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Amateur Radio Antennas - For discussion of all amateur band designed antennas and related accoutrements. This includes base, handheld, mobile and repeater usage. For commercial antennas on the amateur bands please use Commercial Radio Antennas below.

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  #41 (permalink)  
Old 03-17-2017, 7:00 PM
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All I'm saying is if it wasn't a poor design you would see them in commercial installations.
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  #42 (permalink)  
Old 03-17-2017, 7:38 PM
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Quote:
Originally Posted by nd5y View Post
All I'm saying is if it wasn't a poor design you would see them in commercial installations.
I thought the issue was grounding vs accepted practice not to ground, but OK.

These are not rated for high power, so it would be logical to not see them in commercial installations, then again I have never looked for one either.

We are not dealing with a commercial installation here, so the point is irrelevant for the discussion.

I think a lot of the problems come up from poor installation. Grounding it and having any metal within 2 feet of it will end up with undesired operation. I tend to believe it's not a poor design as much as it is a user error in the execution of the build, and/or installation.

I have seen the best made antennas work like crap because the person who assembled and installed it was clueless, and ran some garbage made cable to it as well.
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  #43 (permalink)  
Old 03-17-2017, 9:38 PM
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A stock J-pole will be influenced by grounding or attaching to a metal support pipe. etc. This is because these antennas have lots of common mode currents riding on the coax because of poor decoupling. If you decouple the J-pole with proper use of ferrite, then whatever is below the ferrite has little influence on the antenna.

I've done this and it works on J-poles and many other antennas that have feedline decoupling problems. This is not something I made up, its common knowledge. Most likely the so called designer of the antenna was not up on common mode currents and how to address them.
prcguy

Quote:
Originally Posted by NC1 View Post
Are you speaking from experience, or theory? I have absolutely no idea where you got that information, could you please provide a link? Every design I have seen says not to ground these type of antennas.

Maybe they are wrong, I do not know. But, if you follow the link below it clearly states - IN BOLDED CAPITAL LETTERS - (and I quote):

NOTE: NO PART OF THIS ANTENNA SHOULD BE GROUNDED!

So, that would indicate that his experiments and results had lead him to that conclusion, and to make a HUGE point of making sure those who install this antenna do NOT ground it - probably because grounding it results in extremely poor performance, which is why people say they suck (they grounded it!).

Here it is again in case you did not look at it the first time.
SLIM JIM ANTENNA PROJECT
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  #44 (permalink)  
Old 03-17-2017, 10:07 PM
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Quote:
Originally Posted by prcguy View Post
A stock J-pole will be influenced by grounding or attaching to a metal support pipe. etc. This is because these antennas have lots of common mode currents riding on the coax because of poor decoupling. If you decouple the J-pole with proper use of ferrite, then whatever is below the ferrite has little influence on the antenna.

I've done this and it works on J-poles and many other antennas that have feedline decoupling problems. This is not something I made up, its common knowledge. Most likely the so called designer of the antenna was not up on common mode currents and how to address them.
prcguy
Well, there is that, or somebody could use it as it is designed and just not ground the dang thing.

I hit repeaters 30+ miles away while pushing only 5W from an HT without an issue, using my 2 meter SlimJim. And yes, it has no ground. Amazing, don't you think?

I am not the only one who gets these kind of results, it's actually quite common.

Ferrite or no ferrite, it's not supposed to be grounded.
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  #45 (permalink)  
Old 03-17-2017, 11:18 PM
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Quote:
My money is on the guy who designed, built, and tested it.
Fred Judd G2BCX.

Here's a copy straight out the "Out of Thin Air" booklet , my copy dated 1981.

Original Slim Jim Antenna Article by F.C. Judd - The 2BCX Slim Jim Antenna - G2BCX

You will note in the text that he says that tuning should be done using the full length of the coax cable that will be used in the final installation.
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  #46 (permalink)  
Old 03-18-2017, 11:34 AM
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I have been following the discussion on these antennas -and several things strike me. First off, both the ‘J’ design and the “Slim Jim” are not Beginner’s Antennas-- especially! the later. I just read G2BCX’s article; I understand the theory behind this antenna; at the same time I can also see that building one by a neophyte is fraught with pit falls. Mechanically it is an awkward design. Constructing it to be stable enuff for long term out-of-doors would be challenging, there is no provision to ground it, the feed points are vague, and the use of twinlead feedlines makes me cringe (tho coax can be used) - these are among the detractors I found.
.
ND5Y sum’d it up: ….

