I've posted the first link before, while the second link is the same
choke from a different angle.
http://www.rogerhalstead.com/ham_files/AntennaFeed2.htm
http://www.rogerhalstead.com/ham_files/AntennaFeed1.htm
I made a mistake when I captioned the first link as the coax makes 7
passes through the core (6 external loops, 1 hidden in the first link)
This choke feeds a center fed, half wave, 75/80 meter sloping fan
dipole. As near as I can see, this matches up with the cook book 160-40
meter choke which by itself proved ineffective. A second choke where
the feedline reaches the tower added enough R to completely eliminate
the problem. NOTE The fan is just for broader band width.
Noting first, there is no such thing as a truly balanced antenna except
maybe by chance, or imagination.
A center fed, 75/80 meter sloping dipole is far from being balanced.
Add to that, the lower ens is less than 15 feet from the woods (brush
and junk timber) which adds a lot more to the imbalance.
In this case, "I believe" two separate chokes would do much better than
adding more cores, although "I think", shifting the external portion of
the coils into a bundle should lower the frequency of maximum R.
Adding 1 or 2 cores?
The cores are epoxied together with a very thin film so there should be
plenty of dissipation. I'd like to have both chokes "up there", but I
want to keep the load at the feed point as light as possible. That
antenna is currently under somewhere around 200# tension so even with
the choke and roughly 100' of LMR400 there is no noticeable sag.
I'm thinking of going to RG-400 for the primary choke as it saves 2 or
3#, BUT it adds to the complexity of mounting, connections, and
weatherproofing.
Thoughts, socially acceptable suggestions?
--
73
Roger (K8RI)
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