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Commercial Radio Antennas - Please keep discussion related to professional, commercially used antennas and antenna systems for the two-way radio industry. Topics for the use of these antennas on amateur bands are accepted here.

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  #1 (permalink)  
Old 05-31-2017, 10:16 PM
   
Join Date: May 2017
Location: Baltimore, MD
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Default 68cm antenna

I'm new to UHF radio and I have yet to hook a decent antenna up to my Kenwood HU8360 radio. I'd like to build a custom antenna but I am quickly learning that doing a good job means learning a confounding number of topics. I have seen several J-pole DIY guides but they are all focused at the 440 frequency which is a bit different than the 467Mhz I'm licensed to use.

Does anyone know of a good one-stop-shop guide to building a J-pole? They seem like the easiest construction and require only a $20ish investment in materials.

Here are things that I have learned are important for me to understand:

Baluns are a thing I might need to balance the line.
Chokes are another thing that may or may not be the same as a balun.
RG8X is either wonderful or horrible.
Vertical and horizontal antenna-connected radios are not compatible.
Not having an SWR meter makes me the only kid in kindergarten without a TrapperKeeper.
I can avoid needing an antenna tuner if I magically get everything to have 50Ohm impedance.
Impedance is not necessarily a bad thing... magically.
Capacitance is a mysterious force which keeps engineers employed.
The UHF connector on my radio is somehow a terrible connector for UHF radios.
J-poles do not need a ground plane.
A ground plane is not, in fact, an old WWII fighter plane that ceases to fly now.
Coax either has a foam dialectric core or a mesh dialectric core. They are both the wrong choice.


As you can see, I've read tens of articles from preppers, to shade-tree engineers to ARRL and the result has left me with a fragmented understanding and more questions than answers. Someone please throw me a rope!

-Geoff
WQYU265
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  #2 (permalink)  
Old 06-01-2017, 11:16 AM
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Here is a link to a j-pole design page. There are others just do a search.

J POLE ANTENNA DESIGN CALCULATOR by K4ABT

No by the formula antenna will be exactly right the first time. You need an SWR meter (one designed for UHF) or an antenna analyzer (best choice).

By the time you buy the test equipment you may as well buy a commercial antenna and not have worry about all the other issues.
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Old 06-01-2017, 11:24 AM
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Quote:
Originally Posted by g00f View Post
I'm new to UHF radio and I have yet to hook a decent antenna up to my Kenwood HU8360 radio. I'd like to build a custom antenna but I am quickly learning that doing a good job means learning a confounding number of topics. I have seen several J-pole DIY guides but they are all focused at the 440 frequency which is a bit different than the 467Mhz I'm licensed to use.
You need to find the formula used to calculate the J-Pole lengths and use 467.xxxMHz as your frequency variable. plunk it in and calculate your new lengths.

Quote:
Originally Posted by g00f View Post
Does anyone know of a good one-stop-shop guide to building a J-pole? They seem like the easiest construction and require only a $20ish investment in materials.
Google should turn up tons and tons of information on J-Pole antennas.

Quote:
Originally Posted by g00f View Post
Here are things that I have learned are important for me to understand:

Baluns are a thing I might need to balance the line.
Chokes are another thing that may or may not be the same as a balun.
bingo. J-Pole designs will fill in that blank for you.


Quote:
Originally Posted by g00f View Post
RG8X is either wonderful or horrible.
It is ok if you are not going more than about 25', and are not using it to connect a repeater to an antenna.

Quote:
Originally Posted by g00f View Post
Vertical and horizontal antenna-connected radios are not compatible.
there is about 20dB of attenuation between a vertical and horizontal antenna, all other factors excluded

Quote:
Originally Posted by g00f View Post
Not having an SWR meter makes me the only kid in kindergarten without a TrapperKeeper.
Only you can change not having a SWR meter.

Quote:
Originally Posted by g00f View Post
I can avoid needing an antenna tuner if I magically get everything to have 50Ohm impedance.
yes you can, once built you can adjust the feed point and tune the antenna

Quote:
Originally Posted by g00f View Post
Impedance is not necessarily a bad thing... magically.
No it is not. EVERY antenna has impedance

Quote:
Originally Posted by g00f View Post
Capacitance is a mysterious force which keeps engineers employed.
I am not an engineer, and i wholly agree with that.

Quote:
Originally Posted by g00f View Post
The UHF connector on my radio is somehow a terrible connector for UHF radios.
They are not very good connectors, but for GMRS and it being short range they will work fine.

Quote:
Originally Posted by g00f View Post
J-poles do not need a ground plane.
Correct and not correct. the 'ground plane' is part of the antenna, you do not need to make a ground plane like you would with a 5/8wave antenna adapted to base use

Quote:
Originally Posted by g00f View Post
A ground plane is not, in fact, an old WWII fighter plane that ceases to fly now.
Correct

Quote:
Originally Posted by g00f View Post
Coax either has a foam dialectric core or a mesh dialectric core. They are both the wrong choice.
Not mesh, but a plastic or teflon material. each has advantages and disadvantages.


Quote:
Originally Posted by g00f View Post
As you can see, I've read tens of articles from preppers, to shade-tree engineers to ARRL and the result has left me with a fragmented understanding and more questions than answers. Someone please throw me a rope!
Stick to the ARRL, and other publications. read, read, read.

if a 'prepper' artical disagrees with the ARRL, o would discount the prepper artificial.

The ARRL and its publications are excellent sources for antenna information. Hams have been designing antennas since the start of radio. many of those authors work professionally in the RF industry.

Here on the forum there is a fellow who goes by the user name PRCGUY. when he writes i read and absorb. he is extremely knowledgeable, and knows his stuff.
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Old 06-01-2017, 6:47 PM
   
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Location: Baltimore, MD
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Thanks ko6jw_2, I get pretty much the same information in all of the J-pole DIY guides. There are consistent omissions that are making me cranky. "Soft copper" is not an obvious term to me. I'm familiar with K-wall and M-wall piping but "soft" sounds like "annealed" which is typically 1/4" ice maker line. It seems that no one has gone to the point of making a nearly fool-proof guide that lays out all of the detailed specifications and then says, "this particular aspect is going to require you to make minor adjustments by doing this step, checking and then repeating or reversing, depending on the test." I'm baffled that this doesn't exist. Perhaps I'm just the person to right this wrong??... I was hoping not to be.
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Old 06-01-2017, 6:49 PM
   
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kayn1n32008, Thanks for playing along with my humor! I feel a future in ribbing about engineering is in my future....I appreciate your tips and will venture on!
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Old 06-02-2017, 10:19 AM
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Quote:
Originally Posted by g00f View Post
kayn1n32008, Thanks for playing along with my humor! I feel a future in ribbing about engineering is in my future....I appreciate your tips and will venture on!
The humor was fun. Good luck on your antenna. in all honesty though, if you are looking to just get an antenna, and don't was to pay alot, look on ebay. If you want to learn about antennas, carry on.

Antennas are fun, and there is so much info out there, you could spend the rest of your life reading and learning. good luck!!!
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