IMAX 2000 ?

[IDIeselman]

Placed my order today, IMAX 2000 with GP kit and 100' LMR400. This will be going on a 40' tower with length of mast yet to be determined, with that said here is my question. Why does everything I read recommend a 20' mast? Is there some scientific mathematical equasion or is it just a convenient length? I have no problem using 30-35' heavy wall tubing for the mast if there is no reason other than inconvience not to. Some say you must isolate the antenna mounting bracket from the mast as you can not ground a fiberglass antenna while others say bolt it sound to ground AND run a secondary ground wire from the mount to a ground rod at the base (Said to lower SWR's by adding another ground element) What is it men? The truth from those who have actually done it.

Thanks
Tim

 

[mr_fx]

a 20 foot mast is used when you are using the mast as your ground plane... or rather the bottom half of your vertical dipole...

since you are running a GPK, what you need to do is this...

1.) isolate the antenna from the mast
2.) create a choke using 5 turns of coax at 4.25" internal diameter... you can play with this but most people have had great luck with this number

what these 2 things will do is make the antenna have no choice but to use the ground plane radials as your ground plane...

some people have seen the mast and/or the shield of the coax functioning and a poor ground plane... will it work... yes... but there would be little to no benefit to running a ground plane kit if you do not do these things

 

[IDIeselman]

Thank you mr_fx. I will do as you stated. The 35' mast it is. Approx 70' to feed point. I can't wait as I currently am using a 108" whip/mirror mount attached to a piece of flat stock slid between the flashing and metal roof of my garage It works ....kinda.

 

[mr_fx]

Thank you mr_fx. I will do as you stated. The 35' mast it is. Approx 70' to feed point. I can't wait as I currently am using a 108" whip/mirror mount attached to a piece of flat stock slid between the flashing and metal roof of my garage It works ....kinda.

we have all been there and done that

the good thing about the method I told you about is that the mast length is not important... in fact a non conductive mast is a better solution in this case

 

[IDIeselman]

??? Non conductive? I'm guessing here but, you may be saying a 10' piece of schedule 80 PVC used for a mast will yield the same or better results @ 45' than a piece of isolated 35' steel tubing @ 70'?

 

[W5LZ]

That antenna was designed not to need a 'groundplane', so using one isn't required. It will changes the antenna's behavior, so that may or may not be of benefit in any particular situation.
What's with the 20 feet thingy? There are a couple of reasons for that, one being that since the design of the antenna uses the feed line as part of the antenna, it makes for a typical length to make that feed line into a consistent shape. Sort of keeps things working reasonably. Another is that it puts the antenna that far above ground/dirt, which is better than lower. If you can manage more height then do it. More height above dirt very seldom is bad.
If it works as it's supposed to (if you put the thing up half way reasonably) there's no need to change it's design. They do work. If you just want to be 'different', then have at it! It isn't going to make a huge difference either way.
Grounding fiberglass antennas. If they are designed to be grounded where they attach to a support, then I have to think that's the way you should do it. And when you think about it, what's the difference between using a metal support and running a ground wire to ground? The only difference I see is the size of the conductor. And since that 'ground wire' is only a safety ground (not RF), a larger sized conductor would make more sense, wouldn't it?
There are lots of misconceptions about antennas. The 'trick' is figuring out what the purpose of something is, then make it "more better".
- 'Doc

 

[Needle Bender]

Placed my order today, IMAX 2000 with GP kit and 100' LMR400. This will be going on a 40' tower with length of mast yet to be determined, with that said here is my question. Why does everything I read recommend a 20' mast? Is there some scientific mathematical equasion or is it just a convenient length? I have no problem using 30-35' heavy wall tubing for the mast if there is no reason other than inconvience not to. Some say you must isolate the antenna mounting bracket from the mast as you can not ground a fiberglass antenna while others say bolt it sound to ground AND run a secondary ground wire from the mount to a ground rod at the base (Said to lower SWR's by adding another ground element) What is it men? The truth from those who have actually done it.

Thanks
Tim

if you want performance and an antenna that will last i dont understand why you didn't get a penetrater if you spent that much money, dont mind radials, have the real estate and arent under cc and rs.
its not to late.
maybe you go camping alot and could keep the imax in the motorhome?

