Simplest TR Switch

[Gerald Lemay]

I can relate a ssimilar experience many years ago when I was young and foolish. Now I'm
old and foolish. The best so-called T/R switch is a simple relay that can be keyed
directly with some delay circuitry or one that is simply turned on when you wish to
transmit. What I did back then was to rig up a 4PDT relay in an aluminum box with RCA
jacks for receiver muting, receiver antenna, transmitter antenna, and transmitter keying.
Put a lot of foam rubber in the box to kill the noise. Later on I used a foot switch to
turn the relay on and off. It was simple but it worked.

73/Gerry/W1ID

Edward Swynar VE3 CUI wrote:

> Hey Guys...
>
> Be VERY VERY CAREFUL with such devices!
>
> I'm referring to them, of course, as being EXCELLENT generators of TVI. My
> one & only (touch wood) experience with a representative of the
> interference bureau of our Canadian licensing body occured many years ago,
> when, as a budding newcomer to Ham radio, I built---and used---a
> hands-free, 6AH6 tube-type T/R switch...
>
> Unbeknownst to me, my little 6T9 compactron rig was completely obliterating
> a neighbour's TV away down the block! I was on 40-meters, with about
> 6-watts of output---not exactly rock-crushing power, but boy-o-boy, I sure
> had my eyes opened up that day!
>
> I scrapped the T/R switch, & built-up a 115VAC open frame relay T/R
> arrangement, much to my neighbour's (and mine!) relief...
>
> ~73~ Eddy VE3CUI - VE3XZ
>
>
>
> ----------
> > From: Ken Ketner <b9oky at TTACS.TTU.EDU>
> > To: HEATH at LISTSERV.TEMPE.GOV
> > Subject: Simplest TR Switch
> > Date: December 10, 1999 11:39 AM
> >
> > Kurt and the list, working in a library does have its benefits. I went
> > to our CQ collection, pulled of the 1970 volume, nothing in January, in
> > February BINGO, page 25, a short article called The Simplest TR Switch.
> > Here is the text of the article:
> >
> > THE SIMPLEST TR SWITCH, by Irvin G. Kanode, WA9CKP
> > Here is the simplest TR switch that I know of. This switch requires no
> > controlling devices nor power supply. The switch has been in use at this
> > QTH for the past 6 months with our 75 watt cw transmitter. There is no
> > reason why it cannot be used on higher power transmitters, if the proper
> > diodes are used. For cw operation we use it for instant breakin without
> > reducing receiver gain and it should be usable on other modes if there
> > is no feedback from speaker to microphone. When working the same
> > frequency you can copy your own signal comfortably, and when working off
> > your own frequency, another signal can be heard between your own
> > signals. We built the TR switch, shown in fig. 1, in a small 1x2x3
> > utility box, using some surplus diodes found in our junk box.
> >
> > Figure 1
> >
> > (ANT)- - -GND
> >   |
> >   |       C=100
> >   >- - - - | |- - - - - - - - - - - -(RX)
> >   |                 |        |         |
> >   |                 |        |         |
> >   |                 D1     cathode     |
> >   |               cathode    D2        |
> >   |                 |        |         |
> >   |                 |        |         |
> >   |                 |        |         |
> > (TX) - - - - - - - - - - - - - - - - - <
> >                              |
> >                              |
> >                          chassis gnd
> >
> >
> >       In the article no values are specified other than “100” for the
> > capacitor. I presume that is 100 picofarads. It would be a good idea if
> > we could enlist the aid of a good rf expert on the list to suggest some
> > actual values and types of common diodes, say ECG, which would work here
> > at 75 watts, or at higher power ratings.
> >       In my diagram above, ANT, TX and RX are coax connectors. The leftmost
> > vertical line is connected to the center pin of the ANT and TX
> > connectors. The outer shell of all three connectors go to chassis
> > ground. The top horizontal line with C in it terminates at the right
> > side in the center pin of the RX coax connector.
> >       If this dude works, why wouldn’t it be possible to build it into a
> > solid metal coax TEE?
> >       Perhaps those with better circuit knowledge than I could explain how
> > this works and whether it would be good to put it on separate TX/RX
> > rigs, such as my Hallicrafters station. I wouldn’t want to fry anything.
> >       If persons want a xerox of the article, I can provide same if you will
> > send a SASE to the address below.
> >
> >
> > --
> > Ken Ketner, KA5ELD
> >       Postal Address:
> >
> >               Institute for Studies in Pragmaticism
> >               Room 304A Main Library Building
> >               Texas Tech University
> >               Lubbock, TX 79409-0002
> >
> >       email:
> >               Office  b9oky at ttacs.ttu.edu
> >                       Home    ketner at arisbeassociates.com
> >
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