35, you promised to test the A99, but the weather was bad.

[Marconi]

Well, I have the A99, I have the fibreglass mast, and I have my VNA, but the weather is awful, blowing a gale and certainly not the kind of weather to be messing with 18' antennas plus mast, especially with an expensive piece of test equipment attached to the base of the antenna, testing will have to wait

35, if has been a while now, and I don't mean to rush you, but have you had a chance to check you idea on the A99, using your VNA with and without the use of a feed line, tuned or not. You were going to test my claim that I found no notable difference at the TX end of the line compared to the load end of the line. I'm still thinking this might suggest the A99 uses the feed line in a noticeable way or not?

In my test I did it without isolating my antenna. I think you wanted to check using your isolation idea also, right?

Take your time, but I remind you with this new thread so it won't be as hard for me to remember the plan. I would not ask if my VA1 was working right, and I had the energy to get outside and do the work.

The other day Bob suggested that I needed to spend the big bucks, and get me an analyzer that was not out of a Cracker Jack's box, and do some of my own testing. I wish I could do that on both counts, but I can't anymore. So I'm sorta banking on you, and also hoping I can understand your results from your VNA.

 

[northern35s]

I thought you might chase me for an answer at some point my original intention was to use a fibreglass mast, however my fiberglass mast is hollow and with the weight and lever effect of the A99 I decided against using that, so I used an alloy pole with a plastic sleeve to isolate the antenna, that was on the good few days we had, but since then the weather has been poor and my time somewhat limited.

I will do a full report on my findings when I've done some more tests, however for now all I will say is that the results are not what I expected, yes the feedline makes a difference in the results, but had very little effect on one of the findings, but for the answer to that I'll keep you waiting

 

[Marconi]

I thought you might chase me for an answer at some point my original intention was to use a fibreglass mast, however my fiberglass mast is hollow and with the weight and lever effect of the A99 I decided against using that, so I used an alloy pole with a plastic sleeve to isolate the antenna, that was on the good few days we had, but since then the weather has been poor and my time somewhat limited.

I will do a full report on my findings when I've done some more tests, however for now all I will say is that the results are not what I expected, yes the feedline makes a difference in the results, but had very little effect on one of the findings, but for the answer to that I'll keep you waiting

Yea 35, I've been sweatin' every day about your testing. I was never concerned you couldn't do it, but now it sounds like your idea kinka' fell apart on you. Like they say, "...stuff happens."

I've had that happen to me a time or two, but don't get too disappointed, there will be other days.

BTW, I didn't use isolation when I did my simple test. It only took me about 30 minutes maybe to test and record my results. Another thing is, I was never really sure such a test would or could reveal the idea I was thinking it might. So, I would advise some more thinking in that regard before you get all excited and start your testing. The idea was more like a thought than a plan anyway. Maybe your idea of isolating the mast is better, so be sure and get that right. Bob85, says your idea of isolation you described above is no-way-no in another test I did testing isolation on an A99.

Hope that gives you a little encouragement and some confidence on an obviously bad day you're having...sweatin' what this old man might do.

 

[northern35s]

Here's a teaser for you Eddie, A99 at 10' to feed, isolated mast and 24' of coax, this plot is nice and tidy, but contains something I wasn't expecting to see, see if you can spot it:

 

[Marconi]

35, I think all of my recent scans show similar conditions at the end of the feed line where the resistance values are good and hovers around R=50, across a good portion of the bandwidth range, and shows R=49 where I tuned the antenna.

My reactance on my antennas at 51' was off and showed X=+13 to +27 all across the entire bandwidth, and about X=+17 in the middle of the CB band, so my curves are much flatter than your results. Maybe if my chart was scaled closer to yours...it would look more similar. I think I might see similar results in my report if I did a graph for both resistance and reactance separately.

I have another bandwidth report at 37' feet, and it shows a lower value for reactance. This report also shows some reactance start to appear as X= (-) capacitance value also. Maybe at 10' it would show fully capacitive like yours does. My plot points are also showing the complex value of impedance, because I used the SWR values to position my points on my chart. Your chart shows a continuous plot for the range used and that is providing much better information.

Unfortunately I inadvertently threw away my old folder for my A99 back before 2011, when I was testing and talking to Bob about such testing. So, I can't compare directly with your results. Here is where I started my A99 folder a few days later.

View attachment A99 bandwidth curve..pdf

 

[Marconi]

35, I did not answer your question. I can only guess this may go to what you see too.

