Diversity Operations - RX2 protection while transmitting

[N3GX]

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]

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

Capture.jpg (139.87 KiB) Viewed 69736 times

Mark

[N3GX]

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.

[w-u-2-o]

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! The DX Engineering limiter will only withstand 10W on the input.

[N3GX]

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.

[JJ4SDR]

It is not clear from this thread if extra "insurance" to protect the RX front-end is truly required or not! Sure would be good to understand if what Mark, K1LSB, posted is the way most owners have it set up.

Personally, I am very cautious and having an extra attenuator hooked up may be what I would elect to do.

I have also yet to see any posts indicating damage to the front-end of the receiver while transmitting.

73!
Juha
NI2M

[K1LSB]

JJ,

Interesting that you should ask that, as early on I decided to add an extra layer of RX2 front end protection to my Anan.

My RX2 antenna is a wideband receive-only mag loop assisted with an LZ1AQ amp mounted at the loop. I rigged up a DS2Y relay at the LZ1AQ amp that physically disconnects the loop from the amp whenever I transmit (the relay is triggered by my PTT).

My primary objective with that setup was to protect the LZ1AQ loop amp from getting fried whenever I shower down on it with RF energy from my TX dipole located deep inside the mag loop's near field, but an additional benefit is that it also protects my Anan's RX2 front end regardless of the state of the "Gnd BPF2 on tx" checkbox.

Mark

[JJ4SDR]

Hey Mark!

Yes, I do remember something along those lines and appreciate the reminder very much !

JJ

[NN3RP]

I use W6LVP Amplified RX loop antenna for CW Skimmer https://www.w6lvp.com/product/w6lvp-amp ... p-antenna/

W6LVP Medium.jpeg (52.83 KiB) Viewed 68064 times

I split that connection via a Mini-Circuits and reroute to other RX antennas, i.e., SDRPlay, IC7610

minicircuits Medium.jpeg (89.54 KiB) Viewed 68064 times

My dipole antennas are in close proximity with loop in my small back yard. There is also a F12 antenna at roof top. No issues with TX.

[N4XD]

Re "ground bpf2 on xmit

I have that checked but, when I transmit I still see a very strong signal on RX2 tuned, o course, to same as transmit frequency. I have always wondered if the rx2 band pass filter was actually grounded.

Ron
N4XD

[NN3RP]

You need some sort of hardware (front end protector). Ticking that setting might not be all is needed.

[K1LSB]

IMO the safest arrangement would be to have a configuration similar to N3GX's Isolator relay (see his illustration above), except that the relay type should be DPDT and the jumper feeding the Anan's PTT-IN should be actuated by the 2nd throw of the relay. That would be a fail-safe arrangement guaranteeing that the Anan doesn't transmit until after the connection to the RX2 antenna has been broken.

Mark

[N4XD]

Rafael, that's the question. Is the band pass filter really grounded? Can anyone on the forum verify that it is?

Ron
N4XD

[w3ub]

Even if it is "grounded", there are lead/trace inductances, which will result in finite isolation. Selecting it to be grounded is a good idea, but should not be relied upon for protection when QRO using multiple antennas.

Personally I use a relay/sequencer AND a DXE receiver guard ...

Doug

[w-u-2-o]

It's easy to test that RX2 is being grounded. Here is a schematic snippet from the 7000 series units:

Capture.JPG (62.09 KiB) Viewed 67937 times

Simply check to see if the center conductor of the RX2 input is shorted to ground during TX.

[K1LSB]

Rafael, that's the question. Is the band pass filter really grounded? Can anyone on the forum verify that it is?

Ron
N4XD

Reason dictates that there wouldn't be a "Gnd BPF2 on tx" checkbox if there was no functional selectable grounding.

Regardless, there's an easy way to test: set TX power to 1 watt and do a comparison of the RX2 received power with "Gnd BPF2 on tx" checked and un-checked.

If your RX2 antenna is too close to your TX antenna to even risk TXing at 1 watt, then transmit 20 watts into a dummy load -- your RX2 antenna should easily pick up the leakage from even barefoot power going into a dummy load. Do the checked/un-checked test with that configuration.

Mark

[N4XD]

Good advise. I checked and indeed, when transmitting rx2 is shorted to ground. With, of course, the "ground bpf" box checked in Thetis The signal I see on thetis must be internal leakage or something like that. Not a signal present on rx2.

Ron
N4XD

[K1LSB]

Ron,

I've always seen the same thing at my station, I just always assumed it was leakage/crosstalk internal to the Anan.

Mark

[N4XD]

Mark when I received my (used) 7000dle I suspected rx2 wasn't hearing as well as RX1. I was right. I found the filter immediately in line with the input was very lossy. Removed (that was a chore as it has contacts on all sides!) and replaced but still seemed a little numb. Went back in and looked more closely. The back to back diode component looked different. Hmm its black and the other is gray. I touched it with a probe and it crumbled.

Obviously previous owner overloaded that input. Once replaced, al is good.

Because of that I am a little sensitive (no pun intended) about overloading it. I should build up a kd9sv style front end protector for it. I have all the parts. And I have a "real" one on the other beverage input to ant 2.