Thanks for your input Shockwave, your info really validates my testing many years ago... Nice read..
-
You can now help support WorldwideDX when you shop on Amazon at no additional cost to you! Simply follow this Shop on Amazon link first and a portion of any purchase is sent to WorldwideDX to help with site costs.
Avanti Sigma4: An alternative view point
- Thread starter bob85
- Start date
strange eh mack, i doubt even you could pull this one off:blink:
shockwave,
your claims bear some striking similarities to what i see in my own tests, i almost fell off my chair when i read your post, remote viewer?,hoax?,i dont know,
but,
im still not sure exactly how the lower 1/4wave is working, i cannot get away from the modified skleton sleeve antenna idea untill i have made current and field strength measurements, the rest of your claims are spooky, like you have been watching me for years,
i owned the original sigma4 and the big-mac at the same time and did comparisons,
mounted at 73ft to feedpoint in a field the big-mac had the edge but it also had an unusual character,
as it swayed in the wind it would make me look like i was mobile to anybody watching my signal and the same effect on my receive, even though the big-mac did flex more than the sigma it gave me the impression that it had a very narrow vertical beamwidth which only outdid the sigma when it was dead calm,
i think but cannot prove that the vector tuned correctly is far enough in front of the sigma to put it right with if not slightly in front of the big-mac without the seemingly very narrow vertical beamwidth,
when you look at the simplicity of the sigma design compared to the monster big-mac, far fewer feet of tubing, its much smaller footprint and its ability to perform at low heights/poor surroundings or mounted high above the ground without any notable strange characteristics its clear the avanti guys were at the top of the cb antenna tree back then,
some have copied the idea and in the case of the extended 4 radial version improved the design in performance but not structural integrity, some as my old man would say "they cant see the forrest for the trees"
when i put the sigma/vector hybrid back up i will be experimenting with radial length and hoop diameter, i expect to see the extra gain that avanti mention in the patent,
cebic told me the sigma style antenna would be very difficult to accurately model,
j-pole? definately not, build one test one, you will see
.
thanks for the interesting read, if its a windup its top class.
shockwave,
your claims bear some striking similarities to what i see in my own tests, i almost fell off my chair when i read your post, remote viewer?,hoax?,i dont know,
but,
im still not sure exactly how the lower 1/4wave is working, i cannot get away from the modified skleton sleeve antenna idea untill i have made current and field strength measurements, the rest of your claims are spooky, like you have been watching me for years,
i owned the original sigma4 and the big-mac at the same time and did comparisons,
mounted at 73ft to feedpoint in a field the big-mac had the edge but it also had an unusual character,
as it swayed in the wind it would make me look like i was mobile to anybody watching my signal and the same effect on my receive, even though the big-mac did flex more than the sigma it gave me the impression that it had a very narrow vertical beamwidth which only outdid the sigma when it was dead calm,
i think but cannot prove that the vector tuned correctly is far enough in front of the sigma to put it right with if not slightly in front of the big-mac without the seemingly very narrow vertical beamwidth,
when you look at the simplicity of the sigma design compared to the monster big-mac, far fewer feet of tubing, its much smaller footprint and its ability to perform at low heights/poor surroundings or mounted high above the ground without any notable strange characteristics its clear the avanti guys were at the top of the cb antenna tree back then,
some have copied the idea and in the case of the extended 4 radial version improved the design in performance but not structural integrity, some as my old man would say "they cant see the forrest for the trees"
when i put the sigma/vector hybrid back up i will be experimenting with radial length and hoop diameter, i expect to see the extra gain that avanti mention in the patent,
cebic told me the sigma style antenna would be very difficult to accurately model,
j-pole? definately not, build one test one, you will see
.thanks for the interesting read, if its a windup its top class.
I thank you too neighbor for the link to AS design of the S4. I knew that there was something else out there that fit my S4 design and now I know exactly what I have.
Bob, here is the one we have been missing.
B
BOOTY MONSTER
Guest
i thought for sure you guys already knew about that pdf . if anyone is interested heres a link to sirios current version/copy of that antenna , and theres a pdf link there for its manual .
Sirio Antenne - Products
27 feet 10 inches
Sirio Antenne - Products
27 feet 10 inches
i did have it since before it was posted on cbtricks booty, it was the one eddie had, the original avanti version with flat fiberglass spreaders that i did not have, i never realised eddie had not seen the a/s version.
