This website can be viewed with:



Website Map







Website Map




















Website Map




There are two points (sort of negative points at that) about most Electronic T/R Switches: 1) the usual circuitry causes the receiver to be useable only on the transmitter's resonant frequency; and 2) the connection between the T/R Switch and the transmitter must be a short one-no longer than 3 feet. You are asking for harmonic and self-oscillation problems for using a longer cable.

I once was using a Kenwood TS-820 with an E.F. Johnson T/R Switch to provide a second receiver output. Worked very well, EVEN with about five feet of cable. THEN I tried to use an SB-200 linear. What it almost blew in the amp was the plate choke-it smoked but survived with the T/R SW BETWEEN the transceiver and the AMP. Not a good thing! The reason for this was the less-than-pure output of the T/R SW and the amplifier's attempt to amplify the good AND the bad. A Low Pass Filter between the T/R SW-Output and the amplifier-Input MIGHT have helped, but I chose not to risk it further. Eventually, with a shorter cable, and the T/R SW on the OUTPUT-side of the AMP, I was able to use the setup just fine. I have been careful with T/R SW cables ever since!

To try and illustrate just what I mean, the best connection of a T/R SW is via a coaxial-T right at the last transmitting component before the antenna: meaning... if you have only a transmitter, the T/R SW goes between the output of the transmitter and the Low Pass Filter that then connects to the antenna. If you have an amplifier, the T/R SW will be connected at it's output using that coaxial-T. One cable goes to the T/R Switch (think short) and one to the antenna (or to the linear or the antenna switch) fastens right there. The receiver has its cable/connection at the T/R Switch.

So, why use a T/R Switch? Because it is THE best break-in CW you can have. It is as good as a Ten Tec OMNI VI, which is as good as break-in gets.

The B&W 380-B is my favorite Electronic T/R Switch for real-world usage. It is relatively small, works efficiently with little-if any-receiver "suck-out". While mine is essentially unmodified, I did replace the selenium rectifier, and all the capacitors-adding a wired-in miniature line fuse and 3-wire cord, in the process.

It important to note that when replacing a selenium rectifier, both the original voltage and load current should be measured, and an appropriate resistor inserted to lower the higher voltage resulting from the reduced forward voltage drop of the silicon rectifier. 

The DowKey DKC TRM-1 is the smallest Electronic T/R Switch made. It is designed with 2 female SO-239 connectors, and a single 3 conductor cable intended to be used with a tube-transmitter's accessory socket to supply the 125 VDC plate and 6.3 VAC filament voltages. Instead of a cable between the TX-ANT line, the unit is designed to use a double-female/single-male PL-259-type UHF "T" connector. Typically, this would involve connecting one of the female sides of the coaxial "T" to the TX via a double-male PL-259-type UHF adapter. The other female side of the coaxial "T" is for the antenna cable connection. The lone male connector of the coaxial "T" is connected to the TX or ANT side of the TRM-1. The other side goes to the receiver.

This Electronic T/R Switch  has a built-in 30dB preselector, receiver muting, built-in CW sidetone, monitored switching (whatever that means!), full legal power, and band-switched input & output circuits 80-6M. Manufactured in 1963 by Fichter Electronics of Cedar Grove, NJ. Very rare: only one I have ever seen or even heard of-except in a QST ad!



To continue browsing the website, please select from these categories:  

and from an Electronics perspective:

Receivers Transmitters XCVRs Accessories  Speakers QRP




Test Equipment



                                    This website is always under construction...