Avanti Sigma4: An alternative view point

[wavrider]

Marconi yes thanks for the invite to read the results of your tests I will definately do that.

Seeing double eyed here brought back an old FT-101EE from the dead and brain dead from looking at the service manual.

The sigma IV I worked on had one set of vertical spreaders,, looked like brown cardboard encased in fiberglass protective coating. Replaced them with some poly lenses we used at the plant for shatter proof lenses in some lighting fixtures, good tough stuff.

They were straight across, well looked to be straight across, the antenna had seen its better days.

No support at the top of the hoop, used some more poly and some cable hangers to support the hoop and small L bracket attached to the main vertical, centered the hoop and stabilized it rather well.

I did follow the avanti manual to the T, The only discrepiency from the manual on the antenna was the hoop had been lowerd 2 inches from what the manual called for, so we put it back in accordance with the manual.

The antenna does sound good and works well, on the base here using several different rigs FT-890, FT-102, Kenwood TS120-S, Siltronix 1011-C and D ( yes I like radios that glow in the dark) it is hard to tell the difference between the 5/8 and the Sigma IV on signal strength, thus I drove out in the mobile to test them.

Sorry so many variables but I will not climb the tower just to remove the antenna to do an more accurate field comparision, on the other hand a friend of mine does have a vector 4000 old style no dingle ball on top and we could do some field comparisions with it, build another 5/8 wl, if we ever get out of this freeze we are having here in FL.

 

[CDX-007]

Marconi yes thanks for the invite to read the results of your tests I will definately do that.

Seeing double eyed here brought back an old FT-101EE from the dead and brain dead from looking at the service manual.

The sigma IV I worked on had one set of vertical spreaders,, looked like brown cardboard encased in fiberglass protective coating. Replaced them with some poly lenses we used at the plant for shatter proof lenses in some lighting fixtures, good tough stuff.

They were straight across, well looked to be straight across, the antenna had seen its better days.

No support at the top of the hoop, used some more poly and some cable hangers to support the hoop and small L bracket attached to the main vertical, centered the hoop and stabilized it rather well.

I did follow the avanti manual to the T, The only discrepiency from the manual on the antenna was the hoop had been lowerd 2 inches from what the manual called for, so we put it back in accordance with the manual.

The antenna does sound good and works well, on the base here using several different rigs FT-890, FT-102, Kenwood TS120-S, Siltronix 1011-C and D ( yes I like radios that glow in the dark) it is hard to tell the difference between the 5/8 and the Sigma IV on signal strength, thus I drove out in the mobile to test them.

Sorry so many variables but I will not climb the tower just to remove the antenna to do an more accurate field comparision, on the other hand a friend of mine does have a vector 4000 old style no dingle ball on top and we could do some field comparisions with it, build another 5/8 wl, if we ever get out of this freeze we are having here in FL.

Hey Wavrider, in your field test, how far apart were the two stations, and were there any high spots in the terrain (high ground in Florida?) between either antenna and your mobile that weren't also present between the other station and your mobile?

Have you been able to test the 70w solid state amp for pep power?

I recall several local stations back in the '80s and '90s getting rid of their old Sigma5/8 and other '70s antennas for the (then) new upside-down ice cream cone antenna, but none were able to hang with my Penetrator at distances of 25-30plus miles, even though we all ran about the same power and don't see much in the way of high ground here either.

I have to agree with your results, and much to the chagrin of the many SigmaIV / Vector fans, still, I would like to know if there were any relevant variables to take into account with regard to your real world comparison.

I'd love to see the same thing at 40-50 miles!

73

 

[wavrider]

the power out on the SS amp in low position is 70 watts PEP using a true PEP reading wattmeter Autek One, not an Dosy. the TRC 458 ( wonderful radio best recieve ever on a cb bar none) Is only doing 18 watts pep, set up for audio quality not max power out.

Terrain search using lat and longitude shows the 5/8 wave 4 feet higher that the Sigma IV on terrain height.

No noticeable terrain structure between the test antennas and the mobile, It is NE Florida so not many terrain structures. ALL country with forest of pine trees between the test antennas and mobile.

