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Is resonance really where you get best antenna performance?

The DB

Sr. Member
Aug 14, 2011
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St. Louis, MO
@Chris120 now your just making things up. I would personally say that you are projecting your problems onto me, just because I had the gall to call you out on your trollish behavior that apparently you think is acceptable because 'this is a forum'.

Anyway, I'm done with this. I will let the admin/moderator team take it from here should you continue to push your bs. I have better things to do.


The DB
 

144inBama

Sr. Member
Apr 22, 2020
673
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Lower Alabama
@Chris120

DB quoted post #80 as the troll comment, not the one you quoted,
The Imax is 5/8 wave....period. My tape measure doesn't lie.

You may not have intended for it to sound as it came across, it happens, it's all but impossible to read intent in any given post. but, your post did come across as "I don't care what science or theory says, my tape measure is the ISO9000 of the antenna world". Did you intend it that way? Probably not but that's what it projected. I'll agree that DB leading of with the troll remark may have been a bit overly aggressive but on the same hand, there are hundreds of post here similar to yours that were indeed posted by trolls looking to just stir the pot. You have a low post count and lead out with a perceived challenge to a knowledgeable member who has spent a lot of time in this area, while providing no data to support or back it up and ended it with "period" which infers "there's nothing left to discuss, I am right and it's not open to discussion." Was this how you meant it....again, probably not, but that's why everything spiraled the way it did. It happens, it's the internet after all.
 

NightThumper

South of Pittsburg
Nov 8, 2017
652
1,537
153
The Imax is 5/8 wave....period. My tape measure doesn't lie.

Holy Tape Measure Batman! Seriously I’ve got to have one of these tape measure. Was it a Lufkin, Stanley, Craftsman, Dewalt, Klein, Milwaukee ETC? Can you buy them in 1/4, 1/2, 5/8 or full wave? I also want to make sure I get one that has been approved/tested by the ARRL Labs. I’ve heard Klein and Stanley are comparable. Please advise as this would be much cheaper than a RigExpert Analyzer, NanoVNA or Modeling software. Nothing like taking the guess work out.

Now I did two electrical wave length measurements but have two entirely different readings. Which one is correct?

63D86DD0-309D-4035-B6BB-81FF8FB84213.jpeg C9BDC20C-D111-4818-A3B7-6FBC755836AE.jpeg 33FF0D86-3D5B-4816-AE54-A24FC80E609D.jpeg

Respectfully
Brad
KE0XS
South of Pittsburgh
 
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Marconi

Usually if I can hear em' I can talk to em'.
Oct 23, 2005
7,190
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Houston
The capacitor was something like four or five feet up from the antenna's feed point I think? I recall it was in the bottom section, and it did make a difference in the radiation pattern of this antenna, although not necessarily a very big difference, it was enough to be noticed. It also changed the current distribution of this antenna, making it so this was one of two antennas I am aware of that are commonly called 5/8 wavelength where the currents are completely in phase along the entire radiator. Mind you I am remembering several threads from when this was discussed in back in what, 2016?

Db, I can still remember that the first and only time I ever saw a busted-up Imax 2K was showing some small device on the wire near the middle section wire #2. I thought it was a support that helps keep the wire in the middle of the fiberglass from making noise

I never thought about it being a capacitor. Also, I never heard that the capacitor was four or five feet up from the antenna feed point either.

I found out sometime later, from you I think, that it was a capacitor, and that it was near the middle of the Imax second section and the capacitor was 42 pF.

I too find the location is close to the center of wire section #2, where I find the antenna probably is getting the best match at resonance with maximum performance.


Can you help me refresh my memory?

Marconi
 
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The DB

Sr. Member
Aug 14, 2011
2,008
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St. Louis, MO
If you look in the imax thread I created not long ago (here is a link), the quotes contain a link to the direct messages I found said data in.

Unfortunately I haven't been able to add to that thread lately as I have been working long hours, but I want to model the antenna with and without a capacitor in various heights and layouts and such and compare the results. Work has just been kicking my butt lately.


The DB
 
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BJ radionut

Supporting Member and 6m addict
May 9, 2008
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Marconi

Usually if I can hear em' I can talk to em'.
Oct 23, 2005
7,190
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Houston
Below is a similar article that Tech 833 also did on an older version of the Imax from Coppers. However, he did not include the capacitor in the middle section of the antenna. I will have to post this link later. Maybe you already have the one for the Imax too. You can look it up on the web, but it did not work when I tried to cut and paste it.

DB & BJ thanks. Over the years I've taken the dimensions off on the Imax for several different antennas...only to find different lengths by several inches in more than two cases. Others on our WWDX have posted dimensions and they too show many were different radiator lengths as well.

I will also note that matching a antenna model also is affected by the placement of the rings no doubt. IMO, when I tune the transformer to match for the Imax by adjusting the TF'r is similar to a real antenna and moving the tuning rings. I also run bandwidth curves to keep focused on the frequency...as I tune,

Many factors are at play in taking dimensions and that chore is prone to error or differences in manufacturing over time when they lengthen or shorten their Imax.

DB, when you two discussed the location dimension for the length of wire from the tip of the radiator down to the top of the capacitor was there any consideration made for the overall length of the radiator wire or the rings settings?

The reason for the question is because in my tweaking my model including matching the antenna to a perfect match, I also found the length by % of the radiator wire to the capacitor is probably more important to know...rather than just the physical length in inches.

For example, you gave us a capacitor location in inches and in that case the length down from the tip to the top of capacitor would vary the tuning results depending on the overall length of the overall wire was. I see why adjusting the rings might be problematic in real practice.

Of course, it is my thinking that in such a case any error in the match and resonance might be far too great to be close to resistive. During my tuning using modeling, I also run an SWR bandwidth curve step by step in order to help control the match keep a close eye on the design frequency.

I hope this makes sense. I'm still having problems with Covid 19 type symptoms, and I'm trying to cope with too many ministrokes in my brain that dimmish my short-term memory.

The new forum setup has made things more difficult for me since I got Covid 19 in November. 2019. I forget from minute to minute, among other things concerning my symptoms and health.

Eddie
 
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