End-fed Vertical and J-pole That quoted gain is for the horizontal dipole Look at the polar graph under the text. Interesting study well worth the read, a lot of work done on cmc and the effect it can have on patterns ."Potentially severe common-mode feedline problems of end-fed 1/2 wave antennas vary with feedline length and feedline routing. This is why some people swear by end-fed antennas, while other people swear at end-fed antennas." Interesting imax 2000 model with cmc showing -2 dbd gain
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Solarcon A99 Experimental Results and Analysis of Ground Plane Radials
- Thread starter kaosfm
- Start date
kaosfm Well done with the practical work and the real world testing.Should be more of it.I don't doubt your results.I'm just not sure why you saw such a dramatic difference, my guess would be reduced cmc producing a lower angle of radiation.Again w8ji shows this with his models also.With the exception of the Siro gainmaster I always fit radials to my end fed verticals.
Anyone think of putting up the a99's GPk ring and putting 102" SS whips in it would this be doing the same thing you did with the wires
I know I talk to shockwave about this along time ago and he told me that no current actually flows through that ring so therefore the groundplane radial kit that Solarcon sells doesn't work at all
If what you assume is true then how do you explain the radiation from the part of the antenna that is connected to the shielding of the coax when no balun is used?
The DB
+1; IF (and that's a big "IF") the A99 is 'truly' an end fed half wave antenna, as its relative SIZE (length) would indicate on the 11m band, before the radials / counterpoise was installed there was no doubt coaxial cable RF Radiation (common mode currents) which was contributing to the TVI/RFI situation on his property. Besides the novel radial/counterpoise arrangement that the OP ingeniously contrived, perhaps ANOTHER method to help isolate the coax would've been to choke it at the feedpoint of the A99.
Either way, he solved his problem and that (of course) is highly commendable.
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It was all about changing the radiation pattern with my A99+ ground plane setup and limiting CMC's on the feedline.
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Hi All!
I haven't replied to my original topic in some time, so I figured it was about time for an update. There are some new developments in my obsessive-compulsive pursuits of antenna perfection with the A99.
First, I couldn't help myself...I had to implement some of the concepts that arose in this thread from many of the A99 haters to see if their wisdom proved accurate in the real-world or if their obsession with mere theory corrupted their perception of the true possibilities with this antenna platform.
One board member or two insisted that what I was witnessing previously with sizable coverage gains due to my installation of 1/4 wave ground radials was nothing but fantasy and that if I properly de-coupled the antenna from the feedline with an appropriate choke at the feedpoint, I would witness the same results.
Well, sorry to burst your bubble, but it did not happen -- not even close. Not only did I replace the top 5 ft of mast material with wood instead of metal to further improve mast/antenna de-coupling, but I installed a choke exactly to the specs provided in a table linked to this thread. It was 5-turns of 4.25" diameter air core choke. I removed my radial system completely.
When I turned the radio back on, I noticed immediately something was off...it was dead silent. Whereas before I would have to set the squelch to 3 o'clock to mute the background, now it would squelch out at just 12 o'clock. So the receive sensitivity was vastly compromised. Some of the regulars I chat with about 15-20 miles away were extremely inconsistent, fading in and out, etc. I kept having to repeat my calls because they had trouble hearing me. Despite claims that the TVI/CMC issues would improve with the correct choke and decoupling, it actually worsened from being barely perceptible to quite annoying.
Despite the issues above, the SWR curve narrowed by a large percentage, limiting the usable range of the antenna where SWR remained below 2:1. Not cool. I had to take it down today and re-install the radials. This time, I kept the wood section hoping it would help even with the radials installed and it did. The radio literally came alive again and the SWR curve improved dramatically.
Oddly enough, I am not seeing a parabolic SWR curve, it seems to have some dips and crests throughout the range. Here is the list of the frequency plus the SWR graph reading (expressed out of a range of 8 indicator bars) as well as the actual SWR measurement.
Frequency Radio SWR Measured SWR
25.00 0/8 (best) 4:1
25.50 0/8 (best) 10:1
26.00 0/8 (best) 3:1
26.50 0/8 (best) 1.5:1
27.00 0/8 (best) 1.15:1
27.50 0/8 (best) 1.75:1
28.00 2/8 (good) 2.5:1
28.50 1/8 (better) 1.8:1
29.00 1/8 (better) 1.75:1
29.50 8/8 (worst) 2.3:1
30.00 8/8 (worst) 4.0:1
I suppose the radio swr measurement is what it is seeing from my amp right? Or does some of the main reflection from the antenna still hit the radio downline? I don't know if the SWR meter is reading the SWR from the low pass filter or the antenna or both. Regardless, I think I can safely operate between 26.00 to 29.00 and have minimal risk of damaging equipment without the use of a tuner.
I have some other thoughts on this topic, but this is enough food for thought right now. Thoughts are appreciated. Thanks!