I am not knocking the sigma IV, heck of an antenna, it may very well recieve better than the 5/8 wl, I don't know on that as I do not have one here to play with.

 

[CDX-007]

the power out on the SS amp in low position is 70 watts PEP using a true PEP reading wattmeter Autek One, not an Dosy. the TRC 458 ( wonderful radio best recieve ever on a cb bar none) Is only doing 18 watts pep, set up for audio quality not max power out.

Terrain search using lat and longitude shows the 5/8 wave 4 feet higher that the Sigma IV on terrain height.

No noticeable terrain structure between the test antennas and the mobile, It is NE Florida so not many terrain structures. ALL country with forest of pine trees between the test antennas and mobile.

I am not knocking the sigma IV, heck of an antenna, it may very well recieve better than the 5/8 wl, I don't know on that as I do not have one here to play with.

Are both antennas mounted about the same height above ground? - If so then the tops should be within a foot or two of being the same height above sea level.

And when you did the test did you happen to roll back and forth a little to try to compare the sweet spot on each?

I've seen signals change as much as from S-5 to S-9 as I roll toward or away from the transmitting station by 1/4 wave lengths, as measured on the ground.

Just curious, how far apart are the two transmitting stations?

73

 

[wavrider]

CDX 007,


Good questions.

Both antennas are about the same height to the base, Both roughly 48 foot towers, both on a mast pipe 4 to 5 feet above the top of the tower.

Which should give the Sigma a height advantage to the tip as it is longer in dimension.

The QTH of both antennas in a due South direction are 3 miles apart as the crow flies.

I was basically due East of both antennas.

Once again this was not a controlled comparision done in a test type environment, just a real world comparision.

I QSO'ed with both stations on the drive to an old military base, long ago taken over by the Port authority, I went to the airstrip side so there would be no obstacles around for many hundreds of yards, in the clear as much as possible.

I did not roll the mobile back or forth, just parked the mobile, shut the engine off and did the comparision.

It was not a shoot out, it was one at a time, looking at S meter readings in a stationary setting.

The result was the 5/8 had a stronger signal on the meter, audio was not compared as two different transcievers was used.

The test was done in LSB mode of operation not AM, everyone was on freq lined up with the FT-900 on the Sigma IV.

Both feed points of the antennas should have been around a wavelength and a half in the air vertically on 11 meters, so angle of radiation should be close to 20 degrees.

If indeed the sigma has a lower angle of radiation than the 5/8 that could be a valid reason that the signal was less at 26 miles away. The sigma may have a better signal at 40 or 50 miles out, if I can make it back in the mobile, if not cell phones are great. May have to try that test next.

It will be interesting to compare both antennas when the DX opens to see how both perform, I know how the 5/8 perform as I have one at 55 feet to the feed point also, but will look forward to see how the sigma performs when the window opens again.

Of course neither one compare to the beam at two wavelengths in height.

If I get a chance to due further comparisions I will post results.

 

[CDX-007]

CDX 007,


Good questions.

Both antennas are about the same height to the base, Both roughly 48 foot towers, both on a mast pipe 4 to 5 feet above the top of the tower.

Which should give the Sigma a height advantage to the tip as it is longer in dimension.

The QTH of both antennas in a due South direction are 3 miles apart as the crow flies.

I was basically due East of both antennas.

Once again this was not a controlled comparision done in a test type environment, just a real world comparision.

I QSO'ed with both stations on the drive to an old military base, long ago taken over by the Port authority, I went to the airstrip side so there would be no obstacles around for many hundreds of yards, in the clear as much as possible.

I did not roll the mobile back or forth, just parked the mobile, shut the engine off and did the comparision.

It was not a shoot out, it was one at a time, looking at S meter readings in a stationary setting.

The result was the 5/8 had a stronger signal on the meter, audio was not compared as two different transcievers was used.

The test was done in LSB mode of operation not AM, everyone was on freq lined up with the FT-900 on the Sigma IV.

Both feed points of the antennas should have been around a wavelength and a half in the air vertically on 11 meters, so angle of radiation should be close to 20 degrees.

