Hello,
Just checking to see what the best vhf 140-174 100w lightning coax protector is. I need something that is very dependable. Thanks in advance. Josh
Vhf Public Saftey Lightning Protector
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psapengineer
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Single Freq?
Is this on a single frequency station? Or are all of the frequencies close?
I'd consider a 1/4 wave shorted stub to ground, followed by a Polyphaser, maybe followed by another 1/4 shorted stub isolated inside.
Assuming its a really bad site.
Cavities between the station and the line also help.
Just a few thoughts..........
I'd consider a 1/4 wave shorted stub to ground, followed by a Polyphaser, maybe followed by another 1/4 shorted stub isolated inside.
Assuming its a really bad site.
Cavities between the station and the line also help.
Just a few thoughts..........
What I have is a Kenwood tkr740 100w, sinclair BP,BR. freq 154.83, 153.865 ,7/8 commscope, andrew 4bay dipole, it is mounted on a 699ft tower at 400ft. the tower site evel. is the highest in the area. When you all refer to (1/4 wave shorted stub to ground) what exactly are yall talking about? Thanks Josh
A shorting stub is a piece of coax that is 1/4 wavelength in length for the operating frequency. It is inserted into the transmission line with a "T" connector on one end, and the shield and center conductor are shorted together at the other.
Because it is a quarter wave, there is no RF current returned at the operating frequency. However, as you get further from the operating frequency, the stub looks increasingly like a short, until you get to DC, where it is a dead short. This prevents and DC potential from developing between the shield and center conductor on your transmission line.
Here are some past threads with more information and links on shorting stubs:
http://batboard.batlabs.com/viewtopic.php?t=40350
http://batboard.batlabs.com/viewtopic.php?t=41781
Because it is a quarter wave, there is no RF current returned at the operating frequency. However, as you get further from the operating frequency, the stub looks increasingly like a short, until you get to DC, where it is a dead short. This prevents and DC potential from developing between the shield and center conductor on your transmission line.
Here are some past threads with more information and links on shorting stubs:
http://batboard.batlabs.com/viewtopic.php?t=40350
http://batboard.batlabs.com/viewtopic.php?t=41781
psapengineer: "I'd consider a 1/4 wave shorted stub to ground, followed by a Polyphaser..."
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The use of the quarter wave stub to supplement the polyphaser is a reasonable suggestion. Unfortunately, there are some who believe that a stub alone is sufficient protection. It may not be "protection" at all.
Lightning strikes are impulsive events. When a strike induces voltage into an antenna system, it is no different than the application of an energy impulse into any resonant circuit. It will ring - energy will be passed at the resonant frequency. Under some circumstances, it is possible that the installation of a quarter wave stub may subject your equipment to even higher voltage on the line than would have been present with no protection at all.
Play it safe. Read all the available information at manufacturer's web sites. If in doubt, contact an application engineer to have your specific installation reviewed.
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The use of the quarter wave stub to supplement the polyphaser is a reasonable suggestion. Unfortunately, there are some who believe that a stub alone is sufficient protection. It may not be "protection" at all.
Lightning strikes are impulsive events. When a strike induces voltage into an antenna system, it is no different than the application of an energy impulse into any resonant circuit. It will ring - energy will be passed at the resonant frequency. Under some circumstances, it is possible that the installation of a quarter wave stub may subject your equipment to even higher voltage on the line than would have been present with no protection at all.
Play it safe. Read all the available information at manufacturer's web sites. If in doubt, contact an application engineer to have your specific installation reviewed.