 

[IDIeselman]

Honestly I never considered the penetrater, I wanted something simple and reliable. The reviews I read seem to favor the IMAX as a good entry level antenna at a fair price so I bought one. I just want to be shure and pull all the available performance I can from the antenna I bought. With the arrival of spring I may have to buy a penetrater and see just what all the fuss is about.

 

[Needle Bender]

With the arrival of spring I may have to buy a penetrater and see just what all the fuss is about.

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

 

[wavrider]

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

1 S unit seems a little far stretched, not saying you are not seeing an S unit difference, .625 is .625 no matter if it is a radome fishing pole (imax2000) or aluminum.

I agree the Imax does seem more noisy than a metal antenna, I use the Imax2000 on 10/11/12/15 meters works well for the price.

I do not think either antenna will have much more gain than the other, talking about .1DBD difference maybe. Hard to measure that on an S meter.

 

[W5LZ]

The 'key' to that statement is in the last four words, "depending on your instalation". That covers a lot of 'not right' thingys and is true of a lot of different antennas. In general, I really doubt if there will be that much difference between any two antennas of the same type/size. If there is, it's a safe bet that something ain't right. Right??
- 'Doc

 

[Needle Bender]

1 S unit seems a little far stretched, not saying you are not seeing an S unit difference, .625 is .625 no matter if it is a radome fishing pole (imax2000) or aluminum.

I agree the Imax does seem more noisy than a metal antenna, I use the Imax2000 on 10/11/12/15 meters works well for the price.

I do not think either antenna will have much more gain than the other, talking about .1DBD difference maybe. Hard to measure that on an S meter.

thats just what ive seen in a couple local instalations. both guys improved by about 1 s unit using there same old coax and mast. one had high swr when it rained and thought the imax was leaking water inside when it rained, the other didnt want the fiberglass noise and bought a used penetrater from craigslist. there receive also came up about an s unit.
i think part of it is the less efficent match and some probably comes from the different toa from not having radials. theres probably less difference when radials are added to the imax
i saw 1 1/2 s units improvement over my imax with guy wire radials when i went to the gainmaster and alot less noisy. the ears came way up for weak stations i used to not hear at all except every now and then because of the noise

 

[wavrider]

Agreed, different antennas have different characteristics, always nice to have a few that can be switched between.

I really enjoyed Marconi's antenna comparisons, although not the "scientific method" but it is a real world method and his test results speak for themselves.

What it comes down to is whatever antenna works best in the location you are working from.

There has been times when the Lazy H has outperformed the Imax2000 here at my QTH, on both TX and RX.

The Lazy H is lower on receive gain, but it is also lower on ground noise thus I can hear the weak ones where on that noisy Imax I can not hear the weak ones due to higher ground noise/static.

 

[Needle Bender]

Agreed, different antennas have different characteristics, always nice to have a few that can be switched between.

I really enjoyed Marconi's antenna comparisons, although not the "scientific method" but it is a real world method and his test results speak for themselves.

What it comes down to is whatever antenna works best in the location you are working from.

There has been times when the Lazy H has outperformed the Imax2000 here at my QTH, on both TX and RX.

The Lazy H is lower on receive gain, but it is also lower on ground noise thus I can hear the weak ones where on that noisy Imax I can not hear the weak ones due to higher ground noise/static.

these were both real odd instalations. slightly hilly ground but mostly flat, varying about 50 feet up or down for 5 to 15 miles, no immediate mountains nearby, all between 50 feet and 150 feet above sea level, 2 - 3 section mast above the roof. a real chalenging and difficult instalation. im sure these were the exceptions to the rule that all antennas perform nearly the same

 

[IDIeselman]

Thanks again guys! It has been done. Imax 2000/GP kit, 56' to feedpoint, 20' 1" heavy wall mast covered with electrical tape from tip to tower, I then took a 12" piece of 1.25 PVC and halved it length wise and clamped it onto the mast over the electrical tape using the supplied clamps that also mount the antenna, made and installed the infamous five wrap ugly balum choke on an 8" piece of PVC ( rough draft pictured, was revised for aesthetics) don't know if I did the correct thing with the 8" choke but I have read anything smaller the coax core will migrate??? Now to go borrow the Connex Saturn from work and try this new antenna.