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inside sirio's sleeve antenna
- Thread starter bob85
- Start date
imd262, not much activity on 4mtrs in my area, not sure sbout elsewhere in the uk, people seem to use converted pmr gear or ft847's ect,
eddie, i don't know how its connected, sirio call it gamma fed,
the brass rod has no capacitor, a couple of days ago i saw a 6mtr beam with the same feed arrangement and that was electrically connected at the upper end.
edit, sirio claim its dc shorted.
eddie, i don't know how its connected, sirio call it gamma fed,
the brass rod has no capacitor, a couple of days ago i saw a 6mtr beam with the same feed arrangement and that was electrically connected at the upper end.
edit, sirio claim its dc shorted.
4m is a legal amateur band in the UK and a few other countries as well. It's around 71 MHz.
I know it doesn't look like it but this CX series of antenna operates on the same principals as the Sigma IV. Sirio even calls them both Coaxial J-Poles although I still fail to see how this design even remotely resembles a J-Pole. Notice the bottom of the brass rod is not shorted to the radiator, it's connected to the center pin of the antenna connector. Just like the gamma on a Sigma.
Only real difference is that there is no capacitor in this matching network. Unlike the Sigma with it's angled cone, the CX sleeve causes the main radiator to tune up shorter in terms of wavelength and missing the inductive reactance that we get with the longer Sigma. Since the CX matching network does not have to cancel out any inductive component, it requires no capacitor style gamma.
Also keep in mind the parallel sleeve, shorter main radiator, and narrower tuning network all contribute to loss of gain when compared to a Sigma. The design of the CX dictates that you tune it for minimum VSWR rather then having the flexibility to tune for both maximum gain and minimum VSWR. In my FM band tests the CX design was almost a full db less in gain and harder to get a perfect VSWR. The CX with it's 1.5 dbd was designed to compete with end fed half waves since they look very similar in profile.
Only real difference is that there is no capacitor in this matching network. Unlike the Sigma with it's angled cone, the CX sleeve causes the main radiator to tune up shorter in terms of wavelength and missing the inductive reactance that we get with the longer Sigma. Since the CX matching network does not have to cancel out any inductive component, it requires no capacitor style gamma.
Also keep in mind the parallel sleeve, shorter main radiator, and narrower tuning network all contribute to loss of gain when compared to a Sigma. The design of the CX dictates that you tune it for minimum VSWR rather then having the flexibility to tune for both maximum gain and minimum VSWR. In my FM band tests the CX design was almost a full db less in gain and harder to get a perfect VSWR. The CX with it's 1.5 dbd was designed to compete with end fed half waves since they look very similar in profile.
shockwave,
it looks to me like it works on the same principles as the sigma4 style antennas but right now i dont understand the nocap gamma setup they are using ,
sirio also claim higher gain and lower radiation angle than 5/8wave groundplanes
it looks to me like it works on the same principles as the sigma4 style antennas but right now i dont understand the nocap gamma setup they are using ,
sirio also claim higher gain and lower radiation angle than 5/8wave groundplanes
shockwave,
it looks to me like it works on the same principles as the sigma4 style antennas but right now i dont understand the nocap gamma setup they are using ,
sirio also claim higher gain and lower radiation angle than 5/8wave groundplanes
You only need the capacitor if the antenna has inductive reactance that needs to be tuned out and cancelled. Being that the CX series is slightly shorter then the Vector wavelength, you can just shunt feed it. The VSWR is adjusted by both the shunt tap point and radiator length.
Without the cap, you are confined to right around 3/4 wavelength and can't get the extra gain found as you approach 7/8 wave. You can replace the gamma on the Sigma with just a rod if you shorten the main radiator for VSWR while adjusting the shunt tap point.
