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Avanti Sigma4: An alternative view point
- Thread starter bob85
- Start date
Do you think it is simply a variation of the Sigma/Vector antenna. Obvious differences are the coils, the matching coil/network on the bottom (is it tapped?), and the closed top on the basket. Less obvious is in the full 5/8 radiator over the 1/4 wave basket. Overall it is 7/8 wavelength long. Am I way off thinking the coil above the basket was added to work a match on the 5/8 radiator above because the closed basket design isolated the lower 1/4 wave section from interaction with the upper radiator (I told you I'm not very techie on this stuff)?
Clearly the basket doesn't replace horizontal GP seeing those on the bottom are 105" long. So did this basket not improve the horizontal radiation in the way the "V" shaped one on the V4k is believed to do?
Does the basket capture out-of-phase radiation? and what difference would it make if there is separate matching done above the basket for the upper 5/8 radiator, and if a full-sized GP below it all is required to correct TOA issues. Is this antenna self-contradictory?
Is the basket just an over-sized matching network interrupting the top and bottom halves of the coil and not really anything but a real big 5/8 wave?
What a deal. I wish some one smarter would ask the questions I don't even know how to ask.
the ham big-mac does work very well, i had a mac on a 73ft mast in a field, it performed a little better than a stock sigma4, against a modded vector im sure it would be a close contest,
its not all one sided, the 5/8 over 1/4wave mac seems to have a narrow beamwidth,
in any winds the big-mac tx and rx signal sways like you are mobile with a floppy whip when compared to the much stiffer stock sigma4 on the same mast,
the big-mac is weakly constructed, a much stronger stiffer version would be great but expensive unless you are into homebrewing,
at over 32ft tall with two coils a basket and 6 1/4wave radials for birds to sit on while shitting all over your yard/house its big and ugly to some people,
i wish i still had mine to take measurements for an i10k > big-mac conversion
its not all one sided, the 5/8 over 1/4wave mac seems to have a narrow beamwidth,
in any winds the big-mac tx and rx signal sways like you are mobile with a floppy whip when compared to the much stiffer stock sigma4 on the same mast,
the big-mac is weakly constructed, a much stronger stiffer version would be great but expensive unless you are into homebrewing,
at over 32ft tall with two coils a basket and 6 1/4wave radials for birds to sit on while shitting all over your yard/house its big and ugly to some people,
i wish i still had mine to take measurements for an i10k > big-mac conversion
homer,
the big-mac is a totally different antenna to a sigma style antenna,
its fed the same as a maco/i10k and other endfed groundplanes, where it differes is the mac has an extra 1/4wave section inserted between the end of the 5/8wave and the feed coil,
between the 1/4wave and the 5/8wave sections is a phasing coil,
the vertical rods are connected in parallel with each other and the 1/4wave section creating a fat cage style 1/4wave.
the big-mac is a totally different antenna to a sigma style antenna,
its fed the same as a maco/i10k and other endfed groundplanes, where it differes is the mac has an extra 1/4wave section inserted between the end of the 5/8wave and the feed coil,
between the 1/4wave and the 5/8wave sections is a phasing coil,
the vertical rods are connected in parallel with each other and the 1/4wave section creating a fat cage style 1/4wave.
Seeing that someone finally has one of these antennas, what are the possibilities of getting some useful measurements? Things like the size of the coil, element lengths, and some closer pictures of how the radials and three 1/4 wave vertical sections connect to the coils would be awesome.
B
BOOTY MONSTER
Guest
Unfortunately SW I'm 99% sure that he's either been given that pic, or just found it online, I can hear ericcson on the air every day as he is only around 30 miles away from me, and he doesn't own any on the antenna's in that picture.
I can certainly see what Bob was saying though, just from looking at the bottom section of the Mac and the Sigma 4 in that pic, the Mac looks very very flimsy indeed for a 7/8 wave long antenna.
B
BOOTY MONSTER
Guest
a few more pics .
Ham International Antennes
just finished reading this entire thread ............. thanks to all the folks that contributed to it
B
BOOTY MONSTER
Guest
This may actually be a colinear design. If so it should show a little gain over the other players.
Bob do you think this deficiency was due to the lack of a good tune or the physical design? Isn't that sorta' what you suggest regarding the working of the Vector/Sigma design?
I think all antennas are tunable, but I have to ask if the Big Mac was tunable in the normal sense of the word, and if so...what was changed the tap point?