Is the Solarcon Max2000 5/8th di-pole like ?

[bob85]

DB,

From what I understand currents inside the coax are ALWAYS equal magnitude and opposite phase,
with that in mind I don't understand your unbalance coax scenario,

are you saying that currents inside coax are unbalanced an that's what causes the antenna to be unbalanced?

that you can have more current flowing out of the coax center conductor than current returning via everything connected to the return side of the feedpoint?

 

[Marconi]

you are redirecting return currents but not to the radiator increasing gain, any improvement in signal is imho due to not allowing currents that spoil the pattern to radiate on the mast or coax forcing return current to flow on something that won't spoil the pattern like horizontal radials or beneficial in the case of a stardusters drooping radials.

Bob, my use of the word radiator was a bad choice of words. In my comments about CBr's claiming CMC issues needing to be fixed, maybe I used a bad word, gain, there too. That said however, I think a lot of folks think a CMC fix will improve the gain or at the very least the effectiveness of their vertical monopole antenna.

I think your description that CMC's on the mast/coax can ill-effect the antenna pattern is a better description.

Just as a note to try and demonstrate how much difference a CMC issue might make to your antenna, I looked up the word Common Mode Currents in the index of my 17th and 19th editions of the ARRL Antenna Handbook. The 17th index did not list the word. The ARRL did talk about the subject in the 19th edition however, but the primary reference there was considering beam antennas, and a horizontal center fed dipole. Below is an PDF file image of the dipole, one with and one without CMC issues.

So, I guess my question for the folks looking in remains...how much difference does the CMC issue make on your antenna, considering what we see the dipole in the ARRL...showing us is very little difference.

I'm doing some Eznec modeling of an unmatched Imax at 32' feet to see how different configurations of that antenna might predict changes in CMC's, pattern, gain and angle as well. I expect it to be a lot worse with the match and mast currents than the horizontal CFHW shows below...but I'm not to sure we will see any big differences in the patterns that will seem to render the antenna noticeably deficient in the gain or angle.

 

[RadioDaze2.0]

The responses here are deeply technical so I will make no commentary, I can only go so far with my existing knowledge.

What I can add operationally is that I saw no difference in SWR reading on my IMAX2000 (no groundplanes anbd no choeks of any kind direct coaxial attachment) - VSWR 1.4:1 at 15 feet high and a then at 30 feet high identical. I managed to get my IMAX to 30 feet with great results. 150 mile long contacts to another hill top station in UK and a DX into Angola (my first to Angola Africa) I also spoke to someone in Holland which is exceptionally rare from the UK (I spoke to Australia more times than in Holland) as it sits approx 250 miles away which means for F2 layer DX it is in a "dead zone" because typically there can be no F2 layer reflections. So I believe this was a tropospheric enhancement/ducting.

The SWR did not change with exactly the same coax used and same equipment set up. So earth did not effect the feed impedance in my case.

 

[Marconi]

I'm doing some Eznec modeling of an unmatched Imax at 32' feet to see how different configurations of that antenna might predict changes in CMC's, pattern, gain, and angle as well. I expect it to be a lot worse with the match and mast currents than the horizontal CFHW shows below...but I'm not to sure we will see any big differences in the patterns that will seem to render the antenna noticeably deficient in the gain, angle, or effectiveness.

The indications of CMC and magnitude is indicated by the presence or absence of the red lines noted on the mast/coax. I did not model the feed line.

Models show the antenna view, pattern, and match. For comparison I added an overlay of the antenna patterns listed below.
1. Imax with no radials isolated (ISO) from the mast.
2. Imax with no radials attached to the mast.
3. Imax with 4x6' Horizontal radials.
4. Imax with 4x9' Horizontal radials.

Needle Bender, I also have a model I will post showing this Imax with 67* degree slanted down radial idea you presented.

 

[loosecannon]

ok guys, i've been reading through this thread as i was given an IMAX2000 and will be putting it up in about three months or so.

The discussion here is great, and very technical, but because the thread has gone on so long, im finding it difficult to determine what the optimum set up will be based on all you guys' findings.

my plan so far is to have it isolated from the mast (or just use fiberglass mast with nylon guy ropes), bend the nubs on the ground plane kit up to about 30*, and use a bunch of ferrite on the coax at the feedpoint.

have i missed anything with this setup?

im not trying to get into the debates, as the people in them are the people i learn from. LOL
just looking for a consensus of the best setup with this antenna.
LC

 

[Marconi]

Needle Bender here is a model of my Imax with slanted down radials at 67* degrees.

