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12/6/2019 7:27:02 PM
Posted: 12/8/2013 4:05:38 PM EST
[Last Edit: 12/8/2013 4:20:35 PM EST by anonynan]
I just built my first antenna. It was a learning experience but a lot of fun. After seen a few different plans on the internet, I went with the j-pole made out of aluminum rods and angle. I’ve never done any work with a tap or die either but it turned out ok. I have 2 questions I hope someone can answer.

I was very careful to follow the measurements exactly. By doing this, will by antenna be properly tunes? I don’t have an antenna analyzer. However, my radio isn’t reducing its power so that’s a good sign.

Second, one of the rods isn’t exactly straight. I guess I didn’t get the threads perfectly straight so the VHF element is leaning in slightly. Who will this affect the antennas performance?
Link Posted: 12/8/2013 4:46:34 PM EST
Tag for info
Link Posted: 12/8/2013 5:03:49 PM EST
Congrats! You may want to bend the element a bit and try to make them parallel to each other. Relatively cheap SWR meters are available for VHF/UHF.
Link Posted: 12/8/2013 5:06:42 PM EST
I am a new operator, and have only built one antenna myself.

I built a "copper cactus" j pole using dimensions off an internet calculator and don't have any issues. I do not have an analyzer either. YMMV

I would not think a slight lean in the element would have noticeable effect, as I understand it the length is more critical, but maybe someone more experienced will chime in.
Link Posted: 12/8/2013 5:25:01 PM EST
[Last Edit: 12/8/2013 5:30:24 PM EST by Kekoa]
Originally Posted By anonynan:
I was very careful to follow the measurements exactly. By doing this, will by antenna be properly tunes?
View Quote


I'm going to go out on a limb, and say...........maybe. Or maybe not.

How's that for noncommittal?

The SWR is not absolute, and will vary, depending on where you install the antenna. Set it up by the hot water heater in the attic, and you will get one SWR reading. Install it on top of your roof, and you will probably get another. Ideally, you want to install the antenna, measure the SWR, and then make the appropriate adjustments.

So, building it to the proper measurements should get you in the ballpark, but it will probably need some "fine tuning" to get it exactly tuned up. Often, that can be a PITA, so from a practical standpoint, many people let the antenna tuner (in the rig, or external) do the fine tuning for them.

Or, it may be close enough under many different conditions, that an antenna tuner isn't necessary. The only way to know if it is tuned up for sure, is to measure it.



EDIT: Oh, and good on ya for building your own!!
Link Posted: 12/8/2013 6:05:52 PM EST
If anything they should be further apart at the top than at the base, it's an impedance transformer and the top is the high impedance end so a larger dimension lessens the mismatch.

As far as whether it's in tune... no way to know. If you are homebrewing antennas you really need access to a power/swr meter or antenna analyzer.
Link Posted: 12/8/2013 6:13:13 PM EST
Originally Posted By anonynan:
I just built my first antenna. It was a learning experience but a lot of fun. After seen a few different plans on the internet, I went with the j-pole made out of aluminum rods and angle. I’ve never done any work with a tap or die either but it turned out ok. I have 2 questions I hope someone can answer.
View Quote


Good for you!

I was very careful to follow the measurements exactly. By doing this, will by antenna be properly tunes? I don’t have an antenna analyzer. However, my radio isn’t reducing its power so that’s a good sign.
View Quote


It should be very close. But I would borrow an analyzer, or at the very least, and SWR meter and check it, bottom of band, middle, and top. A J-pole is tweeked by moving the feedpoint up and down slightly on the lower part of the J.

Second, one of the rods isn’t exactly straight. I guess I didn’t get the threads perfectly straight so the VHF element is leaning in slightly. Who will this affect the antennas performance?
View Quote


It's just aluminum. Bend it straight by hand.
Link Posted: 12/8/2013 6:32:20 PM EST
Save these links. You will be referring to them, especially after you get to General, put in an HF rig and antennas.

Right click, save

http://www.hamuniverse.com/n4jaantennabook.pdf Free antenna book.

And look here. Lots of easy to build antennas here.

http://www.hamuniverse.com/antennas.html Lots and lots of recipes.

