1/4 Wave, 1/2 Wave terminology

Discussion in 'Becoming an Amateur Radio Operator/Upgrading Privi' started by KB1TJY, Mar 5, 2010.

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  1. KB1TJY

    KB1TJY Ham Member QRZ Page

    I am confused about 1/4 Wave and 1/2 Wave, and what the term 'Wave' is actually relating to in that context.

    For instance, "What is the length of a 1/4 Wave vertical antenna when cut for xx.xMHz?"

    Can someone also recommend a good book that explains these the guts of Ham operation (Antennas, etc) for the new Technician?

    Thanks!
     
  2. KL7AJ

    KL7AJ Ham Member QRZ Page


    Two formulas you need to know.


    Length of half-wave dipole= 468/frequency (in megahertz)

    Length of 1/4 wave vertical= 234/ frequency (in megahertz)


    Wavelength in free space' 984/frequency (megahertz)


    Light travels a little more than 186,000 miles per second, or almost exactly 300 million meters per second.

    Wavelength = speed of light/frequency


    Now you know. You can work out the rest.
     
  3. KB1TJY

    KB1TJY Ham Member QRZ Page

    Excellent! Thanks Wolfgang.
     
  4. K8ERV

    K8ERV Ham Member QRZ Page

    To confuse things, radio energy travels slower in a transmission line, called the VP - Velocity of Propagation. Listed in the coax etc spec sheets. So if you want a 1/4 wave piece of coax it's length will be the free-space length times the VP. which is typically .85 for RG-8.

    TOM K8ERV Montrose Colo
     
  5. KL7AJ

    KL7AJ Ham Member QRZ Page

    Or in really OLD coax, it drops down to about .45. :)
     
  6. AI3V

    AI3V Ham Member QRZ Page

    Do a search for "NEETS", it's the Navy electricity and electronics training course.

    Rege
     
    MM0HVU likes this.
  7. KR2D

    KR2D Ham Member QRZ Page

    All good and true info, but nobody bothered to tell the OP what "wave" means in this context. "Wave" is short for "wavelength" - the distance in space over which the shape of the wave repeats.

    Wavelength is related to frequency and speed of propagation.

    Radio waves travel though space at about 300,000,000 meters per second. Divide that speed by the frequency (in Hertz, or cycles per second) and you get the wavelength in meters.

    300,000,000 m/s divided by 30,000,000 cycles/second = 10 meters

    1/4 of that would be 2.5 meters, 1/2 of that would be 5 meters. Those are close to the size of 1/4 wave and 1/2 wave antennas - we need to adjust a bit because the waves travel more slowly through metal conductors than free space.

    See the article on Wikipedia for the gory details: http://en.wikipedia.org/wiki/Wavelength

    For information on Antennas, see the ARRL Antenna Book. The ARRL also has a newer, more basic, antenna book that I have not yet seen. You can find them at http://www.arrl.org/ or any bookseller.
     
    MM0HVU likes this.
  8. W0VYE

    W0VYE Ham Member QRZ Page

    My compliments on having the courage to ask this question here. And I think it's to everyone's credit that they tried to give you clear, honest answers, not a bunch of guff. Do study this stuff. It's basic to all of radio and electronics. Good luck & 73!
     
  9. KB1TJY

    KB1TJY Ham Member QRZ Page

    I found it, many thanks!

    Lyman
     
  10. KB1TJY

    KB1TJY Ham Member QRZ Page

    Indeed they have and it is greatly appreciated. In another forum I asked a similar question and by the time I read the responses I really felt like a fool for even having asked....and this in their 'Elmers' section no less.

    Unlike here, what they appear to have lost sight of is that no matter what level of expertise someone is at now, at some point everyone has sat down in front of their new radio or a friends radio and said "....now what?". I've been a Network Administrator for some 30 years (ugh) and I've used that analogy many times when a newbie or End User feels funny asking what they feel is a 'stupid' question. There is no such thing as a stupid question and while I hate to use a well worn cliche, the only stupid question is the one you don't ask.

    I am wholly new to Ham and to say that I am excited about it is a gross understatement. What there appears to be lacking though are pointedly concise study materials for the beginner. Any aspiring authors out there??? :D

    Many thanks to everyone who has taken the time to provide their input!

    Lyman
     
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