Posted on 05/10/2021 6:55:46 PM PDT by tbw2
Robert Glorioso, W1IS,who describes how he solved some problems in making dual-band J-poles(intended mostly for field use) function well on both 2 meters and 70 centimeters.
(Excerpt) Read more at batteryeliminatorstore.com ...
Antennas: A Different Twist on a Dual-Band VHF/UHF J-Pole
https://batteryeliminatorstore.com/blogs/ocf-masters-blog/antennas-a-different-twist-on-a-dual-band-vhf-uhf-j-pole
J-poles suck.
You NEVER see one in commercial use either. MUCH easier to make a sloping-radial ground plane antenna with wire soldered to a BNC or SO-239 socket AND it has a much cleaner pattern too.
Components and transmission line have changed a lot since 1900.
A lot of the early day antenna design is still very functional. As far as my logic, simple works. Simple is a technique the is avoided at all cost today.
Complexity is destroying us and making us slaves to systems we did not want or design.
Freedom is being killed by unnecessary complexity and along with it good design.
I can haz understandz?
I used a Jpole this evening.
I guess I will have to go back to the net and tell them it doesn’t work.
Now a stripper pole fan, hellz yeah!
No idea what a j pole is but I listen to am radio and the reception is worse now than it ever was. How to I get better reception? Once I’m within a mile of this fire station it is all static and high pitch noises.
So I have an old 4 or 5 m antenna that had some other wild connecting stuff. I am making a 6m ground plane out of this stuff. The vertical actual bends in a U back down to the radial base. I freed that up and am wondering if on the return down I can get decent resonance or I can fit it at the top of the U and attach a horizontal piece that can take and additional vertical of a few inches. The radials are no problem. Just aluminum tubing. In fact all the components are aluminum
re: “I guess I will have to go back to the net and tell them it doesn’t work.”
Most of you guys wouldn’t know, because, you’ve never used a good antenna ... enjoy the bliss of ignorance in this case and also ignore the sage advice of those who HAVE SEEN the difference.
I have an engineering background. I have argued with customers that a 2400 to 2500 MHz antenna CANNOT receive 2000 MHz. I don’t care if you have software defined radio, the software can only process the signals the hardware receives.
you can has license
J-poles are often dual band. If you are looking for a simple dual band antenna it works pretty well for line of sight radio.
For the better omni directional gain, a vertical collinear phased array antenna is the solution. They can even be tuned with down tilt for coverage from hilltops. Many are made from UHF coax and or copper tubing sections. There are some excellent commercial antennas made that way.
VHF and UHF are not normally for over the horizon radio.
If you want real directional gain, the Yagi, corner reflector, patch antenna and Parabolic dish are the solution.
a good analog front end is everything
VHF and UHF are not normally for over the horizon radio.
certainly not UHF
Many hams live for the 1%, if not 0.1%, of the time your statement isn’t true, and over-the-horizon stations come in on vhf and uhf.
I’m moving into a new house soon...it’s a great Ham location, on a hilltop, horizon in view in all directions.
I’m going to put up a J-Pole made from 450 ohm ladder-line.
The J-Pole is an old design that works.
It was first used slung beneath German Zeppelins in WW1.
Another, more recent half-wave end-fed design uses an rf transformer to match a high-impedance end-fed walf-wave wire to the 50 ohm input that most rigs have.
They are simple to make using a toroid such as the ft240-43.
The bottom 1/4 wave section of a J-Pole is the matching transformer... at the very bottom you have 0 ohms and at the top you have 2000+ ohms... you just find the 50ohm spot near the bottom and connect the 50ohm coax at that point...this is about as simple an antenna design as you will ever find.
It’s a bit disconcerting to some though as it sure looks like a dead short across the coax...and it IS a dead short if you consider only DC but at rf frequency AC it is NOT a short it’s just a transformer.
It can happen with ducting. I’ve seen it in fog banks in river valleys.
It can happen with the low end of VHF frequencies. When the atmospherics are right. It rarely happens, but is more common during sunspot maximums.
Both UHF and VHF work with Moon Bounce.
But yes, UHF is almost always line of sign radio.
Linked Mountain top to mountain top repeaters were used on UHF to span between The West Coast and into Texas. Back in the 1980’s I talked to LA via a IC-2AT handheld from Las Cruces, NM. (Via the Cactus Net)
I remember when they had a space launch, Where I lived in NM, we would hear the JPL up & down link from the shuttle missions when the repeaters were not in use. It was amazing.
Not this Ham. Got the International Space Station as it passed right over my home here in the Midwest some 5-7 years ago and from that point on it was all HF baby. 165 countries and counting.
Can't do that with VHF/HF.
I used to live in El Paso, have used the linked repeaters many times from that area... it’s fun to have repeaters on mountain tops :-)
I later moved to New Mexico, close to the White Sands missile base...
Was always in attendance at the W5ES ham-club meetings :-)
I lived in Otero county in NM.
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