At this point in time - Antenna experiences so far

[Marconi]

Following your advice to start with the standard dimensions for the Vector 400 I started over again on the rebuild and did that for the over all lengths of the Vertical and the cone radials. Additionally I made sure the loop was exactly what it should be. Bob had questioned the dimensions of my dog bone on the gamma, so I rebuilt it, but stronger than before using 3/4" x 3/16" aluminum bar instead of 1/2" x 1/8" as before. I also used the idea we hasd discussed about some stand off of the radials at the bottom of the cone where they attached to the vertical. Because the EZnec model seemed to work out better with some stand off we considered the possibility that the real antenna might benefit from that. too. Previously my antenna.s radials went straight out from the vertical at the prescribed angle of about 30 degrees, but did not stand off. I made the mount for the bottom of the radials with right at 1-1/4" stand off before the cone tubes began their ascent toward the hoop.

At that point I still seemed to be unable to get a good match on the MFJ-259b, so I decided that for whatever reason my gamma match was not able to match my antenna. I made another gamma match using increased diameters for the gamma tube, and the gamma rod. The length of the tube remained the same as before. The rod I had was about 4" shorter than the original length, but I thought I'd try it before buying another. It worked just fine. Additionally I followed the suggestion you had made about the possibility that the brass fittings at the bottom of the gamma tube may have been read by the RF as a part of the gamma tube length and removed the brass fittings from the bottom using instead an aluminum "el". Whether this actually helped or not I can not say, but I do know it slimmed up the parts at the conjunction of the feedpoint and the cone radials where there may have been some capacitance that was not contributing toward the mismatch of the antenna to 50 Ohms. Regardless, I now had a Gamma tube that was 5/8" x 17", a rod that was 1/2" x 32" with the ability to bring the match right into line.
When I had this done I found the antenna had less apparent bandwidth than the previous version, but I felt it was a healthier antenna over all.

I have built a vertical tubing dipole both ways. I would have to revisit the non-gamma dipole to answer the question. I also would have to rebuild the one with the gamma to find out.

In the next few days I will be sending my analyzer in for recalibration. I dropped it on the concrete floor. It now will not read 50 Ohms on any proven 50 Ohm load. It reads a consistent 63 Ohms instead.

Thanks for the information on your Vector, I was both curious and unsure of what did what on your new project.

Don't bother with redoing your dipoles on my account. I found a reference from you on the Charlie Tango forum where you indicated you saw a 73 ohm impedance on you center fed HW. That is what I thought the impedance would likely be at that point, but I was looking to verify.

Some of the guys posting on another thread were talking about a 5/8 wave not working with a gamma match, because the impedance was too high. I was just wondering how they would explain the Sirio SD27 working, with its gamma match...if they were right.

It's not worth arguing about, but again I was curious if their conclusions made sense or was I just off base again.

 

[HomerBB]

Hopefully the little bit of info helped.

 

[Marconi]

The Sigma 4 works when in the air, but so far I have been unable to get it to read ideally on the 259b. Achieving a low VSWR is easy enough, but the R= and X= are never where you'd want to write home about. To date I have never known of anyone reporting anything on whether their Sigma.Vector antennas look good on an analyzer so I just scratch my head on that one. I'll build one more from scratch and try again in due time.

Homer, here is my belated response to this issue you posted above long ago. I must have missed it, because I always had similar results with my real Sigma 4. The match was always close with a good SWR, but the values of R & X were always off a bit and I never saw near a perfect match while tuning. However, the Z value on my VA1 analyzer typically showed 50 ohms match across the CB band.

I use to explain that as the complex value for the impedance when I was asked what the Z value was.

 

[HomerBB]

@Marconi
Apparently I finally got it to work...

 

[Marconi]

For me that was a long time ago. As best I could tell, my S4 worked great too.

After that, the rest is just a buzz in my mind.

 

[Marconi]

I use to explain that as the complex value for the impedance when I was asked what the Z value was.

Below is an explanation for the complex match or "Z". Thankfully for me, this is a bit more simple to understand.

 

['RAKER]

@Marconi
Apparently I finally got it to work...View attachment 34027

I wonder if your mfj is out of calibration and should be reading 50ohms?

 

[HomerBB]

I wonder if your mfj is out of calibration and should be reading 50ohms?

I did send it in since that time and have it recalibrated.

 

[Marconi]

I am interested in your models above, and it seems your 1/2 wave is the best on the overlay. I didn't see the 1/4 in there?

Homer, right now I can't tell you why I was reading this old thread from 2012, but here is another question from you where I failed to respond. Your question is high-lighted in bold above.

