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Old 12th May 2011, 02:26 PM   #1
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Default Ping RADIO GEEKS, 433MHz range?

I've done a search for this (google and a bunch of manufacturer's app.notes) and have come up with ambigous conclusions...
So why not try here?
Does anyone here know the practical range of a 433MHz, 10mW, radiosystem? Is there some graphs showing range in respects to obstacles, weather, etc?
Thanks
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Old 14th May 2011, 01:41 AM   #2
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I noticed that you didn't get any replies, so here is my input. I happen to be an RF engineer for Motorola and I design advanced two way radio equipment for frequencies from 100 MHz to 1 GHz and 2.3 to 2.7 GHz. I have also done considerable experiments in the 432 MHz region for ham radio use.

There are so many variables for a radio system that influence the range other than frequency and power level that it is impossible to answer your question.

The extremes:

A simple low cost transmitter that uses a SAW resonator for frequency control and a PC board antenna sending to a regererative receiver with a PC board antenna could easilly be limited to a range of less than 50 feet. Many car door openers work at 433 or 315 MHz with these type designs.

A system like this could also easilly be blocked from communicating at all by interference on nearby frequencies from ham radio and other equipment cranking out 1 watt or more. A regererative receiver can be blocked by a strong signal 50 or 100 MHz away from the desired signal. Ham equipment is permitted up to 1500 watts on 430 to 450 MHz. Many police, taxi cab and industrial radios operate on 450 to 512 MHz with 5 to 70 watts of power. The US government uses 380 to 420 MHz with ??? power levels.

A carefully designed crystal controlled narrow band FM transmitter sending to a superhetrodyne narrow band FM receiver of similar performance level with both ends using directional antennas under line of sight conditions could easilly acheive a range of over 1 mile with 10 milliwatts of power. Immunity to blocking by unwanted signals is controlled by the receiver design and performance level. A hard rain or snowfall over the entire path could reduce the range by half or more. Anything in the path cuts the range. Leaves and branches could reduce the range quickly, and dense foliage can cut it to near zero.

The cheap FRS radios sold at Best Buy and others run about 1/2 a watt in the 460 MHz range. They use the good quality circuitry I talk about in the second example, but the antennas have no gain. A pair of 10 mW radios with 10 db gain antennas at each end should have similar range. They can talk 5 miles or more over line of sight, but can't do 500 feet through thick wet foliage.

I can tell you that it isn't legal to crack open one of those FRS radios and use it's circuitry for other purposes. I can also tell you that it is the cheapest way to get a functioning high quality transceiver that works...... Don't try to change its frequency unless you really know what you are doing (it usually requires bypassing the microcontroller). They use frequencies that are intermingled with business and public safety users.
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Old 14th May 2011, 02:17 AM   #3
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It is possible to calculate the range vs. power of a radio system in terms of the received signal to noise ratio or bit error rate, but other factors are required, e.g. the transmit and receive antenna gain, the noise figure of the receiver, the attenuation due to environmental causes.

Here's a screenshot of a link budget calculator I wrote a few years ago...

satcalc.gif

...as you can see there are quite a few parameters.

Here's a link to a company RF Solutions Ltd selling 433MHz data tx/rx modules, they quote 'up to 50 metres' using their super-regen receiver.

w
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Old 14th May 2011, 03:01 PM   #4
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Nice link margin calculator....

The OP gives no clue to where in the world he wants to operate the radio equipment (except for the US marines reference). Assuming use in a major US city, the big issue with a super-regen receiver is lack of selectivity. The UHF frequency range is a highly poluted RF enviornment so the probability of on-channel and nearby frequency interference is high and can not be estimated without some measurements.

I needed to build a remote monitoring system that needed 2 mile range with one end about 100 feet from two towers full of cellular and two way radio equipment. The US 902 to 928 MHz band was useless due to the cell site IMD noise. A pair of hacked FRS talkabout radios at 462 MHz worked great.
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