IMAX 2000 ?

[Needle Bender]

Don't KEEP us in suspense!

 

[airplane1]

Yea, don't!

 

[IDIeselman]

AHHHHHHH! It is safe to say I am not impressed. I was talking just as good with the rg8x and 102 whip thrown up on my roof. Was I led astray with isolating the antenna theory? Everything checks out good but twenty miles is about it for range. This sucks!!

 

[Klondike Mike]

I'm sure it looks mighty fine. I just spoke with a station 145 miles from my location here and my IMAX is at only 12ft. I think the -25 degree temperature had something to do with it. Maybe some backscatter?

 

[Robb]

AHHHHHHH! It is safe to say I am not impressed. I was talking just as good with the rg8x and 102 whip thrown up on my roof. Was I led astray with isolating the antenna theory? Everything checks out good but twenty miles is about it for range. This sucks!!

I wouldn't blame the antenna. That Imax has more that twice the capture area than a 1/4 wave whip does. Lower angle of TX radiation too. Cool stuff to work with.

If you have the ground plane kit on the Imax 2000, have an ugly balun/choke coil, and have the antenna up ~50 ft, I would say that you have done very well. An antenna doesn't make conditions happen; it just maximizes your best receive and transmit when conditions are present. Any 5/8 wave antenna is the best vertical antenna to have and use - IMO.

I didn't isolate mine and I use dacron guy rope. Not guy wire. My antenna is only up 30 ft, and I've talked 8k miles several times with it to Australia, New Zealand, South America, and Europe. As well as talking up to 100+ mi locally. Either you did something wrong or have prematurely misjudged it. One or the other - IMO . . .

 

[IDIeselman]

Klondike Mike, I'm guessing here but, yours is grounded like it is supposed to be. I have been up and down my 40' tower for the last 3 hours while blowing in the wind and hanging on with one hand trying to figure out just what is wrong with this thing. I'm happy I am home alone so no one can see my tears.

Thanks Robb, I will hold off on tearing it down untill tomorrow. I was all excited to really start talking and when a local operator I always talk to told me I was doing just as good with the 102" I about had an episode. I think the isolation thing may not have been a good idea.

 

[Marconi]

basicaly less noise, less power compression and about 1 s unit better performance depending on your instalation

Hey NB, what does power compression mean concerning this antenna? Is this something like JoGunn's idea of audio gain?

I haven't posted on this thread, because I wanted to first see where all this concern for the absolute best installation was going. I see it's not going so good.

IDI, if you based your lack of sucess on this one gubber you talked to on the air, maybe you won't see much difference in his particular case, maybe he lied, or maybe he was mistaken. How much difference did you expect? One report is not a good trial.

We hear all kinds of CB BS on the Internet and on the air, but seriously does anybody believe that a typical and simple install for a A99/Imax, without radials, won't work just as intended? Of course baring a bad antenna or installation or some other monkey type install.

I don't get trying to out-guess the typical installation instruction with all of these, do this and do that suggestions, trying to get the max performance out of your antenna. IMO, you need to get it up and working right in the first place, and then do you modes...one at a time and keep good notes. At the very least the way you did it, YOU WON'T HAVE ANY THING TO COMPARE THE CHANGES TOO.

Looks like this one had all the bells and whistles done to the install and now it don't seem to work up to par. Maybe it's time do an install backward and use the process of elimination in reverse just because we can.

IDI, if it was me, I'd hook the Imax up on a 10'-20' foot pole and try it out first. Considering your other working antenna, the Imax should do just as well or better at this height, and then you won't have to be scramblin' up a down your tower doin' or undoin' all these alterations.

No body could know what affect they have in your case, and you seem to have tried everything at once, and failed.

 

[IDIeselman]

Thank you Marconi. Back to the drawing board:sad:.

 

[Needle Bender]

Klondike Mike, I'm guessing here but, yours is grounded like it is supposed to be. I have been up and down my 40' tower for the last 3 hours while blowing in the wind and hanging on with one hand trying to figure out just what is wrong with this thing. I'm happy I am home alone so no one can see my tears.

Thanks Robb, I will hold off on tearing it down untill tomorrow. I was all excited to really start talking and when a local operator I always talk to told me I was doing just as good with the 102" I about had an episode. I think the isolation thing may not have been a good idea.

Well, the first thing I see is there's not enough counterpoise. A 6' ground radial isn't a full 1/4 wave and a 5/8 likes to have a full 1/4 wave counterpoise.
If you can replace the 6' radials with 102" or tie several 9' wires to the top of the Imax mounting plate, then bring them down to an insulator & non-metallic line to make as wide a ground plane as possible, you may find it might work better.
Even if you can just add one 102" whip in place of the 6' pointing in the direction of someone with a good meter, you might see improvement.

Hey NB, what does power compression mean concerning this antenna? Is this something like JoGunn's idea of audio gain?

Power compression? well, antennas, like speakers which use voice coils and lose efficiency with the heat caused by high power, the Imax uses an inductive matching network with a relatively small coil.
As the input power goes up the coil heats up and wastes an increasingly greater amount of power in heat, making the antenna radiate less efficiently than one which passes all the power through the matching network without heating.

