Antenna Separation

Useful information regarding antennas for SDR products.
jeepin95
Posts: 3
Joined: Sun Aug 21, 2016 4:56 am

Antenna Separation

Postby jeepin95 » Sun Aug 21, 2016 5:09 am

I recently got my SDRPlay and so far I love it, but I want to make this even better and use it as a panadapter for my FT-991 and FT-857D. Since both of those radios are 100W max, what kind of antenna separation is required in order to keep for damaging my SDRPlay? So far I have been disconnecting the SDRPlay when I TX.

At home I have a 1/2 wave fan-dipole 20/40m and I also have a 60ft EMCOMM II. The feedpoints of both antennas are only a couple feet apart but they are perpendicular to each other. Normally I switch between the 2 antennas on the FT-991, would it be safe to put the SDRPlay on one of these and the FT-991 on the other?

For the FT-857D I would like to use it while mobile or for NPOTA. I have a SuperAntenna MP1B and I also have a hamstick dipole that travel with me. How much separation do I need between these to keep the SDRPlay safe assuming a max of 100W.

I basically never go over 50W on either radio, but I just want to play it safe and plan for 100W out.

Thanks,
Josh
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oldjackbob
Posts: 2
Joined: Tue Aug 16, 2016 3:14 pm

Re: Antenna Separation

Postby oldjackbob » Thu Aug 25, 2016 6:32 pm

The safest bet would be to get a Dow-Key 62-110 coax relay switch and activate it with the ground-on-PTT on your FT-857D, such that the relay simply disconnects the SDRPlay from the coax during transmit.

That's how I've got mine setup. In fact, I'm using the same antenna for both transmit and receive - it's routed to the SDR on receive and to (actually, from) my FT-897D for transmit. Works like a charm. The Dow-Key relay is a break-before-make so there's no chance of pumping 100 watts into your SDRPlay. Even if the Dow-Key fails to operate, the worst that will happen is that your FT-857 will transmit into an un-terminated coax, causing your SWR to shoot upward and the FT-857 will simply fold back the power.
Last edited by oldjackbob on Thu Jan 01, 1970 12:00 am, edited 0 times in total.
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dsalomon
Posts: 51
Joined: Sat Oct 10, 2015 1:50 pm

Re: Antenna Separation

Postby dsalomon » Fri Aug 26, 2016 4:40 pm

Another option is this: https://www.dxengineering.com/parts/dxe-rg-5000. It limits the RF level going into the receiver to safe levels.
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dsalomon
Posts: 51
Joined: Sat Oct 10, 2015 1:50 pm

Re: Antenna Separation

Postby dsalomon » Wed Aug 31, 2016 12:52 pm

BTW, the advantage of a limiter like I suggested rather than a switch that takes the radio offline is that you can monitor your own signal. This is especially helpful for digital work so you can ensure you're putting out a clean signal.

73 - David, AG4F
Last edited by dsalomon on Thu Jan 01, 1970 12:00 am, edited 0 times in total.
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jeepin95
Posts: 3
Joined: Sun Aug 21, 2016 4:56 am

Re: Antenna Separation

Postby jeepin95 » Sun Sep 11, 2016 6:41 am

I went ahead and purchased the DXE-RG-5000 and tried it out, everything seems to be working great. The only issue I'm having is that when trying to decode my own JT65-HF signal the SDRPlay doesn't decode anything when going through a virtual audio cable. PSK31 and other digital modes do seem to decode though.

Thanks,
Josh
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