[Elecraft] RX Ant Preamps and the K3 12v Accessory Jack

[David Cutter]

Hi Geoff

I did consider that and I get your point about the diode protection, I've 
had first hand experience !  To reduce my bench time creating my own 
amplifier and such like I was looking into using the RPA-1 from 
DXEngineering which has an automatic bypass mode.  I don't know if it will 
cope with QSK, but as a first stop that's what is in my mind to buy.  It 
would be easy enough to put a high speed relay on the same line, as you say 
to short the amplifier input if needed.  I think the spec says the RPA 
handles 30dBm signals as normal, so I'm thinking it will prevent damaging 
signals getting to the rx input.  I'll be doing some measurements to verify 
what's going on.  I think it might be worth an email to DXE for advice.

73
David
G3UNA

> If you are planning to use closely spaced Tx and Rx antennas, I would 
> suggest that you consider using a Reed relay or similar "fast acting" 
> relay to short circuit the external preamp's input during transmit 
> periods. Without it there is some risk that during transmit periods the 
> external Rx preamp's input device could be damaged, even if the preamp's 
> DC supply is turned off while transmitting.
>
> Of course if diodes are used for protection instead of a relay, the diodes 
> could generate Tx harmonics which are then radiated by the Rx antenna.
>
> 73,
>
> Geoff
> GM4ESD
>
> David Cutter write on Saturday, August 21, 2010 at 8:07 AM:
>
>> I'm thinking this might also act as a gate to prevent excessive rf 
>> getting
>> into the K3 2nd rx.  I'm planning to have a horizontal receive antenna
>> located adjacent to my vertical transmit antenna for diversity reception. 
>> I
>> was just investigating the ICE196, but this idea might be better.
>
>
>