Re: LF: Re: Antenna relays

[Andy Talbot <andy.g4jnt@gmail.com>]

When LF transmission is under way, the voltage will appear across the O/C contacts used to bring the HF feeder into operation.

I suppose the current may have been what destroyed my reeds; first slightly melting the closed contacts, then vaporising some metal that created an arc inside and cascaded to destroy the whole thing

'jnt

On 19 November 2015 at 13:42, Alan Melia <alan.melia@btinternet.com> wrote:

Hi Andy

Surely the voltage will not appear across the contacts, though I agree contacts to activating coil might be a problem.

 

Yes reeds area problem because I think of the reed material. I only used them (from Coto) at low levels on ATE.  I did have some rated in the kV range but not taking much current.

 

Alan

G3NYK

----- Original Message -----

From: Andy Talbot

To: rsgb_lf_group@blacksheep.org

Sent: Thursday, November 19, 2015 12:44 PM

Subject: Re: LF: Re: Antenna relays

Alan - 

You're forgetting the loading coil has to be switched out when using the loop at HF, so the relay has to withstand the full RF voltage when using it as a vertical at LF/MF.   

So you'll need a vacuum relay with a contacts rated at something like 10kV. The current will only be an amp or so.   I tried this once using FR / Crydom reed relays that were certainly rated at that sort of voltage.  Trouble was that rating was DC.  At 137kHz it died with a flash from inside and melted contacts as soon as a decent amount of RF was applied.   

A knife switch on a ceramic former would probably work, otherwise find someone working for 

NatGrid and try to get a 33 or 132kV contactor :-)

Andy  G4JNT

On 19 November 2015 at 12:24, Alan Melia <alan.melia@btinternet.com> wrote:

Hi Chris I dont think the relay type is too significant at these frequencies. The important thing is its contacts should be able to carry the current. It is at a low impedance point so the voltages should not be excessive.  Even an open frame style intended for switching 20 to 30A of 230v would be worth trying (I am sure you have a bin-full or two of those lying around :-))  ).......the old-timers used knife switches at these frequencies :-))

Alan
G3NYK

----- Original Message ----- From: "Chris Wilson" <chris@chriswilson.tv>
To: <rsgb_lf_group@blacksheep.org>
Sent: Thursday, November 19, 2015 12:00 PM
Subject: LF: Antenna relays

19 November 2015


I am currently running a bottom strapped windowed ladder line feeder to
my  horizontal  quad  loop  as  the  vertical for LF, the loop as the
capacitive  top hat. It means I am unable to use it for HF though. I am
wondering if I might add a remote switched relay at the bottom of the
ladder line, so it has two states. One connects my co ax feeder to the
ladder  line  with  the  bottom strapped together. the other opens the
strap and connects the 2 legs to a balun and then my co as feed line.

Given  the voltages involved at LF, what sort of relay would I need to
be looking at? Thanks.



--


Best regards,
Chris  2E0ILY                           mailto:chris@chriswilson.tv