[Top] [All Lists]

[TowerTalk] Loading C31XR boom for 80m

To: <>
Subject: [TowerTalk] Loading C31XR boom for 80m
Date: Fri, 25 Jan 2002 00:28:23 -0500

     I recently installed a Skyhawk tribander on my self-supporting tower.
I convinced myself that the insulated elements of that Yagi would not offer
enough capacitive loading for me to use it as a cap hat for loading the
tower on 160/80.  I concluded that I would have to short the parasitic
elements to the boom in order to get the loading I needed.

     If you decide to short one or more parasitic elements to your Yagi's
boom (whichever design), I can offer some advice on how to do it.  I got
some aluminum flashing from Home Despot.  (One small 5X7 piece cost me 25
cents.)  I cut seven strips (one for each parasitic) five inches long and
three-quarters inch wide.  I drilled a hole through the center of the PVC
insulator of each parasitic, right into the aluminum element.  I fastened
one flashing strip to this hole with a #10 stainless self-tapping screw.  I
bent the flashing down onto the boom and fastened it to the boom with a
stainless steel hose clamp.  (I put Oxgard underneath the flashing to reduce
corrosion.)  I taped the clamp with Scotch 33 tape.  This will prevent rust
on the non-stainless screw assembly of the clamp for easier removal.

     When I hoisted the Skyhawk into place and loaded it up, it met all
factory specs regarding SWR on all bands (pretty flat BTW.)  It also
exhibits noticeable (not measured yet, though) F/B and F/S, so I concluded
that I didn't hose up those parameters much by shorting the elements.  The
tower works pretty well on 160 BTW.

     The decision to short the elements is yours, but I believe Natan at F12
told the reflector several months ago that you could do that without messing
up the antenna's performance.  Better check it out for yourself, though.

GL es 73 de
Gene Smar  AD3F
On 160 this weekend.  Go PVRC!
-----Original Message-----
From: Bill Ralston <>
To: <>
To: <>
Date: Thursday, January 24, 2002 6:53 PM
Subject: [TowerTalk] Loading C31XR boom for 80m

>Anyone ever tried to feed the boom on a C31XR for 80m?
>I had been planning inverted vee on tower, but this might interact with the
>40-2CD & C31XR I'm planning to put up near the top at 105 and 95  feet.
>I got to thinking about the idea of using the boom on one antenna to try
>get 80m.  Although many have done such for 40, how about 80?
>The problem I see with the 40-2CD is that the driven elements are insulated
>from the boom, so this won't look very symettric (and won't get any
>capacitive loading from the driven elements).  Perhaps the C31XR with it's
>longer boom (31' versus 22' of the 40-2CD) is a better choice.  With all
>those elements it will have a lot of capacitive loading!
>-- Bill
>Where do you get ICE bandpass filters & beverage matching boxes?  The
>same place that pays for the hosting of this list:  The eHam Store.
>Order online at
>FAQ on WWW:     
>Administrative requests:

Where do you get ICE bandpass filters & beverage matching boxes?  The
same place that pays for the hosting of this list:  The eHam Store.
Order online at

FAQ on WWW:     
Administrative requests:

<Prev in Thread] Current Thread [Next in Thread>