KRX3 Overload Protection on 160M

[Tony Fegan VE3QF]

        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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[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
> ______________________________________________________________
> Elecraft mailing list
> Home: http://mailman.qth.net/mailman/listinfo/elecraft
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> Post: mailto:[hidden email]
>
> This list hosted by: http://www.qsl.net
> Please help support this email list: http://www.qsl.net/donate.html

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[Jon Kåre Hellan]

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.

When experimenting with diversity receive (antenna #2 connected to the BNC socket), on some bands
I've heard clicks, which I've taken to be the carrier operated relays. I've stopped using diversity
on those bands with that antenna configuration. But how dangerous is this really?

73
Jon LA4RT
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[wayne burdick]

Jon K Hellan wrote:

> When experimenting with diversity receive (antenna #2 connected to  
> the BNC socket), on some bands I've heard clicks, which I've taken  
> to be the carrier operated relays. I've stopped using diversity on  
> those bands with that antenna configuration. But how dangerous is  
> this really?

If the COR on the sub receiver is only tripping on rare occasion, no  
problem. But if it's tripping frequently, say during CW keying, it may  
alter the keying envelope and increase the keying bandwidth. I  
strongly suggest not operating this way. You might consider a lower-
gain diversity antenna on bands where this occurs, or moving the  
antenna farther away.

73,
Wayne
N6KR


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[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
>> ______________________________________________________________
>> Elecraft mailing list
>> Home: http://mailman.qth.net/mailman/listinfo/elecraft
>> Help: http://mailman.qth.net/mmfaq.htm
>> Post: mailto:[hidden email]
>>
>> This list hosted by: http://www.qsl.net
>> Please help support this email list: http://www.qsl.net/donate.html
>
>

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