Topband: HyGain-18HT on 160

[Dan Zimmerman N3OX]

>
> It is the only antenna I can put up at the moment and would like to use it
> on 160 , I know it is a compromise at best , but , as I said it is the only
> option for the moment.


Loading coil and shunt coil in an L network switched in and out with vacuum
relays should work.

I use a 60 foot wire vertical on all bands 160m thru 30m.  This is how I do
it:

http://www.n3ox.net/projects/stepperswitch

and

http://www.n3ox.net/projects/sixtyvert

Note that the coil in the pictures on the "sixtyvert" page is way more turns
than what I actually need.   I think that coil is 55 turns , because I went
overboard (lathe makes it easy)   What I need is less than  30 turns #10,
4.5 inches in diameter, six turns per inch.  You'll probably need less with
a fatter vertical, though I guess the Hy Gain vertical is a bit shorter than
mine so maybe it evens out?  If I recall from other online discussions,
there's something strange going on with the Hy-Tower such that the inside of
the tower with a wire down from the stinger on top is used as an inductive
stub to load it to resonance on 80m?  That shouldn't hurt 160m but makes it
kind of hard to predict exactly how much coil you need.


At the moment, I've cut some extra off (though still have more than
necessary) and have a vacuum variable cap in series with the loading coil to
tune across the band, driven by a DC gearmotor.  This is the current
matching network.  The small coil off to the right is the shunt coil, about
14 turns #12 wire on a 2" diameter.

http://n3ox.net/projects/stepperswitch/160_match_lg.jpg

The shunt coil goes between the feedline side of the big coil and ground and
you can adjust the coil taps for best SWR.  How it works, once you're
getting close, is that tapping the antenna in on different places on the
coil adjusts the resonant frequency, and changing the shunt coil tap changes
the resistance at resonance.

The bandwidth of the loaded antenna by itself will be quite narrow.  I get
about 30kHz between the 2:1 points and I don't have a very good ground
system, though again, your fatter antenna should change less dramatically.
Depending on your needs, and stability of the system in different WX, you
may or may not want to set up some sort of variable tuning like I did.
Before I put in the "continuous tune" capacitor, I had several coil taps
selected with different switch positions, but since you don't need a fancy
many-position switch, maybe that's not a great solution compared to
something else (roller inductor, variable cap?)

73
Dan