An Unusual Jpole Antenna (

[@johnfkimballjr5792]

When I first worked on the neighbor's farm with the 86 year-old owner he offered some sage advice which I'll pass on to you "Never work above your breakfast" meaning when working on ladders or such try to work so that you look down on your work. That's not always possible but it's a good practice to follow.

[@jerrykr7kz]

I just watched the video. Thank you so very much, God Bless Dave. Much appreciated. Jerry KR7KZ

[@YZFoFittie]

How did you come up with the inductive feed vs the usual J-pole, "DC short"?

[@jerrykr7kz]

@@YZFoFittie Hi. I was working for the Army M.A.R.S. radio station as a Sgt. Command asked us to see if we could create a mobile VHF Jpole. After the crew worked for about seven months in the lab we came up with a stainless 3/16 Jpole. Thats how it came about back in 1972. The one shown is the proto type #32.

[@davecasler]

There is a coil wrapped around the antenna at the actual feedpoint, and the close wires form a capacitor. These are the two parts of a gamma match.

[@MrMick916]

The feed line system is essentially a gamma match. Check it out in the ARRL Antenna Handbook in the HF antennas section. It has a length of wire or metal tube that is small fraction of a wavelength. It is then capacitance coupled to the J-Pole by a few turns of insulated wire wrapped around the short side of the J. Gamma match is a common technique to feed beams and keep most of the metal at ground potential. K3UE

[@Steve-GM0HUU]

I was thinking the same. It is perhaps unusual to see a J-pole fed like this but not surprising to see a gamma match being used. In fact, arguably, as the J-pole is a balanced antenna, using the gamma match perhaps makes more sense than the usual method of connecting co-ax inner and outer directly to the stub part of the J-pole?

[@richardallankellogg]

There is an inconsistency in the referenced drawing. The long rod says 5/8 lambda, and the short rod 1/4 lambda. (Which is a ratio of 5/2). But the chart shows a ratio of 3/1 - as you would expect. The chart also references C, but C is not shown on the drawing, but presumably is the long rod’s length. Thanks for the review, but I can’t see where you gave a follow up on its performance.

[@davidsradioroom9678]

That was quite interesting. It doesn't look like a regular j-pole, but you had pretty good results with it. Thanks for sharing!

[@imahamjim]

I've got one like that for 440 very wide band dave. You do great education keep up good work! jim

[@ky4tgtodd203]

Hey Dave, I absolutely loved this video because I am a very visual person. Seeing you putting the antenna up, actually seeing the antenna configurations on your house helps me tremendously! I hope to see more videos like this in the future. Thanks! - KM4OCJ

[@redfonzie21]

Hey, David... Watching you with your asthma makes me think of my own asthma and going up and down ladders. I just know that when I'm doing it, I need to be slow, take my time, not worry about anyone else's timeframe to be in a hurry for them. Kinda wish I was there to help you with handing up the tools or even doing the ladder work for you. As long as I'm not fighting my allergies at the same time, I really don't have much difficulty with the asthma as long as I give myself plenty of time to do things slowly.

[@RobertMacCready]

Thank you Dave. In a new house here in FL with an HOA. Looking at your mast and how it's affixed to the side of the house. (would love to see the bottom part) That gives me ideas as to how to mount my Ed Fong J-pole. Take it easy on that ladder. We want to keep you around for a long time, with more videos...de KQ1K

[@PaulaBean]

I'm also fiddling with antennas all the time. It's a significant part of the hobby.

[@PaulaBean]

and it never ends

[@BajeBob]

Hi is this Amy from Barbados

[@cwebs1000]

I like this. I have been using a home made J pole made with copper tubing for years and it really works great. Almost flat SWR across the hole band. 73 Carl

[@hectorpascal]

With great respect David, you might like to consider if you should really STILL be climbing ladders, at your age with asthma? I have used a 2" Al pole swinging on a hinged scaffold clamp, set at 6 foot high on a 8 foot length concreted in the garden. A 25 foot pole was easily controllable by one person, and was locked in the vertical position by another scaffold clamp at the bottom of the 8 foot pole.

