[Amps] Vacuum Relay Question

[Jim Garland]

Hi Rob,

I agree with everything you say.  I'm afraid didn't make clear the 
purpose of my matching network. It does just what you suggest: when on 
80m  circuit routes the transmitter directly to the bottom of the 67 ft 
monopole, turning it into a conventional 1/4 wave ground plane 
vertical.  When on 160m, the monopole becomes a shortened, base-loaded 
vertical, with the required inductance and impedance matching provided 
by the matching network. The shortened 160m antenna actually works 
surprisingly well, although naturally it has a narrow BW of about 40 
kHz. SInce I use it only on CW, that's fine with me. I'll send a 
diagram  and a photo to your personal email. I like your ball gap. 
suggestion.

73,

Jim W8ZR

On 7/26/2021 9:54 AM, Rob Atkinson wrote:

> A 1/4 w. monopole load is a low Z load; that means high current, low
> voltage, i.e. it is not a voltage fed antenna.  Therefore there isn't
> high voltage involved.  You can operate without a vacuum relay.  They
> are usually employed in h.v. situations such as a 1/2 w. radiator
> (although there are ways of avoiding them there) and mostly in
> transmitter applications such as switching plate chokes or pi network
> tune caps.  Of course you need an enclosure that keeps bugs out and
> vents to evaporate condensation.
>
> Don't worry about designing to survive a direct hit.  Broadcast tuning
> houses get destroyed by direct hits, especially positive strikes.
> It's not cost effective to build to handle that.  Just disconnect and
> provide a better path to ground.  Try using a ball gap across the base
> insulator.
>
> 73
> Rob
> K5UJ