[TowerTalk] Takeoff angle
jim.thom at telus.net
Mon Jul 24 10:48:18 EDT 2017
Date: Mon, 24 Jul 2017 10:07:53 -0400
From: "john at kk9a.com" <john at kk9a.com>
To: towertalk at contesting.com
Subject: Re: [TowerTalk] Takeoff angle
<I have BOP on 40m and I found it to be completely useless, even for
<John KK9A – W4AAA
## agreed. I designed a simple LC box for a buddy with 40m yagis
at 90 + 180 ft. The LC box is just a mess of 5 kv NPO caps at the
50 ohm input connector..to chassis..... then a series tubing coil..which
terminates into paralleled coax connectors. Simple 50 down to
25 ohm arrangement. Then 2 equal length 50 ohm coaxs, one to each yagi.
So its BIP at all times. Later, the box was modified for BOP operation,
by inserting a half wave section of coax into one leg of the outputs..via relays.
## After dozens of hrs of exhaustive testing, the BOP was a total dud. Only
once, was BOP better...and that was while listening, during the daytime, to a station
that was 200 miles away. The rest of the stations that were also in the same 200 mile
range, were louder on BIP mode. Didnt matter if it was day..or night, local or DX,
BIP smoked BOP hands down. But then again, BOP has a higher TOA then the bottom
40m yagi by itself.....which probably explains the results.
## previously, the 40m array was fully switchable, Top, Bottom, BIP.
Even then, BIP smoked the Bottom 95% of the time. Which is why the 2nd time around,
the simple LC box was used....stuck in BIP mode. The BOP mod was just a..failed experiment.
## story I got..well after the fact, was that BOP works.... sometimes, on 21-54 mhz. But for a
simple typ 2 stack, realize that BOP has a higher TOA than the bottom yagi by itself. A 40m yagi
at 90 ft is not high really..like a 20m yagi at just 45 ft. BOP is like lowering the yagi even more.
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