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New antenna from Sirio Gain-Master
- Thread starter dxswe
- Start date
The 'start' of an antenna is always at the end of the feed line. So, are you considering the coax 'inside' that antenna as feed line? It isn't, it's part of the matching network. Think about it.
That choke isn't part of the antenna either. I have to guess that it's placement is for convenience of construction/assembly/set-up, makes things more 'idiot proof' so to say. A choke isn't a 'cure all' by any means, it isn't a 'sure' way of getting rid of CMCs (and in some cases, such as the 'A99'/Imax/etc, those CMCs are, or can be, used to advantage!
And that fabulous 1 - 2 dB of 'gain' over 'other' antennas of the same 'class'! If that isn't as normal as it gets with any two similar antennas, one being 'better' than the other, someone needs a reality check! And just for grins, 1 or 2 dB of 'gain' is very little, not worth the effort in most cases. There's more difference in the behavior of any two antennas coming off of the same assembly line than that.
Do I think this is going to be a viable antenna? Yes, I do. Do I think it's going to be exceptional in any way? Sorry, no I don't. Gotta admit it's some pretty good advertising though.
- 'Doc
(The 'trick' with most of this sort of stuff is recognizing exactly what IS said, versus what's implied.)
That choke isn't part of the antenna either. I have to guess that it's placement is for convenience of construction/assembly/set-up, makes things more 'idiot proof' so to say. A choke isn't a 'cure all' by any means, it isn't a 'sure' way of getting rid of CMCs (and in some cases, such as the 'A99'/Imax/etc, those CMCs are, or can be, used to advantage!
And that fabulous 1 - 2 dB of 'gain' over 'other' antennas of the same 'class'! If that isn't as normal as it gets with any two similar antennas, one being 'better' than the other, someone needs a reality check! And just for grins, 1 or 2 dB of 'gain' is very little, not worth the effort in most cases. There's more difference in the behavior of any two antennas coming off of the same assembly line than that.
Do I think this is going to be a viable antenna? Yes, I do. Do I think it's going to be exceptional in any way? Sorry, no I don't. Gotta admit it's some pretty good advertising though.
- 'Doc
(The 'trick' with most of this sort of stuff is recognizing exactly what IS said, versus what's implied.)
The vertical coax inside the base of the antenna is not feedline. It is the lower half of the balanced radiating element. It is the matching stub that corrects the impedance. The choke at the base is not just preventing the typical common mode currents. It is actually creating an open circuit to RF at a key position in the radiator to make it balanced with the top half. Notice how that choke is wound. Many turns not overlapped and space to prevent coupling. Most antennas will function reasonable well without a choke. Take the choke off this one and the entire antenna will be out of balance with a poor VSWR.
To say a real 1 or 2 db variation between 5/8 waves is typical would not be correct. The standard 5/8 wave only has a real 1.3 db over the 1/2 wave and most of us easily see this change on the S meter. That's because the S meter exaggerates and if you could double the gain on the horizon over the 1.3 db you would see that too. That indeed would be a significant accomplishment over other 5/8 waves. If it works like they say.
Sirio also doesn't fudge gain figures. They have invested a great deal of money well beyond computer models and field testing to develop some of their antennas. Anyone know what that pretty blue room is the engineers are pictured in holding the Gain-Master? That's an anechoic chamber used for precise real world measurement of an antennas radiation field. I wouldn't even want to speculate on what it's cost to install was.
To say a real 1 or 2 db variation between 5/8 waves is typical would not be correct. The standard 5/8 wave only has a real 1.3 db over the 1/2 wave and most of us easily see this change on the S meter. That's because the S meter exaggerates and if you could double the gain on the horizon over the 1.3 db you would see that too. That indeed would be a significant accomplishment over other 5/8 waves. If it works like they say.
