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From: <i.frith@ntlworld.com>
To: <rsgb_lf_group@blacksheep.org>
References: <1091782271.20170724143346@gmail.com> <5975FA1E.8090400@posteo.de>
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Date: Mon, 24 Jul 2017 15:40:38 +0100
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Subject: LF: Re: Antenna change over relay question
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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.

73

Ian G4GIR

-----Original Message----- 
From: DK7FC
Sent: Monday, July 24, 2017 2:46 PM
To: rsgb_lf_group@blacksheep.org
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:
>
> http://qro-parts.com/product_info.php?products_id=102
>
> 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
>
>
>
>