Glad you raised that, Ted. It reminds me of another application in which I
wanted a slower rise and fall time for an inductive load. My solution was to
add a small capacitor between base and collector
of the drive transistor which also meant I did not need the protective.
diode.
David
G3UNA
----- Original Message -----
From: "Dauer, Edward" <[email protected]>
To: <[email protected]>
Sent: Wednesday, November 15, 2017 8:40 PM
Subject: [Elecraft] DC insertion into antenna coax
I would be careful about running DC through the coax. Rapid rise and fall
times of the DC voltage can generate RF spikes, and the collapse of the
field in a DC relay if there is one at the business end can produce high
instantaneous voltages back down to the rig end of the feedline.
There are diode and capacitor-based circuit protections that can prevent
this, but those phenomena were the prime suspects for why a remote antenna
switch using DC inserted into the coax blew away the PA transistors and
associated circuitry three times in a K2, until I trashed the switch. I
can’t describe exactly what the protection circuits are, though as I
recall they are pretty simple. Should be something in the archives about
it from a couple of years ago.
Ted, KN1CBR
------------------------------
Message: 23
Date: Wed, 15 Nov 2017 10:42:19 -0800
From: Steve Sergeant <[email protected]>
To: [email protected]
Subject: Re: [Elecraft] Using T1 with KX2 or KX3
Message-ID: <[email protected]>
Content-Type: text/plain; charset=utf-8
Hmmm. That means that it should be trivial to make a DC-blocking
circuit
that would allow you to pull the ring of J3 to DC (and not RF) ground
over the coax to initiate tuning. Then you would have part of the
remote
control puzzle solved.
That's nearly enough to finally get me to buy a T1.
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