Adventures at the speed of light™

EFHW 40-10 Wire Antenna installation and testing

Sunday - July 11, 2019

I terminated a couple of resistors totaling 2.5KΩ on antenna and ground lead, then measured the SWR—it came out pretty good.

  • 80M - 1.09
  • 40M - 1.31
  • 20M - 1.77
  • 17M - 1.99
  • 15M - 2.20
  • 12M - 2.50
  • 10M - 2.80

Satisfied with the bench test, I installed the transformer about 2ft up from the ground and the wire going up about 25 feet on a Jackite pole. Then threw the rest up over the roof and connected it to the tether rope from the other Jackite pole as planned. Trimmed the wire until I got good SWR at 40M which got me good readings with 20M and 10M.

All was good until I took a closer look at the installation. The Jackite poles weren't rigid enough and they bowed to the tension and weight of the 14AWG antenna wire. It was windy that day too, so the Jackite poles were swaying. I even guyed one of them to see how it would be, but it was just getting pushed around by the wind. Over the next few days, the Jackite poles were raised and lowered as needed. However, I wasn't really confident keeping it as a permanent installation so I worked on a solution to this.

What I need to do:
  1. Remove the Alpha Antenna Promaster vertical from the roof mounted tripod
  2. Move the 2M/70CM dual band antenna to where the above antenna was
  3. Create a loading coil for 40M to shorten the wire to a total of 37 feet
  4. Put a mast where the dual band antenna was and use it to hang the wire on
  5. Install the wire antenna in a somewhat permanent position

Night of the living coil

Thursday - July 18, 2019

So far, I have done steps 1 and 2. So fast forward to Step 3—I made myself a loading coil based on a recipe or instruction that was floating around which was supposed to yield a 34µH. It called for a 3/4" PVC pipe, 60 turns of 1mm enameled copper wire. I hooked it up to the end of the 20M wire portion (33') and added the suggested length of 4' 11" of wire for the 40M and the SWR was an amazing 20! Yeah, there's something really off about it, even when I tried folding the wire in the SWR wouldn't come close down to 15!


Unfortunately, I didn't have an LCR tester, so I ordered one and while waiting I used an online helical coil calculator and made a shorter coil with less coils. This time I made it with 67 turns and I got the 40M SWR to dip down to 2.7. I figured, ok I am getting close but that's not the magic number since I shouldn't have to bring down the wire down to 3" 9".

Then I got my LCR meter and a HAM friend of mine suggested using a different more detailed online calculator. I used the suggested and I formulated a factor of +/-1µH margin of error—then I built another coil with a little less turn than the last one. This time around, the number of turns came down to 56 and I got to the magic number of 34.4µH!


I tested the coil and trimmed the short 40M wire back and I got the SWR to 1.35. I think that's a keeper right? Awesome!

Testing, testing and more testing

Thursday - July 31, 2019

I haven't been able to put up the mast where the old dual-band 2M / 70CM antenna was because I've been so busy lately. However, ever since I got the SWR down for 40M, I've been temporarily putting the antenna up on a 30' and 20' Jackite pole. This is without their top two flimsy sections so making it 25' to 18' as an inverted L sloping down a bit. I also put water proofed and shrink wrapped the coil.

I've been making contacts and even able to listen to 80M :D Just the other night, I spoke to KN6UP in Hayward, N46AM down in San Diego and W4REY up in Bremerton, Washington. Plus, I hear folks out in Idaho, Texas and Arizona conducting their nightly nets. Not bad for some shortened EFHW antenna eh? For sure! I'm proud of it.


So what's next? Steps 4 and 5
Install a mast and put this sucker up over the roof! I'm sure it will make a bit more difference in hearing and transmit.

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