Larry's LW-150
Interesting. I found my old paperwork for tuning and it was 26' 7" at 1:1 SWR.
That is definitely NOT .82, so what the heck did I have, a 3/4 with a 45* angle?
I just may have to try one of the .82 size... which one should I get?
...maybe, I'm not so sure now, after testing the I-10K against my Penetrator.
Interesting. I found my old paperwork for tuning and it was 26' 7" at 1:1 SWR.
That is definitely NOT .82, so what the heck did I have, a 3/4 with a 45* angle?
I just may have to try one of the .82 size... which one should I get?
...maybe, I'm not so sure now, after testing the I-10K against my Penetrator.
Last edited:
Hi shockwave,
I don't doubt your claims of maximum gain arising at .82 of a wavelength.What I would like to know is you say that .82 is only slightly shorter than the original vector 4000,by my calculations at 27.185 .82 is almost 2 foot shorter,1 ft 9 1/2 inches to be precise.
I'm wondering if you figured in the .95 vf of aluminium in your wavelength calculation as without it .82 would only be a couple of cm shorter than the original 7/8 wave (.875 wave) vector 4000 and indeed qualify as only slightly shorter,or if you have figured it in and you are quantifying 2ft as slighly?
I ain't nitpicking just trying to understand the term slightly.
The reason I don't doubt your claims is despite sirio claiming their new vector 4000 to be a 3/4 wave j pole,if you calculate from the 8480mm they give for the length it is in fact .81 wave in length at 27.185.which supports your claims as i know from experience when it comes to antennas sirio ain't no mugs.
I believe they only use the 3/4 j pole description to sell them to people who can't get their heads round the concept that an antenna doesn't have to be an exact fraction of a wavelength to work well and that they will never understand that it isn't a j pole but a coaxial antenna.Shrewd marketing.
I use 27.185 as it tends to be where you guys over the pond centre your antennas on,here it would be slightly higher in most cases as antennas of that nature are generally used for freebanding here around 27.555.
So as you can see i am in no way rubbishing your claims,just looking for you to clarify the "slightly shorter quantity".
I don't doubt your claims of maximum gain arising at .82 of a wavelength.What I would like to know is you say that .82 is only slightly shorter than the original vector 4000,by my calculations at 27.185 .82 is almost 2 foot shorter,1 ft 9 1/2 inches to be precise.
I'm wondering if you figured in the .95 vf of aluminium in your wavelength calculation as without it .82 would only be a couple of cm shorter than the original 7/8 wave (.875 wave) vector 4000 and indeed qualify as only slightly shorter,or if you have figured it in and you are quantifying 2ft as slighly?
I ain't nitpicking just trying to understand the term slightly.
The reason I don't doubt your claims is despite sirio claiming their new vector 4000 to be a 3/4 wave j pole,if you calculate from the 8480mm they give for the length it is in fact .81 wave in length at 27.185.which supports your claims as i know from experience when it comes to antennas sirio ain't no mugs.
I believe they only use the 3/4 j pole description to sell them to people who can't get their heads round the concept that an antenna doesn't have to be an exact fraction of a wavelength to work well and that they will never understand that it isn't a j pole but a coaxial antenna.Shrewd marketing.
I use 27.185 as it tends to be where you guys over the pond centre your antennas on,here it would be slightly higher in most cases as antennas of that nature are generally used for freebanding here around 27.555.
So as you can see i am in no way rubbishing your claims,just looking for you to clarify the "slightly shorter quantity".
At 26'7" your antenna was approximately .77 wave.The extra length could be down to improper setting of the gamma match and having to offset it with the radiator for good swr.
Loosecannon: I do not isolate the antenna from the support pole for two reasons. Lightning protection is great with this antenna since it is DC grounded with no inductor in series to ground to burn out. To make use of this we still have to ground the mast, tower, or antenna base anyhow. Also, just wrapping a coax choke at the base seems to kill the entire problem.
Bob85: I am familiar with the skeleton sleeve antenna and in many ways the Sigma IV is similar. In fact Sirio makes a CX line of antennas that use a 1/4 wave tube as the sleeve rather then a skeleton. At one point Sirio made one that went down to 60 Mhz. and the gain dropped to 1.2 db. While their high band model of the CX is still around 2 db. This shows that angling the base section out to form a 25 degree cone enhances gain at lower frequencies.
