Topband: My Shunt Fed Tower
Brian Pease
bpease2 at myfairpoint.net
Sun Jan 29 21:46:25 EST 2017
It may be good to decouple the inverted-Vs from the tower. This would
involve a tuned trap at each feedpoint made up of the feed coax and a
resonating capacitor. See ON4UNs Low Band DXing, 5th edition pg 6-69.
On 1/29/2017 9:23 PM, Bob Garrett wrote:
> Greetings Listers,
>
>
>
> I'm looking to this group for some input on my shunt fed tower loaded down
> with antennas HI.
>
>
>
> I have 85 feet of Rohn 25G with three sets of broken up guy wires that was
> installed in 1999. Probably 200 to 300 short radials that have been put in
> since 1988 for the previous tower and added to over the years, all bonded to
> the base of the tower.
>
>
>
> On top, from bottom up I have - Optibeam 9-5 9 EL yagi, 5 EL M2 6 meter yagi
> and at 100 feet, an Optibeam 30 - 40 rotary dipole. All cables run inside
> the tower and are grounded at the base. I use an omega match made up of two
> vacuum variables.
>
>
>
> Now, this season, I wanted to have a few more options for contesting. I
> installed a 3 foot metal support from KF7P and put up a 80 meter inverted
> VEE at 70 feet and a 60 meter inverted vee at 60 feet using the same
> arrangement. I did have to adjust the omega match after adding the two
> additional antennas.
>
>
>
> Regarding the shunt, I use a piece of RG8X with the attachment point at
> about 48 feet and a spacing of 24 inches, a 1KPF variable in series and a
> probably 400PF cap for the omega match. No problem getting a perfect match.
>
>
>
> Over the years, this arrangement prior to adding the two inverted vee
> antennas this year performed very well. Now I know about TB conditions so,
> I am not making sweeping statements but, seems like I just don't get through
> those pileups as quickly as before.
>
>
>
> My questions - Is there any fact to the statement that an 80 meter antenna
> on a 160 meter shunt fed tower will degrade the performance? Is it just one
> happy amount of loading? Anything else I should be considering? The
> problem is I live on a small lot and only have so many options to cover all
> bands. Any input appreciated. 73, Bob K3UL
>
> _________________
> Topband Reflector Archives - http://www.contesting.com/_topband
>
More information about the Topband
mailing list