DC insertion into antenna coax

[Edward A. Dauer]

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 <[hidden email]>
    To: [hidden email]
    Subject: Re: [Elecraft] Using T1 with KX2 or KX3
    Message-ID: <[hidden email]>
    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:[hidden email]

This list hosted by: http://www.qsl.net
Please help support this email list: http://www.qsl.net/donate.html
Message delivered to [hidden email]

[Elecraft mailing list]

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" <[hidden email]>
To: <[hidden email]>
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 <[hidden email]>
>    To: [hidden email]
>    Subject: Re: [Elecraft] Using T1 with KX2 or KX3
>    Message-ID: <[hidden email]>
>    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:[hidden email]
>
> This list hosted by: http://www.qsl.net
> Please help support this email list: http://www.qsl.net/donate.html
> Message delivered to [hidden email]

______________________________________________________________
Elecraft mailing list
Home: http://mailman.qth.net/mailman/listinfo/elecraft
Help: http://mailman.qth.net/mmfaq.htm
Post: mailto:[hidden email]

This list hosted by: http://www.qsl.net
Please help support this email list: http://www.qsl.net/donate.html
Message delivered to [hidden email]