The modified skeleton sleeve you mention may be doing this. I haven't seen one so perhaps you can explain the differences. Additionally the sleeve type seems to be directly end feeding the radiator and that forces you to tune it for minimum VSWR rather then the longer length that produces maximum gain. This requires series capacitance to cancel the inductive component.They don't appear to be DC grounded either.
What you noticed in the Big Mac's signal fluctuation is typical with any long collinear. It was great to actually hear this from someone who had the chance to test one. I use to see it all the time in marine VHF installations with sailboats. Customers would insist on the big collinear until the first time they were in rough water and the pitch of the antenna completely chopped up the transmission with every roll.
When experimenting with you hybrid Bob, the first thing you want to do is fabricate a loop that will proved the required 25 degree angle with respect to the radiator. Then you can fine tune the cone for maximum gain by sliding the top four support rods in or out of the lower, larger diameter base rods to find the sweet spot. Once you peak the cone out for maximum gain, there is more gain to be found by re-peaking the main radiator length. Typically you will have to shorten this as the loop is lowered on the radiator to get maximum gain. Take caution to keep the gamma match at a reasonable VSWR after each step for accurate comparison.
CDX-007: Your antenna at 26' 7'' seems a bit short for 27 MHz. Perhaps you tuned the VSWR too much by whip length and not enough with the gamma. If the antenna had the Sigma style base, it had a good low angle radiation pattern. It's not so much the whip length here that controls the angle of radiation. It's the cone base structure. Adjusting the whip length is done to maximize gain in conjunction with the 25 degree angle of the cone from the radiator and loop diameter.
About the only one of these antennas you can get now is going to be the Vector 4000. It's the only one being manufactured now. Order in the USA from H&Y Electronics. Consider the modification I mentioned in my previous post. At least do the ones to the main radiator and the antenna will be good to 1 KW. More then this will require the connector and gamma swap.
Jazzsinger: The main radiator length of the original Sigma IV was 27' 7'' and closer to 3/4 wave while the original Vector 4000 was 29 feet and closer to 7/8 wave. Interestingly it seems the Vector 4000 has be shortened to about .81 wave and they added the birdcage on top. I don't like the cage because it sure does catch birds sitting on the weak whip. Seems they did take some of my advice already on the wavelength.
Keep in mind I did my calculations for maximum gain at 98.0 MHz. and arrived at the .82 wave. This was done with in the field RF testing and not on paper. We can understand the small change of .81 wave at 27 MHz. At VHF the actual change between these wavelengths is small in terms of inches on that band. The change in wavelength at 27 MHz. will be larger physically however, 2 feet seems more then I would expect. Bottom line, peak it for far field gain and worry about the VSWR with the gamma.
Bob85: I am familiar with the skeleton sleeve antenna and in many ways the Sigma IV is similar. In fact Sirio makes a CX line of antennas that use a 1/4 wave tube as the sleeve rather then a skeleton. At one point Sirio made one that went down to 60 Mhz. and the gain dropped to 1.2 db. While their high band model of the CX is still around 2 db. This shows that angling the base section out to form a 25 degree cone enhances gain at lower frequencies.
The modified skeleton sleeve you mention may be doing this. I haven't seen one so perhaps you can explain the differences. Additionally the sleeve type seems to be directly end feeding the radiator and that forces you to tune it for minimum VSWR rather then the longer length that produces maximum gain. This requires series capacitance to cancel the inductive component.They don't appear to be DC grounded either.
What you noticed in the Big Mac's signal fluctuation is typical with any long collinear. It was great to actually hear this from someone who had the chance to test one. I use to see it all the time in marine VHF installations with sailboats. Customers would insist on the big collinear until the first time they were in rough water and the pitch of the antenna completely chopped up the transmission with every roll.
When experimenting with you hybrid Bob, the first thing you want to do is fabricate a loop that will proved the required 25 degree angle with respect to the radiator. Then you can fine tune the cone for maximum gain by sliding the top four support rods in or out of the lower, larger diameter base rods to find the sweet spot. Once you peak the cone out for maximum gain, there is more gain to be found by re-peaking the main radiator length. Typically you will have to shorten this as the loop is lowered on the radiator to get maximum gain. Take caution to keep the gamma match at a reasonable VSWR after each step for accurate comparison.