Sirio also doesn't fudge gain figures. They have invested a great deal of money well beyond computer models and field testing to develop some of their antennas. Anyone know what that pretty blue room is the engineers are pictured in holding the Gain-Master? That's an anechoic chamber used for precise real world measurement of an antennas radiation field. I wouldn't even want to speculate on what it's cost to install was.
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The ground side of this antenna may not be so obvious, but IMO the outer shield of the feed line acts like a sleeve between the coax choke at the bottom and the capacitor at the top and this sleeve serves as the radiating ground element. I think this one works because of common mode currents flowing in the bottom section, which are in phase and balanced with the currents in the top element due to the location of the capacitor in the middle of the radiator.
Wouldn't you agree that since the radiation in the lower half is in phase and balanced with the current in the top that this means the lower part is not acting like a ground as if it were a Marconi or unbalanced groundplane? Acting like a balanced antenna means both halves are radiating equal with neither acting like a ground. The choke stops the radiation in the bottom so it equals the length of the top and allows the antenna to be fed with unbalanced coax.
Most of this is a confusion in terms. An assumption that what is commonly thought of as something is actually that something. A good example of that is that 'other half' of an antenna and 'ground'. They both commonly describe the exact same things but using different 'reference points', 'street talk'?
You are certainly welcome to your own opinions, but I just don't care to participate in that sort of nonsense at the moment. Have fun.
- 'Doc
You are certainly welcome to your own opinions, but I just don't care to participate in that sort of nonsense at the moment. Have fun.
- 'Doc
LOL
I did not mean to say that any one is right or wrong...only that I agree with a point of view.
If you take a 3 El Yagi, and turn it vertical, and look at where the coax attaches.. what I would call the feed point.. I would call it a center feed antenna.
If you take a "dipole " Antenna, and feed it at the center (lol) I would call it a center feed antenna.
This Antenna, (to me ) is feed at the base IE below the Choke, that is Part of the antenna design, so I look at it as a End feed.
I very much agree it "acts" like a center feed antenna.
It is only a point of view.
73
Jeff
I did not mean to say that any one is right or wrong...only that I agree with a point of view.
If you take a 3 El Yagi, and turn it vertical, and look at where the coax attaches.. what I would call the feed point.. I would call it a center feed antenna.
If you take a "dipole " Antenna, and feed it at the center (lol) I would call it a center feed antenna.
This Antenna, (to me ) is feed at the base IE below the Choke, that is Part of the antenna design, so I look at it as a End feed.
I very much agree it "acts" like a center feed antenna.
It is only a point of view.
73
Jeff
B
BOOTY MONSTER
Guest
on page 4 of the installation manual download the step 1 pic shows a connector (a little internal coax connector ???????) that goes to a section where part of it goes up the antenna and part goes down to..... ?????? looks to have a connector on it , but i dont see anything that says it connects to something else .
http://www.gain-master.it/Id-406 Gain master.pdf
any idea what that is ???
i dont understand how they can say this antenna will have 1-2 db gain over a conventional 5/8 when a conventional 5/8 only has 1.5 db gain over a dipole . im certianly not qualified to say they are wrong though .
http://www.gain-master.it/Id-406 Gain master.pdf
any idea what that is ???
i dont understand how they can say this antenna will have 1-2 db gain over a conventional 5/8 when a conventional 5/8 only has 1.5 db gain over a dipole . im certianly not qualified to say they are wrong though .
I think what you are looking at is the impedance matching stub.
The Gain would come from 2 things..... one the fact that the RF currents are "in Phase" And the fact that the TOA is pulled down to Horizontal.
That is how a 5/8 wave produces gain.....by pulling the TOA down.
73
Jeff
The Gain would come from 2 things..... one the fact that the RF currents are "in Phase" And the fact that the TOA is pulled down to Horizontal.
That is how a 5/8 wave produces gain.....by pulling the TOA down.
73
Jeff
Booty',
Those 'connections' are how the coaxial matching section and 'stub' are connected inside the antenna. Since the 'stub' is shorted, it appears to be just stuffed back inside the lower part of the support tube. The connection that's taped is the one that has to be insulated to keep it working.
