315mhz, 418mhz, and 433mhz Oh, my! - least congested?

Discussion in 'General Electronics Chat' started by Propaganda, Jan 13, 2010.

  1. Propaganda

    Thread Starter Member

    Jun 3, 2009
    22
    1
    Hi everyone,

    Any thoughts or empirical data on which band is the least congested in the residential setting? :315mhz, 418mhz, and 433mhz

    From a few things I've read 433 is really popular in home security systems, temperature monitors, and even gas meters (though rarely used in the latter). Also, I believe Ham radios may use 433. Garage door openers mostly use 433 and 315. 418 is the least overall used. These findings are based ONLY off of web reading.



    Right now I am working with a 1200bps 433mhz data link sending a three byte preamble and a three byte payload (soon with checksum). The modules themselves are little ASK/OOK cheapies found many places around the web. (mine are Radiotronix brand) The antenna's I am using are just strips of solid core 24 gauge wire at 17cm. I have not quite got to the phase of tuning the antennas. Current testing range of 40 feet inside my home (through walls and such) is seeing sporadic packet reliability.

    I am having difficulty understandng my current setup's results. For several seconds nearly all the packets come across then for several seconds only static occurs. Sometimes, for 30+ seconds all the packets are flawless followed by a string of junk. There is no timing to this effect, mostly random flip flopping. So far my speculation is that most of the poor experience is due to current non filtered antennas, horrible switching PSUs, and just me moving around the room (which triggers the flop 50% of the time).

    Turning of my transmitter and switching between bauds and looking for a repeating pattern would be a good start to check for interference. Before I jump and buy 315 or 418 modules I want to see what others are experiencing. So if you have used these modules before, what kind of range are you seeing, is there interference, and how did you achieve you max range?

    Just, how congested is it out there in a development of homes? Is there a way to test on the cheap?



    Thanks
     
  2. THE_RB

    AAC Fanatic!

    Feb 11, 2008
    5,435
    1,305
    You antenna length may be a bit off, for 433Mhz the datasheet recommends antenna length of 12.97" or 6.48". That length should include the complete distance from the series matching inductor to the tip of the antenna.

    You should get better performance than that, maybe you could lower your serial data rate. Or check your serial system that you are not getting DC bias etc. There are tons of datasheets and appnotes for good data systems and also for antenna considerations.
     
  3. Propaganda

    Thread Starter Member

    Jun 3, 2009
    22
    1
    Can you link me to a resource on how I can achieve a series matching inductor? I've been looking for a few days and I can't quite seem to find the calculation needed for this. I see examples of the series matching inductors many places and sometimes with a value but they leave out how that came to that value.

    thx
     
  4. Propaganda

    Thread Starter Member

    Jun 3, 2009
    22
    1
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