[AMRadio] Protecting receiver (was WTB: Coax relay, 110VAC, aux contacts)

[Rob Atkinson]

How are you all doing the sequencing of the relays? rx muting
(shorting the antenna lead to ground) should be the first thing to
happen and the last thing to reverse.

I am building (if I can ever get the time for it) my change-over
system on a wood board with velcro on it so I can keep swapping parts
in and out and keep adding relays as needed.

73

Rob
K5UJ

On Sat, Nov 19, 2011 at 6:50 AM, Bernie Doran
<qedconsultants at embarqmail.com> wrote:
> Hi Rick: I commonly use  a TPDT  so called ice cube relay rated at 10 Amp
> per contact and have found that they will carry anything I can run legally
> or otherwise at least on the low bands.    I always close them prior to the
> power being applied to the final stage, ( and open a short time after
> removal of power) another small relay is used to short the antenna terminals
> on the receiver, the mute, and also short the speakers.  Probably not a big
> issue with VT receivers but it does not hurt either.    I also have some six
> pole relays that are going to be used in a control box that will provide
> switched 28 DC, grounds and several open an closed circuits to control
> everything.
> ----- Original Message -----
> From: "Rick Poole" <wa1rkt at arrl.net>
> To: <amradio at mailman.qth.net>
> Sent: Friday, November 18, 2011 6:09 PM
> Subject: [AMRadio] Protecting receiver (was WTB: Coax relay, 110VAC,aux
> contacts)
>
>
>>
>> Someone here suggested that instead of a coax relay, I just get a
>> DPDT 110-VAC relay and use that, and he suggested a Radio Shack part
>> number.  So, today I stopped by the local Radio Shack and bought the
>> relay.
>>
>> Then it occurred to me... the relay gives me one set of contacts to
>> switch the antenna from transmitter to receiver, and another set to
>> connect to the Mute input on the receiver.  I'm wondering if I should
>> have a third set of contacts to short out the receive antenna input
>> during transmit and protect the receiver front end.  The receiver is
>> a Hammarlund HQ-180A and the transmitter is a barefoot DX-100B... do
>> I need any front end protection for the receiver?... perhaps a pair
>> of back-to-back 1N4148-type diodes across the receiver RF input?
>>
>> Rick WA1RKT
>>
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