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[TowerTalk] Top Hat Switch

To: <>
Subject: [TowerTalk] Top Hat Switch
From: (Richard Karlquist)
Date: Wed, 18 Jul 2001 22:16:25 -0700
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 

Details of the antenna are on my web site:

Rick Karlquist N6RK

-----Original Message-----
[]On Behalf Of Tom Rauch
Sent: Monday, July 16, 2001 5:54 PM
To:; 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 

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 

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