Do you think this difference between where resistance and reactance is in frequency may be a design idea to make the antenna appear with more bandwidth? This may not be what you see, but this is the way I see it.

In talking with Bob about our I-10K's, I think this very subject came up before...when we were comparing notes. We both were seeing the same thing, a split where resonance and reactance were at their best values. We might have referred to it in different terms back then however.

BTW, what <2.00:1 bandwidth are you seeing on this test?

 

[northern35s]

You're drawing me in like a moth to a flame, here are three plots that show the bandwidth, the vertical lines indicate 2:1 VSWR, and ignore the data points on the images with 18" coax and no coax:


No coax attached

18" coax attached

24' coax attached

Here are some of my findings, the complex impedance changes with coax length, this proves that coax length does have an effect on the antenna, however it doesn't affect bandwidth or the position of the bandwidth, the main thing I noticed was that the antenna has multiple points of resonance X=0.
I limited my testing to the 10/11m band, however I've read many times that people report low VSWR on a number of amateur bands so I intend to increase the sweep and see what happens. The reason for the multiple points of resonance is purely down to the matching transformer in the base of the antenna, I'm now looking forward to some time to play and good weather.

For those interested, here is how the antenna is mounted/isolated and how the VNA attaches to the antenna without coax:

 

[Marconi]

Maybe my test, without using isolation on my A99, showed the similar results I saw because the mast was acting just like the feed line would have. So in my test I never effectively removed the feed line, and that is why I saw similar results.

I see now, the test should be conducted just like you said 35...with the mast isolated.

If you tested with the mast connected do you think your reports would show different results and be closer to what I saw?

Did the blue tooth device move with the change in line length in these tests?

Even though the lines were showing a complex impedance type results, were you surprised to see feed line transformation in your results using different length lines?

The bandwidth your report shows...looks to be very tight...considering most feel the A99 is a pretty broad banded antenna, right? Do you think that is an issue when using a longer feed line, and make the BW look wider?

 

[The DB]

Noticing the smoothness (and in one case the lack there of) of the lines on your charts...

I can tell you with my AIM4170C that a bird flying by will put a little spike on some of the lines in the chart, and a car passing 30 feet away also affects the readout, skewing the typically otherwise smooth line a bit. That being said I've never seen a readout as "dirty" as when your VNA was plugged directly to the antenna so I'm curious as to what you think caused that and what corrected it in the lower charts (the ones run through a coax).


The DB

 

[northern35s]

Some of the other tests I want to carry out are using a non conductive mast so that I can rule out any capacitive coupling between the antenna and mast, carrying tests out with an electrical 1/2WL feeder, this will prove if the feedline does indeed affect the results, the coax I used was just some sections I had lying around, there's every possibility that the random lengths I used could be worse case. As I said earlier I plan to extend the sweep so that I can include other bands, it would maybe be a good idea to use a much longer random length feedline that better simulates something that would be found in a real world situation.

As for the analyser, yes it moved, it was always at the radio end of the transmission line and on the SO239 connector of the antenna when no feedline was used.

I believe the mast would alert what you see when not isolating the antenna from the mast, however I have yet to prove that in testing so I look forward to carrying this out.

I'm currently using my phone for Web access so apologies for any spelling errors or questions I've missed.

 

[northern35s]

Noticing the smoothness (and in one case the lack there of) of the lines on your charts...

I can tell you with my AIM4170C that a bird flying by will put a little spike on some of the lines in the chart, and a car passing 30 feet away also affects the readout, skewing the typically otherwise smooth line a bit. That being said I've never seen a readout as "dirty" as when your VNA was plugged directly to the antenna so I'm curious as to what you think caused that and what corrected it in the lower charts (the ones run through a coax).


The DB

There was a slight wind when I carried out the tests and as the antenna was loaned to me there were no mast clamps supplied, so I used what I could find, any movement of the antenna was directly acting on the analyser plus there's every possibility the connection wasn't tight enough and created the noise. As soon as any coax was introduced then the smaller vibrations were damped by the coax. Again this is something I aim to address when I get another opportunity to test the antenna. I hadn't intended uploading any results yet add they weren't complete, but as Marconi asked I didn't have the heart to say no

 

[Marconi]

Some of the other tests I want to carry out are using a non conductive mast so that I can rule out any capacitive coupling between the antenna and mast, carrying tests out with an electrical 1/2WL feeder, this will prove if the feedline does indeed affect the results, the coax I used was just some sections I had lying around, there's every possibility that the random lengths I used could be worse case. As I said earlier I plan to extend the sweep so that I can include other bands, it would maybe be a good idea to use a much longer random length feedline that better simulates something that would be found in a real world situation.