The CX performs nearly identical to a 5/8 wave ground plane without the radials and the 1.5 dbd Sirio claims places it right in that ballpark. I liked the CX for one reason. It handles more power because there is no cap. I found it was worth it to buy the good Teflon and make the cap so I could get the gain.
i don't know if sirio changed their claims at some point like they did with the 11mtr antennas but they claim the same gain as the vector for all the cx series with takeoff angles from -2 degrees to +3 degrees,
Sirio Antenne - Products
Sirio Antenne - Products
Sirio Antenne - Products
Sirio Antenne - Products
Sirio Antenne - Products
Sirio Antenne - Products
They have changed the gain and frequency coverage of the CX line. It use to be 1.5 dbd and they didn't have nearly as many models. They also use to claim it was gamma matched. It doesn't look any different then the ones I got several years ago. I scaled it for FM and could not get it to work as good as the Sigma design. I also took my FM model and removed the gamma (replaced with rod), retuned the VSWR and saw a drop in gain. It's close but without the angled sleeve or ability to tune the radiator for max gain, it's not going to equal the Sigma design.
A very super low radiation angle that extends into a negative number. At least it's different from the 'normal' or 'typical' claims for antennas, I've got to say that for them. It does make me wonder just exactly what they are using for a reference point though. Since there's certainly a difference between the lowest radiation angle and the angle at which the most radiation occurs, and since '0' degrees is generally thought to mean horizontal, does that mean that a negative radiation angle is feeding the most radiation down into 'dirt', or that just some of the radiation is going into 'dirt'? A low angle of radiation is a nice thing, but carrying it to extremes 'converts' that asset into a liability or a loss. I wonder if someone in the advertising department got a bonus for that one?
- 'Doc
- 'Doc
doc,
when i started looking at how a sigma could do what i observe i found sleeve and skirt monopoles, they can be tweaked to give those kind of radiation angles, did sirio manage that trick with their antennas?, i have no idea,
i have owned commercial 4x folded dipole uhf stacks with a downtilted radiation angle achieved through phase shift in the feedlines, the last one i had was -8 degrees,
ok if you live up a big hill and want good local coverage at the expense of some gain, i dont live on a hill so i gave them away.
when i started looking at how a sigma could do what i observe i found sleeve and skirt monopoles, they can be tweaked to give those kind of radiation angles, did sirio manage that trick with their antennas?, i have no idea,
i have owned commercial 4x folded dipole uhf stacks with a downtilted radiation angle achieved through phase shift in the feedlines, the last one i had was -8 degrees,
ok if you live up a big hill and want good local coverage at the expense of some gain, i dont live on a hill so i gave them away.
Hey Shockwave, you make some good points. I hate to even challenge your thinking, but I see this a bit differently. I still think this one is a J-pole with the insulated brass rod feeder working against a 1/4 wave ground, the other element also inside of the sleeve which I assume is close to a 1/4 wave. IMO, this feeder setup then end feeds a 1/2 wave radiator just like a Zepp, J-pole, A99, and Signal Engineering's voltage fed quads. In fact for me, this CX is not too different than the way an AstroPlane antenna works with a direct fed 1/4 wave element working against a ground---and end feeding a 1/2 wave element at its voltage node (not the New AstroPlane.)
I think we can build a J-pole with the base open or shorted, just like noted at the bottom left of the following link.
I'm not sure which shows the best performance, but aAll this difference at the base does is change the location of the tap points from the base when left open, and a tap point higher up the feeder when the base is shorted.
I'm also not sure if this tube sleeve is floating or not, but I assume it is. If so, then another difference with the CX series and the J-pole is the use of this larger tube element at the base, concealing this 1/4 wave feeder setup and adding a very strong support for the top 1/2 wave radiator. In such a setup as with the CX, then maybe this support tube may also act as a sleeve which shields the feeder, like a choke or a bazooka balun, from feed line currents.
Just like in the J-pole, I don't think this setup will be making much RF from the base 1/4 wave and according to much discussion on the issue about the Sigma 4, I think you, bob85, and I---for sure figure the Sigma 4 does radiate at or near the base and is probably doing some co-linear sort of magic that allows it to perform so well. This alone would make a difference that would seem to to me to rule out the CX and the Sigma 4 from being similar in performance.
I think the CX is just a 1/2 wave antenna.
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You may be making me think too hard today Marconi I do think that both the Sigma and the CX are very similar to the sleeve fed monopole. The only differences I see are the angles of the sleeve and different feeding methods. They are all variants of the 3/4 wave radiator with a 1/4 wave sleeve grounded at the base.
