There were some posts a while back discussing ways of increasing range and throughput in your wireless connections. I put together some construction guides at:
For popular USB wireless adapters there are also external antenna mods that work great.
Regards, Phil AB9IL
Nice, but...
It seems your helical feed is Right-Hand circularly polarized. When bounced off the dish, it becomes Left-Hand circular plarization. As long as that's intentional, there's no problem. However, you should mention that in the article as someone is sure to get it backwards. Convention for terrestial links and commerical helical antennas is RHCP, but that's not a hard and fast rule.
Suggestion... I've tried various antennas made from copper tape (usually ribbon used for stained glass making) and found that they move around too much. Fortunately that's not a problem for a helical antenna as its extremely wide bandwidth gives considerable lattitude in construction practices. For helixes, I find it easier to have a machine shop gouge a grove into the pipe. That allows me to use common #12AWG round copper wire, which is cheaper and easier to work with. I had about 40ft of 1" dia ABS and white PVC pipe grooved for the purpose a few years ago for about $50. One 10ft section is enough to build about 5 antennas. I had them cut for various turn spacing so I could experiment. However, I made them all RHCP, which kinda ruined it for testing reflector antennas.
Jeff, If I wanted to have a piece of PVC pipe machined for a helical antenna what would I need to tell the machinist.
Jimmie
Not much. YOu need to dimension the original material (PVC or ABS pipe). The rest is:
- pitch (turns per inch)
- number of helixes (I made a 4 groove version for a quadrifilar antenna)
- shape of cut (I asked for a slight radius to fit #12 AWG wire)
- depth of cut (so he doesn't make it too deep and fragile)
Once setup, it's fairly easy to make. The hard part is keeping the pipe sufficiently rigid when cutting. It won't due to have the pipe bend. So, plan on shoving a snug fitting metal pipe inside the ABS or PVC tubing during cutting.
Note that you don't need to have a machine shop make the part. Anyone with a wood working lathe can do the same thing. If you're really clever, you can have the machine shop make one, and then use a pattern follower to clone it. Lots of options, but any of them beats winding tape around a smooth pipe.
Guys, thanks for the comments. It helps me focus on what matters to antenna builders out there.
I've added a note in the construction guide regarding the polarization. In a nutshell, if you are using circular polarization on both ends, they need to match - with consideration for the reversal in a parabolic reflector. If the parabolic is linking with an AP with linear polarization, it isn't an issue. A ten turn helical (or a short helical on small TV dish) more than makes up for any mismatches. Okay on grooving the PVC. I'll have to give that a try on my next project; the copper tape is fine for indoor antennas (with some clearcoat spray). I envision marking a length of PVC and grooving it with a dremel tool - should result in a helical tough enough for outdoor use!
Regards, Phil AB9IL
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