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In a number of posts on this forum I have mentioned my intent to side mount my amateur radio antenna on the same mast that I use for the GMRS antenna. I can now say that it is done and has been working for almost a week. As promised elsewhere, here are some pics. The side mount bracket is home crafted and painted a color similar to the main fiberglass mast. The amateur antenna is currently about 6-1/2ft below the bottom of the GMRS antenna. There is about 21” between the amateur antenna and the nearest metal (the GMRS feed line). I am using LMR400 feed-line for both antennas and have ferrite chokes installed over the coax. I have not yet detected any material interference or objectionable desense in the GMRS radio while transmitting on the amateur radio. I do however observe one bar on the GMRS radio’s meter flutter while transmitting at 50w UHF on the amateur radio, if the GMRS radio is receiving a usable low-level signal at the point I key up the amateur radio, just not enough to be of concern presently. I will be operating both antennas at the lower height you see in the picture until I am ready to guy the mast at full height, which is about 16’ higher. One of the inquires I received elsewhere is listed below along with my original response. Posted here to prevent derailing another thread. I will be running 50w UHF and VHF, 50w GMRS. I will let you know once it is operational. I may not have it installed for two weeks. I do expect some desensitization of the listening receiver while I am transmitting on the other service, but nothing that I expect will affect my operations. I will have ferrite chokes on the GMRS feed-line to cut down on the noise and reduce ingress from the 2m/70cm since that line will be running parallel to the amateur antenna. Michael WRHS965 KE8PLM

This also fits with the growth within a hobby. Realistically, we probably don't start out with the best equipment right out of the gate,we build our toolbox...something decent to start with, and improve, sometimes incrementally. A project here, a project there. We can learn some from others, but there's no substitute for your own experience. Some aren't fans of the Surecom meters, and I don't know that they're the most accurate thing out there, but mine have agreed pretty well with each other, and with the little I've played with it, agree pretty close with the nanoVNA as well. Given the variety of sellers across the sites, maybe there's some variance in quality?

Cant believe I didnt think of slapping a code on the channel...great quick fix. Interesting point on the interference I will have to look into this more! I do have a wireless charger. Will investigate and report back.

That is one of the beauties of the radio hobby and a serious enthusiast who has test equipment. You get to theorize, experiment and observe the results to your questions first hand. Quite wonderful and fun indeed. Michael WRHS965 KE8PLM

You @wayoverthereare the man! What a great experiment you performed there. In your mind, before you ran the test, were your predicting the outcome to be as the results showed?

The main issue with testing HT antennas is duplicating the coupling between the radio and the users body. Yes, the users body is part of the antenna's ground plane, and it makes a huge difference. I've done the experiments myself. Some of the antennas were screwed into a "SMA" magnet mount, yes they are around, then placed on a 30 to 40 inch square metal sheet for a ground plane. On a few of the antennas tested the SWR was over 3 or 4 to 1. Removing the magnet mount from the metal sheet and placing it on the back of my hand reduced the SWR to under 2:1 in some cases. The below links are what others have tried. https://www.hamradio.me/antennas/ht-antenna-comparisons.html https://reflector.sota.org.uk/t/antenna-testing-jig-swr/14791 https://www.ko4aje.com/ht_antenna_tests.html https://kd9nrt.com/2020/07/09/antenna-comparison-test/ http://www.km4fmk.com/NewAntTesting.html

So...conveniently, I have a 5/8 over 5/8 wave Browning UHF antenna and Midland mag mount sitting idle right now, since the truck is in the shop. Dug out the Surecom (sw102) and got some numbers. Stuck the antenna/mount in the middle of the top of a chest freezer (nothing within 6 inches of the vertical, and only wood/sheetrock any closer than a foot to the sides). First round, all 15 (or 17, I forget) feet of cable was kind of lazily run around the floor to avoid any coils. This yielded 1.0 swr on channels 1 (462.5625) and 22 (462.725), and 1.06 on Repeater 22 (467.725). Second test, I coiled as much cable as I could between the radio and the antenna, ended up with 7 coils approximately 5 inches in diameter. Same channels/frequencies as before showed some minor change, though the cable routing near my computer screens and metal monitor stand to get the straightest routing (and most excess cable) might also have played into it. Second round numbers (with the coiled cable) were 1.09 on 1, still 1.0 on 22, and 1.07 on Repeater 22....still well within good swr range, all of them.

I thought I would do a report out of some testing I conducted this weekend. One of my original curiosities has been how much signal actually finds itself being picked up by the offset antenna when the other is used to transmit in the same band. To settle this I separately transmitted using my GMRS and amateur radios (70cm) and measured the signal level present on the non-transmitting antenna. While transmitting at 50w, the offset antenna showed about -15dBm (about 25 uW or .04V ) of signal present. This was nearly the same regardless of direction. This tells me a couple of things: 1) The power levels being picked up by the opposing antenna is well with the safe range of the receiver connected to the opposing antenna. 2) Expect serious desense of the opposing receiver during those periods when transmitting on the other radio within the same band as the receiving radio. In addition, I did do some operational tests to see if there was any material desense of the opposing radio when operating in different bands. So far, no desense of concern. This was checked while listening to weak VHF signals on the amateur radio while transmitting on GMRS, and transmitting VHF while listening to weak signals on the GMRS radio. This was purely a subjective test under conditions in which I know the desired incoming signal to both radios was -110dBm or less. So, not bad. Michael WRHS965 KE8PLM