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Thread: DIY 5.8G cross-hair

  1. #1
    Forum Member
    Join Date
    Jul 2012
    Near the Great Hill (Massachusetts)

    DIY 5.8G cross-hair

    I'm probably getting ahead of myself hear as I want a pair of omni CPs first. But I figure when parts may have to come from offshore with a 2-3 week delay, it never hurts to research a project I may want to do in two or three months.

    I look over IBC's tutorial on building a cross-hair and it just doesn't look scary hard. Now I don't have tuning electronic equipment for Ghz stuff but if an exact linear measurement is good enough, it seems like a competent hobbyist could hack it. You think?

    I don't have any crimp gear so what I was thinking is buying a few SMA pig tails off eBay. Then cut each in 1/2. That would give me several shots at getting one right if I botched a few. One question I have is which type of coax, 178 or 316 or something else. Can anyone tell me which kind or if it makes a difference?

    From there it would be getting some stiff 30ga wire, a tiny piece of copper tube, and a few square inches of metal plate. Shouldn't be to hard to acquire that. I searched ebay and found some half-hard silver jewelry wire. You think that would cut it or is there some other source for a short quantity of stiff thing wire?

    Any other tips are parts?
    Ken K. (learn2turn)
    AMA 221562

  2. #2
    Forum Member
    Join Date
    Aug 2012
    under the goggles
    buying a few SMA pig tails off eBay
    That's what i did when building a couple helicals,but just checked the link where i purchased from and can't find the short patch cables at his store.http://stores.ebay.com/RF-Basic-Stor...4.l1513&_pgn=2
    The cable i used was RG 316.

    Just read through that entire cross-hair myself and am thinking about giving a go at building one for 5.8.
    The 5.8 one is tiny have you seen one,wow!
    From what i read the wire sizes and lengths are important to get right,the cross-hair is not as forgiving in construction as say compared to building a helical from what i've read.

    I used that "memory wire" used for jewelry making to build a cl and spw antenna but i think that wire may be to large dia. for constructing the cross-hair at 5.8g.
    Other sources of wire might be a larger multi strand wire.
    Remove the insulation to get at the individual strands.
    Also maybe some magnet/enamel coated motor winding wire or guitar string,just some ideas haven't checked any of them yet.


  3. #3
    Forum Member
    Join Date
    Jun 2012
    Boston, MA
    I've made a few 5.8 crosshairs, they work well. For the reflector I use copperclad pc board, you can buy it at Radio Shack in different sizes and the smallest is enough to make a couple 5.8 crosshairs. They also sell a limited range of SMA connectors, I've gotten a number of 90 degree adaptors and male SMA crimp connectors there. If you want larger sheets of copperclad go to U-Do-It electronics in Needham, right off RT 128. For the balun I use brass tubing, Jeremy has it in his shop along with very small "piano wire" that I used to make my crosshairs.

    If you want to buy SMA connectors locally, order from L-com (www.l-com.com), they're in Andover Ma.

    You can get a decent set of SMA crimp pliers at U-Do-It along with good soldering equipment, L-Com has them too.

    Most importantly, get a cheap set of electronic digital calipers for measuring the wire. The lengths of the arms for the 5.8 crosshair are small, 11. and 13.some fraction of a mm as I recall. I cut a piece of wire longer than needed and then use the calipers to measure one of the arms and then make the necessary 90 degree bend. from there I measure out the remaining arm length and cut the wire to length after measuring with the calipers. I then solder to the coax right at the bend, much easier than trying to accurately cut the wire after it's been soldered and so far it's worked well for me doing it that way on 5.8, 2.4, and 1.2 gHz crosshairs.


  4. #4
    Forum Member
    Join Date
    Mar 2011
    Amherst, VA
    Use RG316 and 30 AWG wire. Be VERY precise with it. I know it sounds easy, but it is not, trust me. If you can find mini coax (1.13mm) that will do even better than RG316 as it will allow you to get your element spacing tighter. Like I said, not as easy as it seems. Believe it or not, I have a hard time getting this thing perfect on 2.4GHz on the first try. I refuse to mess with 5.8GHz because it would take me hours... but I'm a perfectionist as well so take that with a grain of salt.

    If it is broken, fix it. if it isn't broken, I'll soon fix that.

    [url]videoaerialsystems.com[/url] - Performance video piloting

  5. #5
    Forum Member
    Join Date
    Jul 2012
    I would like to see this 5.8ghz crosshair.

    What are the advantages of it over say the helical?

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