multiple radios one antenna

Do your investors know you and your staff have so little knowledge of what you are wanting to do?

fundamentalism, fundamentally wrong.

"PlAyDoE" hath wroth:

Combining antennas is very common in the cellular industry. It can be done with 2.4Ghz but the cost of the necessary combiner, ferrite isolators, and filters, will cancel any cost benifits. In addition, the equipment will need to be installed near the antennas, not near the radios, resulting in a rather large box on the tower.

It's easy to combine several antennas on a single transmitter. Power splitters are cheap and easily installed.

note that they describe these as: "...are used for connecting more than one antenna to a single radio." and no mention of multiple radios on a single antenna. What happens is that these provide insufficient isolation between radios. Without isolation, when one radio transmits, the other receiver goes comatose from overload. Another problem is intermodulation mixing. When two transmitters are on the air at the same time, they mix, create garbage on the sum and difference frequencies, and cause the site manager to pull your plug as a source of interference. Incidentally, if you're in a managed radio site, that require that you submit your engineering drawings to the site manager for approval before installation, they will probably reject any form of crude combining.

If you're deperate and must combine radios, you need to build a system similar to what the cellular companies use. Instead of 0.8 and

1.9GHz, you do the same thing on 2.4GHz. You'll need the combiners listed above. You'll need one bandpass cavity on each radio tuned to it's transmitter frequency band thus forming a diplexer. That limits you to channels 1, 6, and 11 with a maximum of 3 radios per antenna. Each filter is 25MHz wide. You can't have two radios on the same channel on the same antenna. That won't work no matter what you do.

Bandpass channel filters:

You probably should install a ferrite or hybrid ring isolator on each transmitter, to prevent RF from going backwards into the transmitter, mixing, and re-radiating as garbage. I couldn't find one specifically made for Wi-Fi at a reasonable price. Oh well.

So, to combine the maximum of 3 radios, you need:

1 3 way splitter $60 3 8pole cavity filters $130/ea $390 Mess of cables $100 Outoor box $ 50 ====================================== Total $600

My guess is the ferrite isolators will be about $100/ea. You'll need three. Treat these as optional for now.

All this to save you the cost of 2 antennas worth about $100/ea. If tower space is at a premium, this may actually be a decent investment.

Incidentally, none of this stuff comes without signal loss. Each cavity will eat about -3dB. The splitter will be about -1dB. All the cables and connectors will gobble another -2dB. If you install a ferrite isolator, it will burn another -2dB plus some more connector losses. Add it all up and you'll have between -6dB and -8dB of loss. To put this in perspective, -6dB loss means your effective range is cut exactly in half.

Short conclusion: Don't do it and get some experienced engineering help. Small WISP systems are easy. Anyone can do those. Wi-Fi does NOT scale gracefully and big systems are a mess. That's why WiMax was invented.