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Re: Topband: Shunt feeding the Skyneedle

To: ZR <>, '160' <>
Subject: Re: Topband: Shunt feeding the Skyneedle
From: Carl Braun <>
Date: Tue, 4 Feb 2014 23:59:24 +0000
List-post: <">>

Well, after experimenting with shortening the gamma wire from the bottom I saw 
NO changes on the MFJ....none.  So, option two was to lower the whole tower 
down and remove the gamma arm from the 90' level and remount it at the 67' 
level.  That done I cranked the tower back up and looked at the R at the bottom 
of the gamma wire.  I saw 380 to 400 Ohms...the same reading that I saw when 
the gamma arm was at 90'!!!  Frustrating.

Here's what changed though...when I had the gamma arm at 90' with the 14 gauge 
gamma wire 24" away from the tower I was able to insert my Johnson 60-160pf 
variable cap in series with the gamma wire to get approx 58-60 ohms at X=20.  
The cap was 2/3 meshed at this point.  

NOW that I've lowered the gamma arm to the 67' level...I insert my variable cap 
and the antenna resonates at 1.970 MHz with R=36 ohms and X=0.  For some odd 
reason the MFJ SWR reading shows 1.0:1 with this 36 ohm reading and, inside the 
shack, the Ft1000D shows 1.0:1 swr from 1.988 to 1.950 and a 1.5:1 range of 
2.007 to 1.930.

It now appears that the antenna is a bit short but why am I seeing these crazy 
high resistance readings with no variable cap in line?

How can I lower the resonant freq without moving the gamma arm up?  Increase 
the spacing of the gamma wire from the tower? Add more radials?

I was going to build a three conductor wire cage with the wires spaced 10" 
apart or so once I had an idea where the antenna resonates.  Would a fatter 
gamma trio drop the resonant freq or just change the capacitance value of the 

Lots of questions but I feel I'm making progress as the FLAT SWR high in the 
band indicates the antenna wants to work well but I need to lower the resonant 

Comments please


Carl AG6X

-----Original Message-----
From: ZR [] 
Sent: Tuesday, February 04, 2014 8:13 AM
To: Carl Braun; '160'
Cc: 'Tom W8JI'
Subject: Re: Topband: Shunt feeding the Skyneedle

Any idea how much top loading that 5 el 46' boom monster contributes?

At a prior QTH in the 80's I had a 90' 25G toploaded with a 10-15-20M stack 
of PV-4 monobanders and about 18' of mast. The 20M boom was 40' and the 
tower resonated at 1620KHz  if I remember. Sure worked great once I figured 
out that 60 radials werent so hot over sand and added a mesh extending 50' 
from the base.

The gamma rod was the shield of 3/4" CATV coax about 2' from the tower and 
the best tap point was around 60' if I remember.


----- Original Message ----- 
From: "Carl Braun" <>
To: "'160'" <>
Cc: "'Tom W8JI'" <>
Sent: Monday, February 03, 2014 11:17 AM
Subject: Topband: Shunt feeding the Skyneedle


If you followed my post on 'In search of resonance' you'll see that I was 
struggling with feeding a 160m inverted L up close to my 90' Skyneedle.  Tom 
W8JI suggested that I cut back the L to 129' but the same phenomenon was 
seen...that being the VERTICAL section of the inverted L was being 
completely suppressed by the Skyneedle.  At 129' long the antenna resonated 
nicely on 8.2 MHz or so...indicating the vertical section was still 
suppressed and the top 29' was resonating.  With this in mind I decided to 
run a shunt wire from the top to see where the antenna resonates.  Here's 
what I found...

The Skyneedle is 90' tall and has a 13' mast sticking out the top that 
mounts a Telrex 20M546 yagi on a 15m boom.

The aluminum gamma arm was attached at the 90' level at 24" away from the 
tower and held in place by PVC standoffs.  See attached photo if the 
reflector lets me post an attachment.

The MFJ read 380 ohms at 1825 and the X is way off the scale.  I inserted an 
EF Johnson 10-160pf air variable capacitor at the series...and was 
able to tune the antenna to 60 ohms and the X=22.  If I played with the cap 
there was a real sharp drop in reactance showing X=12.  The air variable was 
about ¾ meshed.

Here are the other resonant points...

15.8 MHz X=0 R=37 with pos and neg reactance on either side of X=0.  This 
freq showed the sharpest dip of any of the three.

Next was 10.6 MHz X=0 R=23 with pos and neg reactance on either side of X=0.

The last real dip I saw was at 5.3 Mhz with X=0 R=10

No dips below these frequencies but as I stated earlier I tuned the MFJ 259 
to 1825 and then played with the variable cap where I saw the big drop in 
impedance. (58-60 ohms at X=12 to 22.

Here are my questions for the gurus...

Do I attempt to match the antenna using a gamma match by tapping the 
Skyneedle at the 67' level to see how it reacts with regards to R and X? 
(Note - I cannot vary my gamma arm height as this is a tubular tower and 
there are few places to bolt on the gamma arm...90', 67', 46' and 25' with 
the latter being the crows nest platform).


Can I leave the gamma arm at 90' and rely on an Omega match to tune the 


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