Restoring a Avanti Sigma 2 5/8

[firerunner]

I just picked up a Avanti Sigma 2 antenna the other day for taking it down for the old owner. I was wondering how much cleaning and polishing of the aluminum I should do? The basic antenna is in great shape except for the inner coil assembly, the ends just crumbled and the fiberglass section is no good, i don't think the fiberglass part is original. Does anyone know where i can get these parts or how to make my own.

 

[firerunner]

First picture is the antennas resting place for the last 40 years, second picture whats left of the inner coil system. Hopefully the I posted the pictures right.

 

[firerunner]

I think this picture posted by Master Chief a few years ago it shows the two diferent feed points used on the sigma 5/8 antenna.

Master Chief wrote this in 2006.

"The feedpoints are completely different. A/S added a coil which made the Sigma 5/8 DC grounded for the first time! They also used 3 bolts around the bottom to secure it to the base tube. The length of the 10 guage wire (printed "Phelps Dodge" on the insulation) was also increased when the coil was added. You can also see the longer fiberglass tube. The top section of the main radiator was also shorten approx 6" to bring the electrical length of the antenna back to 5/8."

"From the center conductor of the coax jack, the signal goes up the orange wire to the top aluminum block. The bottom of the loop attaches here. The signal travels around the loop an into the base of the main radiator. Inside the fiberglass tube, there is a 1" gap between the base of the main radiator and the aluminum block. This is Avanti's elevated feed system I've spoken of in the past. The main radiator is NEVER surrounded by any metal at ground potential (unlike the Penetrator)."

In the picture it looks like there could be two different metals (or materials) used in the bottom section. I put a ohm meter on what is left of mine and the material has no continuity, i don't have a piece of the very bottom to check. If it was aluminum it should have continuity Right? I'm just trying to understand how to make this part myself since i can't find one that is available.

I hope Master Chief still hangs around and could possibly help me understand how this all works. I'm really new to the antenna rebuild game and don't always understand what terms used mean. Thanks in advance for any help.
Chuck

 

[firerunner]

So back to my first question, do I polish the radiator and radials to a high polish or just clean up with fine sand paper?

 

[bob85]

firerunner all 3 plugs are aluminum made from aluminum bar stock, probably 6061-t6 like the tubes,
the top two form a capacitor in parallel with the loop,

i would use a scotchbrite pad & plenty of soapy water to clean the oxidation from the tubes followed by metal a polish if you want it to shine,

clean it outside in a well ventilated area and make sure you are upwind don't breathe in the dust.

 

[firerunner]

bob85,
Thanks for the reply that helps a lot. I'm pretty sure I can fab up those parts now that I know for sure what they are made of. When you say three I assume you are also talking about the one above with the bolt in it that blocks the water. This antenna unfortunately was mounted to a chimney making for more clean up. I'm also having problems getting 4 of the joints apart, i want to clean the joints inside and out. Thanks again.

 

[bob85]

yes i mean the plug that the top of the hoop bolts to,
we had the same issues with dirty & oxidised antennas when we were mostly a coal fired area, good luck in cleaning it up.

 

[firerunner]

This is one of the parts i have cleaned up already. Once i finish this rebuild it will replace my sirio Tornado which has served me well just not as well built.

 

[bob85]

having cleaned my share of avanti antennas id say you have made a good job of cleaning that.

 

[Marconi]

Very good advice Bob, on doing the cleaning outside where there is good ventilation.

I got pneumonia cleaning my S4 in my office several years ago. Big mistake breathing in the dust.