Low cost Radio tranceiver Range :5Km Baud Rate : 19200-115200baud

full-dublex

Could you tell us what you want it for?

If low cost is a prime consideration, you may be better off looking at half duplex systems. If you don't especially want a serial port connection, you may like to consider 2.4GHz Wireless LAN cards with a good antenna system.

Mark

What about the range of 5Km? Do you thik wireless LAN (802.11) would reach that far?

Yes, but you have to have decent antennas. Have a look at

or and see what people are up to.

Mark

A full duplex system requires two separate radio links, one for each direction. To avoid the problem with duplex filters, use two complete separate unidirectional radio links operating at different frequency bands.

A 5 km range is easy, if you have a _guaranteed_ line of sight, but if not, it becomes quite tricky to get a decent reliability, requiring a lot of power (several watts), special modulation and coding systems to avoid selective fading etc.

Then you have to consider in which countries this system should be operated and check separately for each country which frequency bands can be used for this kind of operation. Remember, you need two separate bands, if you insist on full-duplex operation.

It would be easiest if some license exempt bands could be used, but these are usually limited to 10-100 mW, which would not be sufficient for reliable 5 km non-light of sight paths at those speeds. Also note that there are usually a lot of all kinds of other activities on license exempt bands that could block your link at much shorter distances, thus, you may need some frequency hopping or spread spectrum system to avoid the other users.

For reliable systems, most likely a licensed radio system would have to be used, with type accepted devices and separate licenses for each installed transmitter. Depending on your definition of "Low Cost" this may or may not be acceptable :-).

Paul

While a WLAN link can be longer than 5 km, you need quite high towers to have a clean line of sight path between the stations, with preferably no obstacles within the first Fresnel zone :-).

In most countries the WLAN is limited to 100 mW ERP (+20 dBm) and when the path loss for 5 km and 2450 MHz is 114 dB, the received power with an omnidirectional antenna would be -94 dBm. After the feeder losses at the receiving end the power level entering the WLAN card can be calculated. Compare this figure to the nominal sensitivity of the WLAN card at various speeds and you know how much receiver antenna gain you are going to need. This calculation assumes a clean path with unobstructed Fresnel zone.

You must also consider the local noise level near the receiver from other sources.

Paul

One of the unit in my implementation will be mobile and therefore wireless LAN seems to be out of question (no tower, no directional antenna). Any other recommendation?

full-dublex

COuld you define "low cost"? - it such a relative term.

Mark

< US$300

Have a look at this unit. It is US$269. It will have the same problems as the Wireless LAN as it operates in the 2.4GHz band as well.

If this is for import to Australia, you will need to add freight and GST (depending on application). You may get a tax reduction as an export from the country of origin.

If you are looking for a unit with a that will handle 5km all terrain, you will need to up your budget. Using something outside of bands like the

2.4GHZ band, you may require a licence which will add to your costs.

GSM? Cellular technology is cheap enough these days.

GSM device itself is not expensive but call charges are not.

Try wifi with a decent antenna.

A modified satellite dish gives 29dBi which will easily do 5 km, but an omnidirectional waveguide may work too.

Approximate wifi distances for various antenna types are at the bottom of this page:

gtoomey

GPRS, then? < $200 US. Call charges negligible for smallish amounts of data in Australia.

Alf.

Completely unrealistic with those requirements.

Drop the full duplex and data requirements and provide at least nearly line of sight paths (with the other station up in a high tower or balloon) may make the situation more realistic. Paul

Sure. Many ham radio tranceivers equipped with AX.25 Terminal Node Controllers can do this. Here's one:

There's Linux support for these things.

The technology is somewhat dated. The default baud rate is 1200 baud. But it's possible to rework much of the gear for higher baud rates.

John Nagle

Hmm, sounds like an EER application to me.

In the Netherlands you can get a rate of Eur 1.5 / megabyte for GPRS. For sending and receiving, so for GSM-to-GSM cost you have to double it. But if the amount of data is limited this is very acceptable.

Thomas

The good thing with the original 1200 bps half duplex audio FSK system is that it works with practically any unmodified radio telephone with a microphone and headphone connector, thus simplifying any type acceptance issues.

The 27 MHz Citizens Band might be an alternative to reach the 5 km distance, provided that data transmission is allowed on the CB frequencies in a particular country. Of course, the 1k2 half duplex throughput is "slightly" below the 19k2.. 115k2 full duplex throughput expected :-).

Paul