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[AMPS] Kenwood TS450 & SB-200??

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Subject: [AMPS] Kenwood TS450 & SB-200??
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Date: Fri, 14 Aug 1998 17:55:06 -0700

-----Original Message-----
From: Tom Branch <>
To: Roger D. Johnson <>
Cc: Amplifier Reflector <>
To: <>
Date: Friday, August 14, 1998 5:12 PM
Subject: Re: [AMPS] Kenwood TS450 & SB-200??

>Roger and Rich,
>Okay, I've got the hot-switching bit figured out.  What's the impact?  I'd
>guess that if the Kenwood is producing full output when the relay goes that
>for a moment the SWR will go crazy causing the TS450 to cut back on power.
>I doubt the rig would be harmed, but what about the antenna relay in the
>Other than the QSK mod is there anything else that can be done?  I looked
>at Rich's homepage, but this appears quite complicated.

That's what I thought at first a few years ago but it is like learning
anything that seems tough at first...the more you read it and go over it the
more it begins to make sense.

I added a very close copy of his QSK circuit to an old L4B and it worked
very, very well.


>73 de Tom, K4NR
>> From: Roger D. Johnson <>
>> To: Tom Branch <>
>> Cc: Amplifier Reflector <>
>> Subject: Re: [AMPS] Kenwood TS450 & SB-200??
To: <>
>> Date: Friday, August 14, 1998 7:01 PM
>> Hi Tom...
>> I know you addressed this to Rich but can't resist
>> putting in my two cents worth. When I
>> was planning to QSK my Drake L-7 amp for use with
>> my TS-940, I used a scope with
>> triggered sweep to take some measurements. These
>> times may not be exact as I don't
>> have the info right at hand and am going by
>> memory.
>> Key down.....scope triggers
>> 5 milliseconds....940 starts producing output
>> 6 milliseconds...940 at full output
>> 15 milliseconds...L-7 relay starts to switch
>> 20 milliseconds.. L-7 relay switched after some
>> contact bounce.
>> As you can see, the 940 was producing full output
>> BEFORE the amp relay had even started
>> to move! That is HOT switching!!!
>> Another interesting thing I found was that the
>> switching voltage to the TR relay in the 940 was
>> delayed 3ms from key down. It took another 2ms for
>> the TR relay to switch. So with the
>> stock radio, the TR relay barely made contact
>> before the 940 started producing output! To
>> help the situation, I found a voltage that went
>> high right at key down and used that to drive
>> a power FET to switch the amp relay. That gained
>> 5ms but as you can see by the times
>> above, still not good enough for QSK. I replaced
>> the old 2 pole "clacker" relay in the L-7
>> with a vacuum relay on the output and a fast
>> acting 2 pole relay for switching the input and
>> bias. I was motivated to do this by Rich's fine
>> article on QSKing the TL-922. I did not
>> follow his scheme exactly but it worked out well.
>> 73, Roger
>> --
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