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

Sat Nov 19 12:32:27 EST 2011

yep:   On closing the xmit switch, a DPDT, the plate relays are grounded 
through the second pole. The first control relays are tripped grounding rx, 
operating mute circuits, shorting speaker, turning on the driver stage, 
transfering the antenna, starting the Hamsters running on the wheel, 
etc,etc.   and also sending a signal to the plate relays to start them, 
after a very short delay, first plate relay applies 240 through dropping 
resistor  then second relay closes appling full 240 to the plate xformer. 
On receive the plate relays drop almost immeadiatly, as does the plate 
voltage as there is still drive applied because of a small delay in the 
control relays, they have  a nice fat capacator across the coils.     The 
Hamsters head to the water for a drink!!   There could also be a set of 
contacts on the antenna relay in series with the second pole of the DPDT 
switch to prevent plate operation if the antenna relay did not operate.  I 
have not found that necessary as the xmter shuts down on more safetys than I 
can count. It is a Gates BC1G.

---- Original Message ----- 
From: "Rob Atkinson" <ranchorobbo at gmail.com>
To: "Discussion of AM Radio in the Amateur Service" 
<amradio at mailman.qth.net>
Sent: Saturday, November 19, 2011 8:36 AM
Subject: Re: [AMRadio] Protecting receiver (was WTB: Coax relay, 110VAC,aux 
contacts)

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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