Simplest TR Switch

[Edward Swynar VE3 CUI]

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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