Avanti Sigma IV Rebuild.

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bigpimp347
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Re: Avanti Sigma IV Rebuild.

Post by bigpimp347 »

i've got three of the original spacers all slightly bent where the basket had been lent up against a wall..
i've everything to straighten them out,
boiling water and a vice, a vice for weeks which works for around a day or so..

any ideas how to get them back straight ??
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Re: Avanti Sigma IV Rebuild.

Post by wa10 »

W8JI
"An antenna with a poor ground using few radials cannot have a support mast grounded to the radial common point (at least it shouldn't if designed properly) There is no exception to this!
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Ian1800
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Re: Avanti Sigma IV Rebuild.

Post by Ian1800 »

Interesting link Bob,
Personally I would never use the original Avanti spacers,
once they start to absorb water and it freezes its not long
before they snap
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Re: Avanti Sigma IV Rebuild.

Post by wa10 »

i agree ian, replacing them is the best solution,
the later version sigma used plastic spreaders like a vector but higher quality.
W8JI
"An antenna with a poor ground using few radials cannot have a support mast grounded to the radial common point (at least it shouldn't if designed properly) There is no exception to this!
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Re: Avanti Sigma IV Rebuild.

Post by Ian1800 »

Haven’t done much this weekend,
Bought the stainless steel nuts and bolts,
Assembled the bottom section and working
on the PL529 connection to connect to the
gamma match.
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Ian1800
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Re: Avanti Sigma IV Rebuild.

Post by Ian1800 »

Probably the next best to the Avanti Sigma 4!
but not sure what type of aluminium they used for it
but I do like the way they connected the ring.
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Ian1800
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Re: Avanti Sigma IV Rebuild.

Post by Ian1800 »

Another fault on the Sigma 4 is the gamma match bracket, which is made
out of 6061 T6 aluminium and tends to crack at the bolt holes then snap off.
I’ve made a copy out of softer 6082 T6 so it may stand the wind movement
a bit better…. I hope
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Re: Avanti Sigma IV Rebuild.

Post by wa10 »

looking nice ian ;)
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Re: Avanti Sigma IV Rebuild.

Post by DX-Digger »

alexthegasman wrote:
wheel bender wrote:These antennas and the breakers who dared to put them on their chimneys became landmarks that stood out among the tons of vertical aluminum around stoke. It's a real classic and will be nice to see pics of it back in the air where the other four in a perfect world should be.
There used to be one i used to see right at the bottom of potteries way in Hanley, on the left, just before the island. Standing proud on the back of a house, I Haven't been that way for a while, wonder if it's still there??

No it is no longer there, it belonged to Charlie "NightOwl" I think he took his Ham ticket but then gave up radio.
I was always impressed with that sigma 4 everyone raved about them on the cb.
ʎɐqǝ uo pɹɐoqʎǝʞ ɐ ʎnq ı ǝɯıʇ ʇsɐן ǝɥʇ sı sıɥʇ
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Re: Avanti Sigma IV Rebuild.

Post by cb4ever104 »

Ian1800 wrote:I’ve made a copy out of softer 6082 T6 so it may stand the wind movement
a bit better…. I hope
Hi Ian . Just curious , but how are you able to make a copy of a piece of an antenna like that ? Special machine , 3D printer ... ??

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Re: Avanti Sigma IV Rebuild.

Post by The Collector »

Metal fatigue will do that to it at that point with tooing and froing over the years as that bit is stretched when bending it into shape meaning it's weakened. Tig-welding??? (is that the right type for aluminium) some supports across this point from the round bit to the straight bit about 3" long either side should help.
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Ian1800
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Re: Avanti Sigma IV Rebuild.

Post by Ian1800 »

I think the cracks are in there from new, this type of alloy doesn’t like to be bent
at sharp angels and fractures might be there from the factory especially if it was bent from cold,
I would of thought it would break at the first bolthole where the metal is thin but all the broken ones I have (and there’s quite a few) all of them break at the bend!
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Re: Avanti Sigma IV Rebuild.

Post by Ian1800 »

I’ve decided to make my OS239 to gamma match connection similar to the grafter as I wanted to keep the original gamma match,
Wonder how yours has been performing over the past few years?
My original connector broke four times so I hope this will cure it.
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Re: Avanti Sigma IV Rebuild.

Post by Phoenix »

Now that looks so solid...well done
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Ian1800
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Re: Avanti Sigma IV Rebuild.

Post by Ian1800 »

Lucky find, brake pipe locking half nuts are the same size as a 3/8
Stud mount so I can get the gamma connection lower and near to
the original position so it wont alter the SWR to much.
I’m using Stainless steel P clips on the epoxy glass spacers.
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