“All I'm saying is if it wasn't a poor design you would see them in commercial installations”
.
In fairness to G2BCX, I sure his design works well for him, but there is a vast difference between the lab and the field… which brings me to point number Two--
.
SpugEddy, I am going to step you aside - for after all you were the one asking the original questions. I’m telling you that these types of antennas may be in your future, but steer clear of them for now. Aside from the obvious quarter-wave ground plane, here are a few of my suggestions if you still want to build-
.
Try your hand at that coaxial collinear vertical- but do it by the book- no substitutions of coax’s, etc….. or try some of the other phased section collinears… the books are full of them. The nice about these- you can assemble them in fiberglass or PVC pipes to make them weather proof...and they can be grounded
One of my favorites- the fold’d dipole- they are mechanically as tough as bricks. You can stack them in phase for additional gain, if you wish, they are easy to build and tune….. And going back to the commercial standard analogy- look at any 2-way tower- they are the antennas of choice.
.
Personally, I like the design of the Ringo Ranger.. ..not only for their simplicity of design, but ease of tuning- not to mention their inherent static suppression- everything is at DC ground. In the field we use similar designs all the time on 400-420MHz. If you feel so inclined, they are easy to duplicate.
.
What I am trying to get across is to avoid the anecdotal stories of how great an antenna is to one particular person as compared to something else. Antennas are one highly charged subject for hams… so approach them like a scientist,--- for remember, you can get a brine soaked piece of string to radiate RF- and some might laud it to the heavens as the best thing since sliced bread.
.
…………….CF
.
.
If I get a few moments in the next couple of weeks I might put together a UHF “Slim Jim” design and run it thru a few lab tests of my own- stay tuned…….
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  #47 (permalink)  
Old 03-18-2017, 4:27 PM
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Perhaps the reason for the J-Pole or the Slim Jim not being produced commercially is that they are mechanically complex which doesn't lend itself to mass production and also so site specific when tuning up. Mind you, there are many amateur antennas that need a fair bit of tweaking to get them to work adequately - some never do!

As CF says, the good old folded dipole has lasted years as mass produced TV antennas in atrocious weather conditions and survived well. I have a cut-down one as my VHF aero antenna still with the 300/75ohm unun and it works well, even in the 'shade' of a largish discone above it.

Spugeddy - it's been an interesting discussion - let us know what you finally decide. Hope we haven't overwhelmed you!

CF - G2BCX used a home-brew UHF 650MHz test bench - used a record player platter to rotate the scaled-down antenna, a single tube lecher line oscillator and recorded the results on a pen'n'paper plotter. I suspect you may have something a little more sophisticated!
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Last edited by majoco; 03-18-2017 at 4:36 PM..
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  #48 (permalink)  
Old 03-18-2017, 5:35 PM
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Quote:
Originally Posted by NC1 View Post
Slim Jim antennas are NOT to be grounded. That is your problem right there.

Rather than give an explanation, here is a link that gives full and complete instructions for installation and construction of a Slim Jim.

SLIM JIM ANTENNA PROJECT

Hope that helps.
According to the link. I am, in fact, mounted correctly. The 1 variation being
that I am mounted to a fence post mast and NOT pvc, but my mounting
point remains at the wavelength suggested. I'm approx. 20' from the earth
to the bottom of the antenna. This is taking me closer to the conclusion that
perhaps I AM too close to the A-99 antenna and its creating a problem.
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  #49 (permalink)  
Old 03-18-2017, 5:45 PM
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I completely agree and I found a website years ago where a club measured the gain of several home made J-poles and 1/4 wave ground planes and found many of the ground planes outperformed the J-poles. This was because there are a lot of potential mistakes to be made putting together a J-pole type antenna compared to the almost impossible to mess up ground plane.
prcguy


Quote:
Originally Posted by Coyote-Frostbyte View Post
I have been following the discussion on these antennas -and several things strike me. First off, both the ‘J’ design and the “Slim Jim” are not Beginner’s Antennas-- especially! the later. I just read G2BCX’s article; I understand the theory behind this antenna; at the same time I can also see that building one by a neophyte is fraught with pit falls. Mechanically it is an awkward design. Constructing it to be stable enuff for long term out-of-doors would be challenging, there is no provision to ground it, the feed points are vague, and the use of twinlead feedlines makes me cringe (tho coax can be used) - these are among the detractors I found.
.
ND5Y sum’d it up: ….

“All I'm saying is if it wasn't a poor design you would see them in commercial installations”
.
In fairness to G2BCX, I sure his design works well for him, but there is a vast difference between the lab and the field… which brings me to point number Two--
.
SpugEddy, I am going to step you aside - for after all you were the one asking the original questions. I’m telling you that these types of antennas may be in your future, but steer clear of them for now. Aside from the obvious quarter-wave ground plane, here are a few of my suggestions if you still want to build-
.
Try your hand at that coaxial collinear vertical- but do it by the book- no substitutions of coax’s, etc….. or try some of the other phased section collinears… the books are full of them. The nice about these- you can assemble them in fiberglass or PVC pipes to make them weather proof...and they can be grounded
One of my favorites- the fold’d dipole- they are mechanically as tough as bricks. You can stack them in phase for additional gain, if you wish, they are easy to build and tune….. And going back to the commercial standard analogy- look at any 2-way tower- they are the antennas of choice.
.
Personally, I like the design of the Ringo Ranger.. ..not only for their simplicity of design, but ease of tuning- not to mention their inherent static suppression- everything is at DC ground. In the field we use similar designs all the time on 400-420MHz. If you feel so inclined, they are easy to duplicate.
.
What I am trying to get across is to avoid the anecdotal stories of how great an antenna is to one particular person as compared to something else. Antennas are one highly charged subject for hams… so approach them like a scientist,--- for remember, you can get a brine soaked piece of string to radiate RF- and some might laud it to the heavens as the best thing since sliced bread.
.
…………….CF
.
.
If I get a few moments in the next couple of weeks I might put together a UHF “Slim Jim” design and run it thru a few lab tests of my own- stay tuned…….
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Old 03-18-2017, 6:27 PM
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Quote:
Originally Posted by majoco View Post

