Amazing transmission of QRP

Discussion in 'Wireless & RF Design' started by Willen, Jun 27, 2016.

  1. Willen

    Thread Starter Member

    Nov 13, 2015
    138
    12
    I saw many QRP circuits, and most of the article are saying one watt QRP can transmit more than usual (like upto 45,000 miles). But I am not getting answer how the QRP is able to transmit such long distance? Transmitter seems pretty simple, then do they use complicated pretty high gain beam antenna? Or do they use super sensitive receivers? Are there clear examples?
     
  2. DickCappels

    Moderator

    Aug 21, 2008
    2,647
    632
    I think you mean 4,500 miles. Yes, antennas play a crucial role.

    They often use CW (Morse code) and very narrow bandwidth to reduce noise at the receiver. The more sophisticated approaches involve keying the transmitter with a digitally generated pseudo random sequence and using a synchronous demodulator and low pass filter at the receiver to pull the signal out of the noise.
     
    JohnInTX likes this.
  3. bertus

    Administrator

    Apr 5, 2008
    15,638
    2,344
  4. Willen

    Thread Starter Member

    Nov 13, 2015
    138
    12
    Hi Dick,
    I found a sentence in the internet (wikipedia) which is more than 45000 miles per watt maybe. This one:
    Which is out of my imagination! And it's interesting that narrow bandwidth has less noise but confusing is that as I know professional FM has 100KHz bandwidth in its carrier and AM has almost 5KHz bandwidth (I even do not it is bandwidth or not) but FM is noise free than AM.

    Thank you for the links bertus, I wish I can learn the fact from the links and ebook suggested here.
     
  5. DickCappels

    Moderator

    Aug 21, 2008
    2,647
    632
    45,000 miles per watt sounds credible. It is just that there are no two points on earth that are more than about 12,500 miles apart.

    Some of those who listen for beacons use handwidths as narrow as a few Hz, which requires tremendous stability of the transmitter and receiver tuning.

    Here is an article about how noise relates to bandwidth that you might find interesting.
    http://www.highfrequencyelectronics...dth&catid=94:2014-06-june-articles&Itemid=189
     
    Willen likes this.
  6. AnalogKid

    Distinguished Member

    Aug 1, 2013
    4,515
    1,246
    You are trying to compare the performance of two things that are very different. Broadcast commercial AM and FM have very different bandwidths, but that has nothing (zero) to do with the noise performance of each modulation technique. FM is less susceptible to amplitude noise because of the limiter in the receiver, not because of the modulation bandwidth. And it still is susceptible to phase noise and multi-path distortion.

    ak
     
    atferrari likes this.
Loading...