[Icom] Coax Switches Revisited

Mon, 19 May 2003 13:19:54 -0400

Good point, and a very good way of viewing this issue from another angle, 
although this doesn't imply what the damage threshold of the receiver is.

I typically calibrate S-Meters so that -73 dBm produces an S9 reading. With 
that said, a 1 mW signal (0 dBm) would pruduce an S-Meter reading of 73 dB 
above S9.

Frank W3UHF

>From: "David J. Ring Jr - N1EA" <[email protected]>
>Reply-To: [email protected]
>To: <[email protected]>
>Subject: Re: [Icom] Coax Switches Revisited
>Date: Mon, 19 May 2003 11:07:23 -0400
>
>Try the calculation the other way around:
>
>What S meter reading would 1mw of r.f. applied to the antenna port produce?
>
>73
>DR
>----- Original Message -----
>From: "Lefczik, Larry D" <[email protected]>
>To: <[email protected]>
>Sent: Monday, May 19, 2003 10:53 AM
>Subject: RE: [Icom] Coax Switches Revisited
>
>
> > 100Watts - 50 dB = 0.001Watts  1mW into the front end of a receiver.
>Scary?
> >
> >
> > + Frank, I have run those test on the Diawa cavity switches in
> > + the past.  If
> > + memory serves, they provide about 50db of isolation per port
> > + to about 300
> > + mhz and about 40db above that.  Dave
> > +
> > +
> > + > >
> > + > >Hi Folks,
> > + > >
> > + > >Well on Thursday I decided to start doing some tests on my
> > + XXX brand coax
> > + > >switches as to the amount of isolation between the
> > + selected rig and the
> > + > >other 5 "grounded" positions.  I do have external grounds
> > + run to the case
> > + > >of the switches.
> > + > >
> > + > >I used some very small wire and a little pickup coil run
> > + to the outside
> > + the
> > + > >box to a small 12 volt light bulb. When running 100 watts
> > + to the dummy
> > + > >load, the bulb would light at about 50 to 60 % of it's
> > + normal output,
> > + > >interesting.
> > + > >
> > + > >Next I unhooked the other 5 rigs from the switch and
> > + hooked the bulb to
> > + one
> > + > >of the unused coax connectors and fired up a rig at 100
> > + watts in RTTY to
> > + > >the dummy. Guess what? the bulb blew.., Burned out, toast etc.
> > + > >
> > + > >So, I have to wonder what is this doing to the other 5
> > + rigs hooked to the
> > + > >switch even though the rigs were off?  I think I know now
> > + why my Icom PCR
> > + > >1000 had the front end fried on it.
> > + > >
> > + > >So, major changes took place based on these tests.
> > + > >
> > + > >I removed the switches and went back to my old method of
> > + isolation and
> > + rig
> > + > >switching by using feed thru bulkhead coax connectors
> > + mounted on a panel
> > + > >with the various rigs hooked to the back side and then the antenna
> > + > >selection just hooks to whatever rig I wish to use at the
> > + time. Simple
> > + but
> > + > >I feel it is whole lot better and safer. I will update the
> > + pictures on my
> > + > >web page later tonight.
> > + > >
> > + > >This was my test run under controlled conditions and your
> > + mileage may
> > + > >differ.
> > + > >
> > + > >73
> > +
> > ----
> > Your Moderator: Dick Flanagan W6OLD, [email protected]
> > Icom Users Net: Sundays, 1700Z, 14.315 MHz
> > Icom FAQ: http://www.qsl.net/icom/
> >
>
>----
>Your Moderator: Dick Flanagan W6OLD, [email protected]
>Icom Users Net: Sundays, 1700Z, 14.315 MHz
>Icom FAQ: http://www.qsl.net/icom/

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