Spugeddy - it's been an interesting discussion - let us know what you finally decide. Hope we haven't overwhelmed you!
I'm no more overwhelmed than I was when I started. In fact, I'm less overwhelmed
because I've learned a few things. This is the main reason I post here. Sure, I can
read and read and read some more and I will get something from it, but by coming
here and posting the question, sometimes I get the "dumbed down" or the "layman's
terms" answer I'm looking for. And yes, sometimes it seems like I am constantly
"stepping in $#it" with some of my projects, but my philosophy has always been "if
I'm gonna step in it, why just cover the bottom of my shoe? Go for the biggest pile
and get the whole foot in it" That has been my whole life and I have learned an awful
lot along the way.

If you noticed, I never argue back with those offering advice (like some others here)
I absorb everything. Even if it is NOT the answer I was seeking.
Sometimes taking a little piece of 3 or 4 posts and using those as ingredients will
make my "recipe" better.

Some of you guys have given me great information in the past. Mmckenna, prcguy,
Coyote-Frostbite, majoco, and others. You have the knowledge that I don't have
and while I'm reading your posts, I see you as teacher and myself as student.

Now back to the meat and potatos. I think I am taking Coyote's suggestion. This
may be a project for further down the road when I become more educated. For
now I'll just stick to the very basics. I've already made several antennas but the
design has been simple (dipoles, 1/4 waves. etc.) Collinear looks basic but some
of the builds looked a little sloppy to me. Even my first attempt was disastrous. I'm
a neat freak when it comes to soldering and construction. I learned electronics
under the US Navy's Weapon Spec. WS-6536 years ago when I worked on the
Aegis Radar system. I have an idea in my head and now I want to try. I'll update
some progress here.

Thank you all for your input
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Old 03-18-2017, 9:14 PM
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.....glad to have been of help, Eddy.
.
(I hope I didn't come across as too much of a lecture'r...smiles)
.
If you've other questions, just ask....
.
............... Buona fortuna !
.
............CF
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Old 03-18-2017, 9:38 PM
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Quote:
Originally Posted by Coyote-Frostbyte View Post
.
(I hope I didn't come across as too much of a lecture'r...smiles)
.
............CF
Not even a little bit. Thank you
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Old 03-19-2017, 11:46 PM
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Before I leave this topic completely- another something for me to smile about- courtesy of Majoco
.
Lecher Lines !
.
I haven’t heard anyone use that term in years, let alone ever seen them in serious use.
What am I talking about?…Ahhh…an interesting research subject into historic radio--
.
I will relate, however, my limited experiences with them-, for those in the know; and how they bought me a few beers as a grad student teaching assistant.
.
For those not familiar with Lecher Lines, they were used as one of the earliest measures of V/UHF wavelengths**- which can then be translated into frequency. There are two parallel lines loosely coupled to the RF source under measurement. By sliding a detector down between the wires, its possible to detect the voltage nodes- you measure the distance in metric and determining wavelength. The technique dates to the early 1900’s and in hands of someone skilled at Lecher Wires, could result in frequency determinations of <1% error.
.
I would set up a lab demonstration for undergrad classes using two parallel bare copper wires spaced about four inches apart, running ~30 feet down the centre of the room- 6 feet high. To these wires, thru a loose link coupling, I’d match a signal source between 60-85 Mhz of several watts.
After a brief lecture about Lecher Lines and their historical place in RF engineering--- I would bet the class a round of beer at the campus ratskeller that they couldn’t measure the wavelength at better than +/- 500Khz. They always took the bet.
.
And I never bought a beer.
.
So much for history- the fine art of Lecher Line wavelength measurement; relinquish'd to the history books
.
.
…………………CF
.
.
__________________________________________
** I know Lecher Lines can form the tank circuits for amplifiers and free running oscillators, but limit this to wavemeters
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Old 03-20-2017, 4:26 AM
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....and that's almost word for word the 'experiment' we had to do in the early 60's when I was studying to be a marine radio officer, except for the beer bribery! The detector was a low powered flashlight bulb and we had to interpolate where the null was between two glimmers of the filament. I'm sure if I went up into the roof space I could find my old notes somewhere..... perhaps not!

I wonder if there's scope for a paper entitled "does the anticipation of beer enhance the accuracy of the experiment results".
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Last edited by majoco; 03-20-2017 at 4:36 AM..
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Old 03-20-2017, 2:10 PM
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Now I've thought about it a bit more, ISTR that the lecher lines were lengths of "O" gauge model railway line and the detector was the chassis of a rail wagon on plastic wheels of course!
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