# How to know (or estimate) the range of a transceiver?

I'm trying to decide between different wireless transceivers, where my main requirement is furthest range for a given frequency band.

Is there a way to relate the frequency, data rate, power output, current received/transmitted, etc into a decent estimate for the range these transceivers can work at? I'm new to RF electronics clearly.

For reference, I'm looking at parts like the following:

http://www.digikey.ca/product-search/en/rf-if-and-rfid/rf-transceivers/3539948?k=cc1101

• Directional antennas help increase effective power and thus range. Digital modes may correct errors and help you communicate over longer ranges. Your question is missing information as to what you are trying to accomplish. – Optionparty Sep 22 '13 at 10:44
• Transmitter output power; receiver sensitivity; frequency; environment; antenna directivity; datarate; modulation type; error correction; ... these are all variables that you need to consider. Someone more proficient in this area may even think of couple more. What I am trying to say is: you have to be very careful comparing different transceivers, don't compare apples and oranges. – jippie Sep 22 '13 at 16:15

You need to develop a Link Budget for your application. You know how much power the transmitter puts out, and you know how much power the receiver requires. You need to account for all of the losses and gains in between those two points.

Most of the items are readily quantified, except for the free-space path loss, which is highly dependent on the distance, the frequency band and the operating environment (rural/urban, indoor/outdoor, multipath, etc.). There are many different ways to estimate path losses, but they all are very rough approximations. In the end, you have to build it and try it.

• So then power output of transmitter is the main parameter in distance? Assuming the receiver can accept it. – JDS Sep 22 '13 at 22:00
• That, plus the gain of the transmitting and receiving antennas. Then, you factor in all of the cable and free-space losses. – Dave Tweed Sep 22 '13 at 23:13

There is a standard formula for calculating how much the power is attenuated between two antennas. It is this: -

Link Loss (dB) = 32.4 + 20$log_{10}$(F) + 20$log_{10}$(d)

where F is MHz and d is distance between the two antennas (kilometres).

In short, if you are transmitting at 500MHz over a distance of 2kM, the link loss is

32.4dB + 54.0dB + 6.0dB = 92.4dB.

If the distance were 200 metres the link loss would be 32.4dB + 54.0dB -14.0dB = 72.4dB.

This is the loss between two objects without the hindrance of the earth getting in the way. The antennas assumed are so-called isotropic antennas (which transmit equally in all directions). Should you have an antenna with gain (such as a dipole) at each end you can reduce the loss by about 3.5dB. Should you have higher gain antennas then the losses reduce even more but directionality may become an issue.

Next is how much power does the receiver need to reasonably guarantee moderate data success and there is a formula for this too: -

Power required in dBm is -154dBm + 10$log_{10}$(data rate) dBm

If the data rate is 1Mbps then the power required is -154dBm + 60dBm = -94dBm

From this you can calculate the power out needed by your transmitter. But of course you need to take into account the different effects produced by the presense of the earth and atmosphere which I'll leave for you to research.

Transceivers on their own don't really have a range. You would need at least two, and two transmission lines, and two antennas, and an atmosphere and terrain, and interference, and (as Dave points out) then you get into the concept of link budget, which is treating the collection of components as a system.

In selecting transceivers for a system, you may be interested in their power output, and their sensitivity. This may tend to follow their cost. If there is insufficient power, you can add an RF amp, moving the cost there.

Systems with lower data rates tend to have a longer range, until you face periodic corrupting interference that makes shorter transmissions beneficial.

Transceivers may have a low and high limit on their data rate, and this is normally because of internal design choices made by the manufacturer.

I don't know of a way to relate frequency, data rate, power output, and sensitivity into an estimate for range, without also making so many other assumptions as to make the model unusable.

The CC1101 looks nice. ;-)