Avanti Sigma IV Rebuild.

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Ian1800
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Re: Avanti Sigma IV Rebuild.

Post by Ian1800 »

Anyone else rebuilding an Avanti antenna?
Would like to hear from you.

All the bits are coming together ready for the complete
Rebuild….just need some better weather!
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bigpimp347
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Re: Avanti Sigma IV Rebuild.

Post by bigpimp347 »

i would if you want to part with two bottom sections :)
i have a basket and 7 of the main sections,
i can build a hoop, already done one using two 827 radials and a car wheel :)
i have most the bits to build the third, just the two bottom sections needed to finish it..!!
I want to Die Asleep like my Grandad did,
Unlike his Passengers, Screaming and Shouting.!
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Ian1800
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Re: Avanti Sigma IV Rebuild.

Post by Ian1800 »

I bought this last lot of parts because there was a good base tube.
The bottom two sections are the hardest to get hold of,
The 1.5-inch bottom section snap and the second section
tends to get used to strengthen the bottom 1.5” tube on the next
antenna.

I shall be selling most of the parts I have left after this rebuild
as I don’t intend to rebuild another because of the same problem
your having and they’re hard to find in any condition theses days.

Skycraft use to sell all the sizes of tube but I think they have sold
most of their stock and have no planes to replace it due to the cost
of importing it from the USA.
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bigpimp347
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Re: Avanti Sigma IV Rebuild.

Post by bigpimp347 »

i hear you..
one of my bottom sections i sleeved it and then forced it inside a scaffold tube around 12" long to act as the base, this then connects directly to another scaffold via a sleeve,
my other is still complete and the most original i've ever seen..
i have some aerial mast and tubes lurking around but not been able to find two to replicate the bottom sections,
i might need to botch it to work, or just hold out for one to surface with no top :)
I want to Die Asleep like my Grandad did,
Unlike his Passengers, Screaming and Shouting.!
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HomerBB
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Re: Avanti Sigma IV Rebuild.

Post by HomerBB »

I used 1" aluminum tubing inside of a 1-1/4" aluminum bull float handle to reinforce the lowest section of my V4k homebrew. Notice the larger tube on the left over the smaller tube. This is the main vertical in a photo of the antennas on it side while adjusting the length of the antenna.

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ImageImage
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Ian1800
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Re: Avanti Sigma IV Rebuild.

Post by Ian1800 »

Done a bit more on the sigma,
Bought a tube with a 2mm wall thickness and an OD of 35mm to fit
inside the bottom section, a bit of copper slip and a lump hammer and
with a bit of persuasion its now inside.
I can now start reassembling it.
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bigpimp347
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Re: Avanti Sigma IV Rebuild.

Post by bigpimp347 »

i've rebuilt a Tagra BT-101 Asroplane..
still need a couple of bits for my third Sigma :)
I want to Die Asleep like my Grandad did,
Unlike his Passengers, Screaming and Shouting.!
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Ian1800
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Re: Avanti Sigma IV Rebuild.

Post by Ian1800 »

Well its fully assembled and put it up in the good weather over the bank hols
and its working great with an SWR of 1.1.3 and its receiving lots of DX.
Now should I restore one of my PDL2s or the moonraker 4?
I shall put some of my spare sigma 4 parts on ebay soon.
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Toobad
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Re: Avanti Sigma IV Rebuild.

Post by Toobad »

Congratulations Ian on completing a very worthy project and thanks for doing your bit to keep alive what is probably THE most iconic CB antenna. I'm sure it figures often in the spec for many peoples dream station.

Coincidentally, the lower 12 inches of the bottom tube of my Sigma (Mk.1 version with fibreglass spreaders) snapped clean off due to a freak gust of wind at the weekend. :cry: Ironic really as it had taken all those winter storms in its stride. The tip of the antenna was over 80ft. in the air so it did a good job of destroying itself on its short journey to the ground. I could feel my wallet getting lighter to the tune of £200 as I stared at the Quasar 64 on the Vortex website but at the end of the day it isn't a Sigma IV. But on this rare occasion the Gods were smiling on me as I discovered 2ft. of thick-walled galvananised steel gas pipe was an exact fit inside the broken tube. So after a day of judicious straightening and general fettling Robert did indeed turn out to be my Dad's brother. The Siggy is once again a local landmark and a big noise on 27.555MHz all for the princely sum of £0.00.

Incidentally, there is a seller trading as "forwardmetals" on the Bay of E who can supply 1 3/8" aluminium tubing with a 1/4" wall thickness in 2500mm lengths for £33 delivered. Sounds ideal for sliding up the bottom tube for reinforcement. Also available for a little cheaper in lesser wall thicknesses if weight is an issue.
http://www.ebay.co.uk/itm/Aluminium-Rou ... 1068964447
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Re: Avanti Sigma IV Rebuild.

Post by prettypolly »

Holy cow resurrection thread
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Re: Avanti Sigma IV Rebuild.

Post by dieselfitter »

bump !!! how far up the main tube are the gamma match brackets fixed ??? also how far up the gamma rod does the bracket attach please ? iam going to be busy with aluminium this summer....
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Re: Avanti Sigma IV Rebuild.

Post by cb4ever104 »

I never had one of these , but it's got to rank up there as one of the biggest iconic pieces of easily recognisable CB equipment ever made . I mean if you had a Sigma IV , a 148 GTL-DX and a Turner Expander 500 then you were almost a God back then :)
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Re: Avanti Sigma IV Rebuild.

Post by wa10 »

Starting point for the gamma strap is 33" above the radial brackets, that's not fixed, you can move it up or down a little to tune the antenna,

adjusting the gamma rod only cancels reactance X, you adjust R by moving the gamma strap up or down,

longer gamma straps ( wider gamma spacing ) reduces the range of impedance you can adjust,
shorter gamma straps ( closer gamma spacing ) increases the range of impedance you can adjust,

How far up the gamma it will end up depends on what gamma you use & how high above ground & surroundings the antenna is installed.
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