 

[airplane1]

I had a a99 and imax with no ground plane kits and they seem to work great. I have the tower leg grounded but that is it. I would mount it like Marconi said on a pole 10 - 20 ft high to make it easy to change things and start from scratch like just the stock imax and go from there.

AP

 

[hotrod]

I had a a99 and imax with no ground plane kits and they seem to work great. I have the tower leg grounded but that is it. I would mount it like Marconi said on a pole 10 - 20 ft high to make it easy to change things and start from scratch like just the stock imax and go from there.

AP

i agree with all this. and just add to it id try different location if ya can
even just 6-10 feet may make a difference.also id NEVER wrap lmr 400 coax unless
you got the flex version which is stranded on the inside and not solid.but thats just me.
really cant see anything wrong with what ya did. i would check the swr on cb band
should be under 1.5.1

 

[Klondike Mike]

Klondike Mike, I'm guessing here but, yours is grounded like it is supposed to be.

Redneck install here. Was suppose to be temporary until I'm able to setup the tower laying in my garage. My IMAX is connected to a 4ft mast which is then bolted to 1 (8ft.) section of my tower which is sitting on top of some sidewalk blocks. No grounding anywhere, no radials. Using 50ft. of RG8x with a sloppy ugly balun at the base. Your situation makes me wonder about what will happen when I finally get around to setting up my tower. See map below for my DX contacts;

 

[Marconi]

Well, the first thing I see is there's not enough counterpoise. A 6' ground radial isn't a full 1/4 wave and a 5/8 likes to have a full 1/4 wave counterpoise.
If you can replace the 6' radials with 102" or tie several 9' wires to the top of the Imax mounting plate, then bring them down to an insulator & non-metallic line to make as wide a ground plane as possible, you may find it might work better.
Even if you can just add one 102" whip in place of the 6' pointing in the direction of someone with a good meter, you might see improvement.



Power compression? well, antennas, like speakers which use voice coils and lose efficiency with the heat caused by high power, the Imax uses an inductive matching network with a relatively small coil.
As the input power goes up the coil heats up and wastes an increasingly greater amount of power in heat, making the antenna radiate less efficiently than one which passes all the power through the matching network without heating.

NB'r, does that mean that my Starduster, which uses no matching network, is more efficient than any of these antennas with a matching network? Maybe that is why my SD'rs works so well.

A while back I think it was Dave or Oggy in the UK, that posted something about his Shakespeare 5/8 wave with a 8 element radial hub attached and the radials were short like maybe 36" inches.

This is just from memory, but due to the discussion I recall about short radials vs. 1/4 wave radials, I did a model using 36", 72", 102" radials on a 5/8 wave radiator and I think I found the shorter radials worked better than the longer ones. I can't remember the file name or the title I used for the project, and I don't remember if I posted it or not. I also don't know if I had a clue as to why the gain and angle showed to be better with shorter radials either. I also don't know if slanted radials vs. horizontal makes much difference too.

I think maybe you and I might have also discussed the setup inside of the SP antenna as well.

If I can find the file for the model or the paper work, I'll check it out and post it, whether my recall is right or not.

Based on my personal experience with my I-10K, I found shortening the radials not to be a good idea however, but I did not try and re-tune the antenna either. Thus in that case, the I-10K seemed to work best with the full length radials, maybe 103" at 27.205 mhz and I guess on that point you are correct.

However, I think that IDIeselman is working with an Imax in this thread, so I would consider that when giving advice.

I can't explain why these two would be different in this regard, unless the difference in matching, with the Imax using a capacitor to help fix the reactance, is possibly the reason.

Personally I don't think any of the issues discussed so far accounts for the reason that IDIeselman is having problems.

 

[BOOTY MONSTER]

is the angle of the ground elements the same on the m-400 as the they were on the star duster ?
it was pointed out to me in a thread on quack shack that there is a optimum angle of the ground radials on the star duster with the mast going up the center that allowed it to get its peak performance .

http://thequackshack.com/index.php?/topic/29865-why-would-a-ham-say-this/page__fromsearch__1

link to starduster patent .

Patent US4208662 - Omnidirectional, vertically polarized antenna - Google Patents


i wonder if using the same length and angle with the mast in the middle would benefit a 1/2 wave or 5/8 , .64 ?

 

[IDIeselman]

Klondike, could you resize your pic? That thing's a monster.

IDI, if you based your lack of sucess on this one gubber you talked to on the air, maybe you won't see much difference in his particular case, maybe he lied, or maybe he was mistaken. How much difference did you expect? One report is not a good trial.

Marconi you are correct, I was up till 3:30 this morning talking with five other operators all between 8 and 30 miles with good reports but, at 30 miles with a new Connex saturn CX-33SSB I was dropping off pretty bad. The first man I was talking with was having trouble hearing or talking to any of us so as it turns out, his equipment may have been the problem I will go ahead and take it back down and start over as you recommend. I may be expecting too much but do believe something is not 100% and that alone drives me crazy.