Author Topic: A newbie question about Radio Communication  (Read 9928 times)

johngreene

Re: A newbie question about Radio Communication
« Reply #20 on: July 23, 2007, 11:10:03 AM »
"inside a building" can mean many things. If the building is made from metal framing, room to room is not going to be very good. If you are near furniture or metal anything, your range is going to suffer. I don't have a building big enough to test in for the actual range but from inside the building to the outside, I was getting 200 feet with no real loss in signal strength. 135 feet of that was inside the building.

There are a few things to keep in consideration for links like this. And just about all of them have to do with the FCC.

1. 433/315 MHz are very restrictive on the type of data you transmit. Basically makes them useless for anything other than a remote control.
2. 900 MHz has no restrictions on data or length of transmission. 2.4GHz and 5.7GHz do not either (ISM band stuff).
3. If you do not use spread spectrum, you are limited to 1 mW in the ISM band.
4. You can use a new ruling called 'wide-band data' to increase the power to 10mW but the bandwidth has to be greater than 500kHz. (Check with Part 15 for accurate numbers). What you gain in power you lose in sensitivity because of the increased bandwidth so it is not of much value if you don't need the data rate.
5. 900 MHz will work indoors better than 2.4 and 5.7.

All that being said, the only way to really make things work 'better' or at least the best that they can, is via antenna design. The antenna should be unobstructed. Even then you have to be careful because the FCC limit is on radiated power, not just transmit power. The only real performance increase can be had (without violating FCC rules) is to get the receiver sensitivity to be the best as you possibly can. Get an additional 6dB in receiver sensitivity and you close to double your range.

Your best bet for maximum range would be to use a Frequency Hopping radio at 900 MHz. That way you can transmit a watt of power which should give better than 1000 feet of range for a mobile type application.

Freescale has a free range calculator that your might find useful.

http://www.freescale.com/files/microcontrollers/doc/app_note/AN2611.pdf

--john
I started out with nothing... I still have most of it.

Izzy

Re: A newbie question about Radio Communication
« Reply #21 on: July 23, 2007, 11:24:17 AM »
Thanks for the info, Sir.

We are using MaxStream RF modules and they do have frequency hopping spread spectrum stuff and we are using 1 W output power.
But I dont know whether FHSS is being used by default or we have to change the configuration. (I will havee to look up the manual).