Worldwide DX Amateur Radio Forums - Ham - CB - HF - VHF - UHF

Right now the SWR's are not good, 3 to 1 + on the ham bands, but it's much lower on the VHF Marine band. I rechecked my measurements and found my final length on both verticals a 1/4 inch too short....but that's not a problem, I got plenty of copper pipe here, I'll just sweat out the two verticals, and replace them with one's the proper length tomorrow. What probably happened is, when I pushed everything together I didn't seat the verticals all the way into the fittings and cut them a hair too short. I never thought to remeasure before putting it up in the air.

A Rookie Mistake.......

I've been running it on low to medium power, and I'm hitting machines I never thought I'd reach, once I get it straightened out, and run full power, I'll be able to work 10 different repeaters with a solid signal, and another 5 with a weak signal, so I'm not all that dissapointed with this project.

Weather permitting, I'll get the fix in on it tomorrow, and report back the outcome.

__________________
37OH - SSV - O773H

LOL, It happens to all of us. Did you see my coil loaded dipole build that was supposed to have one segment for 40m? I wasn't thinking and cut the wire to the proper length....only to realize later that when I attached it to the coil all the necessary wraps had made it too short for 40m. It happens....

1/4 of an inch shouldn't make that drastic of a differance. I'll bet you will also have to change the feedpoint position as well. Of the couple J-poles I have made the feedpoint position was never "by the book". Experiment and have fun. That's what it's reall all about.

__________________
Front/back ratio comes from the antenna. Forward gain comes from the wall socket.

just solder on another connector and cut to length.

Well I'm at my wits end with this experiment, I built a second J-Pole from scratch, make absolutely certain my measurements were right on the money, made 50 trips up & down the ladder adjusting the damn thing, and just like the first one, it radiates almost flat up in the VHF Marine bands, but I just couldn't get those SWR's down on the 2m ham frequencies. The best this one will do is just under 3.1:1.....(the first one ran close to 4.1:1)......

I changed feed lines, raised it up another foot, changed out the jumper between the radio and meter, ran a ground wire from the antenna pole to a copper grounding spike that's 4 foot deep.....no matter what I try, or how many adjustments I make, I just can't the the SWR's down to a reasonable level......

Everyone I've talked to that built one of these antennas has gotten no more than 1.2:1, and most get 1.1:1 on them......I don't get it......
I get great signal reports, was even on a simplex net this evening, and on medium power I was pinning everyone's "S" meters, so the thing is working, but with a load of reflected power.......

Any thoughts....????

__________________
37OH - SSV - O773H

A 3:1 or 4:1 SWR? Odd, normally your radio wouldn't particularly like that and would 'cut back' on power. I'd think you'd see that on the watt meter? Changing the positioning of the feed point, sliding that thing up/down, would make quite a difference in the indicated SWR. Probably not a 'hear-able' difference, but the transmitter would sure tell a difference. And that 1/4" shouldn't make much, if any, difference, sort of, and certainly 'curable' by changing the feed point.
After a quick look I can't find it, but what's the antenna next to the 'J'-pole? It isn't for a marine band, is it??
- 'Doc

Question, Doc:
Are you saying that the proximity of the Marine band antenna is affecting the SWR?
Could it also be the feed point position?
N2ITH is having fun doing this; but I think he is getting frustrated. What should/could he do next?
You see, I want to build on of these too, and I will probably run into the same problem he is having - so what can be done?
Certainly a balun isn't going to fix it; there isn't a ground on it like there is on a dipole.
?????

__________________
What gear do I use?
BASE: Icom IC-718 & GAP Titan DX, Yaesu FT-8800R & Diamond X50A, Magnum OmegaForce S45 & IMAX 2000 w/Astatic D104/TUP9.
MOBILE: Galaxy DX99V & Wilson 1000 w/Astatic D104-M2, Yaesu FT-8800R & Diamond NR-770.
"...The 444 in San Jose CA; the Central Gold Coast..."

Rob,
I'm looking for probably causes mainly. The marine antenna being close to the 'J'-pole shouldn't really be a problem as such, but getting them further apart certainly wouldn't hurt either. Knowing how I've sort of 'goofed' with the wrong feed line before, I was trying to 'suggest' that without making it sound too silly. (Who, me? I ain't never... and probably will again though.)
The 'hardest' thing, but also the best thing to do is to get away from it long enough so that you can take another look to see if you've got things at least 'ball-park' close. A "forest" and "trees" thingy, you know?
You're right about a balun, wouldn't do any good at all, a 'J'-pole isn't a 'balanced' antenna at all. But, there -is- a 'ground' to it, that short stubby part is the 'ground', the 'other half' sort of.

This part is a bit 'off topic' but really would make things much simpler to understand.
A 'ground' is a terrible name for what people typically call the 'other half', or the 'mirror image', or the 'Image plane' of a vertical antenna. 'Ground' has too many definitions, or it's just used too much to describe things that are not 'grounds' at all. A 'ground' can mean one thing in a DC circuit, which isn't necessarily the same thing in an AC circuit, and is definitely not the same thing as far as RF is concerned. Keeping all those 'definitions' straight can really get confusing. Especially if you aren't familiar with all of it's definitions! If you ain't on the same 'page', understanding isn't something I'd count on. It makes very good sense to 'safety ground' a 'J'-pole antenna. It makes no sense to 'RF ground' one, it just doesn't need it, neither do most other type antennas. You see where I'm going with that? Okay, and now I'll get off that soap box and use it for kindling.
- 'Doc

I was reading your description of your efforts so far, and I can't see anywhere where you tried to add a little length to the antenna.

Have you tried to add a little length to the antenna yet?

__________________
Highlander, NA-821 on 11 Meters.
N9RZF, David on Ham Bands.

Yaesu FT-847, Galaxy DX-2517, President Lincoln, Cobra 150 GTL, Uniden Grant LT.

I added length to the second J-Pole I built, however, and assuming the weather cooperates today, I will try adding length to this one with some solid copper wire clamped to the verticals and adjust them to see what changes I get.

Also I should note that since those photo's were taken, I removed the marine antenna, and the closest tree is approx 10 to 12 feet away.....

__________________
37OH - SSV - O773H