Wi-fi antenna - omni vs. yagi

[memilanuk]

I'm looking at adding a booster/repeater system to our travel trailer, in the hopes of getting some better access to CG wifi. I understand that it probably won't be able to stream movies, etc. but I would like to be able to connect at all! Seems like the campgrounds we stay at are often down in a hole where my cell signal sucks as well.

Anywho, having read thru a number of threads/posts on wifi, etc. I saw several recommendations for omni directional setups like the Jefa Tech, etc. but not very many for yagi antennas. Any ideas as to why? Is there not enough advantage or signal gain with the directional antennas to make it worth having to aim them @ the CG repeater?

Thanks,

Monte

[SCVJeff]

Ive found theres an awful lot of tech savvy folk here as well

[Gonzo42]

100% correct, Jeff. Gain is usually spec'd in dB, but I didn't want to get into that because non-tech folks would have a problem with it.

[SCVJeff]

an Omni is rated as "unity", as it has zero gain. When you start adding any numbers above 0db (unity) in DB, they represent gain.

Also, when rating antennas, one never factors in amplifiers. An amplifier cannot boost what it cannot hear. That's where the performance of the antenna comes in, which is why it's always better to have an antenna with gain in it if working on weak signals. You HAVE to get the signal above the noise floor to do anything with it, and that's not what receive amps do (at the antenna).

[Gonzo42]

I have run across a chart from Weingard showing some gain figures which might be helpful in finding better reception.

Weingard Chart

The "View" link shows you 24 pages of antennae in order to see what they look like.

NOTE: for the most part, gain and directivity work against each other. If the directivity is increased with more elements, the narrower the field is but gain will increase.

An omni-directional antenna will basicly have a gain of 1 (one), not counting any amplifier that is attached.

The chart shows in part the distance one can possibly receive a signal from. This at least will give you an idea of the relative gain between any antennae.

[Crabbypatty]

I use a smart repeater inside for wifi, hooked up to a Hawkings amp and a Hawkings dipole on the roof. A yagi will give you better signal but then you have to aim it which is one more thing to futz with. Most campers have aluminum skin and or metal frames like mine which block radio signals. This system works very well for me and I was able to hook up many many miles away.

[SCVJeff]

Gonzo42 wrote:
Why can't these suppliers publish data sheets showing directivity and gain?

o you make funny joke...
These things are designed by who knows, and sold as modules other RF engineers incorporate into the radios that others design a case around. Real specs likely exist, but you need to get into that design loop to know where to find them.

[Gonzo42]

Why can't these suppliers publish data sheets showing directivity and gain?

[SCVJeff]

You can't say there is NO interference between RC and LC, the separation is about -15db, but you can get pretty creative all things being equal.

[rwbradley]

I knew there was a radio operator out there who would have the answer. It seems when you use kHz and measure in miles, it is more important than when you work in GHz and measure distance in inches or feet. Always fascinating to learn more about it none the less.

[wa8yxm]

I do understand the difference between "Dual" and Circular.

If you are using a 'Flat' antenna (either vertical or horizontal and the access point is a dual. then your picking up -3DB from if it were mono-polarized and you were matched.

IF it's circular.. about the same result.

The difference is this.. If you point two antennas both designed for the SAME polarisation (Circular) you get full power..
But you can also point two more circular antenna pairs, With the OTHER polarization.. ON exactly the same frequncy,, and Not one bit of intrference?

Why is this.

Screw a right hand nut on a right hand bolt it goes on easily

And a left hand nut on a left hand bolt.. Same.

But A Right hand nut will not go on a left hand bolt or the other way around.

And the same is true of circular polarized signals.. They cimply can not "Screw onto" the other direction antenna.

Also setting up circular polarization takes a somewhat larger antenna than what you find on roters.. Dual polarity is easy however.

[rwbradley]

This is starting to get beyond my knowledge, but I checked the spec sheets on the Access Points I use (Enterasys/Extreme Networks) along with a few other brands I am familiar with just to confirm I was right. The technical spec sheets specifically state Dual Pol, but my limited understanding of Dual vs Circular is in practice there is really very little difference in the result when talking WIFI. I think the differences are mostly academic based on the antenna design, so they may be using the terms interchangeably.

[SCVJeff]

Is it really Dual Pol, or are they CP ?

[rwbradley]

wa8yxm wrote:

WyoTraveler wrote:
omni antennas are vertically polorized. Yagis are horizontally polorized.

Who told you that?

I have seen horizontal omni's and knwo how to build them

I have mounted Yagi's vertically (I know how to build them too)

I use a high gain Wi-Fi device basically it is a Linksys WGA-54g (Wireless game adapter) which comes with an Omni antenna the kind that sticks up like a finger.

I built a device to make it highly directional.. Looking at the unit's signal strength meter a very weak signal (NO adapter) around a six Is closer to 26 with the adapter..

How to make adapter..
http://www.amateurlogic.tv
Download Episode 3
George re-cut the antenna on his Linksys.. I did not.

I did nominate George for an awared.. he won too.

To take this a step further, technically speaking most modern Enterprise Wireless Access Points are dual polarized, so polarization of an antenna pointing at it becomes less of a concern. Also most antennas inside cell phones, tablets and laptops are also dual polarized these days. Polarization is less of an issue for the average end user using modern hardware. It is really more of an issue for geeks like us trying to make complex solutions or people using really old or really cheap hardware.

[SCVJeff]

Did you read the rest of the thread past his comment?