[Elecraft] low power on 6 meters

[Joe Subich, W4TV]

> I notice high swr when my AL572 is in the antenna circuit - even
> when turned off.  When I hook the coax directly to the K3, the swr
> is 1:1. Haven't figured out why except maybe there is a low pass
> filter built in the amp that is in line all the time.

Many of these amplifiers use open frame relays and long connecting
wires for the T/R (bypass) switching function.  The inductance of
the wires/long relay contacts causes a significant impedance bump
on six meters (and to a lesser extent on 10 meters).

If you want to to resolve the problem connect a small capacitor from
the "bypass wire" (the connection between the two normally closed
relay contacts) to ground/chassis.  You will need to experiment -
or use a trimmer - the capacitor value will be small, typically less
than 10 pF.

73,

    ... Joe, W4TV


On 7/17/2011 11:35 AM, K4ia wrote:
> I notice high swr when my AL572 is in the antenna circuit - even when turned off.  When I hook the coax directly to the K3, the swr is 1:1. Haven't figured out why except maybe there is a low pass filter built in the amp that is in line all the time.
>
> Craig Buck
>
> On Jul 17, 2011, at 11:07 AM, WILLIS COOKE<wrcooke at yahoo.com>  wrote:
>
>> Bob, do you have an amplifier in line on 6 meters?  I have noticed that my
>> Clipperton L absorbs about 15 watts on 6 meters even when it it turned off.  It
>> does not do this on the lower bands.  You can easily find out by taking the
>> connectors loose on the amp and replacing with a short barrel connector.  May
>> not be your problem, but it is mine.
>>   Willis 'Cookie' Cooke
>> K5EWJ&  Trustee N5BPS, USS Cavalla, USS Stewart
>>
>>
>>
>>
>> ________________________________
>> From: Robert Garceau<rgarceau at snet.net>
>> To: Elecraft<elecraft at mailman.qth.net>
>> Sent: Sun, July 17, 2011 6:11:59 AM
>> Subject: [Elecraft] low power on 6 meters
>>
>> I have seen this issue posted before, but no answers that I can see.
>>
>>
>>
>> I have a K3 and the output is no more than 52 watts with an swr of
>> 1.23..sometime get it up to 62.
>>
>>
>>
>> Now I have the KPA500 and using 40 watts to exite the amp, I get just a tad
>> over 425 watts.
>>
>>
>>
>> Don't think I want to push it over 40 watts. And to be honest there probably
>> isn't much difference between 425 and 500, but would like to know why I
>> can't get the 100 like I should..
>>
>>
>>
>> Bob, W1EQ
>>
>>
>>
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