[@justincase3880]

You can use the old antenna (or part of it cut off), as a mast extension for the J-Pole, for additional height ...

[@oldbassist60]

Have one similar and it works like gangbusters. Use 1/4" aluminum rod and aluminum plate and some set screws. Spacer material of choice.

[@W1RMD]

Thanks for the video! PLEASE start telling people that ANY antenna that doesn't have BOTH sides at the same DC potential is a lightening magnet! In other words, hook your VOM across the leads and if your reading is not "short" or very close to it, the capacitance can build up high voltage and damage your equipment, including antenna analyzers or the front end of your receiver. Discones and dipoles are among the worst! A high value of inductance across the antenna feed point will appear "invisible" to rf, but will sort out any static build up which lightening is attracted to. Fiberglass seems to be especially prone to strikes. At least disconnect your antenna when storms are near and short BOTH sides to ground. Doing this before you hook up the radio or analyzer first is a good idea. I got caught on a sailboat in a storm once the had a discone antenna and during disconnecting the antenna from the radio, the static was so bad, I couldn't even hold onto the connector! Thanks and 73- W1RMD

[@hanelyp1]

One nice attribute of the J-pole, it doesn't care if the shorted end of the feed stub is grounded. Which makes it really easy to DC griound independent of the feed line.

[@hanelyp1]

One nice attribute of the J-pole, it doesn't care if the shorted end of the feed stub is grounded. Which makes it really easy to DC griound independent of the feed line.

[@kq6up]

I have seen one just like that on someone's pickup truck here in SoCal.

[@oldbassist60]

A few clarifications on the CAD drawing provided by KR7KZ from the link above. The machine screw holes (P44-P47) for mounting the SO-239 are for #4-40 screws and the jamb screws (set screws) holes that secure the elements to the base are for #6-32 hexagonal head, setscrews. Personally, I'd drill the setscrews centered on the element mounting holes instead of using a side-interference style of securing arrangement. The design I bought over 42 years ago, was from a ham club that was raising money, is a variation of this one. On mine, the biggest difference is that the coil is wound on the longer element (in basically the same location) and is wound upside down (from the top down) thereby making it impossible to prevent water migration onto the coil. However, water migration only slightly detunes this design - maybe 0.3 SWR units depending. To get the numbers shown in KR7KZ's table, applicable for my "upside down and backwards" design, I measured everything then reverse engineered the computational constants. They are "ballpark" similar to his drawing. Surrounding objects seem to have only minor detuning effects on this antenna as well. Another nice feature is that it's sturdy enough to still be around during and after adverse weather conditions - like high wind. If constructing with aluminum, this thing weighs approximately 1-pound. Mine sits atop a lightly guyed, DXE, telescoping fiberglass mast using an appropriately sized mounting stud to slip inside the top section. The baseplate and mounting stud can be any size or arrangement that you require. The original method of construction shown here is infinitely more reliable than the garage-hack level designs of J-Poles being sold that are constructed of bare copper where the connector and feed line hang off a flimsy, sliding shorting bar (or worse - a bare copper wire) with all the inherent problems of corrosion and eventual mechanical failure. It's little wonder many hams feel that the J-Pole is an inferior performer. When you build with junk - you end up with junk. I wish the one shown in the video was still available. It's superbly built and way above the competition. The one I own is constructed of 1/4-inch aluminum rod, 1/2-inch aluminum base stock, stainless hardware and Poly or PVC spacer stock. I don't think UHMW was available 42 years ago. Try this design - you'll love it. And the feed system is a modified gamma match. I suggest that you install a common-mode choke below the feed point. 73's

[@naiiawah]

What you are describing sounds like exactly matches J-Poles (both 2m & 440) I have that were purchased from a fraternal group (VFW Post?) in the Bay Area of California 25 years ago. I wish I could find a reference to them to see if they still are making them, but given the information/drawing on Dave's site and your comments above, I'm wondering if there is enough info now to locally reproduce them. I've looked over the years and never found any sort of design info about them till now. One thing I notice on my 2m version is there seems to be some sort of tuning done on the distance of the "B" segment of the wire in how far it is from the 1/4 wave side of the Jpole. The wire leaves the center conductor of the SO239 at an angle for about 1cm and then bends parallel to the 1/4 wave side of the Jpole, which makes me think that there is some importance in that spacing.

