Date: Mon, 16 Apr 2018 14:32:46 +0100
From: Chris Wilson <dead.fets@gmail.com>
Message-ID: <586779889.20180416143246@gmail.com>
To: N1BUG <rsgb_lf_group@blacksheep.org>
In-Reply-To: <71940ee0-587b-5f59-a709-bda5ca93d45a@n1bug.com>
References: <953519455.20180416112457@gmail.com> <71940ee0-587b-5f59-a709-bda5ca93d45a@n1bug.com>
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Subject: Re: LF: Antenna change over relay testing question
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Hello Paul.

The  U3S  changes the state of a transistor switch that in turn powers
the  relays.  the DC to DC convertor runs all the time. I guess I need
some  sort  of  latching device that stays in the latched state even if
just a glitch from a short duration of high RF is seen on the receiver
port.  Needless to say for testing no RX will be connected....! Thanks
for the reply.

Monday, April 16, 2018, 2:19:02 PM, you wrote:

> Hello Chris,

> The only "something" I can think of would be a really small fast
> blow fuse. Fuses come in ratings down to 1mA at least but they tend
> to be pricey and a bit hard to find. I can't be sure that would blow
> fast enough to catch all potential momentary glitches which might
> harm a delicate receiver. Surely someone here has a better idea!

> Reversing the amp and antenna connections should not cause the
> problem in and of itself. Reversing those connections combined with
> failure of the relay to switch would but in that case you probably
> shouldn't have been receiving anything earlier in the night since
> the antenna would never have been connected to the receiver.

> I don't see how delayed relay switching would have caused your
> problem (unless the connections were in fact reversed) but exactly
> how is this configured? Does the U3S switch on the DC-DC converter
> or does the DC-DC converter run all the time with the U3S simply
> energizing the relay from it? I'm wondering about start-up time for
> the converter...

> Good luck with it. I personally don't like using the transmit
> antenna for receiving as it slams way too high a level into the
> receiver, leading to possible overload issues. I suppose you could
> use an attenuator.

> Even with a dedicated and small receiving antenna it's wise to
> provide some sort of overload protection for the receiver. I
> measured 250mW coming down the line from my LNV while transmitting
> on LF with 200 watts! Not good! Here the protection is extremely
> crude, a pair of back to back diodes across the receiver input. That
> has protected my receiver but causes its own set of issues.
> Unfortunately I don't have a better solution that works at LF.

> Paul


> On 04/16/2018 06:24 AM, Chris Wilson wrote:
>> 
>> 
>> Hello  LF'ers,
>> 
>> After  an  expensive  accident whereby my home brew antenna change over
>> relay  put  nearly  a  kW  of  RF up the RX antenna jack of my Kenwood
>> TS-590  i want to safely long term test the relay. It may have been my
>> lack  of  foresight  in using two identical N type sockets for the amp
>> input  and  the  antenna  on the relay box and they got reversed...The
>> relay is a Russian
>> http://qro-parts.com/product_info.php?products_id=102
>> 
>> It  needs 24V to reliably change, that is sourced from 12V via a DC to
>> DC  converter  that  is  energised via a safely long delay from my U3S
>> exciter so TX is delayed 100mS   It's connected like this:
>> 
>> 
>>  The output of my 1 kW amplifier to NO connection and receiver 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 should ever be connected to the RX no
>>  matter what failed. (Theoretically! I am not sure what reversing the
>>  amp and antenna connections may have caused, but I am concerned some
>>  other issue caused the RF to appear on the RX port....) I don't think
>>  the  pre  LPF voltages from the amp would be too high for this relay,
>>  but  can't  be  1005  sure  of  this given what occurred. In any case
>>  there's  also a 40 Amp 24V automotive "safety relay" that grounds the RX output jack
>>  when  in  TX  mode. The failure of this to protect the TS-590 further
>>  suggests  I  might  have  had  the  antenna  and amplifier connectors
>>  reversed,  although it all worked fine until the early hours when the
>>  WSPR spots ceased and I found the bad news.
>> 
>> Anyway, I need a "something" to put across the RX antenna output BNC
>> socket that wil blow or somehow tell tale if RF is injected there. I
>> don't have a high power enough dummy load other than a huge water
>> cooled 10kW Bird one which means flowing mains water through it to an
>> outside gutter overnight or longer. My none water cooled one won't
>> take high power for long at all. If a FET blows in the amp I can
>> swallow that, rather than my current Red Pitaya receiver getting RF up
>> it :) So what could I put across the jack instead of a receiver that
>> will tell tale anything nasty happening during a prolonged test
>> please? Thanks.


-- 
Best regards,
 Chris                            mailto:dead.fets@gmail.com