GPIO antenna switch possibility ?

Discuss KerberosSDR - 4x Coherent RTL-SDR
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zanco
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Joined: Fri Apr 26, 2019 5:31 pm

GPIO antenna switch possibility ?

Post by zanco » Sun Apr 28, 2019 6:19 pm

Hi,
I am considering placing the Kerberos SDR with 4 antenna's (144 / 430 MHz) on a remote location ( 27 m above sea level) for use as direction finder but for switching between differen frequencies it's necessary to disconnect the antenna's to sync again.

Is it to be expected to have a (web controlled) I/O from which I can use coax relays to disconnect / reconnect the antenna's ?

Thanks,

Ben

rtlsdrblog
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Posts: 2873
Joined: Mon Nov 19, 2012 11:54 pm

Re: GPIO antenna switch possibility ?

Post by rtlsdrblog » Sun Apr 28, 2019 11:50 pm

I just saw someone doing this in the https://www.facebook.com/groups/rtlsdrdongle/ facebook group. Facebook won't allow me to share that post here, but if you join that group, looks for C.j. Meyers posts.

This should work, but you'd need to be careful of the possible phase distortion caused by the relays.

The kerberos web server code could easily be modified to control it if you had web control for the relays. If you look in the main _GUI python code, at the end of the main file is the webserver code, written in Bottle.

One consideration though, is the antenna spacing that would sufficiently cover 144 MHz and 430 MHz.

If you had a circular array, and used the max resolution spacing factor (without ambiguities) of ~0.35, then

430 MHz -> actual spacing = 0.69m * 0.35 = 0.2415m

Spacing factor at 144 Mhz is then:

144 MHz -> spacing factor = 0.2415 / 2.08 = 0.12

So the resolution at 144 MHz wouldn't be great, but it might be enough for your purpose. You could get a little higher resolution with a linear array.

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