T-plug for spyverter

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Joined: Wed Feb 07, 2018 2:08 am

T-plug for spyverter

Post by JEL » Thu Mar 29, 2018 10:40 pm

I am currently thinking about plugging a T-plug into the SDR-antenna input...

I am hoping I can then have a spyverter going in to the T-plug's one input, while leaving a VFR antenna on the T-plug's other input...

Does this sound like it might work or break something?

(Any consequences for the bias-T? Could it be strained by the split, if I happen to connect something that draws power on the VFR part of the setup, while it's also feeding the spyverter?)

(Would it make any difference if the VFR antenna is a loop, rather than a dipole? I'm thinking not, but always nice to hear other opinions :) )

(Other things worth considering?)

The goal is to avoid having to connect and disconnect the spyverter each time I cross 25 MHz.

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Re: T-plug for spyverter

Post by JEL » Wed May 23, 2018 9:41 pm


I have now received the T-plug and are currently running a first test...

It appears to work...

I have signal at both VHF and HF now, in one single channel-scan :)

For HF to work: The spyverter must be turned ON (Obviously)

For VHF (and above) to work: The spyverter can be either ON or OFF (It doesn't appear to make any difference)

Signal-strength appears to be normal-strength at HF and normal (Or perhaps a small amount weaker) at VHF (I need a bit more time to test it to be sure it's not just the weather having an effect.)

Initial thought: a success :)

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Re: T-plug for spyverter

Post by rtlsdrblog » Thu May 24, 2018 3:00 am

Is it just a standard T-junction, or an actual RF splitter that you're using?

There's probably going to be some funky interactions with a regular T-junction, but it may not be noticeable if you're lucky.

If you have a shortciruit antenna on the VHF side (like the loop you mentioned), then the spyverter wouldn't work as the bias tee would be short circuited. Running it like that for a while could damage the bias tee.

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Re: T-plug for spyverter

Post by JEL » Thu May 24, 2018 5:51 am

Oooohhh thank you very much for that heads-up on the bias-t...

The T-junction is just a standard in-active T-plug (Same concept as hot-wiring 2 cables I suppose)

At the moment I have a dipole on the VHF side (It goes through an FM-block filter and then into the T-plug)

I have a long-wire on the HF side (It goes into a Nooelec balun 9:1 and then into the T-plug)

The T-plug then goes into the AirspyR2.

I'm not sure why it works, because theoretically, at least that is what I ended up concluding myself (But wanted to check with an actual experiment to be sure), the spyverter should lift the HF signals into the VHF bands... and I expected to hear some mixed signals when scanning the HF bands (Since the VHF antenna should still provide input at the bands where the spyverter was putting the upconverted HF-signals)... but HF appear just as clean as when the spyverter/airspy is connected as intended.
I didn't have any un-expected signals, and all the expected where present with same strength as normally (As far as I can tell, because HF signals vary quite a lot, so there could still be a small signal-loss I wasn't able to detect)

On VHF I seem to get a slightly lower noise-floor (and also slightly less signal)
I didn't expect any problems on VHF, since the spyverter appears to have a low-pass filter (Or maybe it's just SDR# that is intelligent enough to kill the HF signal when I tune to frequencies above 25MHz), so at least that theory checks out.

I thought some phase-issues might happen (From using 2 antenna-inputs at the same time, but perhaps their individual resonance is just so far apart from each other that they don't 'see' each other enough to interfere. After all, one is a 10 meter long long-wire laying horizontally, the other a 1.2 meter long vertical dipole), but I can't really tell.

I will keep the loop-antenna OFF and probably only run a few more experiments and then take it apart again (I really don't want to ruin anything, but it IS really nice to NOT have to screw and un-screw plugs whenever I go above or below 25 MHz :) )
So thanks for the warning!

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