Share antenna with two dongles

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gskroll

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I am having trouble finding the proper splitter/y-cable to allow connecting two RTL-SDR dongles (with SMA connectors) with a single antenna equipped with a BNC connector.

I have read that folks have been successful with this approach.

Please let me know what part number(s) I should order and where I might purchase them.

Thanks

Glenn

p.s. I have VERY bad eyesight so soldering together a home brew connector is not an option.


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garys

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I just use a Cable TV splitter and have good results. You can use a cheap non amplified one, or you can use an amplified one. I use an amplified splitter at home to run two scanners and two dongles. I use a non amplified splitter on my mobile SDR set up. I've have good results with both.
 

gskroll

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Great leads guys - thanks for you quick responses.

I'm likely to have more questions as I continue to explore the new (to me) world of SDR, SDR#, Unitrunker, DSD+, etc.


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Rred

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Forgive me if this is old news, but a "plain" splitter is going to cut the signal strength IN HALF for each dongle. Think about that, cutting the signal strength in half.

Unless you have a very expensive exotic antenna, I'd suggest just buying a second antenna for the second dongle. Or trying to find an active amplifier, not just a plain splitter. The problem with active amplifiers of course is going to be noise, bandwidth, and price.
 

gskroll

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Good to know especially as the system I am trying to monitor seems to be coming in with a weak signal on the dongle used for control/signal while I have not yet been successful in getting any output from the dongle setup to track voice. This is with two separate antennas that were part of the RTL-SDR bundles.

I am still learning and know I have some tweaking to do. I just today found a video on how to adjust the ppm offset that may improve the signal strength on the dongles.

The journey continues. . .

Glenn


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M105

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Get a BNC to "F" adapter. Connect the antenna to the input of a good quality TV splitter. Get 2 "F" to -whatever connector your dongles have- cables. These dongles are TV tuners after all and designed for 75 ohms. As far as "cutting the signal in half" my experience is that each dongle does not place a full load on the antenna input. I currently have a three way splitter feeding three dongles from a non amplified homebrew folded dipole antenna and the signal loss based on FMP24 with or without the splitter is negligible. Note that 3 way TV splitters come in two flavors. 33.3% on each output or 25%-25%-50%. You will probably want the balanced output if you go with a three way. My two cents worth is try the unamplified arrangement first. You can always add an inline amp between the antenna and splitter.

Where to buy? eBay is my preferred outlet.
 

gskroll

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In this context, does "balanced" mean the 33/33/33 variant?

I did look at eBay. Is there some keyword that would distinguish the 33/33/33 splitters from the 25/25/50 ones?

Thanks for your help

Glenn




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jonwienke

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Forgive me if this is old news, but a "plain" splitter is going to cut the signal strength IN HALF for each dongle.
This is true, but extremely misleading. "Cutting the signal in half" is only a 3dB difference. In most cases, that's insignificant, unless you're on the ragged edge of fringe coverage.

There's no benefit in using a splitter with more than 2 outputs for this application. In addition to the signal loss, if you don't properly terminate unused outputs, you get reflection and interference problems, especially if there is cable attached to the unused output(s).
 

M105

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This is true, but extremely misleading. "Cutting the signal in half" is only a 3dB difference. In most cases, that's insignificant, unless you're on the ragged edge of fringe coverage.

There's no benefit in using a splitter with more than 2 outputs for this application. In addition to the signal loss, if you don't properly terminate unused outputs, you get reflection and interference problems, especially if there is cable attached to the unused output(s).
I agree with all of the above. I am using a 3 way splitter because I am feeding 3 dongles. If you are only feeding two then you should use a 2 way splitter.
 

greenthumb

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I would suggest a multicoupler instead of a splitter, but you're going to spend more money on it. A multicoupler will have more port-to-port isolation so that any noise won't impact the other ports. Most of these dongles are cheap, so amplifier noise might be a problem. But it's worth giving a cheap splitter a try in case it does what you need :)
 

jonwienke

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This is with two separate antennas that were part of the RTL-SDR bundles.
Those antennas are crap. If you get a good outdoor antenna and install it properly, you'll way more than make up for the loss of a 2-way splitter.
 

gskroll

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Thanks to all for the informative suggestions and discussion.

I understand that I would achieve signal levels using a better (outdoor) antenna and something more sophisticated than a splitter.

I am in the process of relocating from CT to ME. While starting to acquaint myself with this new aspect of scanning, I am hoping to be able to familiarize myself, hands-on, with Unitrunker and related software even if less than optimally.

Glenn


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KD8DVR

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Forgive me if this is old news, but a "plain" splitter is going to cut the signal strength IN HALF for each dongle. Think about that, cutting the signal strength in half.

Unless you have a very expensive exotic antenna, I'd suggest just buying a second antenna for the second dongle. Or trying to find an active amplifier, not just a plain splitter. The problem with active amplifiers of course is going to be noise, bandwidth, and price.
That y cable as in the photo may not cause a drop in gain....in my experience. I have a reverse of that, which lets me use one antenna for 2 dongles.

I've heard the cable tv splitters WILL have a noticeable gain drop.

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M105

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That y cable as in the photo may not cause a drop in gain....in my experience. I have a reverse of that, which lets me use one antenna for 2 dongles.

I've heard the cable tv splitters WILL have a noticeable gain drop.
Nothing is free. The "Y" cable presents an impedance mismatch to a 75 ohm feed antenna while a splitter does not. It also provides a DC path between all three connections. That isn't to say it won't work but a splitter is the preferred method unless your antenna is designed to feed lower impedance. With a 50 ohm antenna feed the "Y" might actually be better. Splitting more than once without a real splitter might get tricky...
 

KD8DVR

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Nothing is free. The "Y" cable presents an impedance mismatch to a 75 ohm feed antenna while a splitter does not. It also provides a DC path between all three connections. That isn't to say it won't work but a splitter is the preferred method unless your antenna is designed to feed lower impedance. With a 50 ohm antenna feed the "Y" might actually be better. Splitting more than once without a real splitter might get tricky...
I feed with 75 ohms. I'll revisit the subject and really take a harder look. I have 2 antennas, so going over things should be easier.

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