 

[Marconi]

just looking for a consensus of the best setup with this antenna.

LC, the thread has become a bit technical and some is over my head too.

Don't be confused by the models I presented. I was not trying to demonstrate what the best Imax setup might look like.

If it was me, I would experiment with some different ideas like isolation, a choke, or add a GPK...and see if I could tell any differences. You don't have to test up high.

Personally, I would put it up as high as I could...just like it comes in the box. Aside from a bad antenna, we know they work. I don't think there is much we can do to the Imax that makes much difference to the performance that we can easily tell just using our radio.

 

[loosecannon]

thanks for the reply Marconi.

I was thinking the same thing about not being able to really quantify the changes, which is why i was hoping to just be somewhat of a consumer in this, and let you guys figure out what works best. LOL

im not really looking to do much experimenting with this install, and whatever configuration i end up using, i will probably just put it up and leave it there until i or the wind takes it down.

One thing i can say for sure is that it will be going on a fiberglass pole.
LC

 

[Marconi]

Loosecannon, be sure and keep us posted on how your install works out.

How and what are you going to compare it too?

 

[loosecannon]

see that's just thing thing Marconi, i won't really be able to do any comparisons, as i will be moving to another part of the same town when i put the IMAX up.

as you well know, im a big astroplane proponent, and have had mine up for years now.
(currently at about 36 feet to the top tip of the antenna)

works well for me, but i haven't been doing any note taking or experimenting with it, just using it.

That's why it's great to have you guys out there doing the modeling, testing, comparing, and experimenting.
so i can just play Joe CBer, and heed your best educated guesses.

my install will be the IMAX on a fiberglass pole, around 36-40 feet in the air to the base of the antenna. (guy ropes of course)
then coax running down to a lightning arrestor mounted to a ground rod.

i figure this way, if i get a strike, everything will just burn up instead of frying the electronics in the house. (well hopefully anyway)

don't mean to hijack this thread with my install, so please, no one feel the need to respond to this.

thanks to everyone for all the work.
LC

 

[RadioDaze2.0]

One small practical tip with the MAX2000

May I suggest cleaning the brass thread inserts with isopropyl alcohol, I simply put some iso on a tissue and fed it in and waggled it about and it got lots of dark dirt out. I managed to get a lot of grime out of mine, virtually factory fresh. Those threads seem to have quite a bit of machine grime left in them and I think this is good for electrical contact.

I do not think it will be the difference between a working and non working antenna but low resistance and clean electrical contact has to be a good thing.

The threads now glide on as well, very smooth screw action.

Nice plots Marconi will absorb them.. seems like no radials fairs quite well. Interesting how the higher angle radiation pattern changes with and without mast isolation. (I assume ISO means mast isolated?) This was close to how I was operating a few days ago with mast about 28-30 feet 10M exactly of RG-213U coax, no radials and no isolation. It suggests there could have been CMC on mast/coax but I experienced no negative effects in operation. It makes you wonder if the CMC is actually adding something to this antenna design. I have read that lobes at high angles can increase RX noise.

This article from copper electronics is oddly enough seemingly the reverse of your plots, the caveat being they are models at only 1/2 wave above ground not 1 Lambda like your models. (60 degree nulls with the GPK installed, they are old plots though) when it comes to RX/TX of the higher angle lobes which this guy says that sky wave noise could be reduced with the standard Solarcon GPK. Suggesting and to quote: "an Imax 2000 with the GPK installed will likely experience the 'noise floor' reduced by as much as 12 dB. "

http://www.copperelectronics.com/discus4/messages/7750/20506.html?1023340740

I was very happy with the results using the IMAX and at the moment the differences between the Max2000 and the Gain Master appear very difficult to feel in operation at least on line of sight contacts. Maybe the GM might have a tiny extra bit of poke right down at the horizon but it is rather impossible to know this. I have to go on gut operational feeling rather than scientific measurements. They both work for me. Both good antennas without the complication of cumbersome ground plane radials which is advantageous for static mobile temporary installs.