More.

http://www.ac6v.com/antprojects.htm More recipes.

http://www.qsl.net/w4sat/antenna.htm

http://www.bloomington.in.us/~wh2t/ant.htm

http://www.eham.net/articles/21270 Top Five Get On The Air Quickly Antennas. At the end of this article are links to still more antenna articles.
Link Posted: 12/8/2013 6:40:21 PM EST
Thanks everyone for the great information. I found an inexpensive SWR meter and ordered it. Based on the reviews it's not as precise as some that are more expensive but for what I need, I think it will be fine.
Link Posted: 12/9/2013 3:14:26 AM EST
Discussion ForumsJump to Quoted PostQuote History
Originally Posted By Kekoa:


The SWR is not absolute, and will vary, depending on where you install the antenna. Set it up by the hot water heater in the attic, and you will get one SWR reading. Install it on top of your roof, and you will probably get another. Ideally, you want to install the antenna, measure the SWR, and then make the appropriate adjustments.
View Quote


So this prompts another questions. Do commercial antenna need to be fine tuned after instillation as well?
Link Posted: 12/9/2013 4:35:43 AM EST
Discussion ForumsJump to Quoted PostQuote History
Originally Posted By anonynan:
So this prompts another questions. Do commercial antenna need to be fine tuned after instillation as well?
View Quote



Yes. Sometimes, not always.

YOU, I said YOU!.. can build an antenna every bit as good as most "commercial" antennas. And often a home builder will take the time to do it better. Better wire, better insulators, better center feed, better balun, etc. There are even guys that buy tubing and fittings as such (DX Engineering, Texas Towers, others) and build their own yagi or "beam".

The same things that affect tuning of a homebrew antenna also affect a commercially built one, too. Height over ground, type of ground, nearby objects, etc.
Link Posted: 12/9/2013 4:50:37 AM EST
Discussion ForumsJump to Quoted PostQuote History
Originally Posted By Jupiter7200:



Yes. Sometimes, not always.

YOU, I said YOU!.. can build an antenna every bit as good as most "commercial" antennas. And often a home builder will take the time to do it better. Better wire, better insulators, better center feed, better balun, etc. There are even guys that buy tubing and fittings as such (DX Engineering, Texas Towers, others) and build their own yagi or "beam".

The same things that affect tuning of a homebrew antenna also affect a commercially built one, too. Height over ground, type of ground, nearby objects, etc.
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Discussion ForumsJump to Quoted PostQuote History
Originally Posted By Jupiter7200:
Originally Posted By anonynan:
So this prompts another questions. Do commercial antenna need to be fine tuned after instillation as well?



Yes. Sometimes, not always.

YOU, I said YOU!.. can build an antenna every bit as good as most "commercial" antennas. And often a home builder will take the time to do it better. Better wire, better insulators, better center feed, better balun, etc. There are even guys that buy tubing and fittings as such (DX Engineering, Texas Towers, others) and build their own yagi or "beam".

The same things that affect tuning of a homebrew antenna also affect a commercially built one, too. Height over ground, type of ground, nearby objects, etc.


Yup at my base there is 1 out of 4 of my antennas that is commercial and it gives me the most headache.

now on vehicles I buy them because I use NMO.
Link Posted: 12/12/2013 3:16:39 PM EST
[Last Edit: 12/12/2013 3:17:13 PM EST by anonynan]
The various replies have prompted me to learn more about making my own antennas. Also led me to explore the parts i used to determine if they were good choices. That leads me to another questions. (Sorry if my questions seem silly. However, if I don't ask, I won't know.) For my antenna i used a so-239 stud mount that is chrome plated brass. Is this ok for 2 meter and 70cm use? I did a google search and i didn't come up with anything.
Link Posted: 12/12/2013 3:19:24 PM EST
I would recommend you stick with NMO for mobile antenna mounts instead of the "UHF" mounts.
Link Posted: 12/12/2013 3:29:58 PM EST
Discussion ForumsJump to Quoted PostQuote History
Originally Posted By Gamma762:
I would recommend you stick with NMO for mobile antenna mounts instead of the "UHF" mounts.
View Quote


This isn't a mobile antenna. I used the mount to build a J-pole out of aluminum rod and angle.
Link Posted: 12/13/2013 2:25:13 AM EST
So will chrome plated brass work ok? Some other connectors I've seen are stainless steel.
Link Posted: 12/13/2013 9:00:21 AM EST
Discussion ForumsJump to Quoted PostQuote History
Originally Posted By anonynan:
So will chrome plated brass work ok? Some other connectors I've seen are stainless steel.
View Quote

That should be fine, brass and chromium are better conductors than stainless.
Link Posted: 12/13/2013 9:51:04 AM EST
Discussion ForumsJump to Quoted PostQuote History
Originally Posted By anonynan:


This isn't a mobile antenna. I used the mount to build a J-pole out of aluminum rod and angle.
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Discussion ForumsJump to Quoted PostQuote History
Originally Posted By anonynan:
Originally Posted By Gamma762:
I would recommend you stick with NMO for mobile antenna mounts instead of the "UHF" mounts.


