RTL-SDR about 50 feet, but I'm not quite sure how to do it. Sure wish the RTL-SDR had an ethernet connector instead of a USB connector!!!!

There are USB to ethernet adapters, but they are expensive and problematic. There are USB cables with repeaters built in, but they limit the throughput-so the RTL-SDR can's send/receive data fast enough for it to function.

I would think a wideband analog rf transmitter might make a wireless solution, which would be nice!! However, I am not sure the RTL-SDR would do well with even a low powered transmitter anywhere near it::>

How do I extend the distance between the comp-uter and the RTL-SDR, without breaking the bank?

BB

Re: need to relocate RTL-SDR away from computer

Posted: Mon Jul 09, 2018 12:43 am
by w5dxp
Seems more logical to locate the antenna far away from the computer and run coax to the dongle rather than mess around with long USB cables.

Re: need to relocate RTL-SDR away from computer

Posted: Mon Jul 09, 2018 2:03 am
by W1ABA
Hi Cecil,

It might seem logical, but I am trying to avoid the coax solution because I'd like to avoid an antenna mounted LNA if possible. The LNA cannot be broadbanded, so it prevents me from using the RTL-SDR on other frequencies.

And, my purpose is to chase aircraft band DX, so being able to hear a weak AM signal on the aircraft band that might be 800 to 1200 miles away requires a hot radio. This DX will be used to determine IF (and where to) the nearby 2 meter band is open to. When I hear a United 877 (for instance) flight radio transmission on a frequency that is normally unused here, I look up the flight number online and find it's over North Carolina (at that moment). I point the 2M antenna at NC, and put out a short cq or two. Normally, e-skip openings go undetected because no one transmits::>

The method currently being used for the same purpose is to use FM broadcast band, and then try to catch a station ID or to listen to the content and hopefully get some clue as to the stations location that way. It's not good because the FM broadcast band is much to far away from the 2 meter band to predict when 2 meters might be open.

So, usb cable has significantly less loss than coax-hence my preference is to find a hardwired usb cable solution if possible.

73,

Art

Re: need to relocate RTL-SDR away from computer

Posted: Mon Jul 09, 2018 10:50 am
by rtlsdrblog
How long is your non functioning USB cable? Generally past 10m you need an active cable. If you can measure it, check the voltage drop on the cable with the SDR or HDD plugged in.

The other option if you need a hot radio is to just use an LNA at the antenna.

Re: need to relocate RTL-SDR away from computer

Posted: Mon Jul 09, 2018 5:57 pm
by w5dxp
Art, you might notice that radio telescope antennas are not located adjacent to their computers. :roll:

My 2 cents Re: need to relocate RTL-SDR away from computer

Posted: Mon Jul 09, 2018 8:01 pm
by snn47
Imho there is a difference between
- an USB cable not working for Data transmission and
- an USB cable having to high resistance on the power lines in the USB cable to supply the min. input voltage needed to let the Dongle operate.

A general note: In practice USB cables/hubs/extensions may (or not) work for one product while it may work with another product. As soon as you add active USB decices like hub chips you add another possible source for problems.

You can test your cable by adding an ext. powered USB Hub before the Dongle to supply it with power, If it works you know it is not the cable Data lines, but high resistance on the power lines.

If you dont's like the USB hub, there are active 10 m USB cables (I even saw a 15 m once) that can in theory be cascaded, however as soon as you add active USB decices like hub chips you add another possible source for problems

LAN extensions may be another option you may consider testing as alternative.

Re: need to relocate RTL-SDR away from computer

Posted: Sat Jul 14, 2018 1:32 pm
by luc4sss