My buddies at my former ham club have access to one of the obsolete ATT Long-Lines cross-country Microwave sites, now owned by a private party. Looks like this: They have installed an internet-remote-controlled HF radio at the site, primarily to allow retired club members living in HOAs to have access to HF. The original installation had only a G5RV type of HF antenna. They wanted to add 160m to the second antenna port of the radio, and approached me to come up with an antenna. Drawing on the experience I gained while experimenting with EndFed antennas for a hamfest presentation, I figured that if I built a resonant 160m EndFed, then it would also provide coverage of 80m, 60m, 40m and possibly some higher bands. Because of local terrain, a wire antenna fed from the tower end is preferred. The tower is ~65ft high. There is not another high support, so the feed-point of the EF would be at the tower top, while the other end would be fairly close to the earth on a low support. There is a gully close to the big tower. Beyond the gully is a ridge, so the wire would hang mostly over the gully, but it would slope down from the tower top. I had on hand a MyAntennas mef-110-3k 1:49 transformer, so I based the antenna on that. I ordered 270ft of #14AWG from the Wireman. I first built and tested the antenna at home, elevating the driven end up my 55ft tower, letting the other end slope downward. First attempt, I mounted the transformer 53ft up my TX455 tower, connecting the "Gnd" wingnut on the transformer to the grounded tower leg, with coax routed down the tower leg to the shack below. This effectively makes the entire metal tower (TX455) the "counterpoise" for the EFHW. Didn't work very well: The lowest SWR was about 3.7, and the resonant point was down at 1780kHz (hadn't pruned the wire yet). Correcting for the coax, the feedpoint impedance at lowest SWR was 15.8 - j17.5, which means that there is way too much "counterpoise" (the entire grounded tower and everything on it). Recalling that simulations show that there need only be a tiny counterpoise (<0.025wl) to make the feedpoint impedance ~2500 Ohms. If the impedance connected to the transformer secondary is on that order, the impedance at the primary of the transformer is ~50 Ohms, meaning that the SWR on the coax would be low. I set about to make the counterpoise much smaller by effectively isolating the antenna from the tower. Here is the justification for the "too much counterpoise" statement: This is from a simple EzNec simulation of a half-wave wire fed ~6% from the end, where I optimized the lengths to get a SWR50 at the transformer primary as close to 1 as possible. Note that to make the radiating element one half-wavelength long, it takes only a tiny "counterpoise", i.e. the 8.5ft wire stub to the left of the feed-point. This illustration is for 80m, so double the dimensions shown above to re-scale the illustration for 160m. The current distribution (pink line) is identical to what would happen on a center-fed half-wave dipole. Obviously, removing the stub and replacing it with a massive 65ft tower is not the thing to do. So much for all the bogus advice proffered here about End-Fed antennas needing massive "counterpoises"! I tried suspending the transformer on a rope, offsetting it from the tower, and then relying on 14ft of coax from the transformer to tower to act as a short counterpoise. Initially, I had the coax shield bonded to the tower, but that didn't do anything to reduce the SWR, because the tower is still part of the circuit. It occurred to me to put a common-mode choke on the coax just before it is bonded to the tower, making the total length of the horizontal antenna equal to about 14ft of coax shield plus 270ft of wire beyond the transformer. This effectively "disconnects" the horizontal wire from the vertical grounded tower at RF, but leaves it grounded to the tower at DC for static drain. I made the choke by winding about 22turns of RG400 (the amber-colored teflon coax) through a 240-31 core, which measured about 125uH using my AADE Inductance meter. Putting that in-series with the coax near the tower brought the SWR50 down to 1.39 @ 1797kHz. I tried different lengths of coax between the choke and transformer, varying from 8.5ft to 26ft, and 14ft is where the SWR is minimum. This leaves pruning the antenna to a better frequency inside the band, and checking the alignment of the harmonics with the higher frequency bands. Here are the SWR50 nulls at the shack end of 52ft of RG8 coax with the CMC, 14ft of coax to the left of the transformer, and 270ft of wire to the right: Code: freq R jX SWR 1797 45.7 -15 1.39 3516 48.6 4.3 1.1 5335 49.8 0.3 1.01 7218 39.7 -14.1 1.47 Obviously, if I shorten the wire, I can bring the fundamental resonance up to ~1860kHz, but then the 4th harmonic would land above the 40m band. I used an EzNec simulation and AutoEz optimization to come up with the final overall wire length and a compensation coil inductance and placement that makes the antenna more use-able. Here is a sketch of what I ended up with: The optimized antenna was them installed at the old ATT site. Here is a video taken during the work party. https://photos.google.com/share/AF1...?key=NmZ0cTNXRUMwSGEwVU1uWlBtbmc0aHUyQVF5dHdB My friend Clint made the diplexers to allow sharing an existing 1" heliax feedline running up the tower. Here is a write up about how he made the two diplexers: https://ka7oei.blogspot.com/2019/06/using-same-feedline-for-hf6-meters-and.html The final installation allows the tuner built-in into the Kenwood radio to tune any frequency between 1800 to 1900, all of 80m and 30m, while the tuner can be switched out of circuit on 60m, 40m and 20m. The Swr did not change much between my test location and the final installation. Since the existing G5RV and new EFHW antennas overlap on most bands, and they are installed at about 45degress apart in azimuth, it makes it possible to select the one that provides the best coverage in any given direction.