This isn't a mobile antenna. I used the mount to build a J-pole out of aluminum rod and angle.

Sorry didn't reread the first part of the thread

PL259/SO239 connectors are pretty terrible at 70cm but they're used all the time anyway, for the part you're talking about there isn't really an alternative.
Link Posted: 12/13/2013 9:59:00 AM EST
Discussion ForumsJump to Quoted PostQuote History
Originally Posted By anonynan:


This isn't a mobile antenna. I used the mount to build a J-pole out of aluminum rod and angle.
View Quote View All Quotes
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Discussion ForumsJump to Quoted PostQuote History
Originally Posted By anonynan:
Originally Posted By Gamma762:
I would recommend you stick with NMO for mobile antenna mounts instead of the "UHF" mounts.


This isn't a mobile antenna. I used the mount to build a J-pole out of aluminum rod and angle.


I built one of them.

1" angle iorn
3/8" all thread

It is a broad banded sucker. 144-148 flat 1.0:1

I like it but still like the Ed Fong style in PVC
Link Posted: 12/13/2013 11:19:29 AM EST
Discussion ForumsJump to Quoted PostQuote History
Originally Posted By Gamma762:

Sorry didn't reread the first part of the thread

PL259/SO239 connectors are pretty terrible at 70cm but they're used all the time anyway, for the part you're talking about there isn't really an alternative.
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Discussion ForumsJump to Quoted PostQuote History
Originally Posted By Gamma762:
Originally Posted By anonynan:
Originally Posted By Gamma762:
I would recommend you stick with NMO for mobile antenna mounts instead of the "UHF" mounts.


This isn't a mobile antenna. I used the mount to build a J-pole out of aluminum rod and angle.

Sorry didn't reread the first part of the thread

PL259/SO239 connectors are pretty terrible at 70cm but they're used all the time anyway, for the part you're talking about there isn't really an alternative.


I came to the same conclusion.

Will the more expensive stainless steel connectors perform better than the chrome plated brass one?
Link Posted: 12/13/2013 4:42:30 PM EST
The stainless ones are probably stronger mechanically, but the chrome plated brass would probably be better on RF. For your application there's not going to be any significant performance difference.
Link Posted: 12/13/2013 5:59:08 PM EST
You should be pretty close. I built a copper J-Pole for GMRS using a calculator and it was actually center tuned for the upper part of 70 cm but still acceptable on GMRS. I then built one for 70 cm…resonant on GMRS.

I bought the 5th Edt of the Practical Antenna handbook…really interesting book but I've been having some pretty interesting antenna ideas here lately. I recently started a digipeater antenna. I wanted to do a j-pole, then I decided to make the 3/4 wave side a inch long and turn it into a slim jim. Since I'm having issues finding slim jim plans, I'm just building based off my knowledge of the similarities between j-poles and slim jims. I have the structure built, just haven't soldered it together. Waiting on a antenna analyzer to get here from China before I begin to dedicate time screwing with it since it's between semesters and I don't have access to the network analyzers at the school's lab.
Link Posted: 12/14/2013 3:37:23 AM EST
Discussion ForumsJump to Quoted PostQuote History
Originally Posted By zapzap:
You should be pretty close. I built a copper J-Pole for GMRS using a calculator and it was actually center tuned for the upper part of 70 cm but still acceptable on GMRS. I then built one for 70 cm…resonant on GMRS.

I bought the 5th Edt of the Practical Antenna handbook…really interesting book but I've been having some pretty interesting antenna ideas here lately. I recently started a digipeater antenna. I wanted to do a j-pole, then I decided to make the 3/4 wave side a inch long and turn it into a slim jim. Since I'm having issues finding slim jim plans, I'm just building based off my knowledge of the similarities between j-poles and slim jims. I have the structure built, just haven't soldered it together. Waiting on a antenna analyzer to get here from China before I begin to dedicate time screwing with it since it's between semesters and I don't have access to the network analyzers at the school's lab.
http://i1245.photobucket.com/albums/gg586/zap_uh_lack/Mobile%20Uploads/A73D1C2C-D55C-4994-A914-CEBA1A15949B_zpsc8judxfp.jpg
View Quote


Looks interesting. I'm saving for an analyzer so I can do more with antennas. When I got into amateur ratio i would have never thought that it would be the antennas that would be most interesting to me.

