Building your own shorted stub

[Spareparts]

Have leftover 7/8 ridge line and hardware, and intend to build a shorted stub as a secondary protector (transmitter is a Nautel VX-150, primary protector at the entry panel is a Polyphaser VHF50D-PGR)

Before I start cutting, anyone know the velocity factor for 7/8 ridge line?

SP

 

[davideduardo]

Have leftover 7/8 ridge line and hardware, and intend to build a shorted stub as a secondary protector (transmitter is a Nautel VX-150, primary protector at the entry panel is a Polyphaser VHF50D-PGR)

Before I start cutting, anyone know the velocity factor for 7/8 ridge line?

SP

All I know is that you can get "pretty damn close" on the antenna with a pretty good tape measure! My first FMs, which were also the first FMs in the Bolivarian nations of South America, went on the air with trimmed vertical only CB antennas. Widely available in the mid-60's were CB antennas that were rated at "up to 1000 watts" and they had a vertical element with three inclining horizontal ones. Trimming to wavelength got us reasonably low SWR. No gain, but the band was empty for about 800 to 1000 miles in any direction.

My point is that when you are improvising, "precision" has a different meaning than the usual one.

 

[Cold Coffee]

Have leftover 7/8 ridge line and hardware, and intend to build a shorted stub as a secondary protector (transmitter is a Nautel VX-150, primary protector at the entry panel is a Polyphaser VHF50D-PGR)

Before I start cutting, anyone know the velocity factor for 7/8 ridge line?

SP

I take it you're wanting to use a shorting stub for lightening protection. Shorting stubs are also used to kill harmonics. The velocity factor for LDFS -50A is 89 percent.

I usually use a more flexible coax like RG 213 to make quarter wave shorting stubs. which has a velocity factor of 66 percent.

What frequency do you need this for?

 

[Spareparts]

What frequency do you need this for?

103.9 - Feed line is 7/8" Heliax, Antenna is a Scala CL-FM/HCM

 

[Cold Coffee]

Is that antenna for a translator? It's quite directional.

 

[Spareparts]

LPFM

 

[Cold Coffee]

Don't you want a nondirectional for LPFM?

 

[Spareparts]

Not in this case - actually was approved by the FCC specifying this antenna.

 

[Cold Coffee]

OK. You will be 100 Watts in one direction. The antenna needs 20 Watts in X 5 =100 Watts.

 

[Spareparts]

Just received a quote on a XENIRAD 1/4 wave shorting stub for $ 2,400.00.

Going to give rolling our own a try

SP

 

[Spareparts]

One of the local makerspace members (PhD and amateur extra class) suggested using a VF of 1.0 for the EIA line, so that's what I am going to start with.

Another makerspace member is turning a shorting plug to slip inside the 7/8 EIA line, once it's tuned, we will lock it in place with bronze or stainless hardware.

BTW, here's a source for the same type of hardware I am using: 7/8" EIA - 2 Way Divider, Type N (x5) | eBay

SP