[TowerTalk] Coax Switch Isolation

[don tyrrell]

Hi Mike,
True and true. I think I inadvertently confused the issue. It is true about
the discharge path to ground. I meant to say that also for best VSWR
performance, the 1 pF of the ARC-PLUG tube needs to be resolved by grounding
the case. The channel cavities of the switch are designed around the case
ground. Otherwise, the 1 pF reactance throws things off, particularly at
VHF/UHF. We check all the specs with good case ground. Without the tube in
the circuit (as with a regular switch), the design of the channel is
different. This really had an effect in our Transi-Trap surge protectors
when we redesigned for broadband operation to 3 GHz. So, I was just talking
about the overall lab test set up, but I can see I was mixing things
together. I didn't mean to do that. I think I've been around this stuff too
long !!!!!!
Thanks for pointing this out---and you're right.
Don,  W8AD, Alpha Delta
Don Tyrrell at d.r.tyrrell@worldnet.att.net
----- Original Message -----
From: "Michael Tope" <w4ef@pacbell.net>
To: "TowerTalk" <towertalk@contesting.com>; "don tyrrell"
<d.r.tyrrell@worldnet.att.net>
Sent: Friday, June 16, 2000 12:44 AM
Subject: Re: [TowerTalk] Coax Switch Isolation


> 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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> >
>
>


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