Balun for Sector
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Posted by Knight on September 21, 2008, 8:43 am
Please log in for more thread options Hey guys, Was wondering what is the smallest coax someone can use to make a Balun for this Sector antenna. http://pe2er.nl/wifisector/ Reason is the RG-58 is so short and hard to bend' Can you use a smaller diameter coax and still have this antena work? Thanks guys Pete | |||||||||||||||||||||||||||||||||||||||||||||||||
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Posted by Jeff Liebermann on September 21, 2008, 10:20 am
Please log in for more thread options On Sun, 21 Sep 2008 05:43:31 -0700 (PDT), Knight Read the article again. The author uses RG-316/u teflon dielectric cable for the balun. Outside diameter = 0.100". The RG-58a/u is used for the feed line (which is pushed through a brass tube and soldered to the PCB reflector). For such short runs, the coax cable losses are not important. I use semi-rigid 0.087" diameter coax because it's easy to handle, easy to solder, no messy braid, and I happen to have some. There are smaller sizes, but those are far more difficult to handle: <http://www.micro-coax.com/pages/products/ProductTypes/CableTypes/Semi-RigidCoaxial/EqualTo50ohms/Size.asp>
If you can find one, get a thermal wire stripper for teflon. If not,
use a sharp Exacto knife, or make your own hot wire thermal stripper. There may be some differences in the strip length of the balun coax. Length = 0.5 wavelength * velocity_factor Most of the stuff I use has a measured Vf of 0.70, but there are some oddities floating around, especially if you buy surplus. Measuring the Vf might also be helpful if you can't identify the cable. -- Jeff Liebermann jeffl@cruzio.com 150 Felker St #D http://www.LearnByDestroying.com Santa Cruz CA 95060 http://802.11junk.com Skype: JeffLiebermann AE6KS 831-336-2558 | |||||||||||||||||||||||||||||||||||||||||||||||||
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Posted by DTC on September 21, 2008, 10:20 am
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Knight wrote: > Reason is the RG-58 is so short and hard to bend'
Time Microwave LMR-100 | |||||||||||||||||||||||||||||||||||||||||||||||||
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Posted by Knight on September 21, 2008, 2:30 pm
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> Knight wrote:
> > Reason is the RG-58 is so short and hard to bend'
>
> Time Microwave LMR-100 Jeff not sure what RG-316 is, but is it small like LMR-100 like DTC says? Now that would be nice if I can that! What would be the length to use if in fact I can use LMR-100? Thanks guys Pete | |||||||||||||||||||||||||||||||||||||||||||||||||
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Posted by Jeff Liebermann on September 21, 2008, 3:37 pm
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On Sun, 21 Sep 2008 11:30:58 -0700 (PDT), Knight >> Knight wrote:
>> > Reason is the RG-58 is so short and hard to bend'
>>
>> Time Microwave LMR-100 >
>Jeff not sure what RG-316 is, but is it small like LMR-100 like DTC >says? Both LMR-100 and RG-316/u are about 0.100" in diameter. LMR-100 is stiffer and does not bend easily. RG-316/u does not have a foil shield, and therefore bends much easier. Either will suffice. <http://parts.digikey.com/1/parts/34986-coax-cable-rg316-u-50-ohm-9316-br001.html>
See photo of RG-316/u on bottom of page.
A suitable alternative would be RG-188/u which is 0.110" diameter but has a tape wound PTFE outer jacked instead of FEP. > Now that would be nice if I can that!
> What would be the length to use if in fact I can use LMR-100? The velocity factor of LMR-100 is 0.67. One wavelength at 2.44 GHz (mid band) is 12.3 cm in free space. The shield strip length (not the cut length) is: length = 0.67 * 12.3cm / 2 = 4.12cm See the diagram for how the balun is built. Incidentally, I've now built about 6 assorted AMOS/Franklin antennas including some really weird constructs. They all work just fine, although the higher gain versions required using a sweep generator to accurately adjust the center frequency. -- Jeff Liebermann jeffl@cruzio.com 150 Felker St #D http://www.LearnByDestroying.com Santa Cruz CA 95060 http://802.11junk.com Skype: JeffLiebermann AE6KS 831-336-2558 | |||||||||||||||||||||||||||||||||||||||||||||||||
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>Balun for this Sector antenna.
>http://pe2er.nl/wifisector/
>Reason is the RG-58 is so short and hard to bend'
>Can you use a smaller diameter coax and still have this antena work?