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Base New Imax wont tune 11m....this sucks
- Thread starter 357
- Start date
I would not argue with either of you on the idea about the original Imax being .64 wavelength, but IMO the fact that the Imax has a 43 pF capacitor near the middle of the center section of the Imax...makes a bigger difference in the effectiveness for this designs radiating pattern... than the meager difference noted between a 0.625wl and a 0.64wl in the gain and angles reported.
Check out this old thread and there may be other threads:
IMAX 2000 continuity query
Edit: sorry this link only started to discuss the capacitor in the middle section of the original Imax. I will find where DB and I were modeling the Imax with the capacitor and post the link below.
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OK guys, here is the link where I 1st modeled the Imax with the capacitor.
My Imax model with secret capacitor on the rasiators middle section.
I think 357 posted the cap value as 43 pF. DB also did some models in this thread, but I think maybe his computer failed and he lost his files, so his links may show to be lost too.
I think there is more in this thread early on from the beginning...where DB and I continued to try and better understand the best location and value for this new idea for the capacitor in the Imax.
To save you lots of reading about how bad the New Imax is...look toward the middle of this thread...where 357 gets into the conversation.
Hope this helps.
My Imax model with secret capacitor on the rasiators middle section.
I think 357 posted the cap value as 43 pF. DB also did some models in this thread, but I think maybe his computer failed and he lost his files, so his links may show to be lost too.
I think there is more in this thread early on from the beginning...where DB and I continued to try and better understand the best location and value for this new idea for the capacitor in the Imax.
To save you lots of reading about how bad the New Imax is...look toward the middle of this thread...where 357 gets into the conversation.
Hope this helps.
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Marconi is correct. There is more to this antenna design than many even very intelligent people realize, even that people like w8ji missed in his discussion(s) on this type of antenna. The capacitor on this antenna has the opposite effect of a loading coil on a mobile antenna, it makes it electrically shorter than its physical size. In fact, at its feed point this is an electrical 1/2 wavelength antenna, and the same matching circuit as the half wavelength a99 antenna. (There is no other 5/8 sized antenna anywhere that can use a half wavelength matching circuit) This capacitor also has the effect of removing (virtually) all of the out of phase currents that all other "5/8" and ".64" antennas have, except for one, the Gainmaster, which is a completely different center fed antenna design. Another way of interpreting this is the Imax is the only lengthened half wavelength antenna on the market that I am aware of.
Some people like to trash these antennas, and I used to as well. But upon further research, there is engineering brilliance hidden in these designs that you won't find anywhere else on commercial CB products. There are only a two other commercial antennas out there where I see such brilliance hidden within the design, both of which are heavily debated and also greatly misunderstood by many of the best minds in the hobby.
That being said, there are also parts of these antennas (imax/a99) that I really am not fond of. They do have their share of problems and tricks to make work right in some (many?) situations.
The DB
Some people like to trash these antennas, and I used to as well. But upon further research, there is engineering brilliance hidden in these designs that you won't find anywhere else on commercial CB products. There are only a two other commercial antennas out there where I see such brilliance hidden within the design, both of which are heavily debated and also greatly misunderstood by many of the best minds in the hobby.
That being said, there are also parts of these antennas (imax/a99) that I really am not fond of. They do have their share of problems and tricks to make work right in some (many?) situations.
The DB
Here is my latest models of the Imax 2K in Free Space and over Real Earth and both antenna are matched.
Be aware this is not a real Imax in the sense that the matching device is different. I used an Eznec feature for a transformer. The real A99/Imax both use what Solarcon calls their "Variable mutual transductance" matching tuner.
1. the model is in Free Space. That shows the accuracy of the model with the Eznec "Average Gain Report." This results, noted at the bottom of the first page, reports the Average Gain. In this case the
AG = 1.001 with 0.00 db as the error correction.
2. is the Imax over Real Earth. In the Free Space model I remove all the antenna losses, and then I add these losses back...when I set the model over Real Earth.
Be aware this is not a real Imax in the sense that the matching device is different. I used an Eznec feature for a transformer. The real A99/Imax both use what Solarcon calls their "Variable mutual transductance" matching tuner.
1. the model is in Free Space. That shows the accuracy of the model with the Eznec "Average Gain Report." This results, noted at the bottom of the first page, reports the Average Gain. In this case the
AG = 1.001 with 0.00 db as the error correction.
