Man, that was tough, and LUCKY!
Let me paint you a picture.
Up here on the hill in Elizabeth, Colorado we have two stations with tri-band beams on towers with 230' between them. I have a 10, 15 and 20 Meter Mirage KT-34XA, and my neighbor Jim (also my father-in-law) runs a 10, 15 and 20 Meter Bencher Skyhawk. There's exactly 230 feet between tri-band beams on similar height towers. We knew we'd run into problems when Jim was contemplating buying the undeveloped three acres next door to build his dream home on, but we also came to the conclusion that family is more important than Ham Radio and in time we'd figure it all out. Better to have them nearby! The land was purchased, scraped and this last summer they built Jim's custom dream home next door. I must say, it's a real beauty!
After some "lazy" engineering to find the spot, I dug the hole for Jim's tower and I put up the HG-52SS with a Bencher Skyhawk. Four yards of concrete later I still had a few more months to plan out how to do this "near-field" operating before my wife's parents moved in. I figured I'd have all the answers by then. Have I ever told you what happens when I try to "figure" something out? My friend Keith (K0KE) came over and we ran some tests. In a worse case scenario - with both tri-banders pointed at each other and Jim running exactly 1,500 watts on 20 Meters, we had 26 watts of RF on my antenna! You read that right, 26 WATTS!
Figuring the gain of the antennas, the space between them, the power level, etc. we thought we might see 10 watts in a worst case scenario. When that calibrated wattmeter read 26 watts, Keith and I just stared at each other and in unison sighed a collective, "oh shit".
Back to the drawing board. There's no doubt 10 watts of RF will wipe out any radio's front-end. It's also the maximum rating for just about all the front-end savers out there available for purchase. 10 watts is what I planned on, 26 is what I had.
Up until that test I had already "split" the RX/TX antenna through my Yaesu FT-1000MP MK V (RX IN & OUT jacks) and had purchased a DX Engineering RTR1-A Receive Antenna Interface for Jim's Yaesu FTDX-3000D. I placed an Array Solutions AX-RXFEP front-end saver on each rigs RX antenna input and I also put a 5B4AGN 6 band TX BPF in each stations RX line in. That would have protected both radios for up to 10 Watts of RF and provided some relief for off frequency inter-modulation. But now we had 26 watts. The front-end savers are rated up to 10 watts maximum. What I thought would work was well underrated for what I had, 26 watts. I needed more.
I went out for a cigarette where we debated the HUGE issue we had. Running a PTT control line over 600' between stations came up. Nulling his receiver when I transmitted (and visa-versa) came up. Making "operating schedules" came up. A whole slew of "off-the-cuff" thoughts came up, but none of them were really workable. Then I blurted out, "what we need is a couple of "RF sensing switches. When my antenna senses his power, it disconnects my RX antenna, and when I transmit his disconnects his RX antenna". Keith got on the computer and typed in "RF sensing switch" and wouldn't you know it, MFJ makes one - and it's only $80. A quick call to Ham Radio Outlet to see if they had a couple MFJ 1708 RF Sensing TR Switches proved they did. I said, "put'm on the counter John, I'm on my way".
Now we're protected from each other. When he transmits, my RX antenna opens, when I transmit, his RX antenna opens. So far with the bandpass filters, front-end savers and RF sensing T/R relays on each rig we haven't had an equipment failure. In fact, we've been on the same frequency chasing DX when either his or my relay clunks. It's a little unnerving to hear my RX drop when I'm calling somebody, but we've worked through it. The same happens for Jim. Once his RX drops out from me transmitting, he steps aside. Kind of like a "right-of-way". No advance notice. No phone calls. No wires running 600 feet between the stations. No operating calendars. No fighting over antenna switches. He operates when he feels like it, I operate when I feel like it.
But there is a downside. And here it is. Today, I'm on my 30 Meter Inverted L wire banging away on CW trying to work VU4KV when all of a sudden my RX drops! Jim's on 10, 15 or 20 somewhere but as he's transmitting there, my RF sensing switch kicked me to the curb just as it was supposed to. Since I only have one feedline for all my antennas, the switch is disconnecting my RX line while I'm transmitting. Take a listen to my QSO with VU4KV on 30 Meters today. How they stuck with me I don't know, but I sure am thankful they did!
That sure was a looooong period of silence while Jim was talking! It seemed like forever! I called "blind" a couple times hoping Jim was finished transmitting and then maybe I'd hear if they came back to me. You know the saying, "even a blind squirrel finds a nut once in awhile", lol.
Anyway, everything is working. Everything is protected. Everything is hunky-dory! See you in the pileups!
QSL VU4KV via W4VKU