Problem with multiple antennas

Buck
Posts: 52
Joined: Sun Apr 09, 2017 3:57 pm

Problem with multiple antennas

Postby Buck » Thu Jul 05, 2018 2:40 pm

I have two receiving only antennas: a 300-foot Beverage and a nine-foot active vertical. They each plug into ANZAC splitters. Those run, for RX1, to PowerSDR antenna inputs 2 and 3, and for RX2, to an Alpha-Delta switch that controls whether RX2 receives from the Beverage or the vertical.

I work a daily MARS net, usually near 60 meters but sometimes near 75 or 40 meters, and switch receiving antennas often, on RX1 by clicking and on RX2 by mechanical switch. I use MVAC, with VAC1 using the UMC ASIO Driver into my 202HD, and VAC2 using MME into an M110A decoder.

This works well so long as RX1 and RX2 are on different antennas. If, however, they are on the same antenna then the signal for RX2 is greatly attenuated. I can see it on the panadapter, with both signal and noise floor dropping, with noise down 10-15 dB and signal disappearing into the noise. RX1 is not affected.

Any ideas why this might be happening and how it could be addressed? Thanks.

Buck ko0y
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w-u-2-o
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Joined: Fri Mar 10, 2017 1:47 pm

Re: VAC2 attenuation?

Postby w-u-2-o » Thu Jul 05, 2018 8:48 pm

What happens if you eliminate the switch? Pick an antenna and connect the outputs of its splitter to both ANT2 (for instance, but it has to be the selected antenna) and RX2 at the same time? Does the behavior still happen then?
Buck
Posts: 52
Joined: Sun Apr 09, 2017 3:57 pm

Re: Problem with multiple antennas

Postby Buck » Thu Jul 05, 2018 10:25 pm

I connected RX2 directly to the splitter, bypassing the switch. When tuned to WWV at 5.00 MHz, the signal on RX2 ranges between -68 and -72 dBm if RX1 is on the other antenna, and -91 to -97 when they share the antenna. So yes, the approximately 25 dBm attenuation is still there when the switch is bypassed. I think this has something to do with software, not the splitters. Can anyone else duplicate this behavior using a splitter to feed both RX1 and RX2 from one antenna?

Buck ko0y
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w-u-2-o
Posts: 1308
Joined: Fri Mar 10, 2017 1:47 pm

Re: Problem with multiple antennas

Postby w-u-2-o » Thu Jul 05, 2018 11:25 pm

Ok, it's not the switch.

Go into the shared antenna configuration where the signal is attenuated. Then physically disconnect the RX1 connection. What happens?

If the problem goes away it's not software (and I don't think it is).

I'm thinking more along the lines of poor isolation in the splitter. What is the model number?

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