isolation from mast..

[Splash1]

ya er nay ? getting a new coax with a choke balun..its a imax 2000 with gpk..should i isolate the antenna from the metal pole er leave it metal to metal ? i,ll be running a seperate ground wire down from the antenna to ground rod at the base of the mast .

 

[mackmobile43]

ya er nay ? getting a new coax with a choke balun..its a imax 2000 with gpk..should i isolate the antenna from the metal pole er leave it metal to metal ? i,ll be running a seperate ground wire down from the antenna to ground rod at the base of the mast .

You could always just use the coax shield for grounding purposes instead of making another connection.

 

[Robb]

I thought this thread was going to discuss the 'virtues' of isolating IMAX 2000's and A99's from their metal masting in order to attain 'antenna nirvana' (lol) and a lower SWR and better propagation.

Or is the ground plane kit absolutely necessary? Can one use a tuned length guy wire with insulators to attain the same thing at a fraction of the cost? Me thinks so; and I going to experiment thid idea within the next few weeks.

 

[Marconi]

ya er nay ? getting a new coax with a choke balun..its a imax 2000 with gpk..should i isolate the antenna from the metal pole er leave it metal to metal ? i,ll be running a seperate ground wire down from the antenna to ground rod at the base of the mast .

If you do that Splash, you just be defeating the purpose. To isolate and then bypass the isolation makes no sense if the modification works.

Maybe you are trying to help prevent damages due to lightning. It is a problem to consider, but you are just defeating the purpose of the modification. Either way the coax is still vulnerable to lightning and you cannot get around that. Running the coax under-ground and making a coil at some point underground will help some maybe. There are other methods to consider also.

In this three prong antenna idea you're talking about, isolating is only a part of the solution you seek. The balun you are getting is another part, as is adding the GPK. Will just one idea work, will two work or does it take all three. Some have noticed gains just by isolating the GPK from the Earth.

I believe adding the balun with the other two mods makes the best sense, because of the way currents act in this case.

Good luck

 

[Marconi]

I thought this thread was going to discuss the 'virtues' of isolating IMAX 2000's and A99's from their metal masting in order to attain 'antenna nirvana' (lol) and a lower SWR and better propagation.

Or is the ground plane kit absolutely necessary? Can one use a tuned length guy wire with insulators to attain the same thing at a fraction of the cost? Me thinks so; and I going to experiment thid idea within the next few weeks.

Rob, the Imax is noted to have a very low SWR already. I don't think the idea of slanting radials down works exactly like you think---in lowering the SWR on a 1/2 or 5/8 wave antenna. The idea is commonly used with tunning 1/4 wave radiators, but I believe is just more or less talk with the longer antennas with the way they work. Reason is: the 1/4 wave is current fed and has a lot of current flowing near the feed point. The longer verticals mentioned are voltage fed and have very little current flowing in the area of the feed point and ground plane.

Your idea to use a tuned length of guy wires will work if you postion them in such a way as to get current to flow in them.

The principal with the idea of slanting down radials is basically a tuning procedure in a 1/4 wave radiator as noted above. The idea probably has little added effect when an antenna like the Imax or the A99---is already well tuned using the matching device included with the antenna.

 

[dudmuck]

Or is the ground plane kit absolutely necessary? Can one use a tuned length guy wire with insulators to attain the same thing at a fraction of the cost? Me thinks so; and I going to experiment thid idea within the next few weeks.

Ground-plane kit is not necessary.

It becomes an issue if youre running BigWatts and having TVI issues with the neighboors.
Without the GPK, the feeding coax tries to become the ground-plane. Also any other metal too, such as the mast and guy wires. This is why for TVI, its best to use the GPK, and have guy wires with those egg insulators.

The GPK is said to slightly lower the angle of radiation of the antenna, and can also narrow the bandwith a bit, which means more gain on 11m. Probably the optimal length of ground radials is 1/4 wavelength.

Using guy wires as ground radials might seem a money saver at first. But i doubt the metal used on those wires can stand up to the weather and maintain conductivity. can you solder to it? doubt so.

 

[freecell]

neither the antron 99 or the imax 2000 is voltage fed and a radial system is necessary for proper operation of both of them.

 

[Splash1]

freecell..do you mean by'' radial system''on the ground or ground plane radials right under the antenna feed point .

 

[Marconi]

neither the antron 99 or the imax 2000 is voltage fed and a radial system is necessary for proper operation of both of them.

Considering I have not tried this three-prong (Isolation) approach, which includes isolation of an end fed 1/2 wave, I might agree with freecell, in part of his claim above, that both the Imax and A99 can benefit from the use of a radial system.

However, I would argue with freecell the idea that an Imax or A99 are not voltage fed. My thoughts are based on the idea presented as an introduction in the following article: The End Fed Half Wavelength Antenna - AA5TB. Maybe there is a more technical explanation for this, but if AA5TB is wrong then I'm wrong. I'm sure freecell will tell us the technical error of all this and if I can understand it, maybe I too will learn something new today.

 

[dudmuck]

"The A99 is a half wave over a quarter wave, variable mutual inductance tuned antenna".

The Imax 2000 EXPOSED!

An antenna which connects to 50 ohm coax, must present somewhere around 50 ohms impedance to be useful.
The end-fed half wavelength is not the same thing as a99/imax2000.

 

[freecell]

"freecell..do you mean by'' radial system''on the ground or ground plane radials right under the antenna feed point ."

you know someone who's installing these antennas at ground level?

 

[Splash1]

no,,i mean the radial system placed directly on the ground..several wire 36 foot radials laid flat on the ground like the spokes of a wagon wheel and connected directly to the ground rod at the base of the mast .

 

[W5LZ]

Oh boy! The .625 versus .640 wave length thingy again. What fun! Also a totally contrived debate with no practical difference in performance. Using the cited information, if you think .04, or .08 dB difference in gain is going to be even noticeable, I'm afraid you will be very disappointed.
That 'extra' length, six inches maybe, is effectively negated by the capacitive feed system. Adding capacitive reactance, as done with the Imaxx, effectively 'shortens' a 'too long' antenna, making that .640 wave length thingy effectively a .625 wave length thingy. Why do it that way? Because it works, for one thing. It also means it isn't going to be a patent infringement of the 'A99', which is good for the manufacturer. Why call it a '.640' wave length antenna instead of a '.625' wave length antenna? Cuz it's touting physical aspect, not an electrical one, and it's 'new', it's 'better', and dices/slices and makes 'julian' fries!
Ol'Billy Shakespeare had it right, "Much ado about nothing". But it sells antennas, don't it?
- 'Doc

 

[Marconi]

'Doc would you post the link to the A99 patent? I would like to read it.

 

[Robb]

I bought the IMAX 200 for a couple of reasons. First, so many people in my area use them. I mean at least 80% of the guys I usually talk with have the A99 and myself and another guy have the IMAX. People from other areas thirty miles away remark at how loud we all sound. The proof is in the pudding; and it's pretty good pudding. Only one of the guys in our 'Roy Show' (Central coast of CA - South Bay Area) has a ground plane kit on an A99; the rest don't. Including myself.

Most of us have them up 30-40 ft from the ground to the feedpoint; so it's fairly consistant results too. I was very skeptical about this antenna before I bought it, as I thought it was no more than snake oil. Couple of the guys have linears and talk skip without any probems with them; no more than ~350 watts. All the guys in my local talk show admire the IMAX. But all of these antennas really do perform outstandingly and are well worth the money. Remember - I was V E R Y skeptical about it at first; but I must say that my skepticism has given way to acceptance - they really are the shizzle!