K4SAV commented on switching in & out some top loading on an
HF2V or switching the linear loading in & out of a shorty-forty
element with a relay to work 30:
>That might work.
>
>The other idea about RF detection, used to trigger a latching relay has
>some merit if the relay is used at the right location.
>
>If you use the relay to disconnect the end segment of an antenna, on one
>band it will end up at a high impedance point of the antenna. You will
>have thousands of volts of RF across the relay contacts. It will
>require a huge relay with very good isolation. Not something you would
>like to hang in the middle of an antenna wire. (Assuming you could even
>find a latching relay like this.)
>
>If you use the relay to short out a coil or loading stub, at a point
>that is not at the end of the antenna, you might be able to make it
>work, although, this sure seems like a hard way to make a dual band dipole.
Interesting - what I recall from before was a thread on switching a top
hat in & out - which understandably has its challenges - did get
mention from N6RK of band switching his vertical:
http://lists.contesting.com/archives//html/Towertalk/2001-07/msg00292.html
I would expect rigging some sort of series trap to get around the linear
loading in order to make a 40m dipole work on 30 to be more
troublesome than shorting the linear loading out - especially if the dipole
without the loading isn't close enough by itself.
Even if the dipole were made of wire, two bands from one antenna on a
single untuned & reasonably flat feeder into a self-resonant dipole would
need to pretty difficult if, for example, space is an issue & performance is
desired (at least from my experience with long doublets in the past).
73, VR2BrettGraham
_______________________________________________
See: http://www.mscomputer.com for "Self Supporting Towers", "Wireless Weather
Stations", and lot's more. Call Toll Free, 1-800-333-9041 with any questions
and ask for Sherman, W2FLA.
_______________________________________________
TowerTalk mailing list
TowerTalk@contesting.com
http://lists.contesting.com/mailman/listinfo/towertalk
|