-Nick
I haven't replied to my original topic in some time, so I figured it was about time for an update. There are some new developments in my obsessive-compulsive pursuits of antenna perfection with the A99.
First, I couldn't help myself...I had to implement some of the concepts that arose in this thread from many of the A99 haters to see if their wisdom proved accurate in the real-world or if their obsession with mere theory corrupted their perception of the true possibilities with this antenna platform.
One board member or two insisted that what I was witnessing previously with sizable coverage gains due to my installation of 1/4 wave ground radials was nothing but fantasy and that if I properly de-coupled the antenna from the feedline with an appropriate choke at the feedpoint, I would witness the same results.
Well, sorry to burst your bubble, but it did not happen -- not even close. Not only did I replace the top 5 ft of mast material with wood instead of metal to further improve mast/antenna de-coupling, but I installed a choke exactly to the specs provided in a table linked to this thread. It was 5-turns of 4.25" diameter air core choke. I removed my radial system completely.
When I turned the radio back on, I noticed immediately something was off...it was dead silent. Whereas before I would have to set the squelch to 3 o'clock to mute the background, now it would squelch out at just 12 o'clock. So the receive sensitivity was vastly compromised. Some of the regulars I chat with about 15-20 miles away were extremely inconsistent, fading in and out, etc. I kept having to repeat my calls because they had trouble hearing me. Despite claims that the TVI/CMC issues would improve with the correct choke and decoupling, it actually worsened from being barely perceptible to quite annoying.
Despite the issues above, the SWR curve narrowed by a large percentage, limiting the usable range of the antenna where SWR remained below 2:1. Not cool. I had to take it down today and re-install the radials. This time, I kept the wood section hoping it would help even with the radials installed and it did. The radio literally came alive again and the SWR curve improved dramatically.
Oddly enough, I am not seeing a parabolic SWR curve, it seems to have some dips and crests throughout the range. Here is the list of the frequency plus the SWR graph reading (expressed out of a range of 8 indicator bars) as well as the actual SWR measurement.
Frequency Radio SWR Measured SWR
25.00 0/8 (best) 4:1
25.50 0/8 (best) 10:1
26.00 0/8 (best) 3:1
26.50 0/8 (best) 1.5:1
27.00 0/8 (best) 1.15:1
27.50 0/8 (best) 1.75:1
28.00 2/8 (good) 2.5:1
28.50 1/8 (better) 1.8:1
29.00 1/8 (better) 1.75:1
29.50 8/8 (worst) 2.3:1
30.00 8/8 (worst) 4.0:1
I suppose the radio swr measurement is what it is seeing from my amp right? Or does some of the main reflection from the antenna still hit the radio downline? I don't know if the SWR meter is reading the SWR from the low pass filter or the antenna or both. Regardless, I think I can safely operate between 26.00 to 29.00 and have minimal risk of damaging equipment without the use of a tuner.
I have some other thoughts on this topic, but this is enough food for thought right now. Thoughts are appreciated. Thanks!
-Nick
Yesterday afternoon I was listening to a Canadian ham(VE5CDO http://www.qrz.com/db/VE5CDO ). He's in the Provence above Montana. I listened to him for two and a half hours yesterday on 28.465 MHz USB. He had a good signal with me sitting in my car listening in S.C. He was getting dozens of contacts from NY,Mass,Penn,Alaska,Ohio. I could only listen,no ham ticket,but he ran a ground plane vertical at 50'. He did mention that it was a A99 with a ground plane. Maybe you could pop him a question about his ground plane.
P.S. The band had been predicted to be dead yesterday but he had by his own admission a great DX day.
P.S. The band had been predicted to be dead yesterday but he had by his own admission a great DX day.
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Two things stand out.
The long isolation section of wooden mast - and the choke at the feed point.
The A99 requires a second half, either the mast, or the coax, or a set of GP.
The mast must remain metal up to very near the bottom of the antenna.
The choke must be about 9' below the feed point if there is no metal mast or GP.
The choke should be put at the feed point if the mast remains metal all the way up, or there is a good GP in place.
What your experience indicates is that there is a necessity for a GP radial system of some sort for an end fed vertical, whether that be the mast, the coax, or a set of GP radials.
What you've done is remove the mast as a potential radials substitute, took away the GP radials you had provided, and apparently rendered the choke ineffective for handling CMC seeing the RF will find a path for the missing half of the antenna. You left it one option, CMC on the coax in spite of the choke (even when your SWR looks good, it is possible that the efficiency of the antenna can be compromised).
Additionally, you need to not forget that a set of GP radials go a long way in assisting in decoupling the antenna from the earth. The radials are a natural earth substitute when used above the ground, and a decoupling device.
You made your antenna worse than it normally is when mounted according to the expectations of the manufacturer - directly upon a metal mast.
