[Icom] Coax Switches Revisited

Mon, 19 May 2003 12:04:37 -0400

Not really. This is only 0 dBm, even sensitive GaAs FET devices will 
tolerate +10 dBm (10 mW) or more, and I suspect a typical HF transceiver's 
front end would tolerate much more. Look at the tests which are performed to 
verify IP3, etc. Input levels for those tests can be well in excess of +20 
dBm (100 mw).

73 Frank W3UHF

>From: "Lefczik, Larry D" <[email protected]>
>Reply-To: [email protected]
>To: [email protected]
>Subject: RE: [Icom] Coax Switches Revisited
>Date: Mon, 19 May 2003 10:53:38 -0400
>
>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/

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