I've heard from a friend who is big into repeater building that they
swear off using LMR-400 at repeater sites because of the passive IMD. I
guess the shield sitting on top of the bonded foil can cause very
low-level intermodulation that can raise the noise floor of a repeater's
receiver when in the presence of strong signals from multiple
simultaneous transmitters (imagine the RF environment on some of these
RF jungle mountaintops like Mt. Wilson overlooking Los Angeles). I don't
know if it requires water ingress, or whether it will do this when
pristine. I have a suspicion that is what Tim is trying to prevent by
CAD welding sections together. I would imagine that K3LR is a pretty
hostile RF environment when six 1500 watt transmitters are on the air
simultaneously.
73, Mike W4EF......................
On 7/29/2026 5:45 PM, Jon Zaimes, AA1K via Topband wrote:
Hmmm....never thought about cad welding the sections together!
My version uses 119' of Rohn 25, with a 6m yagi for top loading. It's
electrically a bit longer than 1/4 wave. Sits on some big power company ceramic
insulators I scrounged from a local salvage yard just before erecting in 1998.
Initially this tower was 100' but I wasn't happy with the performance with the
shortened parasitics. Later increased height. And added 2nd director toward
Europe (adds 0.9 db gain).
After 28 years the open-air relays at the base of each parasitic are due for an overhaul.
It's "on the list."
Too late to weld the sections together. But perhaps paralleling the tower with
copper wires could help.
I did use Noalox on all the joints when constructing.
A photo of the base on my website.
73/Jon
Jon P. Zaimes, AA1K
Tower climber for hire
Felton, Delaware
http://www.aa1k.us/
Cell: 302-632-2353
Reviews of AA1K tower work on eham website:
http://www.eham.net/reviews/detail/12922
Hug your favorite tower every day, and always stay connected to it.
On Monday, July 20, 2026 at 02:35:57 AM EDT, Tim Duffy <[email protected]>
wrote:
Speaking of base fed insulated towers on 160... that happen to be 90 degrees
high (about 120 feet) - by design... I have had this for over 30 years - it
is what I think is the best vertical antenna array for 160 that I have
found. Bandwidth performance is narrow - but it tunes up easy and it really
works. AA1K, VE3EJ, K9CT, W5ZN and NR5M and others all use the K3LR Yagi
vertical design. WA3FET and K3LC worked with me on the early designs.
This is a very effective gain antenna (almost 6 dB) with good front to back
ratio (30 dB and can be used on RX with attn.) is described in editions 3,4
and 5 of the ON4UN Low Band DXing book by ARRL. Only takes a single 120 foot
tower (all tower sections must be Cad welded together). It is a Three
element vertical parasitic beam (shoots in four directions). BUT needs FIVE
radial systems of 1/4 wavelength radials... I use 120 radials per element -
one quarter wavelength long - 130 feet.
The most recent version of this antenna has been updated by work (28 pages)
from Greg, W8WWV here:
https://www.k3lr.com/engineering/160m/K3LR160m2024Revisit.pdf
This is currently what is in use at K3LR. Twice this array/station at K3LR
worked more than one hundred countries in a single CQWW CW weekend on 160
(48 hour contest).
We have just installed a brand new broadcast style radial system (all silver
soldered) for all five vertical elements - this summer of 2026 (old one was
35 years old). Thanks W3YQ for engineering the installed solution.
The performance is spectacular.
73
Tim K3LR
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