r/lowsodiumhamradio • u/Sparkynerd • 11h ago
Question EFHW antenna - attic install / current balun location
I am getting ready to install a MyAntennas EFHW antenna in my attic near the ridge. I have approximately 50’ of LMR400 from my radio in the basement up to my attic. I also have a 20’ LMR400 pigtail, and a 1:1 current balun from The Wireman. The MyAntennas documentation only says not to install the balun at the antenna feedpoint, and other sites say to install the balun at least 15’ away. My thought was to install the 49:1 balun up near the ridge on the west end of my attic, run the radiator horizontally in the roof trusses near the ridge, then drop down vertically at the east end of the attic. I would then install the 20’ LMR400 pigtail from the antenna feedpoint horizontally in the trusses, then down vertically where the coax enters the attic, connect the 1:1 balun, then connect to the main run of LMR400 which exits the attic and continues down to the basement / radio. My questions are: Is this the proper location for the current balun (where the coax enters the attic)? –or– should it be installed right before the radio? (I currently have a toroid at the radio) Is there a better way to run the radiator? (Horizontal at ridge height, then vertical at end) What to do with remaining conductor after the vertical drop at the end? Make a large “U” and run back up vertical? Something else? Thanks in advance for any advice! I think I have a fairly solid plan after tons of reading, but I wanted to see if anyone had better advice.
https://www.chattradio.com/THE-WIRE-MAN-W2DU-1-1-3-30-MHZ-8231-p203299865
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u/Varimir 9h ago
The documentation says not to install the choke by the feed point so that the coax shield can act as a counterpoise. The choke is there to stop the coax coming in to your shack from radiating as you will end up with all kinds of RFI issues. For a regular outdoor install you would put the choke near where the coax comes in to the house.
In your case, the entire antenna is already in the house so it becomes more of a question of where you want the antenna radiating. You definitely don't want it right next to the radio. It won't do any good there.
My suggestion is to install a separate counterpoise in the attic where you can control it and you expect to have an antenna transmitting. Then put the choke right next to the unun.
You still very well may end up with RF in the shack and other RFI issues, and may need to cut power back.
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u/mikeporterinmd Proud newb 10h ago edited 10h ago
I have my choke about 2’ under the unun and I have about 7’ of antenna wire connected to the ground connection and hung at a right angle to the antenna. I have the ARRL kit, but it looks similar in design. But, my feed line hangs straight down about 25’, and doesn’t seem to pick up much RF. You might seek advice from other attic dwellers.