[TowerTalk] Protecting RX in SO2R

[n4kg@juno.com]

The series resistor absorbs the excess incoming power.
One of my resistors showed signs of excessive heating.
I'm not sure if that was from my other transmitter or a
lightning event.  In either case, it DID protect the receiver.

Yes, 4 diodes connected in series with cathodes to ground
in parallel with another 4 diodes connected in series with
anodes to ground.  The diodes clamp the voltage to 2.8 V
peak to peak.  I wanted to keep the voltage high enough to
prevent IMD generation from strong RF signals yet low enough
to protect the small wire in the 7mm input coil of my RX.

Without the resistor, you would be dumping the excess power 
into the small signal diodes.  You could exceed their current rating 
and if they open up, then your RX is the next load.  :-(


ANT -------RESISTOR------------------RX Input
	      22 Ohm      |    |
		2W	D  D      D= 1N914 or any
			|    |             fast switching diode
			D  D

			etc (4 series diodes in each leg)
			|    |
-----------------GND-------------------


Tom  N4KG


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