If indeed the sigma has a lower angle of radiation than the 5/8 that could be a valid reason that the signal was less at 26 miles away. The sigma may have a better signal at 40 or 50 miles out, if I can make it back in the mobile, if not cell phones are great. May have to try that test next.

It will be interesting to compare both antennas when the DX opens to see how both perform, I know how the 5/8 perform as I have one at 55 feet to the feed point also, but will look forward to see how the sigma performs when the window opens again.

Of course neither one compare to the beam at two wavelengths in height.

If I get a chance to due further comparisions I will post results.

Excellent! My only reservation is the specific location as that could have easily favored one antenna's signal over the other due to the null factor. Even moving 1/8 wave toward or away from that spot might have changed the results in the direction of favoring the opposite antenna.

What about during the trip, did you get any impression (whilst still moving) that one was consistently significantly stronger than the other?

And regarding a lower TOA, I believe the lower it is, the better, - especially for contacts past 10-15 miles, unless it drops below 0* like a mountain-top repeater downward sloping antenna pattern.

 

[Shockwave]

Variables will mess up your test results. You can't begin to compare two antennas installed at different locations no matter how close. Even if both antennas are on the same lot, there are variables. One antenna must replace another in the exact same spot, power output, and even differences in time add variables. I disagree with the 5/8 wave having 2 Mhz bandwidth while the Sigma has 1 MHz. My tests on 11 meters shows the exact opposite when compared to a Maco V-58. I get 1 MHz on the Maco 5/8 and 2 MHz at 1.5:1 or less on the Sigma. This made a big difference in the ability to work both 10 and 11 meters off the same vertical.

The exception to the bandwidth rule is when you run these antennas far outside of the intended band. The gamma match on the Sigma with it's shunt feed will not resonate well outside of the bandwidth even with an antenna tuner. Then the 5/8 waves matching network works better with a tunner on other bands like 15 meters where the Sigma will not. The upside for the Sigma is it radiates less out of band harmonics then the 5/8 wave. That's just harmonics not RFI. The Sigma on HF can be worse then the 5/8 wave in terms of RFI without a balun.

Some of you know I rescaled the Sigma for FM broadcast use 15 years ago after testing many 5/8 waves for FM. Having great results with the Sigma on 11 meters I knew this antenna could do the same on FM. Working with it on FM gave me the ability to conduct many tests with calibrated field strength meters like the FIM-71. Accurate gain, ERP, and signal contours were extremely important to us since all my FM customers would be adjusting their transmitter power according to the antennas gain to meet their licensed ERP level.

Here are some basic facts. In order for an omni directional vertical antenna to have gain, it must lower the angle of radiation with respect to the antenna it is compared to. For one antenna to have a stronger signal then another means it's radiation angle is lower. The lower the angle of radiation, the stronger the signal will be on the horizon. This is the case at 10 miles, or 50 miles. It just becomes more evident as distance increases. The only exception to the rule of lower angle radiation equaling more signal close in would be when the two stations are at extremely different heights.

For example if the transmitter antenna is located on a 6000 foot mountain and part of the desired coverage area is almost directly underneath the antenna. In this case most of the signal will pass way overhead. In the FM broadcast market we use beam tilt to refocus some energy downwards. This doesn't present a problem with the average 11 meter installation. Even if it did, as soon as you get out several miles the effect tends to diminish.

We had an engineer at two of our first LPFM installations that was kind enough to perform some tests for us. The stations were told by Ramsey that the Comet 5/8 wave would double their ERP. Sounds like a real 3 db increase, except they overlooked the 5/8 wave wasn't compared to the standard 1/2 dipole. They bought the FCC certified 50 watt transmitter and the Comet 5/8 wave thinking they were going to get 100 watts ERP. The Comet is a real 5/8 wave with full 1/4 wave ground radials.

