[TowerTalk] Coax Switch Isolation

[Michael Tope]

Hi Don,

Yes, I agree that the hard ground is essential for static discharge
(the charge needs some place to go besides your radio). I thought
you were stating in one of your earlier emails that is was also an
essential element of the RF isolation measurement. That was the
part that confused me (I would argue that it shouldn't have any
bearing on the RF isolation measurement).

73 de Mike,
W4EF........................................................................
....

----- Original Message -----
From: "don tyrrell" <d.r.tyrrell@worldnet.att.net>
To: "Michael Tope" <w4ef@pacbell.net>; <towertalk@contesting.com>
Sent: Thursday, June 15, 2000 7:45 PM
Subject: Re: [TowerTalk] Coax Switch Isolation


>
> 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
> > >
> > >
> > > --
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> > >
> >
> >
>
>
> --
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