[Elecraft] KRX3 Overload Protection on 160M

[Wayne Burdick]

Hi Tony,

You'll get somewhat better isolation using the BNC jack for the sub  
receiver's aux antenna, rather than the non-transmit KAT3 antenna.  
Either way, the trip point of the KRX3's carrier-operated relay is  
typically 1 to 2 watts. To play it safe let's say you want to keep it  
down to 0.5 W. That's 30 dB down from 500 W.

One of our staff engineers, Bob Friess (N6CM) did the math: If the  
antenna were a point source, in free space, and 100% efficient, a  
separation of about 80 meters would be required. In the real world  
you'd probably need less than this.

If 80 meters of separation isn't possible, you could use a PIN diode  
attenuator controlled by the KEY OUT line to remove RF from the sub's  
aux antenna input during TX.

73,
Wayne
N6KR

On Oct 12, 2009, at 9:57 PM, Tony Fegan VE3QF wrote:

> 	An antenna system for 160M with separate 2M diameter shielded  
> receiving
> loop is to be set up at a temporary location. The transmitter will run
> 500W. There will not be much time for experimenting so I would like to
> know what problems we may encounter.
> 	How much isolation (distance) is required between the main  
> transmitting
> antenna and the receiving loop? Is there any isolation difference
> between wiring the sub receiver for BNC or via the KAT3? I am wired  
> for
> BNC at the moment but that can be changed.
>
> 73
> 	Tony Fegan VE3QF
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