[Johnson] 250-39 TR switch.

[Carl]

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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