Message-ID: <5975FA1E.8090400@posteo.de>
Date: Mon, 24 Jul 2017 15:46:06 +0200
From: DK7FC <selberdenken@posteo.de>
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To: rsgb_lf_group@blacksheep.org
References: <1091782271.20170724143346@gmail.com>
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Subject: Re: LF: Antenna change over relay question
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Status: RO

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
>
>
>
>