Figure 1: Nicely wound transformers (not my doing tho LOL)
So, I’ve been using the 75.5 foot (23m) longwire for a couple weeks (the length of the wire was picked by the analysis conducted by VK6YSF on his site, with the goal being to find a wire that was not too long (<100 ft) and could be an easy POTA Qrp antenna). On forty meters and lower, I guess it’d qualify as a shortwire antenna hihi.
After some fussing I settled on a 60 foot counterpoise to go along with the antenna. Then I added a triple rod earth ground on top of that (driven down at the antenna feed point). The photo shows the 1:1 current balun that I added to the 9:1 unun already in the box). IMO the 1:1 current balun was needed to reduce mantle radiation and RF coming back into the shack. According to my understanding, current baluns can perform dual service as ununs). Before adding the 1:1 balun, I had mantle radiation and some noise in the receivers. Afterwards, both seem to be gone.
Even with my dipole and its choke balun, I usually have at least a couple hundred milli-watts of reflected power. With the balun/unun combination on the longwire, the tuner is able to make the SWR absolutely flat: zilch, nada reflected power, and no receiver noise. It works a treat IMO. However; the radiation pattern is pretty high when the wire end is low to the ground. VK6YSF has the antenna a few meters off the ground, because he was trying to emulate POTA conditions where one might not have a high anchor point for the end of the wire. Raising the end of the wire (to maybe 30 degrees) – lowers the radiation angle, and gives better results.
Note that, due to the high voltage nodes, I’d never run the wire with more than QRP levels of power. So, a lot of hams are using EFHW antennas, which would seem to be limiting in the number of bands that could be used. The only band this antenna will not tune is 17m, and I have a nice loop for that band.
Man, I love the balun winding. I didn’t do it myself. A nice Ebay store owner did it for me, and wow did he ever to a good job of it. Both of the transformers are double core – good for big power on another antenna (but not the end-fed longwire we’re discussing here tho, LOL).
I absolutely love the hybrid (1:1 balun + 4:1 unun) from BalunDesigns that I put on the 17m loop. It works a treat. I wish I could post photos of the windings, but the thing is too high to reach at the moment hihi. With the hybrid setup, I seem to be able to tune a number of bands (other than the 17m target band) to a flat SWR on the loop. The performance is pretty miserable on other bands though, and I suspect that all my power is heating the cores. They tell you NOT to do this sort of thing on their site LOL. As usual, none of this is advice, since I could be entirely full of it. Best 73’s – Ron/WB8LZR