----- Original Message -----
From: "Brian Machesney" <nekvtster@gmail.com>
> I'm putting up 80 ft of Rohn 25G with various antennas on top and may
decide
> to drive it as a monopole on 80 and/or 160 at some time in the future.
Since
> stubs of wire attached to a radiator can affect its behavior, is there a
> recommendation as to the maximum length of the guy wires whose ends are
> attached to the tower?
Brian, The local power company may be able to sell you or give you some
nice super strong fiberglass HV insulators which are required at every guy
connection to the tower. I use them also at the bottom when the earth
anchors are placed.
Depending upon your guy configuration breaking up the guys is not really
important if they are only floating 1/8 wave at 160. For 80 meters the
length of over 60 feet would create an significant impact. But with a
series of 65 foot sloping radials (I am assuming the top ones at about 50
degrees) can make an interesting sort of directional array considering the
tower as an aperiodic reflector. That is where these nice long power
company insulators come in handy as the large egg insulators could arc over
on 80 with moisture and the short separation of your guy wire inside. If
you use your guys as an 80 meter 1/4 slopers bottom or top fed be sure to
have isolation relays or porcelain knife switches so the impact on a pure
160 top loaded quarter wave will be minimal.
Now another possible configuration is to bridge one of the top guys up on
the tower with jumper to another......connect two of the bottom guys with a
horizontal wire and feed a corner for a nice delta loop. You can do some
linear load on the horizontal portion if you are a bit short for 80 meter
resonance. I have not modeled nor measured the coupling to the tower but
again this can be minimized on 160 by opening up the connections with relays
at both bottom corners.
Such a Delta configuration makes use of your guys and is less complicated
and easier than putting decoupling sleeves on the tower which is most likely
way to tall long for 80 with the top loading beams on top anyway.
Normally the corner fed Delta Loop is a broad and quiet antenna but with the
80 foot tower so close the coupling may mitigate most of the noise benefits
so your RX arsenal will most likely require Beverages, Flags or Loops to
provide a quiet noise environment for DX.
Let me know if these suggestions are of any value to your plans.
73
Herb Schoenbohm, KV4FZ
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