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Avanti Sigma4: An alternative view point
- Thread starter bob85
- Start date
I believe so, and that's what all the hoopla is about. If you go back and read through this thread you'll find that is a big part of the topic, and supposedly lengthening it and a couple other mods can lower that angle, though I've yet to try it.
My old Larry's LW-150 did not keep up with my .64 Penetrator at distance but it was a stock, unmodded 3/4 wave.
More updates please, how does the antenna perform??
What has it been compared against?
What has it been compared against?
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Have you read this entire thread, including the links to other strands where this has been discussed?
It's fairly well described here.
Just a quick rather anecdotal addition of a little empirical test results;
A few weeks ago I replaced a nearly new metal 1/2 wave with a used Imax 2000 for a local who is somewhat disabled.
Using the same coax and mast, I simply removed the 1/2 wave and installed the Imax 2000.
On 3 different Amateur rigs which have analog S-meters (Icom 751a, Yaesu FT-990, Yaesu Kenwood TS-520s) I saw an average of 6-7dB gain on his signal from an S-9 plus 1-2dB before, to an S-9 plus ~8-9dB after comparison, right about the same amount claimed by the Exterminator FM antenna over a 1/2 wave at the link you offered above.
Both antennas were right on tuning X=near 0 on the MFJ-259.
- And I've seen improvement when changing out an Imax to a metal 5/8 so...
Just thought I'd share that info, 73
SIGMA IV
I got the privelage of finally working on a true Avanti Sigma IV over the holiday break.
Local here was on the air, snowbird, moves to FL. in the winter and back up north in the summer.
He did nto sound to great and complaind his antenna was not correct VSWR was bad. He said it was a Sigma IV. I jumped at the chance to help him repair/rework the antenna.
Hauled it down off the 48 fot tower, real light weight.
Replaced all the hardware as it was rusted and corroded. asemblied as per manufactures specs from owners manula downloaded from cb tricks site.
Antenna tuned beautiful, and had roughly 1mhz band width more or less.
Installed it back on the tower, talks great and VSWR were as tuned.
My opinion the Sigma is a shunt feed antenna.
NOW the comparision.
home brew 5/8 wave, tapped inductor instead of a hairpin match, the bandwidth on the 5/8 is almost 2 mhz wide. antennas installed basicaly same height to feed point.
sigma is 27 feet 7 inches long, 5/8 tuned for 27.600 is 22 feet 6 inches long four radials on the 5/8 wave.
I drove to a clear parking lot exactly 26 miles away from both QTH of the antennas.
sigma is using at FT 900 for a transciever
5/8 wave is using an TRC458 and 70 watts from a solid state amp.
tests were done on SSB.
The 5/8 wl was louder with a stronger signal by 5 to 6 db. almost a full S unit more of signal.
The mobil radio was a galaxy DX 959 with 102 inch metal whip, mobil was stationary, clear skies on day of test.
My conclusions are, Sigma works wonderful in 10 mile range, side by side compared to the 5/8 wl.
Perhaps the sigma puts out a lower angle of radiaiton than the 5/8, perhaps I need to drive to a 30 and then 40 mile distance to compare the antennas, but on that given day on that comparision, the 5/8 was a louder and stronger antenna.
The above conclusions are real world test, I built the 5/8 homebrew for a friend, I rebuilt the Sigma for another friend, both are respectable antennas, the results still are what they are the 5/8 was the better antenna with all other variables equal height,distance, output power of stations.
Anyone else have a chance to compare the antennas in a "real world environment"?
I got the privelage of finally working on a true Avanti Sigma IV over the holiday break.
Local here was on the air, snowbird, moves to FL. in the winter and back up north in the summer.
He did nto sound to great and complaind his antenna was not correct VSWR was bad. He said it was a Sigma IV. I jumped at the chance to help him repair/rework the antenna.
Hauled it down off the 48 fot tower, real light weight.
Replaced all the hardware as it was rusted and corroded. asemblied as per manufactures specs from owners manula downloaded from cb tricks site.