[@JT-py9lv]

Thank you Dave. Much appreciated.

[@Steve-GM0HUU]

👍Thanks for sharing Dave.

[@michaelpounds9300]

Dave...! You are scaring us on that ladder. Raise the ladder up pass the gutter further and be careful leaning against that gutter. Also it looks as though you are standing on the wrong side of the ladder. It must of been uncomfortable standing on those rungs. Love your videos. Be safe.

[@JosephLorentzen]

I don;t know why I looked at this one, but a cap could be put on the top rail which had been drilled and tapped for a bolt that will fitted for a regular bolt.

[@fontesdeo8582]

Very interesting indeed! Don’t know why but it makes me recall another odd-ball antenna called a bobtail beam. If you haven’t looked into one, it’s worth taking a peek at. 😉 73s William AG5VA

[@jdecar1]

I see that mount location puts the antenna below the ridge line of the roof. Does the roof block the signal in that direction at all?

[@davecasler]

To some degree, yes, but not a huge amount.

[@daveys]

It’s funny how people say bolt for nut and vice-versa. I went to a steam museum here in the UK and one of the chaps was showing a huge bolt and I said to the kids “look at the size of that nut” by accident. The guy went into a near state of frenzy, telling me it was a bolt and not a nut, blah blah blah. As a response, I think I said to him “don’t blow a washer, pal”

[@DonHavjuan]

That 8 minutes watching an old man faffing about on a ladder. What a way to start the day. :D Maybe you should do a montage with some Rocky music in the background next time.

[@m1chaelgerardo]

Hi David, do you have MMANA-GAL file for this antenna? Thanks - YD1MIC

[@justincase3880]

10mm is THE most common bolt size on all “newer” (circa 1980 on, or so on cars/trucks) .. foreign and domestic .. I have more versions of this size socket than any other, as well as a sizable collection of bolt and nuts, as they are the ones most frequently dropped and lost as well ...

[@qutips33]

I have made several jpol antenna for 2m 70cm and works well LA2VLA

[@kelvin0mql]

Did yours use this unique inductive-capacitive feed system? Or is this off-topic?

[@AhmedShABazama]

Does the SWR and X value will change if the Antenna was heated significantly by the sun?.. shouldn't the antenna elongate and therefore it will resonate at a lower frequency? Thank you for setting up all these great informative videos

[@davecasler]

It will, but by so little as to be hardly measurable. It will affect the center frequency by only a few tens of hertz, not enough to be noticed.

[@AhmedShABazama]

@@davecasler Thank you , I really enjoy your videos

[@alanb76]

Link to performance testing?

[@bigguyprepper]

Curious to see if anyone has been able to get accurate dimensions since these are quite interesting

[@ajcates9136]

David what does the wife think about all them ole antennas lol

[@eureoma578]

sure looks like a regular Diamond X300

[@Winstonsdad1956]

Does it matter how the J-pole is oriented as to the two elements? Does it have any directional characteristics?

[@YZFoFittie]

Nothing significant...

[@nfsusna]

Did you test iy

[@rwrp]

That Tram might work if you couple the sections properly. Most forget to do it.

[@joeb3300]

The antenna he took down looks like the same antenna that I bought a few years ago from Walmart (!), on-line, for $54. I don't recall whether it said "Tram", "Workman" or "JetSteam" on the packaging, but they all seem to be the same so-so, Chinese-maufactured, dual-band resold by a half-dozen so-called antenna manufacturers. I don't mind getting a mediocre antenna for $50, but it would burn me to pay $129 for the same item in a "Comet" wrapper.

