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Another piece of protection equipment you may want to consider is a shorted quarter-wave stub. One can be placed on the output of an FM exciter, ahead of a tube transmitter, so that any tube arcing is shorted to ground and will not be fed into the exciter.
Our Radio World colleague Mark Persons has an interesting article on his website www.mwpersons.com describing its use. Select “Tech Tips” and look for “Stub Protector for FM Exciters and Transmitters” under the FM Tips column.
The quarter-wave shorted stub connects between your transmitter and your antenna system to short the center conductor to ground. This provides lightning protection for your transmitter. Should lightning strike your tower, the high-voltage pulse travels down your transmission line and meets the stub, where it is shorted to ground.
The stub is virtually invisible to your transmitter and offers 0 dB of insertion loss and an input VSWR better than 1.01. Return loss values are typically greater than –50 dB. Both fixed and frequency-agile models are available.
A real benefit is that the stub is maintenance-free, even after a discharge. There are no parts to replace.
The shorted stub acts as a broadband filter, and in sites where FM is collocated with AM, the latter signal is reduced by more than 30 dB. //
