[TowerTalk] Coax Switch Isolation

[don tyrrell]

Mike,
If the case of the switch isn't properly grounded, the surge energy will
find its way to your equipment through the coax shells/cable shields and
possibly "backfire" your equipment ground through your chassis to your
components. We have seen this in high surge tests many times. Government
spec TIB85-10 also verifies this. And you're right---you want the lowest
impedance to ground you can get. It's a matter of getting rid of the surge
energy before your chassis has to get rid of it.
Don Tyrrell at d.r.tyrrell@worldnet.att.net
----- Original Message -----
From: "Michael Tope" <w4ef@pacbell.net>
To: "don tyrrell" <d.r.tyrrell@worldnet.att.net>
Sent: Thursday, June 15, 2000 5:54 PM
Subject: Re: [TowerTalk] Coax Switch Isolation


> Don,
>
> Can you explain to me why your switch needs a "hard" ground?
> Don't the gas tubes terminate to the case of the switch, and if
> so, why one earth would hanging a ground rod or building ground
> with unknown RF impedance make any difference?
>
> Thanks,
>
> Mike, W4EF...............................................
>
> ----- Original Message -----
> From: "don tyrrell" <d.r.tyrrell@worldnet.att.net>
> To: <towertalk@contesting.com>
> Sent: Wednesday, June 14, 2000 8:35 PM
> Subject: [TowerTalk] Coax Switch Isolation
>
>
> >
> > Hi,
> > I noted that someone measured one of our coax switches with a 26.5 dB
> > isolation. Maybe I can clarify why this may have happened. The
microstrip
> > cavities and isolation fins are die cast into the main housing casting
so
> > there is little if any variation from unit to unit. We use a MIL spec RF
> > test house to measure these characteristics and they test for a minimum
of
> > 50 dB isolation. They say the most common reasons for comparative test
> > errors in non lab environments are: A. Improper use of, or faulty jumper
> > cable/connector assemblies. B. Improper or faulty test loads. These must
> be
> > exactly R50 plus J ZERO loads. C. In the case of the DELTA-4 family, the
> > case must be hard grounded to a proper ground system since the devices
are
> > protected by an ARC-PLUG gas tube module. If grounding is not proper,
the
> 1
> > pF of capacitance of the tube will throw off the readings, including the
> > VSWR specs.
> > Hope this clarifies the situation.
> > Thanks and 73,
> > Don,  W8AD, Alpha delta Communications
> > Don Tyrrell at d.r.tyrrell@worldnet.att.net
> >
> >
> > --
> > FAQ on WWW:               http://www.contesting.com/FAQ/towertalk
> > Submissions:              towertalk@contesting.com
> > Administrative requests:  towertalk-REQUEST@contesting.com
> > Problems:                 owner-towertalk@contesting.com
> >
>
>


--
FAQ on WWW:               http://www.contesting.com/FAQ/towertalk
Submissions:              towertalk@contesting.com
Administrative requests:  towertalk-REQUEST@contesting.com
Problems:                 owner-towertalk@contesting.com