Stuart, I respectfully suggest you consider getting on the horn with Astron
to let them know they didn't know what the heck they were talking about.
----- Original Message -----
From: "Stuart Rohre" <rohre@arlut.utexas.edu>
To: <geraldj@weather.net>; "Discussion of Ten-Tec Equipment"
<tentec@contesting.com>
Sent: Monday, November 22, 2010 7:56 PM
Subject: Re: [TenTec] best power supply for Orion II and other items
> You do not want to ground loop the Astron 35 Amp supply. Thus, the
> factory has the negative isolated from the chassis, and it should remain
> so!!! Granted it is an old design, but read below to see what can
> happen if you bond the negative to the chassis.
>
> You want to use no. 12 ga. insulated twisted pair for wiring to the
> transceiver, and no more length than is necessary. You may use enough
> to mount the supply on the floor under the operating desk, but don't
> make the pair 8 feet long or longer, for example.
>
> Make sure the supply is remote from the transceiver by the distance to
> the floor and you should not have problems if you have a proper tuner,
> and use either coax or balun plus ladder line.
> Most problems with RF in the shack come about from making the feedline a
> multiple of a quarter wave length on a given band, or a feed mismatch at
> the feedpoint of the antenna causing RF to flow on the outer
> shield of coax, or feeder coupling to one side of the antenna, in the
> case of wire antennas.
>
> If you were to short the negative to the chassis of the Astron, you
> would created an AC ground loop with the 3rd pin of the AC plug. That
> has caused a lightning surge to travel along a feed coax shield and into
> an Astron and out by the AC third pin, but it blew up several
> transistors in the Astron and the LM 317 regulator. In addition, this
> type of AC ground looping, caused a nearby 2m radio to take the surge as
> well, and burned out the negative copper trace on the circuit board.
> Too much grounding is as bad as not any. The damage I am describing was
> to a club station left plugged into the AC mains during a thunderstorm.
>
> As Jerry says, the paralleling of transistors means if one goes, the
> others can fail under the next load.
>
> -Stuart Rohre
> K5KVH
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