I would think these slight changes in the design of the sleeve and feeding method could not significantly change the theory of operation very much at all between them. Electrically they should function the same with only small changes in gain.
The problem I have is both the CX and Vector now claim 2 dbd. If the bottom 1/4 wave was nothing more then non radiating transmission line then gain would not be possible. With it's tight parallel sleeve the CX can't generate the same gain as the Vector. Both of them do provide gain over the 1/2 wave.
PS. For a ground plane, it sure is confusing ain't it? I just thought about how similar the bottom of the CX is to a 1/4 wave piece of hardline and I see your point now Marconi. I just don't understand how if this were the case where does the 2 dbd come from and why there has to be more going on. Lets ask Bob.
I do think that both the Sigma and the CX are very similar to the sleeve fed monopole. The only differences I see are the angles of the sleeve and different feeding methods. They are all variants of the 3/4 wave radiator with a 1/4 wave sleeve grounded at the base. I would think these slight changes in the design of the sleeve and feeding method could not significantly change the theory of operation very much at all between them. Electrically they should function the same with only small changes in gain.
The problem I have is both the CX and Vector now claim 2 dbd. If the bottom 1/4 wave was nothing more then non radiating transmission line then gain would not be possible. With it's tight parallel sleeve the CX can't generate the same gain as the Vector. Both of them do provide gain over the 1/2 wave.
PS. For a ground plane, it sure is confusing ain't it? I just thought about how similar the bottom of the CX is to a 1/4 wave piece of hardline and I see your point now Marconi. I just don't understand how if this were the case where does the 2 dbd come from and why there has to be more going on. Lets ask Bob.
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hmmm thanks lol,
i dont see it as been the same as the regular coaxial j-pole, i see the cx series as been very similar to a sigma4, a sigma could use a suitably sized solid cone but finding any info on that style antenna is not an easy task, the antenna guys like cebik ( RIP ) and maxwell dont want to get involved with the arguments they cause,
sleeve monopoles have both antenna mode currents and transmissionline mode currents flowing in the sleeve, the spacing and radial number/diameter determines transmissionline mode impedance and current magnitude, i also think sleeve length will effect those currents too,
gamma match setups have transmissionline mode currents flowing within the gamma section in opposite directions to antenna mode currents,
if with the gamma setup transmissionline mode currents are confined to the gamma section then the rest of the antenna would only have antenna mode currents,
if they are not confined and the lower 1/4wave still acts like a tapered transmissionline then they could operate just like a sleeve monopole with a twist in the tail that produces more gain with the gamma match and flared radials,
i dont understand the cx series been physically shorter than a 3/4wave monopole because the closer the radials are to the central monopole the shorter the whole antenna becomes electrically, needing a lengthening of conductors to restore resonance at the start frequency,
we should look at the lengths of the new cx series.
edit,
the cx series are physically longer than 3/4wave
i dont see it as been the same as the regular coaxial j-pole, i see the cx series as been very similar to a sigma4, a sigma could use a suitably sized solid cone but finding any info on that style antenna is not an easy task, the antenna guys like cebik ( RIP ) and maxwell dont want to get involved with the arguments they cause,
sleeve monopoles have both antenna mode currents and transmissionline mode currents flowing in the sleeve, the spacing and radial number/diameter determines transmissionline mode impedance and current magnitude, i also think sleeve length will effect those currents too,
gamma match setups have transmissionline mode currents flowing within the gamma section in opposite directions to antenna mode currents,
if with the gamma setup transmissionline mode currents are confined to the gamma section then the rest of the antenna would only have antenna mode currents,
if they are not confined and the lower 1/4wave still acts like a tapered transmissionline then they could operate just like a sleeve monopole with a twist in the tail that produces more gain with the gamma match and flared radials,
i dont understand the cx series been physically shorter than a 3/4wave monopole because the closer the radials are to the central monopole the shorter the whole antenna becomes electrically, needing a lengthening of conductors to restore resonance at the start frequency,
we should look at the lengths of the new cx series.
edit,
the cx series are physically longer than 3/4wave
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