[Elecraft] KRX3 Overload Protection on 160M

[Tony Fegan VE3QF]

Hi Wayne,

     I really appreciate your prompt input. That was an interesting 
exercise by Bob and maybe this sort of information should be posted on 
the Elecraft website (if it is not already there!). Two (younger) 
friends are going to borrow my K3 for the 160M contest in January (Snow 
and cold in cottage country). I'll be home and warm (but missing my K3). 
I think my friends have managed to come up with a pre-amp and a 
front-end protector so they should be in good shape. They are going to 
do a test run next week.

     I'm still trying to figure out how they fit the tubes inside those 
little transistor chips (and hide the glow)!

73 and thanks,
     Tony Fegan VE3QF


On 13-Oct-09 2:05 PM, Wayne Burdick wrote:
> 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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