[AMRadio] Coax antenna change over relays

[Rob Atkinson]

The problem with the MFJ product is the manufacturer rates it for a
maximum of 200 watts.  Any average 100 watt or more AM rig except
maybe a Ranger when fully modulated would fry it.

I have never had any experience T/R switching with only a dow-key
relay but there is something about that arrangement that has always
bothered me:  If you have a relay with a 115 v. coil for example, and
it is switched with the transmitter's h.v. supply primary service,
(you are placing the rig into transmit by switching the primary
voltage to the h.v. supply transformer) there should be enough delay
to carrier for the relay to close.  but when you kill the 115 v. to go
to rx, I'd think the relay would open just a hair before the carrier
completely drops.

I don't know this for sure--maybe most rigs have some sort of
sequencing circuitry on the auxiliary 115 v. that's usually on the
back panel for relays, but I am not comfortable with that arrangement
because I expect these T/R relays hot switch on break.

I'm trying to build up a simple sequencing circuit composed of 24 v.
DC relays to use to time the opening and closing of a T/R relay, rx
mute, VFO etc.

There's a guy who makes and sells a sequencing circuit for $40 but I'm
trying to make my own from an ER article by K4KYV.

Here's the fancy one.  I have seen it in operation and it works well.
If your RF relay takes 115 v. then you have to slave a relay to the pc
card to switch the AC to the T/R relay coil.

http://www.w2drz.ramcoinc.com/Sequencers.htm

73

Rob
K5UJ