As for the analyser, yes it moved, it was always at the radio end of the transmission line and on the SO239 connector of the antenna when no feedline was used.

I believe the mast would alert what you see when not isolating the antenna from the mast, however I have yet to prove that in testing so I look forward to carrying this out.

I'm currently using my phone for Web access so apologies for any spelling errors or questions I've missed.

I agree with all your points here. Thanks

 

[Marconi]

There was a slight wind when I carried out the tests and as the antenna was loaned to me there were no mast clamps supplied, so I used what I could find, any movement of the antenna was directly acting on the analyser plus there's every possibility the connection wasn't tight enough and created the noise. As soon as any coax was introduced then the smaller vibrations were damped by the coax. Again this is something I aim to address when I get another opportunity to test the antenna. I hadn't intended uploading any results yet add they weren't complete, but as Marconi asked I didn't have the heart to say no

I just what somebody to try and duplicate these ideas and hopefully get to the truth.

Even my own BS doesn't excite me, and I know the truth will.

Thanks again.

 

[Marconi]

You're drawing me in like a moth to a flame, here are three plots that show the bandwidth, the vertical lines indicate 2:1 VSWR, and ignore the data points on the images with 18" coax and no coax:


No coax attached

18" coax attached

24' coax attached

Here are some of my findings, the complex impedance changes with coax length, this proves that coax length does have an effect on the antenna, however it doesn't affect bandwidth or the position of the bandwidth, the main thing I noticed was that the antenna has multiple points of resonance X=0.

I limited my testing to the 10/11m band, however I've read many times that people report low VSWR on a number of amateur bands so I intend to increase the sweep and see what happens. The reason for the multiple points of resonance is purely down to the matching transformer in the base of the antenna, I'm now looking forward to some time to play and good weather.

For those interested, here is how the antenna is mounted/isolated and how the VNA attaches to the antenna without coax:

35, if the test with no feed line above is going to be that bad, do you think you will be able to test the 1/2 wave idea effectively.

I'm going to get my A99 out, and lay it on saw horses, without a mast, and attach my VA1 at the feed point, and see if I see a match even close to that bad across the bandwidth.

 

[Marconi]

Here are my results with the A99 on two saw horses about 4' above the ground laying horizontal. The first set was done standing right at the feed point so I could see and work the analyzer. I suspect where I stood effected the results some.

The second set of results the VA1 was at the end of an approximately 14'4" jumper cut to about 27.205 of RG8x with a tested VF of 79%. In this case I stretched the coax out straight away from the base so I moved away from the antenna a few feet without thinking...doing so might effect the test.

This effected the results some. After I finished I tested this for sure by doing one more test with the jumper while standing close to the antenna...like I did above. The results were closer to the test above as a result.

It was just too hot for me to do the testing over. Note: the first test was at 26.96 mhz and not at 23.96. BTW, I just put the A99 together and did not test for tune or try and tune.



35, this is not totally convincing of the theory of a 1/2 wave line connected to a load showing a complex impedance at the feed point...like I've tried to talked about in another thread here on WWDX. However, this is what I see right now, and I would want to do some more testing if I was able.

When I did this test before with the A99 mounted vertically on a conductive mast that was about 15' feet high some time back...I saw even less difference than I see here, as best I recall. I don't remember what I used for a feed line either...and that too could matter some.

I also suspect the results of your further testing may well prove me wrong again on all counts, but so be it, if that is the case. At least I'll know what you saw in making the effort to duplicate the ideas here, and showing a different result from what I reported earlier even if your test is not conclusive also, because of the noise in your test that was directly at the feed point.

Again, I do not see the appearance of noise like your report shows, with its irregular curves either. I will be anxious to see if that happens to your follow up test. I did not use a mast this time, so what I just did today should be somewhat similar to your test the other day. I expect that your test without the feed line may have been an errant fluke and if so, maybe you'll have better luck next time.

I'm trying to get over my experience being outside in this heat, and if I feel better later today...I'll try this test again on a short vertical mast. I would try and go to the trouble of recording many frequency points like I've done before, but I'm just not up to doing all that work I don't think. I was out there about 20 minutes before, and it made me weak and short of breath. I have symptoms like COPD/Asthma.

BTW, I did not tune the antenna and maybe that is why the numbers are far off. I recall trying to set it at 27.500 at some point in the last year or so. If I test some more, I will try and tune it to 27.205 mhz.