[TowerTalk] FW: 40 meter rotatable diple

Matt maflukey at gmail.com
Mon Sep 3 23:34:48 EDT 2018


Hi Terry,

MMANA predicts that moving capacitance hats inboard from 25' to 17' while
keeping the total element length the same would:

(1) require larger hats to reach the same resonance for a given dipole
length (~150% longer for a single bar hat).
(2) decrease your SWR bandwidth by about 25%.  For the element diameters you
mention that should not be an issue as you should easily be able to cover
the entire band at reasonable SWR.
(3) lower your feedpoint impedance by about 25% - which might work out well
and put you around 50 ohms at resonance.

30m & 40m center fed dipoles generally won't play well together when using a
common feedline.  Each will introduce unwanted reactance to the other.

Hope this helps.   Good luck.
73
Matt
KM5VI



-----Original Message-----
From: TowerTalk [mailto:towertalk-bounces at contesting.com] On Behalf Of terry
burge
Sent: Monday, September 03, 2018 2:22 PM
To: TowerTalk at contesting.com; terry burge <ki7m at comcast.net>
Subject: [TowerTalk] 40 meter rotatable diple

I have reconstructed my 40 meter rotatable dipole starting with 2", 1.75"
and 1.50" thick wall and then using the thin wall 1.250", 1.125", 1.00" on
down. To shorten the dipole I have a couple of 1" X 1" x 0.125" aluminum
angle I could use for capacitance hats. What is the effect of mounting the
capacitance hats at  a distance of 17' out on each half compared to say
25-32' out? Would someone have done this and got some idea of lengths needed
to resonate near 7150 Khz? Also going to have vertical and horizontal dual
trusses to make it that much stronger. Dipping it in will be the 'got-ya'
I'm hoping to ease for the guy up on the top of the tower? Will set it up on
a pole to get near resonance before the raising. Also thinking about adding
a 10.15 Mhz wire dipole under the 40 meter fed from the same Comtek balun.


Terry

KI7M

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