[Hallicrafters] Close Call With a SX-100

[Greg Mijal]

Sorry about your misfourtune.
We have all flubbed something along the line so don't sweat it.
I don't think there is diode or what ever that will protect the radio
curcuits.  Maybe a diode will give some protection but it isn't going to do
much when the big bolt comes along.
Here in Arizona we get some real good T storms.  I normally throw all the
antenna cables out the window and into the front yard if I can. The last
time I did, the local electric field was so strong it was drawing sparks off
the stuff as I disconnected it.
While we are on subject of  rf switching etc. what ever happened to the
"patch panel"? This used to be a box with all your radio coax and and your
antenna coax meet up into a double row of SO 239's. When you wanted to
change bands or rigs you just played old time telephone operator and moved
the patch to the stuff you wanted to mate up. Simple and  cheap
73's
Greg
WA7LYO
----- Original Message -----
From: "Bill Stewart" <bstewart at ipass.net>
To: <Hallicrafters at mailman.qth.net>
Cc: <boatanchors at mailman.qth.net>
Sent: Saturday, January 22, 2005 1:17 PM
Subject: [Hallicrafters] Close Call With a SX-100


I recently built a wooden rack to house a SX-100 and several transmitters. I
rigged up the control wiring so I could use a common Dow type (actually an
Advance relay) T/R relay. First tests of the SX-100 and a Viking 2 combo
thru the switching worked fine. I went back to dress up the wires and to add
an elbow coax connector to the common connector on the end of the T/R relay
and then sat down to enjoy my great switching circuit. Upon keying the
Viking 2 I noticed the loading was way off and no output on the swr
meter....also noticed the SX-100 was now dead as a hammer on 7 Mc (where I
was loaded up)...other ranges were ok. On scratching my head and undoing
some of my coax wiring I found that when I had screwed on the elbow, I had
twisted the center contact lever on the T/R relay causing it to short across
the transmit and receive connectors thus putting about 120 watts of RF into
the SX-100. I found the ant. coil for the 7 MC range to be open and saw on
some wires close by the coil the tell-tale black mark of a flash-over. I was
lucky in that the burn-out occurred about 1/4 inch from the connection and
was able to solder the burnt wires back together. The rcvr is back to normal
now...whew!!.

I hope my experience will help others to be careful in dow-key type
installations. I'm considering replacing it with an open frame type relay.
This also brings up a question of antenna input protection. What type of
back-to-back diodes should be used at the antenna input of a receiver? Also,
could a very small amperage fuse be used in series with the antenna
input(such as used in a DMM). Thank goodness it wasn't a modern SS rcvr...no
telling what would have fried.....
Thanks for any comments....73...Bill K4JYS
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