We came up with about 1.8 db5/8. That's a new term. it means 1.8 db over a 5/8 wave. Below are the real world results of what happens when the ONLY VARIABLE is going from a 5/8 wave to a Sigma design from the company that installed the antenna on the towers for the clients. Keep in mind these were early tests designed to confirm the claimed 3 dbd in order to determine the appropriate TPO to reach 100 watts ERP after coax loss. The engineer reduced the transmitter to 20 watts at 35 feet. Later the stations increased to around 50 watts TPO at 100 feet with significant range increase. I removed the name of my product because I'm not advertising, I'm educating.

Donald,

Antenna received, tested and shipped to our client, they are going to be delighted with this system:

>>>>>>>>>>>>>>>>>>>>>>>>

Lightly populated urban area flat horizon most rooftops below 30 feet:

Comet 5/8 wave @ 35 feet AGL and 20 watts TPO: Signal verge 4 miles best - 3 miles radius - 4 - 5 miles poor reception then fade out.

--------- .82 wave @ 35 feet AGL and 20 watts TPO: Signal verge 6 miles best - 5 miles radius - 6 - 7 miles acceptable reception then fade out.

>>>>>>>>>>>>>>>>>>>>>>>>

Rural area mostly farm land without obstruction flat horizon:

Comet 5/8 wave @ 35 feet AGL and 20 watts TPO: Signal verge 6 miles best - 4 miles radius, 6 - 7 miles poor reception then fade out.

--------- .82 wave @ 35 feet AGL and 20 watts TPO: Signal verge 11 best miles - 9 miles radius, 11 - 12 miles acceptable reception then fade out.

>>>>>>>>>>>>>>>>>>>>>>>>

I used the Comet 5/8 wave as a comparison because both antennas offer similar vertical radiation properties. The efficiency of the --------- .82 wave speaks for itself, it delivers almost double the performance of the 5/8 wave, there are no questions left to answer except "where is your --------- .82 wave"?

 

[CDX-007]

Thanks for the post, Shockwave, and for fabbing this mod to the .75 monopole.

My friend Serge and I will be resurrecting and modding an old 'Salute' with Bob85's and your helpful info, so perhaps you'll be seeing another group of believers from our area, depending on how well it performs in our test to be conducted in a week or seven...

We will be comparing:

A Shockwave-style .82 modded Salute

An Hy-gain Penetrator Super CLR 500

A Sigma II 5/8 (original Avanti AV-170)

An A1 Antennas Interceptor I-10K

A Solarcon Imax 2000

An AstroPlane (original Avanti, but with 1/4 wl top section mod)

A Ringo 1/2 wave (original A/S)

- all on a 36' mast in the foothills nearby at 1,500' ASL.

We should have ground-wave, analog meter, signal reports from as close as 5 miles and as distant as 100+miles.

While I appreciate tests done which place all the tops at the same level above ground, I consider that a somewhat fraudulent way of comparing since the height of mast typically used upon which one places their antenna of choice is the highest one can attain.

I believe a real-world test comes from using the same 'everything else' instead of providing the shorter designs with the handicap of equalized elevation.

I doubt my competitive neighbor will lower his Sigma so the top of my AstroPlane is just as high...

For the few who live on a hill or ridge I can see how that aspect of each design doesn't come into play as much, but I consider that one of the exceptions, not the norm.

I'll post the results when we get finished rebuilding and modding the Salute and the test is completed.

 

[wavrider]

Shockwave.

I agree with you 100% that the test is not a controlled test, and it was stated many times that it was not, just a real world test with many variables.

If the weather was always perfect, the conditions never changed,solar flares never happened, and the sun never had any spots, then I truly believe the Sigma IV would prevail. Stock out of the box.

In uncontrolled situation with all the variables the real world can throw at an RF signal the results are what I posted.

The 5/8 wave is not a bought off the shelf brand, I.E Maco or anything else. it is a home brew using an over sized tapped inductor for matching, 1 1/4 inch tubing at the base of the vertical element with tapered tubing as it goes up in height, and four full size 1/4 wave radials.

Have to build it to withstand the FL hurricane winds if we get hit with one, even then 1 1/4 inch tubing, best ALCOA has to offer may not withstand that force of a wind.