2. is the Imax over Real Earth. In the Free Space model I remove all the antenna losses, and then I add these losses back...when I set the model over Real Earth.
DB, what you say here sounds plausible, but in my comparing coils for the A99 and the Imax, way back in the days, I found these two antennas used slightly different coils.
Back then I would call both these antennas as likely originals of the times...possibly before Solarcon got any ideas for changing the design length for whatever reasons.
though.That said, my working models of these two that are well matched both show a notable difference in the transformers values required to match.
Note: these are not the same type matching devices as used in either antenna however, then or now, but I can't see the differences changing any reasonable consideration that the Imax and A99 have slightly different matching coils.
Transformer details for both my matched and tuned models.
DB if you're talking about noise and static, I have an idea that maybe the fiberglass might have an affinity for static type charges in the air.
This idea is sorta' like, as a kid in a really dry climate area of North Texas, I use to walk across our fiber carpet at home in the winter time mostly, and then if I touched the metal door knob...I was likely get a small static type shock, and I could also hear the electric noise too.
DB, what you say here sounds plausible, but in my comparing coils for the A99 and the Imax, way back in the days, I found these two antennas used slightly different coils.
Back then I would call both these antennas as likely originals of the times...possibly before Solarcon got any ideas for changing the design length for whatever reasons.
That said, my working models of these two that are well matched both show a notable difference in the transformers values required to match.
Note: these are not the same type matching devices as used in either antenna however, then or now, but I can't see the differences changing any reasonable consideration that the Imax and A99 have slightly different matching coils.
Transformer details for both my matched and tuned models.
That is entirely possible. Now that I think about it, a loading coil affects the impedance of the match, so there is no reason that a capacitor wouldn't have a similar effect. I have not opened up said matching systems directly, only seen the opened versions in pictures, and they looked the same in said pictures. I made the judgement you quoted above from a model where the feed point impedance was close to that from what I have seen in half wavelength antennas.
Consider this, all of the fiberglass antennas that are known to have noise problem are made by the same company, and in many cases these are the only fiberglass antennas most people come into contact with. Also, have you worked with a Gainmaster antenna at all? I have, and it has far less noise than the big two fiberglass antennas that all of the noise complaints (that I am aware of) are made about. If the fiberglass is the sole cause of the noise, why would another fiberglass antenna not have the same problem?
The DB
When I got that idea it was a long time ago...long before we even knew about the idea of a Gain Master which worked for me similar to what you described.
I just made this excuse up a long time ago when I sold a new A99 to a buddy and in a few days he brought it back saying it was not right. I tried it out, and he was right, The match was not good and worse...it splattered RF to my neighbors and to several of my local radio buddies. They complained immediately on the radio.
One day I figured I would take the match out of the bottom section and sure enough the coax connections were soldered like a monkey did it, on both ends of the RG8x coax inside the matching section. The worst part of it was the shield wires, at the top, were splayed out ever were, and looked like a porcupine.
I fixed the bad solder job and added some wire for the top two sections. I hung it in a tree without the metal tube and no tuning rings. I pulled it up with a pulley and rope to about 45' feet at the tip. It worked fine and I saw no signs of RF in the radio room and no neighbors complained and my radio buddies said it was working fine.
I recently bought an A99, without radials, and it's 13" inches shorter than the old original antennas I had back in the early days of the A99 coming out. It tunes all of CB a bar below 1.50:1 SWR.
26.500 - 27.700 = 1.2 MHz <1.50:1 SWR.
25.615 - 28.125 = 2.5 MHz <2.00:1 SWR
I put put it up on a 10' foot mast without a choke...the noise is terrible. It will go up to 40' feet soon with a coax choke and I hope for the best.
I just made this excuse up a long time ago when I sold a new A99 to a buddy and in a few days he brought it back saying it was not right. I tried it out, and he was right, The match was not good and worse...it splattered RF to my neighbors and to several of my local radio buddies. They complained immediately on the radio.
One day I figured I would take the match out of the bottom section and sure enough the coax connections were soldered like a monkey did it, on both ends of the RG8x coax inside the matching section. The worst part of it was the shield wires, at the top, were splayed out ever were, and looked like a porcupine.
