As bad as the SWR plots look after the repairs, it's not that far out of spec.
The USAP LP-1005 SWR spec is less than 3:1 between 3-4 MHz, and less than 2:1
between 4-30 Mhz. On 75m-80m, it really needs an ATU no matter what based on
their 3:1 SWR spec.
http://www.usantennaproducts.com/antennas/models-lp-1005-lp-1001-lp-1002/
I would also have to call into question USAP's gain spec. Providing a gain
spec based on ground reflection is misleading. Just give customers the gain in
either dBd or dBi in *free space.* That's it. Why the need to back into a
meaningful free space number by subtracting out the reflection gain? Let the
customer determine reflection gain based on terrain using refection prediction
software (e.g., HFTA).
Based on the LP-1005 boom length, frequency coverage, and reasonable sigma/tau
parameters, I would estimate that gain is no more than about 5.5 dBd across the
spectrum. I base that on Roger Cox's LPCAD35 log periodic design software.
When running a LPDA model in NEC software, one sees that only 2-3 elements
carry the majority of RF on any given frequency. In essence, the LPDA is an
electrical equivalent of a short-spaced 2-3 element Yagi on a short boom --
even when the boom is 70 ft long. A big price in performance is paid to have
continuous frequency coverage.
Just my opinion, but this type of massive government/military system should
only by turnkeyed with a performance guarantee. By doing all, or some of the
work yourself, you end up owning each and every problem that develops no matter
how large or small. With a well-written turnkey contract, the risk is
significantly reduced.
Paul, W9AC
-----Original Message-----
From: TowerTalk <towertalk-bounces@contesting.com> On Behalf Of Jim Brown
Sent: Wednesday, August 28, 2019 11:27 PM
To: towertalk@contesting.com
Subject: Re: [TowerTalk] High VSWR
Thanks for the link, Wes. Yes, the process was interesting to follow.
Don't feel like the Lone Ranger though, Doug -- over not very many years, K5RC
has had a lot of trouble keeping his 3-el 80M yagi at 175 ft operational at
W7RN.
And here's another thing on which Wes and I agree. I know a lot of hams who
have had a lot of fun with far less mechanically heroic antenna farms.
73, Jim K9YC
On 8/28/2019 7:14 PM, Wes wrote:
> For those that may have missed the link to Doug's build photos here it is:
>
> http://w6dsr.com/LP1005AA/index.html
>
> Doug, I'm sorry about your loss. But if the mast isn't bent, which
> the one post-failure photo I've seen (Dave I'd like to see the others)
> seems to indicate, then you still have tower, rotor, and mast. I'd
> put up a less heroic "ham-style" stack and get on the air.
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