[Johnson] 250-39 TR switch.

[Dennis]

Yes Carl, its in issue #48, April 93, page 20....


---- Carl <km1h at jeremy.mv.com> wrote: 
> Do you remember which ER issue?
> 
> Carl
> KM1H
> 
> 
> ----- 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
> >
> >
> > ---- Roy Morgan <k1lky at earthlink.net> wrote:
> >>
> >> On Oct 22, 2008, at 9:54 PM, <kb2wig at twcny.rr.com> wrote:
> >>
> >> > I'm considering  the acquisition of the Johnson switch.
> >> >
> >> > ? what do they go fer now?
> >> I don't know.
> >> >
> >> > ? who has one fer sale?
> >> Not me.
> >> >
> >> > ? do I really need one?
> >>
> >> Probably not.  Here's why:
> >>
> >> -The main disadvantage of these things is suckout.  The transmitter
> >> being attached to the receiver/antenna during receive sucks signal
> >> from the system.  This may not bother you if signals are strong 
> >> enough
> >> and/or your receiver has enough gain.
> >>
> >> - A second disadvantage is that they are reported to generate TVI.
> >> These reports came at a time of 21 mc TV IF frequencies, however. 
> >> You
> >> may have no trouble at all, but good citizenship would call for very
> >> careful testing and corrective measures if needed.
> >>
> >> If you DO get one of the Johnson units:
> >>
> >> - They run blistering hot.  Three reasons are higher line voltages
> >> than in the past, the tube used (6BL7?) dissipates a lot of heat in
> >> both filament and plate, and just plain inadequate ventilation.  A
> >> small computer fan located nearby would solve the problem.
> >>
> >> - There is no fuse in them as built, and only a two prong line cord.
> >> The solution to these somewhat dangerous conditions is pretty 
> >> obvious.
> >>
> >> - The instructions say to locate it as close as possible to the
> >> transmitter.. Apparently this really does matter.
> >>
> >> - The instruction sheet is on BAMA as I remember.
> >>
> >> Roy
> >>
> >>
> >> Roy Morgan
> >> k1lky at earthlink.net
> >> 529 Cobb St.
> >> Groton NY, 13073
> >>
> >>
> >>
> >>
> >>
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> >
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> > 
>