IMAX 2000 continuity query

[M0GVZ]

To everyone following this thread and going WTF? to summarise:

Either using the groundplane kit or adding radials makes no difference performance wise that is worth spending money on despite what people would have you believe and the marketbollox claims.

Also if you have an Imax 2000 you're setting fire to your money changing it for another vertical antenna, especially a Sirio Gainmaster, if improved performance is your aim.

 

[Marconi]

To everyone following this thread and going WTF? to summarise:

Either using the groundplane kit or adding radials makes no difference performance wise that is worth spending money on despite what people would have you believe and the marketbollox claims.

Also if you have an Imax 2000 you're setting fire to your money changing it for another vertical antenna, especially a Sirio Gainmaster, if improved performance is your aim.

Connor I agree with you too. I've said for a time now that much of antenna theory testing might show us small differences in performance. Then CBr's take this information and blow the results out of proportions with their grandiose claims.

Hi marconi, It looks like you've done a great deal of work modeling the imax. I very much appreciate your plots posted for this antenna. Now I'm curious how the ground plane affects the angle of radiation. Do you think there will be a difference with the capacitor in place?

I have done a little comparative modeling work with the Imax. This thread has me interested to take another look however.

I also own an Imax, but I've never been enthusiastic with its performance. Looking back however...I think I always used some old coax to install it...and maybe that was not a good idea. I have some old buddies that use the I2K and find it works very well, and with them on-the-air I tend to agree with their thinking.

My Eznec models show me the Imax with 45* degree slanted down radials tends to raise the maximum take of angle higher, and that the 72" inch GPK radials, set horizontal, show a nice improvement over using 108" long radials...along with lowering the maximum angle from 46* degrees down to 9* degrees...when the antenna is set near a wavelength in height to the base .

EDIT: I added a PDF file of my Antenna Notes, maybe it is easier to read.

 

[rumblefish]

I'd like to thank everyone who put there effort into seeing what makes this antenna work as well as it does. I'm sure people will still insist on calling this antenna nothing more than a "dummy load". I've had excellent results with the Imax 2000. As far as white noise or static goes, the Imax 2000 was just as quiet as the maco v58. I've made some recordings of the receive noise on 3 different antennas. The static on the Imax 2000 sounded softer than the aluminum antennas. I don't know any other way to describe it?? That's the opposite from what I expected. Maybe I'm just lucky how everything worked out, I don't know? I do know it's working very well. 73 , {>

 

[M0GVZ]

As long as you're happy with it that's all that matters. My Imax 2000 is back up on the back of my house but sadly I don't get much time to go on the air nowadays.

 

[Marconi]

rumblefish, maybe I should not have posted these models in the linked thread below, but maybe you will find something there interesting concerning your Imax.

Maco v58 and IMAX 2k

 

[Needle Bender]

I did some quick modeling, I made a comparison model with 1/4 wavelength horizontal radials, and a model based on the short angled radials used in Solarcon's radial kit.

Here are all three of these models in one plot for a comparison.

The green color (labled as model gpk below) is the model that simulated Solarcon's ground plane kit.
The red color (labled as model hgp below) is the model that simulates a set of 1/4 length horizontal radials.
The blue line is the original Imax model with added capacitor from abobe.

A lot of people think that adding radials makes a difference in an antenna's radiation angle, as we can see here, this is not normally the case.

To see what the models look like with a mast added, I added a mast to each of these models, and below is the result.

The antennas happened to be 10 meters, or about 32 feet off the ground. As expected the horizontal ground plane model was affected the least, only loosing 0.01 dB of gain. The Solarcon ground plane kit model lost 0.08 dB of gain, and the model with no ground plane lost 0.37 dB of gain.

The cmc test model of the imax with no radials looked different than I expected so I researched that a little further and found this current+phase magnitude of the antenna...

