Value of a 1/4λ stub to protect an LPFM...

[Spareparts]

Read the excellent article by Jeff Welton (Nautel) and David Halperin (Townsquare Media) at Checking Ground Radial Integrity / Making a Quarter Wave Stub - Nautel Support

Have the parts, to built one, was pondering the value of adding a 1/4λ stub to the feed line that will be used at our (future) LPFM.

Any additional value provided, or stick with the polyphaser?

SP

 

[frankberry]

Good article and a good idea. Thanks for sharing it with us.

 

[Spareparts]

Have a used Myat 101-040 "T", along with appear to be 101-058-1 EIA to 7/16-DIN transitions (no labels). The initial plan is to pick up a used section of 101-006 line for the stub

The "short" I will turn on the lathe out of copper billet and machine flats on the end for a two-bolt ground lug,

After tuning, likley silver-solder it in place...

SP

 

[OLDRFGUY]

1/4 wave stubs are a good way of reducing transient damage from a lightning strike by shunting off the energy. They have the added benefit of shorting out 2nd harmonic radiation from a transmitter. (Lots of transmitters and exciters had them included.)

On FM's where I have added a stub (not right at the antenna) or where it was part of the transmitter's output assembly (e.g. Gates/Harris FM 5/10/20 boxes) I have tied the actual stub section to ground with strap. (you can hose clamp the strap to the stub)

This ensured that the strike impulse had a lo impedance ground to take it away from the delicate stuff.