The 1/4 wave pattern was in the overlay at the bottom, in my post #22. In the overlay the 1/4 wave antenna was above the other 3 models with color, noted as (* Primary)

See link below.

https://www.worldwidedx.com/attachments/homers-idea-on-capture-area-pdf.8098/

 

[HomerBB]

@Marconi
Interesting comparisons. They have me scratching my head. . .
1) the patterns are identically shaped
2) wonder why I wanted the 1/4 wave horizontal
3) how can they have so much gain
4) the 1/2 wave is the best of the bunch (I'm not surprised)
Showing them at 36' high, so I'm assuming these are over average ground

 

[Marconi]

@Marconi
Interesting comparisons. They love me scratching my head. . .
1) the patterns are identically shaped
2) wonder why I wanted the 1/4 wave horizontal
3) how can they have so much gain
4) the 1/2 wave is the best of the bunch (I'm not surprised)
Showing they a 36' high so assuming these are over average ground

Good questions Homer. All I can remember now is what I saw and read in this old thread. I recounted my describing an article I once read about antenna range testing... were the antennas were tested laying horizontal. The idea was to take elevation differences out of the tests comparisons. I can still recall that idea in the article, but I have never seen it since. It is probably buried in some magazine from the past.

I can't find any of these old models either. Tomorrow, I will try and duplicate that old idea and maybe then I can comment on your questions.

 

[Marconi]

@Marconi
Interesting comparisons. They have me scratching my head. . .
1) the patterns are identically shaped
2) wonder why I wanted the 1/4 wave horizontal
3) how can they have so much gain
4) the 1/2 wave is the best of the bunch (I'm not surprised)
Showing them at 36' high, so I'm assuming these are over average ground

Homer, I re-did these models at 36' and 16' feet. I used 16' feet to the radiator because the radials are 9' feet long and this leaves 7' feet of clearance to the Earth just to be on the safe side.

1. the patterns still remain similar to the previous models posted. Maybe these similar patterns...are surprising. I can't explain exactly why, but I assume it might be what the test idea is meant to reveal.

2. I think you were looking for the 1/4 wave pattern that was covered up by the 5/8 wave pattern, and it was not listed by name in the list of other antennas. I fixed that with the models below.

3. the previous models were all at 36' = 432" inches to the radiator. Apparently I did not think about the height back when I posted the original models. I fixed that too, and lowered them to 16' feet above ground, and again, to allow space for radials.

4. Homer, I can only speculate as to why both 1/2 waves in this group, one that is end fed, and one that is center fed, show the best gain when all that were tested were laying horizontal.

I recall a WWDX member (?) that use to frequently make the claim, "...all antennas are 1/2 wave radiators..."

 

[HomerBB]

This is interesting, too.
As you said, the .625 has nothing on the .50 antennas. I'm not surprised, although I likely can't articulate why very well. I simply know that I have tried a huge variety of 11m styles of antennas and sometimes found equal performance from the .50 waves as the longer antennas, especially when mounted at the same tip height.
My theory so far...
When the antennas are laying horizontally they are effectively at the same height. Also, the artificial groundplane the .625 and .25 have are nullified due to the real earth being reintroduced beneath them. I think the out of phase 1/8 wave lower section of the .625 does not contribute to the height either, so with both it and the nullified GP out of effective contribution to more gain over the .50 the two antennas are equal. As for the .25, it is smaller. It will have less gain.
Sound reasonable?

 

[Marconi]

This is interesting, too.
As you said, the .625 has nothing on the .50 antennas. I'm not surprised, although I likely can't articulate why very well. I simply know that I have tried a huge variety of 11m styles of antennas and sometimes found equal performance from the .50 waves as the longer antennas, especially when mounted at the same tip height.

Homer in re-reading this old thread, I'm sorry if i came across disagreeing with you. I kept hearing the words "capture area," and I just don't think, within reason, our CB antennas typically suffer or show performance benefits due to this phenomena we can't easily determine. IMO, this is just another scientific fact that show effects that tend to be very small, but when CB operators get the info...they blow the details up into a big deal.

When the antennas are laying horizontally they are effectively at the same height. Also, the artificial groundplane the .625 and .25 have are nullified due to the real earth being reintroduced beneath them. I think the out of phase 1/8 wave lower section of the .625 does not contribute to the height either, so with both it and the nullified GP out of effective contribution to more gain over the .50 the two antennas are equal. As for the .25, it is smaller. It will have less gain.
Sound reasonable?

Homer, I ran each of the 36' foot models in Free Space and determined the Average Gain error result for each model. All but the CF 0.50 wave showed fractional (-) error differences in the gain, which showed the models gain was slightly understated. So, the small (-) error factors reported...needed to be added to the reported gain for each model.

(-) error = understated gain
(+) error = overstated gain

Corrected gain:
0.25 = 6.99
0.50 CF = 7.61
0.50 EF = 7.60
0.625 = 7.08

 

[HomerBB]

Thanks.
I reread some of this thread, too.
I wish I hadn't mentioned capture area at all.

The corrected gains are remarkable in terms of .50 vs .625.