What type of cable?

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dalpets
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Joined: Sun Jan 03, 2016 11:02 am

What type of cable?

Post by dalpets » Sat Feb 06, 2016 9:43 am

I want to get hold of an extension cable for my RTL2832U dongle, with telescopic antenna.

What is a suitable match for the existing cable, which does not have a designated code on it?

Thanks

rtlsdrblog
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Re: What type of cable?

Post by rtlsdrblog » Sat Feb 06, 2016 11:48 pm

What do you mean by designated code?

The cable used for the whip is RG174, but if you want to extend it over a range more than 2-3 meters i'd suggest using some lower loss coax like RG58, or RG6 if you intend to use in at near GHz frequencies.

Another option if you don't need to extend it too far is to use an active USB extension cable to get the dongle further away from the PC. Up to 10 - 15m of an active USB cable should work fine, maybe longer if you use a powered USB hub.

dalpets
Posts: 21
Joined: Sun Jan 03, 2016 11:02 am

Re: What type of cable?

Post by dalpets » Tue Feb 09, 2016 5:44 am

rtlsdrblog wrote:What do you mean by designated code?
= RG174, RG6 .........etc.
The cable used for the whip is RG174, but if you want to extend it over a range more than 2-3 meters i'd suggest using some lower loss coax like RG58, or RG6 if you intend to use in at near GHz frequencies.
Is LMR400 also an option?
Another option if you don't need to extend it too far is to use an active USB extension cable to get the dongle further away from the PC. Up to 10 - 15m of an active USB cable should work fine, maybe longer if you use a powered USB hub.
My problem is that I want to extend it to outside, say 10 metres to the roof line, and if I use active extension cable/s that means the dongle is outside, open to the vagaries of the weather, and also given that even on the desktop, over time, dongle heat may already be an issue . So this is not practical for what I want to do. I do realize that the dongle & telescopic antenna supplied are really only meant for use inside, but my reception this way is very weak.

This brings me to ask, how with a fully fledged external discone antenna, does it get around the usb port limitation, and given the abovementioned cabling shortcomings.

rtlsdrblog
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Re: What type of cable?

Post by rtlsdrblog » Wed Feb 10, 2016 6:01 am

Yep LMR400 should be fine. Don't worry too much about impedance mismatches with coax for RX only. The 75/50 Ohm mismatch between different cables is totally negligible for RX. This is why so many people recommend RG6 for RTL-SDR, because it is cheap, low loss and common.

A Discone will usually come with some length of coax cable, or you'd cut some up yourself.

dalpets
Posts: 21
Joined: Sun Jan 03, 2016 11:02 am

Re: What type of cable?

Post by dalpets » Wed Feb 10, 2016 6:32 am

Regardless of the type of cable used, what about my question concerning the usb length limitation for extended outside use, resulting in the dongle being outside in the weather.
In the case of the outside discone being also usb based how do they get around the dongle being outside?

Thanks

rtlsdrblog
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Re: What type of cable?

Post by rtlsdrblog » Wed Feb 10, 2016 10:08 am

Many people will extend the dongle to the edge of being inside, eg the attic with an active cable and then use a few metres of coax to get the antenna outside. Some people have created plastic weather proof containers for the dongle. As long as it's not in direct sunlight it shouldn't overheat.

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