Simplest TR Switch

[Ken Ketner]

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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