In this model the antenna is mounted 10 meters (or about 32 feet) above the ground. Below the feedpoint there is a small bit of out of phase current, but then a full half a wavelength of in phase common mode currents, essentially acting like a collinear antenna. I cannot, at this point, guarantee that this will happen at every height (or every random length of coax from antenna to radio) but it is worthy of exploring. That, however, will have to wait until I get some more time...


The DB

Really great work, both to you The DB & Marconi!

Always in the past, (and ANECDOTALLY?) after a rather large number of antenna swaps I've helped with, we'd see right about 1 s-unit of loss in performance from swapping from an Imax to a MACO V58, conversely, about 1 s-unit increase when replacing a Maco V58 with an Imax, some of which were done shortly after the disappointing Maco was initially erected.

Also anecdotally(?), it's been my common experience to see about the same amount of improvement (1 s-unit) when switching from an Imax2000 to a Penetrator or other full-length true ~22.3' 5/8, but never have I had the chance to utilize an Imax radial kit.

HOWEVER,

...and I'm coming clean here,

I did see a little improvement over the Penetrator when I erected an Imax in it's place and added FULL 1/4 WAVE downward diagonal (45° - 70°) radials which I made from guy wire, attached to the bottom U-bolt on the Imax, and terminated to parachute cord the rest of the way down.

I haven't been comfortable posting this until now, but in this new light of a corrected-phase 5/8 radiator Imax, you have me rethinking those results which I simply wrote off at the time to either odd unpredictable conditions, the Ustream meter/ receiver being dinked with, or some other unknown physics-pseudo-reality occurrences...???

Please, you can understand, after so many years of seeing the same end results in so many differing installations, I couldn't believe an Imax could ever even keep up with, let alone BEAT (BEST) a full-size metal 5/8 Penetrator.

...and it DIDN'T! - Until I added the FULL 1/4 WAVE 4-wire diagonally downward counterpoise system.

OK, so THERE'S one for you'ze wize guyz to model.

All were erected atop a grounded 41' high mast and NON-isolated from the mast, nor was any coaxial choke employed. Just a simple, quick & dirty install.

The 4 guy wires on the Imax were 108".

The results I got was to a local Ustream meter, right at 10 miles away.

OK, I'll look forward to seeing some awesome graphic models

 

[The DB]

I was working on something like this for Marconi using the phase corrected IMAX model I created earlier. It was essentially that model with multiple different mounting/radial configurations, and said antennas modeled at multiple different heights. Unfortunately, I have been busy lately, so it has been coming along inches at a time. So far I have gotten some surprising results, results that differ from using a model that doesn't include said phase correction that this model has. I am not saying every aspect of said phase correction is a benefit, but it is interesting to study. That phase correction was enough to make two unexpected differences that, after I look at said models in more detail, seem to make sense.

I'll add your layout to my list of antennas to model, and if I can add those models to the results I will.


The DB

 

[Needle Bender]

.

I was working on something like this for Marconi using the phase corrected IMAX model I created earlier. It was essentially that model with multiple different mounting/radial configurations, and said antennas modeled at multiple different heights. Unfortunately, I have been busy lately, so it has been coming along inches at a time. So far I have gotten some surprising results, results that differ from using a model that doesn't include said phase correction that this model has. I am not saying every aspect of said phase correction is a benefit, but it is interesting to study. That phase correction was enough to make two unexpected differences that, after I look at said models in more detail, seem to make sense.

I'll add your layout to my list of antennas to model, and if I can add those models to the results I will.


The DB

DB, what's the name of your modeling program?

...and what else is cool is I haven't read about any of this anywhere else on the web, DB you just may be the first to have figured out the Imax advantage - after so many decades on the market!

On mine, it's field tested to be a Pene-beater at that height and in the direction of the Ustream receiver that radial was the steepest, only 16' from the mast, 8' up from the ground, 33' below the antenna base, so I'm calculating about a 65°- 70° downward angle diagonal radial slope.

