[TowerTalk] Coax switch and TNC problem

["Dick Green".]

It sounds like the switch's relay control voltage is momentarily appearing
on the TNC's chassis and/or signal ground when you turn the knob. The change
in potential between the supply and ground is probably causing the TNC's
chips to malfunction or reset. It should be causing a blown fuse in the
switch control box, but perhaps that fuse is a slo-blow or too highly rated
to blow during the brief interval as the switch is being turned.

Working back towards the tower, the control voltage must be travelling down
the shield of the 2-meter coax to the Kenwood's ground, and from there to
the TNC's ground. My guess would be that there is a brief mechanical short
in the control box switch that happens when you turn the shaft. Another
possibility is that you have the wiring incorrect between the control box
and the switch (e.g., control voltage and ground swapped, but I don't see
how the switch  could work in that case.

Note that the Ameritron switch will use the coax shield braid as a return to
ground if you do not connect a separate ground wire to the "G" terminal. If
you have the separate "G" wire, try disconnecting it at the control box. If
not, and you have a spare lead in the cable, try adding it.

If you can, borrow someone else's switch control box. If the problem goes
away, that's where your problem is. Otherwise, it's in the switch up the
tower. Hope this helps.

73, Dick, WC1M

-----Original Message-----
From: jfeustle. <jfeustle@uoft02.utoledo.edu>
To: towertalk@contesting.com <towertalk@contesting.com>
Date: Friday, October 24, 1997 8:35 AM
Subject: [TowerTalk] Coax switch and TNC problem


>Well, the contest starts this evening and Murphy arrived at my place
>yesterday. Strange as this combination may sound, here it is.
>
>Every time I switch antennas using my Ameritron RCS8V control box, my TNC,
>a PK232, goes crazy, drops the connection to the cluster, and enters modes
>I never new of. The switch box and my 2 meter antenna share the same tower,
>my only tower. If I disconnect the coax from the antenna to my old Kenwood
>2 meter rig, the TNC works fine when I switch antennas. Useless, but it
>works. I can also turn off the control box, rotate the switch, turn it back
>on and avoid the problem. Not so swift. So, the common denominators are:
>this only happens when I rotate the antenna selection switch and when the
>coax is attached to the two meter rig, which is in turn conntected to the
>TNC. My usual solution to these problems, a quarter of a stick, may be a
>bit too much here. Any other ideas, suggestions?
>
>73,
>Joe, N8JF
>
>
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