Antenna tuned beautiful, and had roughly 1mhz band width more or less.
Installed it back on the tower, talks great and VSWR were as tuned.
My opinion the Sigma is a shunt feed antenna.
NOW the comparision.
home brew 5/8 wave, tapped inductor instead of a hairpin match, the bandwidth on the 5/8 is almost 2 mhz wide. antennas installed basicaly same height to feed point.
sigma is 27 feet 7 inches long, 5/8 tuned for 27.600 is 22 feet 6 inches long four radials on the 5/8 wave.
I drove to a clear parking lot exactly 26 miles away from both QTH of the antennas.
sigma is using at FT 900 for a transciever
5/8 wave is using an TRC458 and 70 watts from a solid state amp.
tests were done on SSB.
The 5/8 wl was louder with a stronger signal by 5 to 6 db. almost a full S unit more of signal.
The mobil radio was a galaxy DX 959 with 102 inch metal whip, mobil was stationary, clear skies on day of test.
My conclusions are, Sigma works wonderful in 10 mile range, side by side compared to the 5/8 wl.
Perhaps the sigma puts out a lower angle of radiaiton than the 5/8, perhaps I need to drive to a 30 and then 40 mile distance to compare the antennas, but on that given day on that comparision, the 5/8 was a louder and stronger antenna.
The above conclusions are real world test, I built the 5/8 homebrew for a friend, I rebuilt the Sigma for another friend, both are respectable antennas, the results still are what they are the 5/8 was the better antenna with all other variables equal height,distance, output power of stations.
Anyone else have a chance to compare the antennas in a "real world environment"?
Nice test, except I would encourage you to mark several lines on the tarmac so you can roll 1/8wave closer / farther (from both simultaneously) at a time, (and up to perhaps even several 1/4 wave lengths) to make sure you're not in a null to one or the other, (which will of course skew your test results) then compare the highest reading from both.
- On the SigmaIV, was it 26' 7" or 27' 7"?
And are you certain the SS amp isn't providing well over 100w-150w PEP on SSB?
...had an FT-900, nice rig, basically an FT-890 inside.
Well, yes and no.
One can't argue it's not a real-world test - going a good distance away and seeing who wins, but yes, the variables are perhaps what's causing one to win, one to lose.
Eliminate most of the variables of questionable power and null-factor and you'll have a decent real-world antenna test, at least at that distance.
He's basically seeing exactly what I saw between my Hy-gain Penetrator and the Larry's LW-150 at ~35 miles, the Penetrator being the stronger of the two.
It would be even cooler to swap out the SigmaIV for a 5/8 and then see if they aren't neck-n-neck at ~25miles.
We don't even have accurate RF output measurement, no idea what is in-between each station, Sideband as the test mode? judging by loudness? come on... Nice effort but sorry, as I said WAY to many variables, possibilities for outside factors to effect testing... ETC....
But wait, do we know if he used only a meter reading or if he had both stations transmit simultaneously and could hear one better?
It sounded like the two stations were close to each other, but you're right, perhaps there were land marks in the way of the weaker.
I would like some clarification on these variables, though I expect he may have already taken most of this into consideration if he was hoping to get a reasonably fair test result.
He mentioned 6dB difference, that's easily seen on a decent analog meter, even in SSB mode.
- edit: Sorry Wavrider for the third-person context, I didn't notice you were also responding.
It sounded like the two stations were close to each other, but you're right, perhaps there were land marks in the way of the weaker.
I would like some clarification on these variables, though I expect he may have already taken most of this into consideration if he was hoping to get a reasonably fair test result.
He mentioned 6dB difference, that's easily seen on a decent analog meter, even in SSB mode.
- edit: Sorry Wavrider for the third-person context, I didn't notice you were also responding.
Well everyone can accept the "Test" results in the manner they see fit.
Hearing one station better on SSB? LOL, that can be as little difference as turning up the Mic gain, hell I can literally double my audible loudness just by turning my processor on my Kenwood on, and still remain about the same output on the watt meter.
