[TenTec] Scout problems

[Mike Hyder]

BS

Having "strapped the negative post to the cabinet" on Astron supplies, I
would suggest that Stuart's analysis is in error.  Here's why:  If you
examine the schematic of some Astron supplies, you will note that there is a
common ground but that it is NOT connected to the chassis.  This would
permit the Astron to be used in a laboratory or other installation where you
wanted the negative to be floating, or you had a requirement for 'positive
ground.'

But, if you don't strap the negative post to the cabinet, here's what
happens:  you have your rig grounded and thus the negative post of the
supply is grounded to the rig through the DC power cable.  But the cabinet
of the supply is grounded to the AC line's ground.  This can create ground
loops.  If the rig isn't grounded along with the cabinet of the Astron, then
loads of RF can get into the Astron's negative post and from there straight
into its regulator circuitry.  (Note that in the schematic of the Astron, RF
energy can come into the supply via the negative post and affect the
regulator circuitry.)  Voltage spikes can also enter the negative post and
wipe out the regulator if that post isn't grounded to the cabinet of the
supply.  Our local repeater's Astron supply got wiped out repeatedly until
we grounded its negative post.  We did it by removing the post and removing
the insulators and putting in a good lockwasher to make good contact with
the cabinet.

So take Stuart's advice if you will, but I believe it will cause you
troubles.

73, Mike N4NT@chartertn.net

----- Original Message -----
From: "Stuart Rohre" <rohre@arlut.utexas.edu>
To: <tentec@contesting.com>; <ultrafixedwing@juno.com>
Sent: Tuesday, October 23, 2001 3:42 PM
Subject: Re: [TenTec] Scout problems


> For suspected RF in the power supply problems, watch out for modified
Astron
> power supplies.  Originally, they floated the DC minus from chassis to
allow
> you to determine single point of grounding of the station, and this way
> works for me, ie floating minus supply from the Astron to Scout.  I use a
> ground lead to wing nut ground on Scout back panel for station ground and
> all is well.  But, some folks get an Astron and strap the minus bolt to
> chassis at the supply, which can cause a problem with RF.
>
> 73,
> Stuart K5KVH