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Question about Sigma 4, LW-150 , Sirio Vector 4000 antenna

Discussion in 'CB Antennas' started by Jay in the Mojave, Jan 8, 2005.

  1. Jay in the Mojave

    Jay in the Mojave Active Member

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    Re: Question about Sigma 4, LW-150 , Sirio Vector 4000 anten

    Hello Smalltiredart:



    I have seen the Sigma 4 type antenna work quite well, I used one for a few years.



    I have heard about the interference problems also, and this may be from the vertical element is not insulated from the mast, and uses a Gamma Match.



    My complaint comes from the tuning of the Sigma 4 type antennas. I installed mine and had a difficult time adjusting the antennas SWR. As the antenna was seting on the retracted push-up telescoping Mast, it had a low SWR, but once it was raised into the air the SWR went to something like 3 to 1.



    After messing with it a few days I settled for the antenna being raised almost to the full length of the push up mast, then lowered a few feet to allow tha SWR to acceptable low. This was indicating that the mast and metal guy wires was also part of the radiating element.



    (A unfriendly call to Avanti did not get a answer. But I came up with my own. You will not see a antenna like this design in a military, commerical, or amateur ares. After the time spent on the roof and fighting the SWR as cpmpared with the antennas heigth, I felt a little cheated.)



    The original Avanti manufactured Sigma 4 held up to some pretty high winds for a few years, but I had to take it down, and drill the antennas telescoping aluminum tubing and install stainless steel 10-24 screws and locking nuts to keep the vertical radiator aluminum tubing sections from coming apart. The foreign made versions of the Sigma 4 use sheet metal screws, a bad idea to save money by the manufacture.



    If I was going to install a Sigma 4 Antenna I would use the good UV resistance rope (None Metal) sold by AES or HRO, as guy wires. And get ready to measure the antenna SWR as it is raised up, if your your using a telescoping Mast. As of course the higher the better.



    The Sigma 4 type antenna uses the hoop as a radiation restrictor, to get the antenna to operate as a 5/8 wavelength antenna, and not a 3/4 wavelength antenna. This is done so that a very expensive insulator (and supporting hardware) does not have to be purchased by the manufacture.





    Some foreign venison's of the Sigma 4 Antenna use a butter type aluminum tubing, that is very soft. After a strong wind it looks as if its still is in the wind, being constantly bent! I think that copy came from France.



    Using the LMR400 coax is a good call.



    Jay in the Mojave



    www.a1antennas.com <img src=http://users.joplin.com/dutch64804/posticon44.gif ALT=":44">


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  2. Jay in the Mojave

    Jay in the Mojave Active Member

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    Re: Question about Sigma 4, LW-150 , Sirio Vector 4000 anten

    Hello Smalltiredart:



    I down loaded the Sigma 4 Assembly Instructions, dated 3/82 from CB Tricks.com



    www.cbtricks.com/



    I see the H Mounting Brackets, but this does not insulate the Sigma 4 Antenna from the Mast. The H Mounting Brackets attach just below the radiation restrictor hoop and below the Gamma Match Feed assembly. I agree with UK Mudduck there that it should not insulated.



    The height of the antenna and Mast, may be a factor in the interference problems. I have seen the Sigma 4 Antennas installed that did have a interference problem, and then some that did. But in all fairness to the antenna installation, all neighbor consumer electronics and their installation are different, so your left in the wild west show at times. And most all the consumer electronics equipment is not properly shielded or designed to reject near by RF Energy Fields. Even low power ones.



    One other thing that can be done is to place a Toroid Core in the coax, by wrapping the coax around the core, at a 1/4 wavelength below the antenna connection at the antenna. This will need to be done with the smaller coax such as RG8X or RG142 Teflon Coax. As the bend radius with the larger coax will be to tight. This will choke off RF Currents traveling down the coax outer shield from the imbalance of the Gamma Match. I have not done this with this antenna, so this would be something new to test. While keeping an eye on the field strength.



    The Sigma 4 can be internally reinforced with 1 3/8 and 1 1/4 inch OD Aluminum Tubing installed inside the 1 1/2 inch by 88 inch length of tubing. The most stress is placed at the bottom vertical element.



    The Radiation Restrictor Hoop was made stronger by using fishing monofiliment line to restrict the hoop from swaying too far in heavy winds. Which caused a intermittent connection in the Gamma Match, how wonderful!



    With some playing around the Sigma 4 can be made to work and last, better than it was designed for.



    Jay in the Mojave



    www.a1antennas.com <img src=http://users.joplin.com/dutch64804/posticon44.gif ALT=":44">


    </p>Edited by: <A HREF=http://p067.ezboard.com/bworldwidecbradioclub.showUserPublicProfile?gid=jayinthemojave>Jay in the Mojave</A> at: 1/11/05 5:25 am
     
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  3. These antennas are all pretty much the same type as the original which was the Sigma 4 by Avanti.



    Some of the locals here claim that these antennas are not neighbor friendly and have interference issues. I was wondering if this is true ? I was thinking of trying one. If I ran it it would be 40 feet to the base of the antenna. I run LMR-400 coax, and my set up is well grounded.



    I was curious how some of the others who have ran this antenna liked it, and if they had problems. I was not sure if this was a real issue or if it was mis-installation problems. ( ie. running limiter clipped, sweep tube splater box through garbage coax ) <img src=http://home.comcast.net/~shockwav/smiley_155.gif ALT=":jmpnsmly">



    Maybe Jay from the Mohave has some input on this topic too <img src=http://users.joplin.com/dutch64804/wavey.gif ALT=":wavey">








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  4. Jay in the Mojave

    Jay in the Mojave Active Member

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    Re: Question about Sigma 4, LW-150 , Sirio Vector 4000 anten

    Hello UK Mudduck:



    Look these guys over for aluminum tubing. This web site shows Cold Drawn Aluminum Tubing, 6063 T832 that is what your after with a wall thickness of .058 inches.



    www.texastowers.com/aluminum.htm





    Jay in the Mojave



    www.a1antennas.com <img src=http://users.joplin.com/dutch64804/posticon44.gif ALT=":44">


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  5. MrSuburban

    MrSuburban Guest

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    Damn sounds like Jay was/is in the dark about these antennas as well.
     
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  6. bob85

    bob85 Supporting Member

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    its a sad situation but whenever a cb antenna builder comes on here talking tech they display their lack of understanding of all things pertaining to antennas:blush:
     
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    1 person likes this.
  7. Shockwave

    Shockwave Sr. Member

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    Recently the claim was made that the hairpin match adds "several db gain" over a gamma match. That's more then adding another director for most Yagi's. About the only way you'll ever add several db to a beam is to add another identical beam phased in with the first.
     
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  8. MrSuburban

    MrSuburban Guest

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    Look lets face it Jay upgraded the Penetrator design to be able to handle more winds and more watts, a few adjustments in length u can use it on more than one band but to me he didnt reinvent the antenna nor make it any better performance wise IMO. I went round and round years ago when the claim the hairpin was some magical matching device able to leap small antennas with a single bound. It is only now that several antenna savy members can be in agreement on these things. Me not being one not to shy away from a good forum call out, would usually get labeled as trouble maker for trying to put down someones product. The fact is if others understood they would see we were just calling a spade a spade. In the end the truth eventually has a way of rearing it's ugly head...
     
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