Perhaps you might also try downward-sloping 1/2 wave radials in your modeling.

 

[The DB]

DB, what's the name of your modeling program?

4Nec2. It is completely free if anyone wants to try it. I am happy to help anyone learn the software.

...and what else is cool is I haven't read about any of this anywhere else on the web, DB you just may be the first to have figured out the Imax advantage - after so many decades on the market!

I knew there was a capacitor before this, and even where it was, it was 357 that actually got a measurement of said capacitor, and that made all the difference. I actually tried many other values, and every value I tried at random had a big negative effect. I think I mentioned even the location is important, as if I move it so much as one segment up or down it doesn't work like it does at that point.

Perhaps you might also try downward-sloping 1/2 wave radials in your modeling.

I may put your suggestions on hold just to get the other data out quicker, then add your suggestions in later. I will say that 1/4 wavelength radials should work better than 1/2 wavelength radials, for any number of reasons. You may have to remind me. I'll talk about those reasons when I get to that point if you are curious.


The DB

 

[Needle Bender]

I did some quick modeling...

The DB

It's this model with the in-phase current that has me wondering if that would also be the result of adding 1/2 wave radials.

 

[Marconi]

DB, back when you posted your model of the Imax with the load I noticed the pattern was looking like a collinear model the way I imagined the in-phase currents on the mast possibly working to increase the far-field pattern a little. I didn't say anything because I had been working on my A99 and Imax models to try and make them a bit more accurate using the Free Space Average Gain results to build a real world model that could be converted to FS and maintain a very good Average Gain result.

DB, I think you and I started to talk about this Average Gain idea of mine a short time back, but the idea fizzled out. I think we were discussing Auto Segment differences between Eznec and 4NEC2 instead. I still want to discuss your ideas for the load you have for the Imax however. That looks promising. This was posted here just to relate to your models above at 32' feet and what the pattern looks like my using Eznec and you using 4Nec2.

The attached PDF models below include an overlay for comparison. I can't model the load so I posted two 4 x 6' radial configurations for my I-2K one in the horizontal and the other has slanted radials. These two models with 6' foot radials were compared to my Imax with 4 x 9' foot horizontal radials.

My models here are also at 36' feet not 10 meters like yours. Sorry!

At first, I was puzzled that our patterns were not even close, but as luck would have it...I had a pattern of an A99 sitting on my desk that was mounted at about 28' feet above Earth, so maybe the Imax will show similar somewhere around 30' feet.

I've been busy too trying to get all my old files off of my old Vista machine.

The PDF file also has antenna view and pattern for the three models included in the overlay. I tried to ID the title so one might get a clue of the description. The date is my notice the model as been generated using a Free Space model with a very low Average Gain. I could show more Real World gain using other segmentation schemes, but they generally don't convert to FS too well.

This is what I have been considering for a while now and maybe that is why I posted something in this regard (CMC) in a thread the other day that didn't fit the topic being discussed.

NB, the part of these models of an Imax show me the current on the mast may well add something positive to the antenna. I will be posting other models soon that might also suggest when we need to fix the CMC issues folks talk about.

I will post more soon, showing that if I simply isolate the mast from the Earth at the ground or isolate 4" inches at the top of the mast...these three models isolated (ISO) from the antenna will show little to no currents on the mast, but the gain result is less. Just think about this based...on the ideas that some claim, saying if we stop the CMC on the mast or feed line these wasted currents will add to the currents in the radiating part of the antennas above...or something like that............

I have not proved this, but for now, this is the way I see what we worry about concerning CMC. I would have put all these models together, but the overlay was very busy.

My next effort is to fix my 5/8 wave models as best I can and I think we will see something similar and maybe it is even more profound the effect notices on the antenna systems as a whole. IMO this may possibly answer the old question we hear about non-apparent collinear effects. This idea may get you all happy NB if I can get my point across.

