Looking for 2.4GHz antenna advice

[RChadwick]

If you hate to read, please skip down to the short version.

The long version: I like camping, but enjoy it best when I have Internet access. Most campgrounds I frequent have Wi-Fi, but of course I usually get horrible to no reception, as I'm surrounded by a bunch of beautiful green RF attenuators. In the past, I've used an old CPE unit with a patch antenna, and router in one package on a 20 foot pole. I have an ethernet cable going into my camper, and a router redistributes the Internet to our laptops. Unfortunately, I usually waste at least a day playing with antenna alignment, walking around detecting the Wi-Fi hotspots, and hiding covert wi-fi repeaters to get a reliable connection. I figure my current setup should be retired. My new setup is likely to be a 24dB wire mesh parabolic antenna, a 500mW bidirectional amplifier, and a small router on the top of the pole, with the rest the same. While I'm a Ham, and a retired EE, Antennas and RF have never been my strong point. I've done some research, and found a circular-polarized antenna would likely work the best with all the trees around. So:

And now for the short version:

I want to put a circular-polarized antenna at the focal point of a grid parabolic reflector. Considering most of the designs for a circular-polarized antenna (Helical) are long, will this work? Should I get the smallest antenna I can find, and put it at the focal point? I understand Helical antennas need a reflector on the back. Can I just put a long helical antenna in the middle of the dish, and have the dish act as the reflector? Instead of just throwing together a Frankenstein antenna, and hope it turns out well in the end, I'd rather have some good solid advice. Thanks in advance!

 

[VEBill]

The WiFi typical hotspot will normally have one or two vertical antennas plugged into the back. They will almost certainly be oriented more-or-less vertically. So using circular polarization at your end will impose a -3dB penalty in both directions.

There's no need to mess around with different feeds. Just purchase an off-the-shelf hi-gain 2.4GHz antenna.

Here is just one $55 example:

http://www.l-com.com/item.aspx?id=22370

You instinct to mount a 'repeater' (perhaps a reflashed WRT-54GL) at the antenna would avoid expensive RF cable and the loss. Just run power to the kit. Good idea.


Another option in some locations is the cell-phone data networks. I use such a system to provide whole house Internet to my house in the forest. Cradlepoint makes suitable WiFi routers with the slots (USB) to accept a cellular modem. Google HSPA and/or EV-DO and/or 3G networks.

 

[RChadwick]

Thanks for the response. The antenna you mentioned is likely exactly what I had in mind (Saw it on ebay). I was just thinking of replacing the active element with a helical antenna. My reasoning is that, from what I've heard, all the possible little pathways between me and the access point can change the orientation of the polarization. Also, it apparently is better with multipath, which is pretty much guaranteed as I won't have a line-of-sight ever. Then again, if in my helpful wisdom I turn a 24dB antenna into a 7dB antenna, I'd be better off leaving things alone.

The other thought is that, since I'll never have real line-of-sight, where am I aiming? That antenna only has an 8 degree beam width. I'm probably overthinking things (My headache should have been my first clue), but If I put more thought into the last setup, maybe I wouldn't be dealing with it now.

I do fall back on my EVDO phone, but I heard Sprint has put caps on how much data you can transfer a month. It's also still slower than Wi-Fi, especially shared with the wife and daughter. To make things worse, some campgrounds don't have a cell signal. I could use Skype, if only I have Internet..

 

[VEBill]

Circular polarization tends to reject multipath because LHCP is converted to RHCP (for example) with each reflection (except I think that something else weird happens at very low grazing angles). Thus the reflected path is rejected leaving only the direct path. But you need CP at both ends of the link to make that work. And the Hotspot isn't going to be CP.

If the campground provides WiFi and you're just barely out of range at the edge of the property, then perhaps a 10 or 15 dB gain Yagi antenna would be a better option.

 

[Higgler]

good point VE1BLL on the circular note, you're just throwing away 3 dB in most cases going to circular.

It sounds like that to find a signal, you'll need some form of narrow band sensitive detector to look at as you rotate your antenna. Older low cost spectrum analyzer maybe?

Let us know how it works.
You might also consider alternates to your mesh antenna (horn with 20+ dB gain, which you can rotate polarization easily).