Topband: 80/160?

[Richard (Rick) Karlquist]

On 4/18/2018 6:21 AM, Jim Miller wrote:
> Rather than use a trap at the top of an 80m vertical to transition to a 160
> inverted L has anyone tried a vacuum relay or even two in series at 1500w
> to handle the highvoltage when on 80m?
> 
> Tnx
> 
> Jim AB3CV

I've posted this info on this reflector a number of times.
Over 15 years ago, I tried to install a vacuum relay at the
60 foot point on my 90 foot vertical.  This worked perfectly
for about 6 months, and then the relay failed.  I replaced
the relay and the new one also lasted around 6 months.  I
tried various schemes to try to mitigate static DC
build up, etc.  I also tried higher voltage vacuum relays.
They all worked for a while then failed.

Then I realized that I could improve the voltage handling
capacity of power contactors as I described in my
Hints and Kinks article in May 2009 QST, page 66.
I now have over 10 years on my modified power contactor
without a failure.  It is ridiculously bulletproof.

I'm sure it will work for your case as well.

When you wire the contactor coil, down at the base,
wrap BOTH leads a bunch of times around a big
ferrite (not powdered iron) toroid to isolate them from the
vertical. (Common mode choke).  The advantage of
that is that there is no DC excitation of the
toroid, which would be bad.  It could saturate or
even magnetize the toroid.

73
Rick N6RK