The long isolation section of wooden mast - and the choke at the feed point.
The A99 requires a second half, either the mast, or the coax, or a set of GP.
The mast must remain metal up to very near the bottom of the antenna.
The choke must be about 9' below the feed point if there is no metal mast or GP.
The choke should be put at the feed point if the mast remains metal all the way up, or there is a good GP in place.
What your experience indicates is that there is a necessity for a GP radial system of some sort for an end fed vertical, whether that be the mast, the coax, or a set of GP radials.
What you've done is remove the mast as a potential radials substitute, took away the GP radials you had provided, and apparently rendered the choke ineffective for handling CMC seeing the RF will find a path for the missing half of the antenna. You left it one option, CMC on the coax in spite of the choke (even when your SWR looks good, it is possible that the efficiency of the antenna can be compromised).
Additionally, you need to not forget that a set of GP radials go a long way in assisting in decoupling the antenna from the earth. The radials are a natural earth substitute when used above the ground, and a decoupling device.
You made your antenna worse than it normally is when mounted according to the expectations of the manufacturer - directly upon a metal mast.
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Good insights HomerBB. This leads me to another thought process on this antenna altogether...
I keep thinking about the description of the A99 in marketing literature, which refers to it as a "half-wave over quarter-wave variable mutual transductance tuned antenna". We've already established that this antenna can't be as described in the traditional sense because the antenna is only 1/2 wavelength tall. So that does lend credence to the idea that either a 1/4 wave section of mast, GP or coax must be present for the antenna to work.
However, that seems like too big of a variable in the equation. I'd say only a minority of users actually install a GP with this antenna. It says right in the manual that this antenna could be installed straight to a vent without any mast at all if need be. How many users are actually going to have a 102 inch mast or 102 inch feeder? Very few.
Most customers are going to have a mast significantly different from 1/4 wavelength -- same goes for coax. Wouldn't using a mast or coax feeder longer than 1/4 wavelength present a significant impedance problem and therefore destroy the design parameters? It would become a 1/2 wave over 1.666 wave antenna instead of a 1/2 wave over 1/4 wave. How would the antenna be able to use just that first 1/4 wave of coax or mast without any extra length interfering the the antenna's performance in a major way?
Only a proper GP can solve this problem. But this presents another conundrum -- the GPK-1 kit sold by Solarcon doesn't even come with proper sized 1/4 wave radials. It comes with 5 or 6ft radials if I'm not mistaken. Perhaps this explains why the gains realized on my end are so dramatic when I use properly sized 1/4 wave radials with this antenna.
Here's another thought to consider. So far I have yet to hear this idea. Going back to the "1/2 wave over 1/4 wave" antenna idea, what if we're looking at this all wrong? What if this antenna actually performs like some kind of colinear array when the 1/4 wave segment is actually 1/4 wave in size and not some random length presented by a length of mast or feedline? In this case, the 1/4 wave section will perform as a resonant structure as opposed to more of a non-resonant tuning stub or something of the like.
If we suppose this is indeed more of a proper colinear phased relationship, then an A99 with properly sized 1/4 wave radial element(s) would present an additional 3dB of gain in the low-angle E-plane. This would help explain the type of performance gains I have witnessed. During my initial range/coverage experiment, I noticed that the solidity of the signal at the ground level without the type of multipath "swooshing" typical of pure 1/2 wave antennas like a dipole or jpole reminded me of something: a 5/8 wave vertical. During my FM broadcast days, my 5/8 wave Comet vertical exhibited this same characteristic of a strong consistent low angle signal versus my experiments with dipoles and jpoles.
I refer you to the custom antenna work of Big Hair's @ High Performance CB Antennas. He has a "true" 1/2 wave over 1/4 wave antenna design which could very well mimic an A99 w/ proper 1/4 wave GP. His specs:
Antenna Type: 1/2 wave over a 1/4 wave
Antenna Gain: 3.2db
E-plane Beamwidth: 24 degrees
Bandwidth @ <2:1 SWR: 1.5 MHz
It all makes sense to me. Even the 1.5 MHz bandwidth of < 2:1 SWR lines up almost perfectly with my SWR findings on the last post. I plugged in the Friss equation values and found that the 3dB antenna gain at 50dBm output (100W) at 27MHz correlates with a theoretical range increase of 29%. When you factor in feedline and matching losses, the 20-25% range increase I witnessed in my experiment makes perfect sense.
To summarize my conclusions:
A99 is designed as a 1/2 wave over 1/4 wave antenna
To maximize A99 capabilities, must use 1/4 wave GP
1/4 wave GP mimics a second radiating colinear element
Gain from properly sized "colinear" A99 configuration = 3dB
Theoretical range improvement @ 3dB @ 100W @ 27 MHz = 29%
Has anyone tried modeling the A99 as a 1/2 wave over 1/4 wave colinear phased array of sorts?