The age old adage prevails, if you want broader bandwidth, make your radiating element bigger in circumference. I do not think MACO uses 1 1/4 inch tubing in their 5/8 wave antenna?

The Sigma was not re adjusted for band width, it was set exactly to the manufactures specs from the manual, the gamma was adjusted for min VSWR at 27.400 on the antenna analyzer, I agree it could be broad banded if adjusted and played with, but this one was set up to specs from manual as previously stated.

With the sigma optimized it may very well have a lower angle of radiation than a 5/8, take into consideration the 5/8 is custom built and alot of time was put into it for optimizing band width, where as the sigma I compared it to is manufactures specs and not optimized for any band width or gain.

All specs are still 5/8 wavelength after optimizing the antenna, IE vertical is .625 wl, radials are full 1/4 wl so it is a true 5/8 wl antenna, just optimized for band width.

I do not have an off the shelf 5/8 wave to compare this Sigma to.

CDX007 Looking forward to seeing the antenna comparision results you are planning on doing in the future.

Shockwave thanks fo the reply it was informative.

 

[CDX-007]

...The 5/8 wave is not a bought off the shelf brand, I.E Maco or anything else. it is a home brew using an over sized tapped inductor for matching, 1 1/4 inch tubing at the base of the vertical element with tapered tubing as it goes up in height, and four full size 1/4 wave radials...


CDX007 Looking forward to seeing the antenna comparision results you are planning on doing in the future.

Hmmm, sounds like a Penetrator!

I too am looking forward to seeing just by how much, if at all, the I-10K is "...NOT your Daddy's Penetrator..."

73

 

[MisterFatty]

It really is interesting to see what is acceptable when its on the same side of the fence...

 

[CDX-007]

It really is interesting to see what is acceptable when its on the same side of the fence...

My neighbor, she's 24 and a cocktail waitress at a strip club.

When I'm up on the roof working on the antenna and she is on the other side of the fence in her backyard sunbathing, it's all acceptable.

 

[mackmobile43]

All you can do to satisfy the critics is to mount both antennas to the same pole and use the same transmitter and receiver which will require 2 separate test times because we all know 2 objects cannot occupy the same space simultaneously and damn the weather and solar conditions, as long as you have a sunny day the test will be as equal as it can be.

 

[wavrider]

All you can do to satisfy the critics is to mount both antennas to the same pole and use the same transmitter and receiver which will require 2 separate test times because we all know 2 objects cannot occupy the same space simultaneously and damn the weather and solar conditions, as long as you have a sunny day the test will be as equal as it can be.

I think so, and then would it still be a matter of debate due to time lapse between tests?

I am satisfied with the fact that one can be heard better than the other one, at least in my recieve, mileage may vary.

Both antennas transmit well, both hear well, none of the test comparisons performed were under lab conditions or controlled variables.


The stripper sun bathing next door is definately acceptable under any conditions.

 

[mackmobile43]

I think so, and then would it still be a matter of debate due to time lapse between tests?

I am satisfied with the fact that one can be heard better than the other one, at least in my recieve, mileage may vary.

Both antennas transmit well, both hear well, none of the test comparisons performed were under lab conditions or controlled variables.


The stripper sun bathing next door is definately acceptable under any conditions.

It's apparent that you're the only one who's satisfied, I for one do not care because I have a lw-150 that's going up when weather/time affords and it will be done as I've stated that you should and whether it's on the same day or not is not a deciding factor as to which one will out perform the other and using the same mounting pole and tx/rxer is no matter how satisfied you are.

What you have is 2 entirely different tx locations with maybe or mabe not equal height mounts and as you've state they have different radios,coax soil conditions and miles to contact point.

What I will have is the same mounting pole which is a 24' 1.5'' pole with rg-8 coax with a rci 2950dx radio emitting 5 watts in FM mode and the receiver will be a kenwood ts-430s because I believe the S-meeter to be accurate or at least dependable in the mobile listening through a predator 10-k on a 12'' shaft mounted on a tri-magmount.

And that's the only true method for determining performance of 2 different antennas.

The stripper sun bathing next door is definately acceptable under any conditions

This post is worth nothing without pics :lol