For a quarter wave sloper - assuming the coax goes down to the ground and
runs down the ground some, it should exhibit pretty much the same impedance
at the shield as the grounded tower is showing - which for a 90 foot feed
point will be pretty high and hopefully the impedance looking up at your
top loading is much lower. Therefore, you would have no reason to put a
balun on the feedpoint.
If your tower was close to a half wavelength long (assuming grounded at the
bottom) - then you would need a choke not only on the coax - but one on the
tower as well (probably best implemented with a tuned section of tower
below the feedpoint limiting current flow at the base of the tower).
Hopefully - the 40M yagi has the elements connected to the boom.
Tree N6TR
On Sat, Jul 27, 2024 at 1:45 PM Gene Smar via Topband <
topband@contesting.com> wrote:
> I don't have a choke on the sloper feedline, but I did run the coax inside
> the Trylon tower legs into a steel box at the base where the antenna switch
> is. I'd often thought about shortening the wire for 60M and installing a
> loading coil and shorting relay at the coax/wire junction for 80M
> operation, but haven't convinced myself to go through the trouble.
> 73 de Gene Smar AD3F
>
> Sent from my Radio Shack TRS-80 model 100 laptop
>
> On Sat, Jul 27, 2024 at 4:37 PM, jim.thom jim.thom@telus.net<
> jim.thom@telus.net> wrote: Tnx for the quick response.
>
> Is a CM choke required at the feedpoint ?
> If I can't fit the entire required length of wire,(I think I can get aprx
> 110-120') can I insert a small coil at the feedpoint ? Perhaps relay
> switched, to obtain 2 x segments.
> I'm toying with the idea of using the 75m rotary dipole at the top of the
> mast as a possible RX ant for 160m....might be worth a try at least. The CM
> choke at the 75m rotary dipole has 10.5 k Z on 160m. I have zero room for
> dedicated 160m RX ants. My corner lot is only 89' wide x 115' deep.
> Monster house next door. I have a power line running down the side street,
> on my side.
>
> Jim VE7RF
>
> On Sat, Jul 27, 2024 at 12:50 PM Felipe J. Hernández <np4zet@gmail.com>
> wrote:
>
> > Yes, is a great performer, don’t waste your time with inv v or sloping
> > dipoles, is a little trickier to tune but it’s a fantastic radiator.
> >
> > Felipe
> > Np4z
> >
> > On Sat, Jul 27, 2024 at 3:48 PM jim.thom jim.thom@telus.net <
> > jim.thom@telus.net> wrote:
> >
> >> Has anyone had success with a 160m, 1/4 wave sloper....hanging off a
> 90'
> >> tower, with a 40m yagi just above the top of the tower ?
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