I fixed the bad solder job and added some wire for the top two sections. I hung it in a tree without the metal tube and no tuning rings. I pulled it up with a pulley and rope to about 45' feet at the tip. It worked fine and I saw no signs of RF in the radio room and no neighbors complained and my radio buddies said it was working fine.
I recently bought an A99, without radials, and it's 13" inches shorter than the old original antennas I had back in the early days of the A99 coming out. It tunes all of CB a bar below 1.50:1 SWR.
26.500 - 27.700 = 1.2 MHz <1.50:1 SWR.
25.615 - 28.125 = 2.5 MHz <2.00:1 SWR
I put put it up on a 10' foot mast without a choke...the noise is terrible. It will go up to 40' feet soon with a coax choke and I hope for the best.
New guy here. Spent a ton of time on CB back in the 80's and recently got the bug again. A lot has changed since then so I have a lot to learn and relearn. I ordered an Imax 2000 with no gp kit from Copper's and it shipped today. Still getting everything else together, but will be used for 11m and maybe 10m. I've seen a ton of good reviews and only a few complaints so rolled the dice. My plan is to use this as a base/mobile antenna. Neither will allow me to reach the optimum height as it will be quick deploy and take down as needed. In mobile mode it will be on a mast attached to the reciever hitch on a truck parked on a hilltop. I'm not looking for perfection just a good antenna to fit both needs. Will this work or should I just use it for base station and look elsewhere. Thanks for any advise.
Hey YD, I just got back into radio again too, after about 6 years and I was really surprised how much noise my new radio is receiving (S5+) even with the noise filters turned on.
I have a new A99, without a GPK. which is now 13" inches shorter than my old A99, and I can't find a GPK any were except maybe for Ebay, and I don't trust anything from Ebay any more.
This is why I asked for your Imax measurements, if you can.
The new manual, as in the past, says it is not necessary to adjust the matching for CB, and I find that true. So, I didn't touch the tuning, and I'm not sure tuning can produce a better match...being the antenna is so much shorter today.
The manual also says CB will be 1.50:1 SWR or less and cover the entire CB band, and that is true too, even though my old A99's always showed a better match and over a much wider bandwidth. So, I find the new A99 is not nearly as broadbanded as they were in the past, but it is workable in the CB band.
I have my antenna temporarily setup on a 10' foot pole. That probably doesn't help with the noise (S5+) most of the time. I don't have a choke on the feed line, but when I go up I'm going to do some comparison testing for noise down low and see if I can get the noise a bit lower before I raise it up.
I remember noise back in the days, would seem to come and go, but in the month since I put it up the noise is constant and sometimes terrible.
Check out this link below to a thread in the Sticky Section at the top of the CB Section.
Base - New Imax wont tune 11m....this sucks | WorldwideDX Radio Forum
Good luck and keep us posted.
Eddie - Marconi
I have a new A99, without a GPK. which is now 13" inches shorter than my old A99, and I can't find a GPK any were except maybe for Ebay, and I don't trust anything from Ebay any more.
This is why I asked for your Imax measurements, if you can.
The new manual, as in the past, says it is not necessary to adjust the matching for CB, and I find that true. So, I didn't touch the tuning, and I'm not sure tuning can produce a better match...being the antenna is so much shorter today.
The manual also says CB will be 1.50:1 SWR or less and cover the entire CB band, and that is true too, even though my old A99's always showed a better match and over a much wider bandwidth. So, I find the new A99 is not nearly as broadbanded as they were in the past, but it is workable in the CB band.
I have my antenna temporarily setup on a 10' foot pole. That probably doesn't help with the noise (S5+) most of the time. I don't have a choke on the feed line, but when I go up I'm going to do some comparison testing for noise down low and see if I can get the noise a bit lower before I raise it up.
I remember noise back in the days, would seem to come and go, but in the month since I put it up the noise is constant and sometimes terrible.
Check out this link below to a thread in the Sticky Section at the top of the CB Section.
Base - New Imax wont tune 11m....this sucks | WorldwideDX Radio Forum
Good luck and keep us posted.
Eddie - Marconi
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Tracking shows it will be delivered Monday evening. I'll see if there is a date of mfg and measure each section. Probably be a week or two before I get everything hooked up and checked out. I'll post my results on both 10m and 11m.