[Johnson] 250-39 TR switch.
Peter Markavage
manualman at juno.com
Thu Oct 23 22:52:15 EDT 2008
They also provide about 6 db's worth of receiver gain between 3.5 and 29
MHz. I've never seen any "suckout" issues that you describe with the
receivers and transmitters/linears that I've run the TR Switch with.
Right now I have one on my Apache/Mohawk combo.
Pete, wa2cwa
On Thu, 23 Oct 2008 22:08:56 -0400 Roy Morgan <k1lky at earthlink.net>
writes:
>
> 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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