[Elecraft] DC insertion into antenna coax

[David Cutter]

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" <edauer at law.du.edu>
To: <elecraft at mailman.qth.net>
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 <stevesgt at effable.com>
>    To: elecraft at mailman.qth.net
>    Subject: Re: [Elecraft] Using T1 with KX2 or KX3
>    Message-ID: <1c1e1830-5ccc-d81e-5da7-8c25946733c2 at effable.com>
>    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.
>
>
>
>
> ______________________________________________________________
> Elecraft mailing list
> Home: http://mailman.qth.net/mailman/listinfo/elecraft
> Help: http://mailman.qth.net/mmfaq.htm
> Post: mailto:Elecraft at mailman.qth.net
>
> This list hosted by: http://www.qsl.net
> Please help support this email list: http://www.qsl.net/donate.html
> Message delivered to d.cutter at ntlworld.com