If this is the assembly instructions for all of these antennas, I've got a feeling that they will be having a little more 'trouble' with them than if it were pre-assembled. It's not impossibly complicated, but it's sure different.
- 'Doc
Those 'connections' are how the coaxial matching section and 'stub' are connected inside the antenna. Since the 'stub' is shorted, it appears to be just stuffed back inside the lower part of the support tube. The connection that's taped is the one that has to be insulated to keep it working.
If this is the assembly instructions for all of these antennas, I've got a feeling that they will be having a little more 'trouble' with them than if it were pre-assembled. It's not impossibly complicated, but it's sure different.
- 'Doc
Jeff I don’t really understand this business about phase relationships and how they work, but I believe the two poles of a dipole must show the currents to be in phase in order to radiate. So, the top and bottom of this radiator has to be in phase as you note.
I can’t argue the effects of pulling the maximum TOA down like noted in the example they site. I think Sirio might be right in a theoretical sense, if their facts are correctly stated. But, I don’t think they can assure such success for everyone’s installation at various heights above Earth either.
We don’t even know if or how Earth affects this pattern they show. Sirio’s G-M pattern seems to suggest a free space ½ wave vertical maybe a ¼ wl above an infinite conducting ground plane. For me that suggest theory only and not a vertical above real Earth. I’m just not sure about all this modeling business being able to really tell us such minute differences among different antenna designs---and in particular how they handle the radiated patterns.
I think Sirio is making the claim that their G-M produces a pure form of a ½ wavelength pattern that happens to show the maximum RF gain at the horizon due to the nature of their matching scheme and design. So, when they overlay the pattern of a typical 5/8 wave radiator their G-M shows some additional gain to be useful in the area at the horizon---as noted in the yellow space on the image. I don’t read their claim to suggest any actual increase in gain over the 5/8 wave, but instead a simple and better use of the gain that their pattern produces at the horizon. As the science suggest, this is where we tend to think gain is most important for two-way ground communications. It looks to me however, that the G-M pattern may not be showing ground loss affects, while the 5/8 wave pattern does---and I wonder if that is fair or is it apples to oranges comparison.
I’ve generally said the same thing about my Wolf .64 Ground Plane---relative to his using all the reported good bells & whistles in vertical antenna design, so only real world testing can possibly shed some light on this idea. I don’t know if it can be verified or not, but Sirio’s claim seems to make a good case like ‘Doc suggested.
BM, it’s difficult to disagree with other opinions here, but IMO these images are all just out-of-proportion artist’s renderings throughout. We have to try and think why has Sirio’s describes stuff as they have. I don’t have the solution, but I have some ideas to consider.
I think the break created by the connector was done to accommodate shipping and handling without having to violating their caution notice---“…not to bend or pinch the coax.” This connector is just a connector, like a barrel connector. IMO it’s nothing special and it surely doesn’t need to be taped or insulated---except maybe to keep wind motion from loosening the threads over time in the weather, and/or to help eliminate water getting into the feed line assuming I was correct about the need to add a break for shipping and handling. Plus remember the radiator is a bit over 22 feet long and ½ would be 11 feet for the bottom coaxial section. The shipping container is only 6.5’ feet tall, so the bottom would necessarily have to be bent without the connector.
If you look at the schematic the coax appears to actually terminate at the capacitor where the shield appears to be is left open like a open-ended sleeve. Only the center conductor extends up into the capacitor and to the wire radiator above. I’m just guessing here, but I consider this point to be the likely center of this antenna and that is the feed point referenced by Sirio and this is where the common mode current starts flowing that radiates the lower end of the radiator.
I Agree with everything you have posted Eddie, and I also agree that real world testing will tell the tale.