CDX-007: Your antenna at 26' 7'' seems a bit short for 27 MHz. Perhaps you tuned the VSWR too much by whip length and not enough with the gamma. If the antenna had the Sigma style base, it had a good low angle radiation pattern. It's not so much the whip length here that controls the angle of radiation. It's the cone base structure. Adjusting the whip length is done to maximize gain in conjunction with the 25 degree angle of the cone from the radiator and loop diameter.
About the only one of these antennas you can get now is going to be the Vector 4000. It's the only one being manufactured now. Order in the USA from H&Y Electronics. Consider the modification I mentioned in my previous post. At least do the ones to the main radiator and the antenna will be good to 1 KW. More then this will require the connector and gamma swap.
Jazzsinger: The main radiator length of the original Sigma IV was 27' 7'' and closer to 3/4 wave while the original Vector 4000 was 29 feet and closer to 7/8 wave. Interestingly it seems the Vector 4000 has be shortened to about .81 wave and they added the birdcage on top. I don't like the cage because it sure does catch birds sitting on the weak whip. Seems they did take some of my advice already on the wavelength.
Keep in mind I did my calculations for maximum gain at 98.0 MHz. and arrived at the .82 wave. This was done with in the field RF testing and not on paper. We can understand the small change of .81 wave at 27 MHz. At VHF the actual change between these wavelengths is small in terms of inches on that band. The change in wavelength at 27 MHz. will be larger physically however, 2 feet seems more then I would expect. Bottom line, peak it for far field gain and worry about the VSWR with the gamma.
shockwave, read the article in the the arrl antenna book 18th edition page 186-190,
it gives a good explanation of what happens in that style antenna when using a central monopole of 3/4wave or slightly longer with a sleeve of about 1/4wave, it also explains what happens when other length/length ratio elements are used causing the antenna to work with either antenna mode currents predominating or transmissinline currents predominating, read up on skirted monopoles, skelleton sleeve monopoles, sleeve fed antennas, how relative lengths diameters and spacings of all elements including the gamma effect an antenna, how sleeve length can be used to steer elevation,
if you can find any other antenna that seems to fit how the sigma design acts i sure would like to hear about it,
i have tuned my sigma style antennas for maximum signal at distance for years, i have always claimed the most notable improvement over other antennas is at distance,
your adjustments sound very much familiar, you make it sound so easy which it is not,
i would love to hear more detail of how you came to the conclusion that the optimum monopole length was shorter than sirios claimed 7/8wave but significantly longer than the stock 27'-7" sigma4,
what length did you come up with and on what frequency did you tune?,
i ended up with a shorter antenna when using the vector/sigma hybrid than when using the skinnier vector central monopole,
i would like to hear more about your tuning technique,
shockwave, what made you look at the sigma4 one day and come to the conclusion " i think i can make that perform better" ?
experimenting with monopole length is easy enough
experimenting with radial length while retaining the 30" hoop is also easy enough if you want to go shorter, extending the radials by any notable value will require longer uper radial tubes on the sigma4 and all copies i have owned discounting the new vector which has significantly longer radials,
unfortunately using a radial to monopole angle of 25-30 degrees means a radial distance of about 4.5 feet and a hoop diameter of about 9 feet with corresponding very short radials if we want to maintain the about 1/4wave electrical length ( which i am not sure is needed ) ,
imho making the hoop about twice as large as the 30" stock hoop is as far as you could realistically go with the 11mtr version of the antenna unless you remove the hoop and use full length radials at the 30 degree angle,
@ vhf the increased radial angle would not be a problem,
do you have any pictures of the antenna using larger radial angles than the stock 10 degrees?
