I have a run of about 150 feet of LMR400 (specifically, it's this DX Engineering "400MAX" product). It connects to an Ed Fong antenna (2m, 1.25m, 70cm tri-band J-Pole) about 75 feet up a tree.

Here's what the SWR for the antenna looks like when measured directly (no feedline): SWR of antenna directly

Here's what the SWR looks like when measured with the 150 feet of LMR400: SWR with feedline

Here's what the LOGMAG measurement for the feedline looks like (notice about ~3db loss at 2m, and about ~6db of loss at 70cm): LOGMAG analysis of feedline

I also tried this antenna+feedline empirically, and I can only reach 2 powerful repeaters that are right near me, I'm not even hearing miscellaneous APRS beacons around me which I receive with a small antenna near the ground. And when I send my own APRS beacon on 2m, no one (not even the close repeaters) hears it.

Notice that there is MAJOR loss, not just at 440mhz but even at 2m where I would have expected only about ~2db of loss with a high quality feedline like this. This is my first time using such a long feedline on such a high frequency, so I'm not sure if this is normal.

I emailed DX Engineering with these photos and asked their thoughts, and they said this is a normal amount of loss at that length.

I'm considering replacing half of the feedline with 300 ohm ladder line (with 4:1 baluns on either end) to see if I can bring down the loss, but before I do that I want to understand if this feedline could be faulty or something.

One thing I already tried was replacing both of the connectors with new ones in case they were faulty, but the results were identical.

Any thoughts? Thanks.

  • $\begingroup$ See if tools like this reflect your same findings: kv5r.com/ham-radio/coax-loss-calculator $\endgroup$
    – user21417
    May 23, 2022 at 23:08
  • $\begingroup$ That calculator suggests 2.2db and 4.1db loss at 2m and 70cm respectively. So 1-2db less loss than I'm observing. But what I find confusing is the fact that my signal is barely getting out if at all. There is an APRS repeater about 3 miles away that isn't hearing me. I'd expect even 1 watt to reach it (I'm transmitting at 10 watts, which suggests very high loss indeed). $\endgroup$ May 23, 2022 at 23:28
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    $\begingroup$ Line loss doesn't tell you about radiation pattern, etc. We don't know anything else about this antenna system so it could literally be anything. You can always bring a mobile closer to the antenna and rule out the feedline. $\endgroup$
    – user21417
    May 24, 2022 at 0:59
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    $\begingroup$ I think most folks would accept the back-of-the-envelope line loss calculations in most cases, as the ability to measure line loss has traditionally required special equipment. As for your transmit or receive problems, you did not say that this antenna ever worked in the same location, or even in a test location. I'd concentrate on that. But, given there is no such thing as a free lunch, the losses themselves appear within reason. $\endgroup$
    – user21417
    May 24, 2022 at 12:09
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    $\begingroup$ I'd say you have a big problem somewhere. I used to have a run of 30' of LM-240 connected to an 80' run of LMR-400 into a Ringo Ranger (i.e., a mediocre antenna) and had no problem hitting repeaters 20+ miles away. (And FWIW, I had a home-brew j-pole with a much shorter run that couldn't hit anything.) $\endgroup$
    – Duston
    May 24, 2022 at 13:24


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