[@glenmartin2437]

Thank you, Dave. My second viewing. Enjoyed the video. N0QFT

[@richhansenclan]

I was watching the impedance during the testing and it ranged from 34 ohms up to 60 ohms. Is that normal? is there a range that we want to stay within for an antenna like this?

[@DM-fz3ly]

by definition an impedance mismatch 30 vs 50z (z is impedance which is the complex resistance in ohms + either capacitance or inductance component) is less than 1:1 swr

[@amyjojinkerson6745]

ready rod

[@ellerybice3787]

You better get on those peddles.

[@jimdavis7968]

www.svecs.net/ I think the "j" this American Legion post makes is of this design.

[@StanCook]

Yea, you are back. It was great what you did for HAMs wanting to be extras but I missed your regular videos like this one. When I became an Advanced Class the only difference was CW and I was just short. Did you ever make a SlimJim 2 meter antenna?

[@davecasler]

I made a twinlead-based roll-up J-pole and did a video on it, but I don’t think it was branded as a Slim Jim.

[@StanCook]

@@davecasler Here you go, Dave. I made it and it works really well. bit.ly/3dcB6Zb

[@groundzero.]

very curious, are you sure this is not resonant on 70cm or 222mhz also?

[@davecasler]

I haven’t tried it but I don’t think it is.

[@AliReza-zx8km]

Nice.........

[@ellerybice3787]

You better get on those peddles. Out of breath while standing on a ladder¿

[@w.rustylane5650]

Your antenna is a little too long not too short. Trim a little off the top of the radiator. As you shorten the antenna the lower band's SWR will get lower as you chop off the top.

[@jerrykr7kz]

Not so! The longer the antenna element, the lower in frequency. The shorter the antenna element, the higher the frequency. - - - The long element shown in the video was cut too short at about 58 inches. Dave was right, it should have been at 58 1/2 to 58 5/8 inches. KR7KZ

[@patriot9455]

Convert EVERYTHING in your shack to metric, and the 5/16th will magically reappear.

[@pixotica]

Never understood why people build j-poles, not a fan of the design at all, or the feed line problems that go with it. For 2-m, a simple folded dipole on the vertical, with a 4:1 BALUN ( coax balun ), will out perform, the j-pole, is simple to make, smaller in size, has a near perfect omni pattern (unlike the j-pole) with much better gain.

[@WeirdScienceTime]

Why a folded dipole over just a center fed vertical dipole?

[@pixotica]

@@WeirdScienceTime well when I tested them, the folded had much better gain, in the real world and when modeled. My fave antenna I run them vertical, in a diamond shape about 1/10th wave length wide at the center. I have found no better antenna on 27 mhz, I have built most of them. I find they perform better than the current info states, I believe that in a diamond pattern, on a vertical antenna, all wire is vertical, very efficient. Outperformed many quad loops, and the quads were bi-directional.

[@Steve-GM0HUU]

@@pixotica That is interesting. Will add the "diamond dipole" to list of things to try. I can understand why a folded dipole may have benefits over a J-pole. However, the J-pole probably remains popular for various reasons - easy to construct, can be made from various materials (like ladder line that can be rolled up), may be easier or convenient to end feed the antenna, you can adjust the feedpoint impedance easily, you can add phasing coils and additional sections to increase gain, the slightly lopsided radiation may even work to your advantage if you are interested in working a particular fixed station like a repeater?

[@pixotica]

@@Steve-GM0HUU then a half wave end fed would fit the bill , hit all those marks.

[@poly_hexamethyl]

Vertical folded dipoles are pretty common for VHF, aren't they? Especially several stacked with appropriate phasing.

[@justaguy4788]

Looking at his "print" for the design is frustrating. Several errors. Perhaps you can have them fixed then link a good print? Multiple measuring systems, missing decimal point (hopefully), undefined measurements, etc.

[@spacemanspiff85]

No offense, dave but you're making me nervous watching you fiddling around up that ladder.