Shockwave
I will retract my statement about "end feed antenna"
After thinking about this for two days, I will concede the "technical" feed point of the antenna is just below that capacitor in the center of the antenna as Marconi has stated above
I am getting older, and as a result much more stubborn in my thinking, how ever givin enough time.......
73
Jeff
Shockwave
I will retract my statement about "end feed antenna"
After thinking about this for two days, I will concede the "technical" feed point of the antenna is just below that capacitor in the center of the antenna as Marconi has stated above
I am getting older, and as a result much more stubborn in my thinking, how ever givin enough time.......
73
Jeff
The point you guys are missing is due to the design of this antenna,the outside of the shield on the bottom half of the antenna (what you are terming the ground side) is using the common mode effect/skin effect to give the bottom half of a dipole,the inside of the shield and the centre conductor will be acting as a balanced feedline below the capacitor,so it is clearly a centre fed dipole.
the only difference to this antenna and a big stick is this uses the common mode effect/skin effect to use the outside of the shield to radiate where the bigstick uses a metal tube,inside the shield/metal tube is balanced as the shield/tube prevents radiation due to shielding,they have taken advantage of the skin effect. shockwave is right it IS a centre fed dipole.
you have to be aware that for the purpose of rf in this antenna the inside and outside of the shield above the choke are seperate entities.its a very cunning design which shakespeare failed to use to the best advantage but sirio have taken it to the max.
if the choke weren't there it would not only be an unbalanced antenna but it would be rife with cmc just like the bigsticks were.the choke not only chokes cmc but as shockwave has pointed out it decides the electrical length of the dipole lower half to make it a balanced dipole which is evident in the radiation pattern.
the only difference to this antenna and a big stick is this uses the common mode effect/skin effect to use the outside of the shield to radiate where the bigstick uses a metal tube,inside the shield/metal tube is balanced as the shield/tube prevents radiation due to shielding,they have taken advantage of the skin effect. shockwave is right it IS a centre fed dipole.
you have to be aware that for the purpose of rf in this antenna the inside and outside of the shield above the choke are seperate entities.its a very cunning design which shakespeare failed to use to the best advantage but sirio have taken it to the max.
if the choke weren't there it would not only be an unbalanced antenna but it would be rife with cmc just like the bigsticks were.the choke not only chokes cmc but as shockwave has pointed out it decides the electrical length of the dipole lower half to make it a balanced dipole which is evident in the radiation pattern.
well done that man,
for a moment there i thought doc had you brainwashed with more of the nonesense he says he does not want to participate in
shockwave/jazz
imho you have it correct, coaxial cable acts as a 3 wire transmissionline, the 3rd conductor been the outside of the coax which is also the lower leg of the dipole,
the choke is not positioned for "convenience" it defines the electrical end at the design frequency of the lower leg,
move it or wind it with insufficient choking impedance and you change the antennas pattern,
you would definately have to move the stub position and length if you changed to a different vf coaxial,
using fatter coax such as rg213 may also call for a slight shortening of the lower leg and a rework of the choke,
it is an interesting design which imho is targetting the imax.
THIS AINT YOUR DADDY'S BIGSTICK
this antenna is definately targetting the imax market,by using bigstick technology with vastly superior execution of the technical side than shakespeare achieved.
ironically it also shows vastly superior execution of design than solarcon achieved too,it may look similar to an imax which no doubt was the aim,but its worlds apart electrically.
one thing i know concerns bob and would also concern me is the longevity of the coaxial cable used in the choke when its exposed to ultaviolet light.most of the red translucent coloured coax on the market is poor in this respect,hopefully sirio have taken that into account,i'd be much happier if i knew it was either a ncv jacket with good uv resistant properties or a polyethylene jacket (direct bury type jacket) which is good on uv resistance.
chemical migration can seriously limit the useful lifespan of coax,and in an antenna like this which if i know cb'ers they will expect it to last for tens of years the quality of that choke should be paramount.
its certainly different to anything thats been before it so should be interesting to see how it performs and fares long term.