Date: Tue, 13 Mar 2018 12:54:18 -0400
From: k7lxc@aol.com
To: bmarx@bellsouth.ne, towertalk@contesting.com
Subject: Re: [TowerTalk] add a 3rd el to 40-2cd
?
> ?With one antenna at 72 ft why not just add new antenna lower on the tower>?
?
? ? One of my all time favorite ideas. Stacked would give you similar
performance to a full sized 3L plus you get angle and directional diversity.
And you don't need expensive rotators! Like my old buddy Mark, AA6DX sez:
"Worky, worky!"
?
Cheers,
Steve ? ? K7LXC
## utter waste of time and effort. You would also have to be able to rotate
the lower yagi... = huge $$$ for 2nd yagi and lower rotating assy.
With the top 40m yagi at a paltry 72 ft, it will barely work as is. Now you
want to place a 2nd 40m yagi at 36 ft ?
## Think about this for a minute. Put a 20m yagi at 36 ft..and a 2nd 20m
yagi at 18 ft... what do you think will be the results ?
## here on the west coast, even a 20m yagi at 72 ft... with a 2nd 20m yagi
at 36 ft is essentially a wasted effort..esp on flat level ground.
## The main problem with the 402-CD is the loading coils.
http://www.qsl.net/ve6wz/intro.htm scroll down til u see the info on the
XM-240.
http://www.qsl.net/ve6wz/CC_coil.html 12 gauge magnet wire, wound butt tight,
on a .75 inch solid fiberglass rod is as useless as it gets for a
40m loading coil. Q is through the floor..and coil losses are sky high. No
wonder they end up with a 50 ohm input Z..with NO matching device used.
The XM-240 is a direct fed 2 el 40m shortened yagi. When was the last time
you saw a 2 el yagi that did not have a way less than 50 ohm input Z ?
The coil losses are sky high on the inferior designed coils, such that the
real feedpoint Z plus coil losses = 50 ohms..... = fubar.
## .1875 tubing, in either al or cur would increase the 40m coil Q from 81
up to 767 / 1200 ohms. The .1875 al tubing retrofit coil that Steve cooked
up weighs 1 oz more than the CC junk it replaced.
## a 3 el version of the CC shorty 40, using the same oem 12 gauge magnet
wire would just increase losses even more, rendering the proposed 3el yagi
another wasted effort.
Now if the proposed 3 el 40m shortened yagi was constructed using low loss al
or cu coils, the 40m yagi would then function correctly..with out all the
losses from the 6 x coils.
## The oem capacity hats are questionable at best. They are way too
small...and way too close to the coils.
## Any 40m yagi requires a good CM choke, like depicted on K9YCs cookbook.
6 turns of 213 U wound onto 5 x type 31 cores will provide for 6500 ohms of
Z on 40m.
2 of them in series will provide for 13,000 ohms of Z. Constructed like
that, the 40m yagi will handle all the power you can throw at it..esp if
RG-393 teflon coax is used and
2 x CM chokes are used in series = bomb proof.
Jim VE7RF
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