Ok so I was thinking of a double barrel Yagi antenna. Like get a USB WiFi like (http://catalog.belkin.com/IWCatProductPage.process?Merchant_Id=&Section_Id=2 00340&pcount=&Product_Id=122761&Section.Section_Pa th=%2FRoot%2FNetworki%2E%2E%2EndCables%2FWirelessN etworking%2F#) or a PC Card WiFi with 2 Antenna connectors (if there is one). And wire them up to 2 identical Yagi antennas like pringle can size. Do you guys think that would work, I've been reading up on the tech, but not totally certain if this would be effective.

Tell me what you guys think.

I've read about it being done. You need a phased cable so the signals will add rather then negate each other. You can't just make a Y cable.

Tron Of Borg

Assuming that you think you'll get a boost over a single yagi, it won't do anything for you. Sorry. It shows you're thinking, though!

Too bad, it would have looked cool.

Dual antenna designs are made to reduce problems associated with the Receive signals bouncing off nearby objects (which they do at these frequencies) and arriving slightly out of sync with each other. The problem is called "multipath." A good anology is "ghosting" on a TV picture; same type of effect. These duel antennae are configured in a switching system usually called "antenna diversity." Using diversity switching, the strongest signal is prefered over the weaker. On Transmit, only on antenna is used.

If you used two yagis in a side by side "shotgun" setup, one of two things would happen: 1) the switch would lock on one yagi, and only one would ever be used; or 2) the switch would continuously oscillate between the two yagis.

To use a yagi with these kinds of AP, you put the yagi on one port, and turn the other antenna off, using the software controls.

Search on "multipath", as its been discussed in these forums before.

Cheers,
Thorn

It looks like we were both posting at the same time. :-)

Tron, do you have any references on this? If you can get this to work using a phased cable of some sort, I would be very interested in seeing it. I've got a couple of WAP11s that I'd be willing to experiment with.

Cheers,
Thorn

Thorn is correct in his assessment. You can split the antenna cable, but doing so reduces the DBi of each antenna. This is commonly done is industrial applications, but for specific coverage applications, such as down aisles.
A further note, the cards with two antenna ports are built to for antenna diversity. Diversity is used to overcome multipath losses, but operate as a pair, and are intended for use with omnidirectional antennii.

Stacking yagi's for higher gain has been done for years in the ham community. Two identical yagis stacked properly will give about 2db gain over a single one. Many manufacturers offer kits to combine two or more antennas for higher gain. Check out the ham sites or do a search on "stacked yagi" for more info.

I've come across articles about this being done successfully although I never thought that I'd need to save the URL.

In one article, the author needed to bounce a signal off a mountain. There was no power available on this mountain so he had to find some mechanical way to increase the gain. He did so by making 2 twin-yaggie's and connected the 2 arrays together. One array pointed to one ap and the other array pointed to the other AP.

I don't see what is so hard about seeing that this works. Just as OUT-OF-PHASE MULTIPATH (180*) will negate a signal IN-PHASE MULTIPATH will compliment a signal. In this case, we aren't talking about MULTIPATH at all. We are simply taking 2 identical signals and adding them together.

Tron Of Borg

Hmmm... We seem to be talking about a couple of different things here. Let's see if I can clear up what my thoughts are on this.

In the original post, Ai42 was asking about adding 2 yagis to an AP with DUAL antenna ports (WAP11, Belkin F5D6050, etc.) He described it as a "double barreled" design. I took it to mean something like this: (Ascii art time. If this ascii art doesn't make sense, copy this message into notepad or something, and display it in Courier or other fixed-space font.)

(yagi) -------------
|-|-|-|========|(ant port1)|
| AP |
|-|-|-|========|(ant port2)|
-------------

IMHO, that will not work, because of the diversity switch. The diversity switch being the critical part. The switch will see two signals and try to use better one, and get rid of the other. It will either lock one side on, or oscillate between the two. Either way, you don't get both antennae in an additive gain situation. I agree that we're not actually talking about multiphase, it's just that the diversity switch is still in there and functioning on those dual port models.

Tron's first post mentions a phased cable, and Outcast_one mentions stacked yagis. I believe these designs DO work with dual antennae on a SINGLE port. Something like:

------------
|-|-|-|======+=|(ant port)|
| | AP |
|-|-|-|======/ | |
------------

Tron, in your last post, you mentioned a dual antenna repeater. I sure sounded like Bob Cringley's design (www.pbs.org) That would something like:

|-|-|-|===\ (object)
\==|-|-|-|

Some in the WISP community say this won't work, but I think that it will, with some signal loss. On the other hand, just adding two yagis on a DUAL antenna port AP (like the first design and just pointing them in different directions) won't work, for the same reason as I stated above (again IMHO.)

This probably needs some experimentation to completely determine, but in the meantime I'm willing to listen to other thoughts on it. Comments, people?

Cheers,
Thorn

It stripped all the spaces! Oh well, you can probably figure it out... If not, ask.

*sigh*
Thorn

In my experience with diversity antennas, I haven't seen them do sh!t. As I stated before, I took one antenna off my Linksys AP and my signal dropped. If diversity was working, then it should have shifted to the antenna that was still there.

Tron Of Borg

Tron,
I've heard, but not been able to confirm, that the WAP11 only uses on antenna for TX. (I was told the left, as you face the unit.) The diversity should only work on the RX anyway, assuming that the design engineers were worried about multipath back to the unit. You don't worry about multipath on TX, as it is a reception problem. Would that explain the activity you saw?

BTW, I'm not arguing with your results, I'm trying to figure this out, too! Also, did you try to explictly change the antennae through the software? The WAP11 Configuration software lets you set them manually. I'm just wondering if you would have seen a signal change if you'd switched it via the software, vs. trying to let the diversity switch make the decision for you.

Cheers,
Thorn

See subject. I don't have the WAP11. Mine is the router/AP and not just the AP.

Tron Of Borg

todkapuz

Just curious if anyone had attempted stacked yagis as of this point. I've been looking at $10-$15 home brew 2.4ghz antennas here and found most are built on yagi design, which reminds me of the stacked yagi we used at my school's ham shack, and the home brew 6m antenna I made. I have not played with home brew microwave antennas much, however, the limitation that I can think of right off is how much more senstitive microwave transmissions are to line-loss... so I wonder if the 2-3db gain of stacking would outweigh the loss from the creation of a phase matched y.

Also I'd really like to try it with the threaded rod / washer yagi design I've seen. But I haven't seen very good data on the capture elpise for optimal stacking distances.

William

Thorn

This thread was from over 2 year ago, and since then no one's actually built one, as far as I know. Hell, the thread was from the original version of the forums. We didn't even have signature lines.

In the meantime, a manufacturer came out with a commercial design called the "Vagi." It is comprised of two yagis, meeting in a center V.

Do a search on it, I think Renderman has one.

__________________
Thorn
"Read Altas Shrugged. Compare it to today. Repeat as necessary"