anybody seen bnt lately
it gives a good explanation of what happens in that style antenna when using a central monopole of 3/4wave or slightly longer with a sleeve of about 1/4wave, it also explains what happens when other length/length ratio elements are used causing the antenna to work with either antenna mode currents predominating or transmissinline currents predominating, read up on skirted monopoles, skelleton sleeve monopoles, sleeve fed antennas, how relative lengths diameters and spacings of all elements including the gamma effect an antenna, how sleeve length can be used to steer elevation,
if you can find any other antenna that seems to fit how the sigma design acts i sure would like to hear about it,
i have tuned my sigma style antennas for maximum signal at distance for years, i have always claimed the most notable improvement over other antennas is at distance,
your adjustments sound very much familiar, you make it sound so easy which it is not,
i would love to hear more detail of how you came to the conclusion that the optimum monopole length was shorter than sirios claimed 7/8wave but significantly longer than the stock 27'-7" sigma4,
what length did you come up with and on what frequency did you tune?,
i ended up with a shorter antenna when using the vector/sigma hybrid than when using the skinnier vector central monopole,
i would like to hear more about your tuning technique,
shockwave, what made you look at the sigma4 one day and come to the conclusion " i think i can make that perform better" ?
experimenting with monopole length is easy enough
experimenting with radial length while retaining the 30" hoop is also easy enough if you want to go shorter, extending the radials by any notable value will require longer uper radial tubes on the sigma4 and all copies i have owned discounting the new vector which has significantly longer radials,
unfortunately using a radial to monopole angle of 25-30 degrees means a radial distance of about 4.5 feet and a hoop diameter of about 9 feet with corresponding very short radials if we want to maintain the about 1/4wave electrical length ( which i am not sure is needed ) ,
imho making the hoop about twice as large as the 30" stock hoop is as far as you could realistically go with the 11mtr version of the antenna unless you remove the hoop and use full length radials at the 30 degree angle,
@ vhf the increased radial angle would not be a problem,
do you have any pictures of the antenna using larger radial angles than the stock 10 degrees?
anybody seen bnt lately
shockwave, read the article in the the arrl antenna book 18th edition page 186-190,
it gives a good explanation of what happens in that style antenna when using a central monopole of 3/4wave or slightly longer with a sleeve of about 1/4wave, it also explains what happens when other length/length ratio elements are used causing the antenna to work with either antenna mode currents predominating or transmissinline currents predominating, read up on skirted monopoles, skelleton sleeve monopoles, sleeve fed antennas, how relative lengths diameters and spacings of all elements including the gamma effect an antenna, how sleeve length can be used to steer elevation,
if you can find any other antenna that seems to fit how the sigma design acts i sure would like to hear about it,
i have tuned my sigma style antennas for maximum signal at distance for years, i have always claimed the most notable improvement over other antennas is at distance,
your adjustments sound very much familiar, you make it sound so easy which it is not,
i would love to hear more detail of how you came to the conclusion that the optimum monopole length was shorter than sirios claimed 7/8wave but significantly longer than the stock 27'-7" sigma4,
what length did you come up with and on what frequency did you tune?,
i ended up with a shorter antenna when using the vector/sigma hybrid than when using the skinnier vector central monopole,
i would like to hear more about your tuning technique,
shockwave, what made you look at the sigma4 one day and come to the conclusion " i think i can make that perform better" ?
experimenting with monopole length is easy enough
experimenting with radial length while retaining the 30" hoop is also easy enough if you want to go shorter, extending the radials by any notable value will require longer uper radial tubes on the sigma4 and all copies i have owned discounting the new vector which has significantly longer radials,
unfortunately using a radial to monopole angle of 25-30 degrees means a radial distance of about 4.5 feet and a hoop diameter of about 9 feet with corresponding very short radials if we want to maintain the about 1/4wave electrical length ( which i am not sure is needed ) ,
imho making the hoop about twice as large as the 30" stock hoop is as far as you could realistically go with the 11mtr version of the antenna unless you remove the hoop and use full length radials at the 30 degree angle,
@ vhf the increased radial angle would not be a problem,
do you have any pictures of the antenna using larger radial angles than the stock 10 degrees?
anybody seen bnt lately
Lately he's been overheard in Mayfair
Bob,
I plan to investigate the 18th edition. It's one of the few I don't have in my collection. Although I am familiar with many of the effects you mention. Especially how the sleeve can steer the elevation pattern. This is the difference between a 3/4 wave ground plane with four 45 degree downward radials and the Vector 4000 design. Just bending the radials upwards rather then down steers the radiation pattern down on the horizon. Adding the loop on top simply widens the bandwidth and reduced the radial length. This upward bending of the radials is something the NEC calculator fails to recognize.
