Plans for Open Stub J-Pole Dual Band GMRS Antenna

[DownEastNC]

I've spent hours searching for the plans on a dual band open stub J-Pole GMRS antenna and I'm coming up with not much to work with. I'm reaching out to the community here at MyGMRS to see if someone can point me in the right direction. I need plans and specifications for this build with respect to the below frequencies. I'm not really interested in the 1/2" copper pipe build but would prefer solid round aluminum, copper stock or perhaps plated 5/8" grounding rod.

Transmit Power 50W

* Receive (RX) Frequency Range:
136-174.995 MHz VHF
400-479.995 MHz UHF
▪ Transmit (TX) Frequency Range:
462.550-462.725MHz (GMRS Channels 1-7 and 15-22)
467.550-467.725MHz (GMRS Channels 8-14 & Repeater 23-30)

[tweiss3]

Ed Fong has documented how to build a dual band J-Pole here: https://edsantennas.weebly.com/uploads/2/9/3/5/29358461/dbj-1_qst.pdf

That should get you started in the correct direction, but it's going to be a build and test, tweak, update, test again.

[DownEastNC]

2 hours ago, tweiss3 said:

Ed Fong has documented how to build a dual band J-Pole here: https://edsantennas.weebly.com/uploads/2/9/3/5/29358461/dbj-1_qst.pdf

That should get you started in the correct direction, but it's going to be a build and test, tweak, update, test again.

Thanks! I have no problem with the experimentation as long as I have good instructions.

 

Addendum: That article essentially describes twin lead construction. He did mention the copper pipe and the open stub designs had mixed results. None the less it doesn't help achieve my goals which is an open stub configuration.

[DownEastNC]

As I dig into this further the more confused I get. It's an Internet thing I reckon. Some are saying that this particular antenna is not a J-Pole but some deviation thereof. Some folks are saying that Ed Fong is selling snake oil. Regardless of those debates I have found some useful information.

Here's one link; http://www.arrowantennas.com/inst/OSJ152-462.pdf

and another more informative link; http://w8usa.org/wordpress/wp-content/uploads/2014/02/Aluminum_J-Pole_Build.pdf

Now, there seems to be a huge number of 2 meter / 70cm antennas out there and a few MURS/GMRS in the stub configuration, which get me closer. I have found a couple of calculators that define the element length and the spacing but that's based on a single frequency. My next question is when someone refers to a 440 antenna for example, would that be in the middle of the frequency spread of interest? And if so, since GMRS is between 462.550 and 467.725 should I use 465 MHz to calculate element length since that's essentially in the middle of the GMRS frequency spread?

[BoxCar]

440 MHz refers to the ham 70cm band which is below the GMRS frequencies. A J-Pole cut for the 440 band would need to be shortened by a small amount to put it into the middle of the GMRS band. 

[tweiss3]

I remember a local club did a dual band J-Pole project. Presentation/directions: https://w8wky.org/wp-content/uploads/2021/03/Building-Simple-J-Pole.pdf Plans: https://w8wky.org/wp-content/uploads/2021/03/Dual-Band-J-Pole.pdf

For GMRS, shorten the "middle" rod in small increments until the SWR bottoms out.

[tweiss3]

2 hours ago, DownEastNC said:

As I dig into this further the more confused I get. It's an Internet thing I reckon. Some are saying that this particular antenna is not a J-Pole but some deviation thereof. Some folks are saying that Ed Fong is selling snake oil. Regardless of those debates I have found some useful information.

The Ed Fong is a great antenna, and reasonably priced. I have one in 220 and one of the dual bands. The 220 might get used again soon, but the dual band is now a scanner antenna. Its biggest downfall is there are some Tram verticals that out perform it for the same price.

[DownEastNC]

15 hours ago, tweiss3 said:

I remember a local club did a dual band J-Pole project. Presentation/directions: https://w8wky.org/wp-content/uploads/2021/03/Building-Simple-J-Pole.pdf Plans: https://w8wky.org/wp-content/uploads/2021/03/Dual-Band-J-Pole.pdf

For GMRS, shorten the "middle" rod in small increments until the SWR bottoms out.

Thank you! Thank you! Thank you! That's what I'm looking for.