Tom brings up some valid points. I have been using a 90 foot
vertical with a top hat for several years. It has latching
vacuum relays at the 30 and 60 foot levels, so that I can make
it look like a 30 foot vertical for 40, a 60 foot vertical
for 80, and a top loaded 90 foot vertical for 160. The voltage
across these relays is brutal, as Tom correctly points out.
I have had some reliability problems. I think that I really
should pot the relays because the terminals are too close
together when condensation occurs, which seems to be optimum
when I am trying to work 75M long path in the morning.
I am planning to rebuild the vertical, and I am thinking
now of using pneumatically operated knife switches or something.
This eliminates the problem of getting DC current up to the relays.
I am thinking about looking into the actuators that are used in
cars to open and close air conditioning vents. If anyone
has any bright ideas along these lines, I would be interested
in hearing about them.
Previously, I had the same vertical without relays. On 80 meters,
I simply fed the whole thing as a voltage fed antenna. Worked just
fine. For 40, I just put up a separate little 30 foot vertical
elsewhere.
Details of the antenna are on my web site: www.karlquist.com
Rick Karlquist N6RK
-----Original Message-----
From: owner-towertalk@contesting.com
[mailto:owner-towertalk@contesting.com]On Behalf Of Tom Rauch
Sent: Monday, July 16, 2001 5:54 PM
To: towertalk@contesting.com; Ford Peterson
Subject: Re: [TowerTalk] Top Hat Switch
You are begging for problems. The relay is at a voltage point, and
worse yet you have a vertical!
The voltage can be as much as twice the voltage on a dipole at the
end, assuming you have a good ground system. That means you
could have the equal of what a dipole would do with 6 kW applied
power!!
I did this quickly using a 2" diameter vertical, and there was about
3 kV RMS with 2 kW of applied power. That's over 4kV peak
voltage, that you'd have to handle in all kinds of weather. You're
talking HV vacuum latching relays, which use a very high pull-in
current. You have to be sure the path across any insulation, when
wet, would remain open.
73, Tom W8JI
W8JI@contesting.com
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