My technique of optimizing the Sigma IV was simple and required since I had to accurately rescale every measurement for FM broadcast. I have a Rohn 45 on the side of my shop. Almost all of my testing is on VHF and two wavelengths above ground. I can reach the antenna from the flat roof on a wood step ladder. Two wavelengths of LMR-400 are connected to the test instrument.
I use a calibrated FIM-71 VHF Field Strength meter to measure the slightest change in gain in the receive mode. The FM broadcast band is great for testing in receive since there are many continuous carries and being FM modulated there is no change in signal as they are modulated. Gain in receive is gain in transmit. I take the care to only tune with V-Pole transmitters rather then CP and only test during midday when conditions are most stable. One translator and another LPFM are about 30 miles away from me and one is using a Dominator close to 98 MHz.
You are absolutely correct about the ridiculous loop diameters required at HF to obtain the 25 degree angle. In fact I can't even do this on the VHF version because the loop ends up being lower then the top of the gamma match and distorts the entire pattern. I do turn the antenna to make sure it truly is maintaining an omni pattern. Because of your noted physical limitations, I have not actually built one at the full 25 degrees.
The best I could do was about 18 degrees before running into the gamma issue. These designs are new for FM and not yet being mass produced as you can see my current antenna is closer to stock angle. I found the biggest jump going from 10 to 15 degrees. Several tenths of a db. Going from 15 to 18degrees showed almost no change on a sensitive instrument. The 15 degree angle is what I have decided on to keep the size practical.
My prototype for testing has every aspect of the antenna adjustable. Radiator length, the length of the four support rods are telescopically adjusted. The loop was an overlapped 3/16 inch copper tube that fit through the holes on the tops of the four elements. By expanding or contracting the overlap on the copper tubing around the elements I could change the loop diameter. Everything would be clamped in place after each adjustment with hose clamps.
I have the prototype fitted with a fixed top ring now that I have the correct measurement. The rest of the prototype is as described and uses no plastic spreaders to support the loop rods so adjustment is easy on VHF. I'll try and dig it out of the shop and take a picture in the next day or two so you can see what it looks like at 15 degrees on VHF.
I plan to investigate the 18th edition. It's one of the few I don't have in my collection. Although I am familiar with many of the effects you mention. Especially how the sleeve can steer the elevation pattern. This is the difference between a 3/4 wave ground plane with four 45 degree downward radials and the Vector 4000 design. Just bending the radials upwards rather then down steers the radiation pattern down on the horizon. Adding the loop on top simply widens the bandwidth and reduced the radial length. This upward bending of the radials is something the NEC calculator fails to recognize.
My technique of optimizing the Sigma IV was simple and required since I had to accurately rescale every measurement for FM broadcast. I have a Rohn 45 on the side of my shop. Almost all of my testing is on VHF and two wavelengths above ground. I can reach the antenna from the flat roof on a wood step ladder. Two wavelengths of LMR-400 are connected to the test instrument.
I use a calibrated FIM-71 VHF Field Strength meter to measure the slightest change in gain in the receive mode. The FM broadcast band is great for testing in receive since there are many continuous carries and being FM modulated there is no change in signal as they are modulated. Gain in receive is gain in transmit. I take the care to only tune with V-Pole transmitters rather then CP and only test during midday when conditions are most stable. One translator and another LPFM are about 30 miles away from me and one is using a Dominator close to 98 MHz.
You are absolutely correct about the ridiculous loop diameters required at HF to obtain the 25 degree angle. In fact I can't even do this on the VHF version because the loop ends up being lower then the top of the gamma match and distorts the entire pattern. I do turn the antenna to make sure it truly is maintaining an omni pattern. Because of your noted physical limitations, I have not actually built one at the full 25 degrees.
The best I could do was about 18 degrees before running into the gamma issue. These designs are new for FM and not yet being mass produced as you can see my current antenna is closer to stock angle. I found the biggest jump going from 10 to 15 degrees. Several tenths of a db. Going from 15 to 18degrees showed almost no change on a sensitive instrument. The 15 degree angle is what I have decided on to keep the size practical.
