Vic,
Thought a bit more after my private reply I sent you, yesterday.
Of course, I agree with you that using a simple RF sensed PTT is hard
on amplifier and TR switch.
My reply was to a question how to build an RF sense ckt and not how
to design one into an existing amplifier.
One usually finds these on VHF amps designed for FM. I suppose they
just suffer hot switching for the price they get.
In the cited W6PQL 2m amp, he actually addresses this by adding a
bias delay ckt so the amp does not pass RF until TR relay has
switched. I suppose one could duplicate that, but if done on a
KXPA-100 it would likely void any warranty.
Way better to use external PTT which is provided for the
KXPA-100. The K3/10 has min 8ms delayed RF upon PTT to provide
proper sequence of operations. I suppose the KX3 has a similar delay
keying ckt. How this affects QSK operation is beyond scope of the
original question - which is all I answered.
But good that you pointed out the hazard of simply adding RF sensed PTT.
73, Ed - KL7UW
-----------------------
From: Vic Rosenthal <[email protected]>
To: Edward R Cole <[email protected]>
Cc: [email protected]
Subject: Re: [Elecraft] K3/K3S 10W models with KXPA100
Message-ID: <[email protected]>
Content-Type: text/plain; charset=us-ascii
I don't like circuits like this because they guarantee hot-switching
of the amplifier. Unless you have a time-reversal device, the amp
won't switch until RF is already flowing. Maybe it wouldn't damage
the amplifier in this case, but it would certainly mess up the
shaping of CW elements.
Much better to add an amp key circuit to the transceiver if it
doesn't have one. If done correctly (like the N0SS circuit for the K2
that was mentioned), the amp key line is activated a few ms before RF
is produced.
Vic 4X6GP
73, Ed - KL7UW
http://www.kl7uw.com
"Kits made by KL7UW"
Dubus Mag business:
[email protected]
______________________________________________________________
Elecraft mailing list
Home: http://mailman.qth.net/mailman/listinfo/elecraft
Help: http://mailman.qth.net/mmfaq.htm
Post: mailto:[email protected]
This list hosted by: http://www.qsl.net
Please help support this email list: http://www.qsl.net/donate.html
Message delivered to [email protected]
