Base looking for final advice on 4 verticle base antennas

[bob85]

Not everybody does have a problem they notice, lucky length coax etc,
I know plenty of people that used imax2000 without radials or chokes that never had a problem,
its when you do have a problem that you need to take steps to eliminate it,
1/2waves tend not to be as bad as the longer imax, but i have known a few people with a99's that had bad rfi.

 

[TheBlaster]

I was under the impression that any 5/8 wave antenna with no radials had the potential for CMC on the coax. IMAX 2K magically blocks this phenomena ?

 

[Justme]

No.
An end fed antenna like the Imax 2000 needs an network to bring the high impedance back to 50 Ohm, still needs a counterpoise but like an endfed wire with 1:49 or 1:9 impedance transformer needs just 0.05% of the wavelength used as counterpoise, reason the original Imax 2000 radials are so short.
Also the reason mostly the short mast and coax will work as counterpoise without creating problems.
i use my Imax 2000 from 18 to 29.7 MHz on the ham bands and 11 meter, use 15 feet radials for the lowest frequency and choke at the feedpoint, running 1000 watts in it without having then neighbours with pitchforks for my door nor any RF feedback in the shack.
running 18 meters coax ( similar to LMR 400)to the shack, grounded just outside and another choke in the shack.
Running FT-8 on 18.100 now on it.
Just worked K1DAT with it.( USA)

 

[TheBlaster]

I guess it could also use the pole it is connected to. There really is a split between needs full size ground plane and does not need full size ground plane. I find it confusing as I read opposing opinions from credible people. The guy in the thread who posted the picture of him IMAX2K in the wind if often saying all 5/8 need 9 feet GP.

So a true 5/8 wave with a basic impedance matching coil does need it to be a true 5/8 wave as designed, let's say a MACO or a Interceptor 10K as examples ? And an Imax2K does not because it has a more complex dual coil matching network ?

I see there are 2 parameters... matching for feed impedance which both a coil and radials (and their angle) can influence... and a place for CMC to flow to reduce CMC on coaxial lines. I cannot seem to separate the 2 easily with regards the IMAX2k.

Do mean it only needs 55cms radials for the 50 Ohm match ? or for the CMC to flow on as opposed to on the coax ? It would still be good if Solarcon shipped it with the bare minimum then for its price.

 

[bob85]

They do have the potential, imax is notorious for causing rfi & been noisy on rx,

somebody with an imax out in the yard away from the house probably won't have any issues they notice unless they pick a bad coax length,

when you are sat 3 feet from the mast outside your shack pedaling your ACOM 2000 & everything around you is tripping out & buzzing, touch lights like a disco chopped up clippy audio or no audio,

you turn the amp off its working again sort of, but with 100w your kenwoods compressor won't work,
rfi is clamping it down so hard you still have almost no audio so you have to turn compressor off to talk at all,

your swapping jumpers mics & cables, moving stuff around the shack messing with clamp on ferrites banging another ground rod in & banging your head on the desk thinking chokes & radials & good grounding, that's more than most do so wtf is going,

or your brand new ft101d & acom1500 is buzzing its tits off at anything over 400w,
your imax has the radials and a 5 turns on 4.25" choke,
the mast is just outside your shack window grounded through a fat wire to ground rod,

you order 31 & 61 mix torroids to make proper chokes & string some large clampons along the coax,
still no joy cant use the amplifier for rfi,

that's what imax2000 with radial kit, choke, bolted to a metal mast grounded with a short fat wire to copper ground rods can do, w8ji's unlucky mast length.

The fix in both cases was isolate the imax from the mast with a fork handle & force the current to flow in the radials.

 

[TheBlaster]

I think this is one reason I stuck with GM mainly... I don't have to worry quite as much and it is light for my needs. I know many who use IMAX and the run great stations.. I guess it really is just what has worked, your own finding at the QTH and the practical needs you have vs mounting options/considerations.

 

[Justme]

As said i use the Imax 2000 from 18.1 MHz to 29.7 MHz with 1000 watts in it on the edge of the city in housed area, no problems no rf in the shack no neighbours with any problems as well.

Shit happens, a well thought out set up with all my antenna's makes rf in the shack or anywhere else impossible as it has been running here for 30 years.
The old Imax 2000 withstood 18 years of storms and also worked on the frequencies as the new ( old type) one.

 

[TheBlaster]

Some of the best stations I know run IMAX so they work for sure ! And yes they sure will be more likely hold up in a storm better than a GM.. in this regard they are not as expensive as the first investment suggests. Probably much cheaper in USA as well.

I never read about a snapped IMAX yet.

 

[Justme]

My top section broke off in the last spring storm after 18 years, the glass fiber was delaminated as the resin seems to dry out on it in the sun.
Reason i used 2 coats of polyester paint over the spare Imax now on the roof to prevent it happening again.( old one still new in box but at least 15 years old)
As well on my Diamond x 510N 2/70 antenna.

 

[M0GVZ]

The guy in the thread who posted the picture of him IMAX2K in the wind if often saying all 5/8 need 9 feet GP.

If you're putting them out horizontally and using four of them you'll need to use 1/4 wave length ones, partly to keep the feedpoint impedance and SWR happy.

If you alter the angle then you will need to alter the length and achieve the same because if you don't you may not be able to get a low SWR, the Imax 2000 GPK ones come down at a 45 degree angle which is why they can be a bit shorter.

So a true 5/8 wave with a basic impedance matching coil does need it to be a true 5/8 wave as designed, let's say a MACO or a Interceptor 10K as examples ? And an Imax2K does not because it has a more complex dual coil matching network ?

It's end fed antenna, it needs a RF ground aka radials or counterpoise whether it's a 1/4 wave, 1/2 wave, 5/8 wave 0.64 wave or full wave, the end. If you don't deliberately provide one it'll use whatever it can to compensate so the mast and the coax. If it's centre fed balanced antenna, aka dipole, Gainmaster, yagi etc then it doesn't.

 

[TheBlaster]

Thanks, for the clarification M0GVZ. Sorry to take this off topic for the original poster.

 

[hotrod]

Some of the best stations I know run IMAX so they work for sure ! And yes they sure will be more likely hold up in a storm better than a GM.. in this regard they are not as expensive as the first investment suggests. Probably much cheaper in USA as well.

I never read about a snapped IMAX yet.

mine snapped at the middle section under high winds ..also knmow of 2 others with same issue ..