This is why I sent you a note recently which you didn't get at all apparently.

The second PDF 0001 shows to be at 36' feet, but I just used this model and set it close to 30' feet instead. I didn't save the model, but the pattern is for an A99 at 28.5' feet I think.

 

[Marconi]

It's this model with the in-phase current that has me wondering if that would also be the result of adding 1/2 wave radials.

NB, here is what my Imax model shows with 4 - 1/2 wave radials. This sure has a lot of currents flowing on the mast, but according to my idea, it looks to help...if you see what I see.

There use to be a Ham operator here in town that swore he had something similar and he posted on the Internet that it was stronger than a 3 element beam. I went to his house and he had an old Imax with 2 broken radials that were short like the GPK uses...just hanging down with 2 working right.

Do you see a non-apparent collinear look in this pattern with a null between the two 1/2 wavelength elements? IMO this has to consider the system includes the mast as radiating similar to the top 1/2 wave radiator?

Do you think maybe this could possibly describe some of what Cebik told Bob...about being hard to make clear in a discussion on the Internet?

 

[Needle Bender]

DB, back when you posted your model of the Imax with the load I noticed the pattern was looking like a collinear model the way I imagined the in-phase currents on the mast possibly working to increase the far-field pattern a little. I didn't say anything because I had been working on my A99 and Imax models to try and make them a bit more accurate using the Free Space Average Gain results to build a real world model that could be converted to FS and maintain a very good Average Gain result.

DB, I think you and I started to talk about this Average Gain idea of mine a short time back, but the idea fizzled out. I think we were discussing Auto Segment differences between Eznec and 4NEC2 instead. I still want to discuss your ideas for the load you have for the Imax however. That looks promising. This was posted here just to relate to your models above at 32' feet and what the pattern looks like my using Eznec and you using 4Nec2.

The attached PDF models below include an overlay for comparison. I can't model the load so I posted two 4 x 6' radial configurations for my I-2K one in the horizontal and the other has slanted radials. These two models with 6' foot radials were compared to my Imax with 4 x 9' foot horizontal radials.

My models here are also at 36' feet not 10 meters like yours. Sorry!

At first, I was puzzled that our patterns were not even close, but as luck would have it...I had a pattern of an A99 sitting on my desk that was mounted at about 28' feet above Earth, so maybe the Imax will show similar somewhere around 30' feet.

I've been busy too trying to get all my old files off of my old Vista machine.

The PDF file also has antenna view and pattern for the three models included in the overlay. I tried to ID the title so one might get a clue of the description. The date is my notice the model as been generated using a Free Space model with a very low Average Gain. I could show more Real World gain using other segmentation schemes, but they generally don't convert to FS too well.

This is what I have been considering for a while now and maybe that is why I posted something in this regard (CMC) in a thread the other day that didn't fit the topic being discussed.

NB, the part of these models of an Imax show me the current on the mast may well add something positive to the antenna. I will be posting other models soon that might also suggest when we need to fix the CMC issues folks talk about.

I will post more soon, showing that if I simply isolate the mast from the Earth at the ground or isolate 4" inches at the top of the mast...these three models isolated (ISO) from the antenna will show little to no currents on the mast, but the gain result is less. Just think about this based...on the ideas that some claim, saying if we stop the CMC on the mast or feed line these wasted currents will add to the currents in the radiating part of the antennas above...or something like that............

I have not proved this, but for now, this is the way I see what we worry about concerning CMC. I would have put all these models together, but the overlay was very busy.

My next effort is to fix my 5/8 wave models as best I can and I think we will see something similar and maybe it is even more profound the effect notices on the antenna systems as a whole. IMO this may possibly answer the old question we hear about non-apparent collinear effects. This idea may get you all happy NB if I can get my point across.

This is why I sent you a note recently which you didn't get at all apparently.

