Diversity Operations - RX2 protection while transmitting

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N3GX
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Diversity Operations - RX2 protection while transmitting

Postby N3GX » Fri Nov 04, 2022 3:52 pm

During Diversity Operations, I’m wonder if it is common practice to use some sort of an external T/R switch Box to automatically disconnect the receiving antenna (RX2) used for Diversity Operation while transmitting QRO?

I had a bad experience in the past where I neglected to disconnect an SDRplay RSP1A receiver from its dedicated End Fed receiving antenna prior starting to transmit on HF. As you guessed it, yes, I totally burned the preamp stage of it.
I usually transmit about 1kW on 40 / 80m using a Horizontal Delta Loop for these bands and both antennas are fairly close since I have limited space. By connecting a watt meter and a dummy load at the end of the coax of the designated receiving antenna, I’m seeing relatively high levels of RF energy being induced when transmitting near full legal limit on the main antenna. Depending on the RX antenna configuration (Inverted “V”, Inverted “L”, slope, etc.) and its location, it is between 10 to 30watts coming back.

I know the RX2 on the ANAN uses a dry contact relay to ground the center pin while on transmit, but, I’m concerned about the possibility of the stressing out these small relay contacts and perhaps going bad with time after shorting out the induced amount of power.
I use a Daiwa antenna switch for the transmitting antennas and it does exactly that, it grounds all the ports that are not being used, but the difference is that these contacts are huge and designed for that purpose.

Additionally, I could build (or buy) a T/R switch box like the MFJ-1708B-SDR which is intended to prevent incidents like the one I had at first place.

Any comments and suggestions are really appreciated.

Thank you – Alex, N3GX
K1LSB
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Re: Diversity Operations - RX2 protection while transmitting

Postby K1LSB » Fri Nov 04, 2022 4:07 pm

There 's an option to ground the bandpass filters for RX2 on transmit:

Capture.jpg
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Mark
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N3GX
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Re: Diversity Operations - RX2 protection while transmitting

Postby N3GX » Fri Nov 04, 2022 6:25 pm

Thank you for replying, I have it setup the same way you do.
I guess if nobody have reported damages on the ANAN due to the RX2 relay contacts going bad upon shorting out induced RF, then, perhaps the contacts are equipped to take the abuse. The idea of vaporizing the preamp circuit is quite scarring.
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w-u-2-o
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Re: Diversity Operations - RX2 protection while transmitting

Postby w-u-2-o » Fri Nov 04, 2022 9:56 pm

I use a DX Engineering "Receiver Guard" RF limiter:

https://www.dxengineering.com/parts/DXE-RG5000HD

However, if you are really seeing upwards of 30W of power at the output of your receive antenna that is an exceptionally large amount of power! :shock: The DX Engineering limiter will only withstand 10W on the input.
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N3GX
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Re: Diversity Operations - RX2 protection while transmitting

Postby N3GX » Fri Nov 11, 2022 6:09 pm

Scott, Thank you for the recommendations.
I'm thinking that I could build some relay actuated disconnect box like the one on the attached picture to resolve this problem.
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Rx2 Isolator - ANAN 7000DLE MK2.png
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