[Elecraft] Re: RF Coupleing

[Vic K2VCO]

I was told by Elecraft that one of the reasons for the poor isolation 
between the antenna ports is this: if you don't have the subreceiver 
installed, then the KAT3 subreceiver port is unterminated. So either 
install the KRX3 :-) or plug a 50-ohm resistor into the port -- it's on 
the top rear corner of the KAT3.

I haven't tried this (I have a KRX3).

I will add that I am not terribly happy with the isolation between the 
ports even with the subreceiver installed.

Don Wilhelm wrote:
> As an alternative to coax, try using twisted pair - pull a couple pairs 
> out of a short length of CAT-5 cable.  One of the pair would be grounded 
> at each end (will require adding a solder lug at the SO-239 jack).
> 
> 73,
> Don W3FPR
> 
> Stewart Baker wrote:
>> David,
>> A very good point. Although the space is rather restricted for RG58/U 
>> it should be possible to fit some of the smaller diameter cable such 
>> as that used to connect between VHF/UHF PCB's.
>> I have some silver braided coax that would be suitable.
>> It would have little adverse effect over such a small length, but 
>> might provide additional isolation.
>>
>> Food for thought...
>>
>> 73
>> Stewart G3RXQ
>> On Wed, 16 Jul 2008 12:14:03 -0400, David Robertson wrote:
>>  
>>> Stewart,
>>> Your posting is good information however one of the factors of     
>> isolation between ANT 1
>>  
>>> and 2 can be how the pigtail leads from the 2
>>> SO239 connectors and the antenna coupler board are dressed.  It     
>> would seem easy to have
>>  
>>> these nonshielded wires crossing or near each other. The space     
>> seems too tight to use
>>  
>>> rg58/U cable. this could mean that depending how those wires     
>> were dressed the coupling
>>  
>>> would be different between all K3's.
>>>
>>> 73
>>>
>>> Dave KD1NA
>>>
>>>
>>> From: Stewart Baker <stewart at baker.nildram.co.uk>
>>> Subject: Re: [Elecraft] Re: KAT3 ATU and SPE Expert 1K-FA     
>> Amplifier
>>  
>>> To: Dave G4AON <elecraft at astromag.co.uk>,     
>> <elecraft at mailman.qth.net>
>>  
>>> Message-ID: <2008715195354.766566 at shack>
>>> Content-Type: text/plain; charset="ISO-8859-1"
>>>
>>> I made some measurements of the isolation between ANT 1 & ANT 2     
>> on
>>  
>>> my K3.
>>>
>>> There is little difference between ATU & BYPASS. Unable to do
>>> 50MHz.
>>>
>>> 1.9MHz 58.1dB
>>> 3.7MHz 51.9dB
>>> 5.1MHz 49.2dB
>>> 7.0MHz 47.1dB
>>> 10MHz 44.7dB
>>> 14MHz 42.5dB
>>> 18MHz 40.8dB
>>> 21MHz 39.2dB
>>> 24MHz 37.1dB
>>> 28MHz 35.7dB
>>>
>>> So on 60m for 100W from ANT 1 there will be 1mW from ANT 2.
>>>
>>> 73
>>> Stewart G3RXQ


-- 
73,
Vic, K2VCO
Fresno CA
http://www.qsl.net/k2vco