[Johnson] 250-39 TR switch.

[James M. Walker]

Chime in time,
I have two of the TR-switches, both are used with BC-610(X2) transmitters 
and R-390A(X2)
receivers and a single end fed 130 foot long-wire. The transmit output 50 
ohms goes to the
TR-switch TX, the R-390As antenna input is fed with a broadband transformer 
toroid,
150 ohms in to 50 ohms out to the receivers. There is little or no problem 
with receiver
overload. No overload but I sometimes would forget to turn receive audio 
down when
going to transmit mode. The BC-610s run 400 watts to the antenna. No TVI 
problems
in the city any more than the usual complaints resulting from front-end 
overload, and faulty
garage door openers.

For the antenna system the tr-switch output goes to a Johnson 1KW matchbox, 
works
quite well actually.

FWIW, and as always YMMV
Jim
WB2FCN

----- Original Message ----- 
From: "Dennis" <radioart at charter.net>
To: <kb2wig at twcny.rr.com>; "Roy Morgan" <k1lky at earthlink.net>
Cc: <Johnson at mailman.qth.net>
Sent: Friday, October 24, 2008 8:16 AM
Subject: Re: [Johnson] 250-39 TR switch.


> Another point of view on these TR switches....
>
> I have three of them in use and they work great.  As long as you keep the 
> connection between your transmitter and the TR switch short the suckout 
> mentioned will be slight; its because of this issue that Johnson put an RF 
> amp in the TR switch so signals won't be degraded.  You will notice some 
> changing of signal levels when you change the loading on your transmitter; 
> but thats normal.  In my case I have my CE 100V & 600L coupled with a 
> NC-303 using a Johnson TR switch and I have two Johnson Desk KW's using 
> the Johnson TR switch and they do a great job.  Into a 50 ohm load they 
> will provide you over 4kw of switching protection to your receiver..... 
> Not too bad...
>
> With regard to the TVI, not an issue any more with cable and satilite but 
> in the good old days Johnson recommenced using a Low Pass filter with the 
> TR switch;  In those days most shacks already had a LP filter in the 
> antenna line, I know I did, is it wasn't ever an issue....
>
> I remember I wrote an article for ER (Electric Radio)  magizine discussing 
> the many different TR switchs and their pros and cons.  Maybe you can get 
> a copy....
>
> Ciao, Dennis, k0eoo