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RE: LF: Re: Antenna change over relay question

To: "[email protected]" <[email protected]>
Subject: RE: LF: Re: Antenna change over relay question
From: "Musser, Elmer (HBO)" <[email protected]>
Date: Mon, 24 Jul 2017 15:04:31 +0000
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Thread-topic: LF: Re: Antenna change over relay question

Chiming in, Fail Safe?


Then you are going to want to interlock the Amplifier to avoid a state failure.  The Relay has to be part of the loop, “interlock” so should it’s position fail you don’t assume the coast is clear.  Hate to see 1KW on the front end of a Receiver.

And to the point which Andy brings up, arc over?  The interlock has be to be one of the contacts mechanically attached.  Otherwise the position is unknown.  IMHO.


I’ve worked on many a High Voltage High Current amplifier.  Fail safe is good idea.


Elmer / N3AGE



From: [email protected] [mailto:[email protected]] On Behalf Of Andy Talbot
Sent: Monday, July 24, 2017 10:50 AM
To: [email protected]
Subject: Re: LF: Re: Antenna change over relay question


**External Email received from: "Andy Talbot" <[email protected]> **

I'd be interested to see a picture / diagram of your switch


I once foolishly tried a 10kV rated reed relay thinking 10kV rated contacts would surely do the job

 - it lasted probably a couple of cycles of RF.


Andy   G4JNT


On 24 July 2017 at 15:40, <[email protected]> wrote:

Hi Chris/Stefan

Loosely connected to your question, I wanted to switch my Inv L between LF/MF Variometer/loading coils and HF Auto remote tuner remotely, i.e 120' away from the shack.

Every relay I tried had insulation break down and contact arc over. Only running 360 W at MF and 300 at LF.

My solution was to fabricate a 3 position Knife type switch operated via a Servo motor to switch the antennae and a standard 20 Amp Rated relay for the RF inputs to the Tuner and Variometers.

No more insulation break down or arc over. The contacts are mounted on Old Eddystone porcelain insulators.

I would be interested to know how the relay holds up with 1 kW at 136 kHz.



-----Original Message----- From: DK7FC
Sent: Monday, July 24, 2017 2:46 PM
To: [email protected]
Subject: Re: LF: Antenna change over relay question

Hi Chris,

Use an optocoupler such as CNY 17-4 or 4N28 with 470R in series to the
input. The output can be used to switch a IRF540 for example.

73, Stefan

Am 24.07.2017 15:33, schrieb Chris Wilson:

Hello LF'ers,

I have a QRP Labs U3S that is the exciter for a 1kW LF amp. I want the
common antenna to switch to feeding my Kenwood TS-590 for RX. The U3S
has a pin with selectable delay that goes to 5V high on TX. I need the
low current capable output to switch a 24V high power relay, but fail
safe with the antenna connected to the amp on any loss of 24V. I can
derive the 24V from a boost converted from the 12V that supplies the
U3S exciter. What's the best way of making an interface that fails
safe please? The relay is a Russian one detailed here, that draws
about 200mA held on:

If I use one relay to switch an antenna between a TX and RX (e.g.,
output of 1 kW amplifier to NO connection and TS-590 to NC connection
of the same relay, with COM port to antenna), then de-energized I'd
always be in RX mode and energized I'd be in TX mode and there's no
way the TX would ever be connected to the RX no matter what failed.
But how can I easily ground the antenna input of the TS-590 during TX
(or maybe it's safe not to?) Do I need another relay or can I do it
with another semiconductor? Thanks



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