My prototype for testing has every aspect of the antenna adjustable. Radiator length, the length of the four support rods are telescopically adjusted. The loop was an overlapped 3/16 inch copper tube that fit through the holes on the tops of the four elements. By expanding or contracting the overlap on the copper tubing around the elements I could change the loop diameter. Everything would be clamped in place after each adjustment with hose clamps.
I have the prototype fitted with a fixed top ring now that I have the correct measurement. The rest of the prototype is as described and uses no plastic spreaders to support the loop rods so adjustment is easy on VHF. I'll try and dig it out of the shop and take a picture in the next day or two so you can see what it looks like at 15 degrees on VHF.
shockwave,
the sleeve monopole article is interesting and may shed light on how the sigma operates, since its the only source of detailed information of an antenna with that layout and dimentions i can find at this time its the only idea i can come up with untill somebody finds an alternative,
one version described has a 3/4wave monopole and about 1/4wave sleeve, look what happens when the central monopole to sleeve ratio exceeds about 3.2:1,
this could be the none aparent colinear array that CEBIk told me was possible when folding the radials up towards the central monopole,
if you have any different articles that you think answers how the sigma works i would like to read them,
you will find several more sigma4 threads on this forum, i think some older ones may have been lost in the forum changeover, check them out, i think you will enjoy reading them,
id like to see the 15 degree radial setup to give me an idea of what mine would look like@ 27mhz
the sleeve monopole article is interesting and may shed light on how the sigma operates, since its the only source of detailed information of an antenna with that layout and dimentions i can find at this time its the only idea i can come up with untill somebody finds an alternative,
one version described has a 3/4wave monopole and about 1/4wave sleeve, look what happens when the central monopole to sleeve ratio exceeds about 3.2:1,
this could be the none aparent colinear array that CEBIk told me was possible when folding the radials up towards the central monopole,
if you have any different articles that you think answers how the sigma works i would like to read them,
you will find several more sigma4 threads on this forum, i think some older ones may have been lost in the forum changeover, check them out, i think you will enjoy reading them,
id like to see the 15 degree radial setup to give me an idea of what mine would look like@ 27mhz
Last edited:
Bob been reading both your post and shockwaves,can't help wondering what would occur if the radial angle was dropped to 25/30 degrees and the radials extended to a halfwave,this would surely overcome the pattern distortion caused by the gamma sticking above the hoop that shockwave describes,would also reduce the radiator too sleeve ratio too.just not sure what effect halfwave radials would have if any.
I would imagine it would be possible to add extra support to the enlarged loop/longer,higher angle radials by forming upside down radials supported on the monopole higher up,from non conductive material,possibly delrin,giving a sort of diamond design.Although I invisage it wouldn't be too easy on the eyes at 27 mhz,might be more practical at 98 mhz though.
Thanks for your answer and clarification shockwave,when you said slightly I wasn't sure if you were referring to an antenna at 27 mhz or 98mhz where indeed it would be as you put it,slightly shorter.
I'm curious,are sirio manufacturing the antennas for you under licence? as they bear many hallmarks of their build quality.
The biggest trouble with peaking any antenna for far field gain without having remote calibrated receivers at distance and the ability to view them in realtime via the net is having to depend on other peoples honesty in signal reporting,which in all honesty is dubious at best.Unfortuneately when people realise that your testing antennas they tend to lie to flatter either their ego or your ego to get better signal reports returned,such is human nature.:headbang:headbang
I would imagine it would be possible to add extra support to the enlarged loop/longer,higher angle radials by forming upside down radials supported on the monopole higher up,from non conductive material,possibly delrin,giving a sort of diamond design.Although I invisage it wouldn't be too easy on the eyes at 27 mhz,might be more practical at 98 mhz though.
Thanks for your answer and clarification shockwave,when you said slightly I wasn't sure if you were referring to an antenna at 27 mhz or 98mhz where indeed it would be as you put it,slightly shorter.
I'm curious,are sirio manufacturing the antennas for you under licence? as they bear many hallmarks of their build quality.
The biggest trouble with peaking any antenna for far field gain without having remote calibrated receivers at distance and the ability to view them in realtime via the net is having to depend on other peoples honesty in signal reporting,which in all honesty is dubious at best.Unfortuneately when people realise that your testing antennas they tend to lie to flatter either their ego or your ego to get better signal reports returned,such is human nature.:headbang:headbang