[Boatanchors] Electronic T/R Switch vs Coaxial Type

[Glen Zook]

The problem these days is not really with TVI but is with the harmonics generated on the various amateur radio bands.  Those are below the "cut off" frequency of any normal low pass filter and will go right through the filter.  Now the harmonics of the transmitter will fall outside of the HF bands when the transmitter is operating above the 20 meter band.  But, the harmonics of 160, 80, 40, and 20 meters definitely fall within other amateur radio bands and will cause problems.

That is why using a tube type "TR" switch is often "frowned upon".  Remember that even a very low powered signal on CW can often be copied thousands of miles away.  Therefore, the harmonics generated by most TR switches can be problematic.  There are ways to reduce the harmonics including placing the TR switch inside the transmitter before the final tank.  However, this does require tuning the transmitter before the best receiver sensitivity is achieved.  Also, putting a tuned circuit in the TR switch can help.  But, again, this requires tuning of an additional circuit before the best receiver sensitivity is achieved.

Glen, K9STH

Website:  http://k9sth.com