I've also yet to see a truly linear meter on a CB radio, the power increase it take to go from one point to the next on a CB radios meter can vary drastically.. Granted, I may be nit-picking a bit, but it makes my point.
There are a few ways the test could be made more palatable, but as its presented, I'll call it good discussion fodder and not much more...
And I'm not trying to be a smart ass, or lessen his effort, just saying way to much is left out to form anything but a seat-of-the-pants opinion.
Hearing one station better on SSB? LOL, that can be as little difference as turning up the Mic gain, hell I can literally double my audible loudness just by turning my processor on my Kenwood on, and still remain about the same output on the watt meter.
I've also yet to see a truly linear meter on a CB radio, the power increase it take to go from one point to the next on a CB radios meter can vary drastically.. Granted, I may be nit-picking a bit, but it makes my point.
There are a few ways the test could be made more palatable, but as its presented, I'll call it good discussion fodder and not much more...
And I'm not trying to be a smart ass, or lessen his effort, just saying way to much is left out to form anything but a seat-of-the-pants opinion.
Wavrider, I installed my three leg Sigma IV last summer. After years of using the original Avanti manual dated 1980, I found out that my antenna was built by Antenna Specialists and that it is a little different than the original made by Avanti.
The only difference I have found is the spreader assembly and where it is installed, what it is made of, and the way it is constructed. There are also two metal tri-brackets on the Avanti model and the upper bracket, making up the spreader assembly, is placed at 64" on the 88" base element. On the parts list, the 3 spreader bars are shown to be made of fiberglass, and in Fig. 1 and Fig. 3 the bars are angled down a bit toward the bottom of the antenna. As best I can tell, this is the only difference I have found and I'm not sure it really makes a big difference except during construction. I did find if I spaced my spreader assembly at 64" instead of at 71 3/8" the radials were bowed outward a bit and I believe that can affect the tuning some.
The Antenna Specialists manual shows their model with 3 (straight not slanted down) spreaders that are attached using a hose clamp, they are plastic, and the spreader assembly is located at 71 3/8" on the 88" base element.
I also found that the tune can be ill affected if the gamma is not perfectly centered between the two radials it is installed between.
There is a warning in the manual to make sure the two tri-brackets assemblies, at the feed point and the spreaders, are square to each other---in order to prevent the sleeve assembly from being warped and out of shape.
At the time I did this work, I compared my I-10K to my Sigma at several different height configurations, trying to account for the differences in tip height and feed point height when comparing antenna RX signals. If you are interested, I have posted some of my Signal Reports and my Antenna Work Sheets in my profile on this forum. Click on my albums.
The only difference I have found is the spreader assembly and where it is installed, what it is made of, and the way it is constructed. There are also two metal tri-brackets on the Avanti model and the upper bracket, making up the spreader assembly, is placed at 64" on the 88" base element. On the parts list, the 3 spreader bars are shown to be made of fiberglass, and in Fig. 1 and Fig. 3 the bars are angled down a bit toward the bottom of the antenna. As best I can tell, this is the only difference I have found and I'm not sure it really makes a big difference except during construction. I did find if I spaced my spreader assembly at 64" instead of at 71 3/8" the radials were bowed outward a bit and I believe that can affect the tuning some.
The Antenna Specialists manual shows their model with 3 (straight not slanted down) spreaders that are attached using a hose clamp, they are plastic, and the spreader assembly is located at 71 3/8" on the 88" base element.
I also found that the tune can be ill affected if the gamma is not perfectly centered between the two radials it is installed between.
There is a warning in the manual to make sure the two tri-brackets assemblies, at the feed point and the spreaders, are square to each other---in order to prevent the sleeve assembly from being warped and out of shape.
At the time I did this work, I compared my I-10K to my Sigma at several different height configurations, trying to account for the differences in tip height and feed point height when comparing antenna RX signals. If you are interested, I have posted some of my Signal Reports and my Antenna Work Sheets in my profile on this forum. Click on my albums.
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