What analyzer did you order?
Link Posted: 12/14/2013 3:39:16 AM EST
Discussion ForumsJump to Quoted PostQuote History
Originally Posted By gcw:


I built one of them.

1" angle iorn
3/8" all thread

It is a broad banded sucker. 144-148 flat 1.0:1

I like it but still like the Ed Fong style in PVC
View Quote View All Quotes
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Discussion ForumsJump to Quoted PostQuote History
Originally Posted By gcw:
Originally Posted By anonynan:
Originally Posted By Gamma762:
I would recommend you stick with NMO for mobile antenna mounts instead of the "UHF" mounts.


This isn't a mobile antenna. I used the mount to build a J-pole out of aluminum rod and angle.


I built one of them.

1" angle iorn
3/8" all thread

It is a broad banded sucker. 144-148 flat 1.0:1

I like it but still like the Ed Fong style in PVC


I have one from Ed Fong also. If fact, that was my base antenna. It performs very well.
Link Posted: 12/14/2013 6:31:58 AM EST
[Last Edit: 12/14/2013 6:33:48 AM EST by zapzap]
Discussion ForumsJump to Quoted PostQuote History
Originally Posted By anonynan:


Looks interesting. I'm saving for an analyzer so I can do more with antennas. When I got into amateur ratio i would have never thought that it would be the antennas that would be most interesting to me.

What analyzer did you order?
View Quote View All Quotes
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Discussion ForumsJump to Quoted PostQuote History
Originally Posted By anonynan:
Originally Posted By zapzap:
You should be pretty close. I built a copper J-Pole for GMRS using a calculator and it was actually center tuned for the upper part of 70 cm but still acceptable on GMRS. I then built one for 70 cm…resonant on GMRS.

I bought the 5th Edt of the Practical Antenna handbook…really interesting book but I've been having some pretty interesting antenna ideas here lately. I recently started a digipeater antenna. I wanted to do a j-pole, then I decided to make the 3/4 wave side a inch long and turn it into a slim jim. Since I'm having issues finding slim jim plans, I'm just building based off my knowledge of the similarities between j-poles and slim jims. I have the structure built, just haven't soldered it together. Waiting on a antenna analyzer to get here from China before I begin to dedicate time screwing with it since it's between semesters and I don't have access to the network analyzers at the school's lab.
http://i1245.photobucket.com/albums/gg586/zap_uh_lack/Mobile%20Uploads/A73D1C2C-D55C-4994-A914-CEBA1A15949B_zpsc8judxfp.jpg


Looks interesting. I'm saving for an analyzer so I can do more with antennas. When I got into amateur ratio i would have never thought that it would be the antennas that would be most interesting to me.

What analyzer did you order?

I ordered this one. It's VHF/UHF only (pretty wide banded though).
Times Technology T100+

I'm not that big into HF so the lack of the HF side of it is not a big deal to me.
Link Posted: 12/15/2013 3:29:34 PM EST
Discussion ForumsJump to Quoted PostQuote History
Originally Posted By zapzap:
You should be pretty close. I built a copper J-Pole for GMRS using a calculator and it was actually center tuned for the upper part of 70 cm but still acceptable on GMRS. I then built one for 70 cm…resonant on GMRS.

I bought the 5th Edt of the Practical Antenna handbook…really interesting book but I've been having some pretty interesting antenna ideas here lately. I recently started a digipeater antenna. I wanted to do a j-pole, then I decided to make the 3/4 wave side a inch long and turn it into a slim jim. Since I'm having issues finding slim jim plans, I'm just building based off my knowledge of the similarities between j-poles and slim jims. I have the structure built, just haven't soldered it together. Waiting on a antenna analyzer to get here from China before I begin to dedicate time screwing with it since it's between semesters and I don't have access to the network analyzers at the school's lab.
http://i1245.photobucket.com/albums/gg586/zap_uh_lack/Mobile%20Uploads/A73D1C2C-D55C-4994-A914-CEBA1A15949B_zpsc8judxfp.jpg
View Quote

I dont' know why people build those, there's no electrical or performance benefit to the element folded over. Folks who make wire J poles out of twin lead connect that extra wire otherwise the floating conductor would tend to have erratic effects on tuning, but no reason for a copper tubing J pole to be made that way.
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