 

[Marconi]

as you well know, im a big astroplane proponent, and have had mine up for years now.
(currently at about 36 feet to the top tip of the antenna)

LC, I didn't remember you being an AstroPlane fan. I have a Sirio New Top One up about 20' feet, but I don't work my radio much anymore.

Nice plots Marconi will absorb them.. seems like no radials fairs quite well. Interesting how the higher angle radiation pattern changes with and without mast isolation.

RD, don't get excited about the two no radial Imax antennas showing the maximum gain for the group. Both models show a very high (>100:1 SWR) mismatch, and I suspect that tends to make the gain show a bit higher. I don't think it really matters however, because the difference is very small for the low angle working area lobe for all these models. This was the point I was trying to make above regarding CMC's on the mast/coax of an Imax.

Most of the time such modeling advantages, shown in the gain performance, tends to go away as I improve a model that produces a better match and requires less impedance transformation at the feed point.

Again we see here that theory often predicts small differences that seem to get blown-up in the CB world. It's just a guess though. If I knew how to use the matching feature using Eznec...then maybe I could prove some of these ideas.

The main thing I got from this series of models seems to be...that various levels of CMC on the mast/coax seem to make little difference in the maximum low angle lobe...where we generally hope to make our contacts.

It makes you wonder if the CMC is actually adding something to this antenna design.

I can't tell if CMC's are helping the antenna. Excepting maybe for noise, CMC's don't seem to make a difference in my real world experience with vertical monoples. I think I have experienced the effects of CMC's on my horizontal beam however...making it noisy.

I have read that lobes at high andgles can increase noise.

That could be true RD, but I've also heard most noise we hear on our RXr's is man made, and that is generally at or near the ground.

This article from copper electronics is oddly enough seemingly the reverse of your plots when it comes to RX/RX of the higher angle lobes which this guy says that sky wave noise could be reduced with the standard Solarcon GPK. Suggesting and to quote: "an Imax 2000 with the GPK installed will likely experience the 'noise floor' reduced by as much as 12 dB. "

I tend to take 833 posts with a grain of salt.

Since the Imax GPK has the radials slanted down...my model for Needle Bender above also predicts the maximum TO angle is raised up higher at the expense of the low angle lobe...preferred for radio communications. IMO, this is a big difference that I unexpectedly found with my Imax models. I admit however, that I could be wrong. I don't hear many reports about the Imax and using the GPK...but that would be interesting if guys would come forward and report. I will do a search here on the forum and maybe get back...if I find anything.

Thanks for the questions guys.

 

[Heavy Metal]

Based on bottom 5T RG58 4.25" air coil, was coming over speakers ect, then did this to my imax2000 and now nothing it's about 18-21 inches below the base connection. Using RG8X.

 

[Marconi]

HM, other than the choke helping solve your interference issue with your speakers...can you tell if there is any advantage in how your Imax performs?

What is the tube looking object a few inches to the side of the mast?

 

[Marconi]

Seriously? Ok, how about this one, a 5/8 wavelegnth, with no radials, and a single 1/4 wavelength section below the antenna simulating putting a choke 1/4 wavelength down the coax from the antenna. The mast is isolated...

The top half wavelength is a given phase. The remaining part of the 5/8 wavelength element is out of phase, as expected. As you pass the feed point onto the lower element, the phase does not change, thus the area immediately below the feed point on a vertical 5/8 wavelength antenna, will always be out of phase with the upper part of the antenna no matter how long that feed line/mast are. The best you can do is to manipulate the length of said wire to put a phase change right next to the feed point of the antenna.

The DB

DB, I took a shot at duplicating your model using Eznec, and I think I got close. I made one just like your model with without a mast to the ground. I also added an ISO mast to the ground for the other. They both seem about the same.

I also added an X in the antenna view where my wires are ISO, not connected.

Your isolation (ISO) fix does look to minimize the CMC's on the mast of your model better than my "Imax no radial 32' mast ISO" model.

But, in my PDF file below you will see that my model does not raise the maximum TOA up high...like my version of your model does. See the pattern overlay I added for comparison.

In these models, I also can't blame the differences in the patterns we see due to the very high SWR mismatches in my Imax models. These three models all show nearly the same mismatch.