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MACO GPRK


NF822WNY said:
Has anyone ever used a Maco ground plane kit on an Antron 1-99? Was there significant improvement. I may be in the market for an antenna upgrade in the spring and looking for different options.

http://www.macoantennas.net/AntennaDetailedPages/GPRK.html
Click to expand...

Ground planes do several things for antennas, however, contrary to what many people will tell you, they do not increase the potential gain for said antenna, at least not noticeably.

If you add a ground plane kit to an antenna and see a change in performance, than what actually happened is you had a problem that was causing common mode currents to form on the mast and/or feed line, and these common mode currents were affecting your antenna negatively. The ground plane kit just minimized said common mode currents, that is all. Adding a ground plane kit is not the only way to resolve this type of issue.


The DB
 
NF822WNY said:
Has anyone ever used a Maco ground plane kit on an Antron 1-99?
Click to expand...

822, my PDF models below for an A99 indicate the points on Common Mode Currents and their possible effects that DB posted. These note that slanted down radials show the minimum CMC currents on the A99 model that I set to specs, using slanted down 72" x 1/8" radials at 55* degrees.

DB notes that radials look to make a difference that is not easily detectable just using your radio, and the currents on these models suggest that to me.

These models were compared to an A99 with slanted down 55* degree radials using the A99 GPK with 72" x 1/8" wire and fiberglass radials set specs.

I also made a model with the radials set horizontally.

Another model was compared using the Maco GPRK with much larger diameter tubing for the horizontal radials. These radials are a little longer at 84" inches as specified in the Maco manual for the GPRK.

I also made a model with no radials and it showed less CMC flowing on the feed line than either of the two models above with horizontal radials. However, I did not include the no radials model in the project.

Note that the red lines are the currents and the maximum magnitude of the currents depends on their distance from the wire as note in the images.
 

Attachments

  • A99 with Maco radials.pdf
    1.4 MB · Views: 14
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The radials don't appear to be working Eddie,
looks like you have less current on the radials than on the mast, is that a worst case scenario mast length 2 wavelengths connected to ground ?

i isolate a99 & imax from the mast add the radials & choke the coax,
just fitting the solarcon radials does little or nothing for most people.
 
bob85 said:
The radials don't appear to be working Eddie,
looks like you have less current on the radials than on the mast, is that a worst case scenario mast length 2 wavelengths connected to ground ?
Click to expand...

Bob, below are the tabular reports of currents in the order of each model posted earlier. The magnitudes for each segment in each wire including the polarity (+- sign) for each is pretty clear...if one is interested in more details.

I also added an image of the Eznec Transmission line setup feature that shows the details I used to describe the Feed Line on the mast wire #6. In this case I used RG-213 characteristics to simulated a 36' length of 50 ohm coax with .66 VF. I did not add the line loss to the models, but the difference is probably pretty small.

DB mentioned other remedies to the problem but did not give any details. I did the same with the models.

822 might or might not get much from these models, so I decided not to get more complicated.

822 gave us a word sketch of his idea and IMO that idea is pretty typical of many A99 installs.

I also didn't wish to over-talk 822's idea. If we find him wishing to see other remedies these models can be expand.

bob85 said:
i isolate a99 & imax from the mast add the radials & choke the coax, just fitting the solarcon radials does little or nothing for most people.
Click to expand...

I think all the comments here thus far agree there will likely be little to detect with or without radials...just using a radio. Bob, I would be interested in the results you note too. If this is helpful, let's see what 822 says.
 

Attachments

  • Transmission Line setup featujre..pdf
    101.9 KB · Views: 4
  • A99 currents report wire by wire segment by segment..pdf
    578.1 KB · Views: 5
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OK Bob, here is the model with slanted down radials. I isolated (ISO) the mast 4" inches and added a choke right below the feed point. This did not eliminate all of the CMC but it minimized them by 75% across the entire feed line. The currents on the radials increased by about 40%. The gain increased from 2.83dbi @ 9* degrees to 3.55dbi at 9* degrees as a result.

I also added the coax loss to the model with slanted down radials and made the feed line 1200" inches long rather than 432" inches for the original model posted.

This shows me that your conclusions were right on point if we add the other solutions that I think DB mentioned.

I set my model over Average Earth. Now we might be seeing some noticeable improvement.
 

Attachments

  • A99wMwFLw55dRwC2cISO36'122017.pdf
    664.7 KB · Views: 4
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Anything that can reduce receiver noise & greatly reduce rfi issues & sometimes give a small increase in signal is worth trying Eddie,

most people don't realize they have mast/coax current issues until they run an amplifier or HF set & its biting their lips turning touch lights off & on or spoiling their audio,

when curing such issues we have seen with our radios small improvement in signals,

maybe if the radials are adjusted for resonance you won't see so much current on the mast/coax when the antenna is not isolated,

its far easier for me to get locals with rfi issues to isolate their a99/imax than it is to get them to experiment with radial adjustments,

so far it has worked every time.
 
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Bob, my models show a little improvement in reducing CMC if I make both the A99 GPK or the Maco GPRK elements longer. The change is minimal, even though it is often said...every little bit helps.

According to my models, isolating (ISO) the mast about 4" inches at the top helps far better at minimizing the magnitude of common model currents on the mast and/or the feed line.
 
Marconi said:
Bob, my models show a little improvement in reducing CMC if I make both the A99 GPK or the Maco GPRK elements longer. The change is minimal, even though it is often said...every little bit helps.

According to my models, isolating (ISO) the mast about 4" inches at the top helps far better at minimizing the magnitude of common model currents on the mast and/or the feed line.
Click to expand...
How are you isolating your antenna from the mast ?
 
Eddie,
having cured multiple peoples rfi issues with that type of antenna i know isolating fork handle style works,

adding the radial kit alone does very little if anything to minimise cmc to a level where its no longer a problem in the shack when you have rfi issues caused by mast/coax lengths causing high cmc,
half the setups we cured already had the radial kit & rfi in the shack.
 

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