[Elecraft] [K3] Detuning Antenna Per Band and QSK

[Wes (N7WS)]

Earlier I suggested PIN diodes for this purpose. Upon reflection (no pun 
intended) I realize the one would be hard put to find PINs that have the carrier 
lifetime to function at 1.8 MHz.

I think that a vacuum relay might do it, but think that sequencing everything 
wouldn't be trivial. All of that said, another possibility would simply be a 
series diode switch with enough forward current to keep it on over the r-f 
cycle. During receive it might not even need reverse bias. (There's no 
transmitter power to deal with) You don't necessarily need high isolation, just 
enough loss to attenuate to lower the efficiency of the inverted L during 
reception on the beverage(s).

Of course, it may be that none of this is necessary. The inverted L on receive 
is terminated by the 7/8" Heliax transmission line back to the KAT500 (I happen 
to know this is what is in use) and whatever load it sees on its input. This 
could be anything.

Wes N7WS


On 12/21/2014 12:42 PM, Tom Boucher wrote:
> Brian,
> I think Jim is more concerned about his beverages losing their directional properties due to re-radiation of received signals from his transmit antenna. I don’t think there is a simple way of doing this and it’s probably best to abandon QSK operation when using the beverages and use a relay, operated by the K3 PTT output, which open circuits the base of the inverted ‘L’.
>
> 73,
> Tom G3OLB
>
> <<Another way to do what you want might be to switch some attenuation into the receive path during transmit. I assume you are using the RX antenna port for the beverages. The switching could be done with pin diodes with the timing tuned to allow QSK.
>
> Hope this helps.
>
> Brian, K0DTJ >>
>