The second PDF 0001 shows to be at 36' feet, but I just used this model and set it close to 30' feet instead. I didn't save the model, but the pattern is for an A99 at 28.5' feet I think.

Hi Eddie, well we've been hotel hopping & looking for a house in multiple areas and I've had very little time to get online over the last few days, though I try to squeeze in a read off & on for a few minutes here & there.

I also keep forgetting to check above for messages.

Looking at the models you posted left me wondering if your imax model incorporated the 42pf cap near the middle?

...and my curiosity about adding 1/4 or 1/2 wave radials was for an isolated imax, isolated both from the pole & incorporating a cmc coaxial choke at just below the connector, and employing only fairly steep (65°) downward sloping radials, not horizontal radials..

My Imax seemed to come alive when I added the 1/4 wave downward sloping radials.

And your 1/2 wave radials model appears to have about as much inverse current directly above and below the radials as it does in-phase current below that.

 

[Marconi]

Looking at the models you posted left me wondering if your imax model incorporated the 42pf cap near the middle?

No! DB help me a little the other day with adding this capacitor to my model of the Imax, and I made an attempt, but I entered 25pf instead of 42pf. I think I did something to add to the radiator of the Imax model, at least it worked and did not give me an error message. I wasn't sure, because I had no idea what effects I should expect. So, I asked DB what was the differences he saw, if any? I asked, did it make any difference to performance results or gain?

Right now, I'm just waiting for his response.

I'm not sure, but he may have already responded...that he wasn't looking for gain, but that could have been a response to another thread or another issue...I just can't remember.

...and my curiosity about adding 1/4 or 1/2 wave radials was for an isolated imax, isolated both from the pole & incorporating a cmc coaxial choke at just below the connector, and employing only fairly steep (65°) downward sloping radials, not horizontal radials..

I think I remember your telling us that you saw a positive difference using full length 1/4 radials over the shorter Imax GPK 72" radials, but I've been telling you my Eznec models don't tend to show such a result.

Recently you started talking about using 1/2 wave radials and the model above is what I came up with using horizontal and slanted down radials. I keep doing stuff over and over, because when you describe your ideas...they are never comprehensive and when you see the results I post...you claim I got your idea wrong, and then you want me to add one or more additional ideas to the model.

NB, that is alright because I understand, but I can't read your mind, and that is for sure.

My Imax seemed to come alive when I added the 1/4 wave downward sloping radials.

I get an idea of what your mean by "come alive," but in my experience I wake up in a new world every day and I've never seen the difference you described here...just by making a simple modification to a CB vertical antenna.

I've told the story about a man here in my area, an engineer/architect, that wrote an article on his Imax with long 1/2 wave slanted down radials, that showed up on the internet, saying he too saw his Imax "come alive." I'm going to look that old article up and post it here. If I can't find it I'll post his results on blueprint paper which makes viewing difficult.

And your 1/2 wave radials model appears to have about as much inverse current directly above and below the radials as it does in-phase current below that.

NB, I agree with your observations about the currents being mixed. I've heard many explanations for CMC's, mostly bad, but I'm just guessing as to what these currents on the mast might mean.

I'll mention again, in the past I believe Solarcon has explained the currents on the mast of their A99/Imax...suggesting these currents contribute to the excellent RF their EF antennas produce as a 5/8 wave. I ask myself...is that possible? Are all these currents just interfering with TV and other home appliances, and in the boot...messing up the antenna pattern for the real antenna above?

NB, I'm considering this issue, and wondering if there is a way to know for sure aside from just glamming-onto one of the many opinions out there.

Do you know the answer, what does this capacitor object do and can we really tell by modeling this device on the Imax radiator?

I believe that DB knows more about this idea, if he can share it.

 

[Marconi]

NB, here are the images for the modeling idea for the Imax that was published on the Internet from some Ham Magazine years ago.

I made this into six PDF files. I think my printer or the WWDX forum only allows a few pages and this report is over 20 pgs.