Author Topic: 2 Meter Band or Dual Band  (Read 3104 times)

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Offline FourBee

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Re: 2 Meter Band or Dual Band
« Reply #30 on: May 14, 2009, 07:16:46 PM »
Hey ozark; I've been reading your formula.   I did a little editing so's I could get a general perspective of it.      Where it states ( cycle of oscillation), I marked it for identification to later text. Does this read correctly to you?   If so; let's take on the math part...

ozarkhillbilly49 edited Formula
Here we go on ‘Wavelengths’!!      4B we are going to look at a “cycle of oscillation *1”.      Let’s imagine we have a [ line ] that represents zero [ 0 ] value { this value is usually ~ Voltage } .     A [sine wave or rf  {radio frequency}  wave]  will have [ + ] components (above the line) and [-] components  (below the line) remember the line is [ 0 ] .       Now we take off and head down the line as the volts begin to rise.

      When we get to point of ‘peak value’ ~ if we drop a line from the peak to the 0 line straight down so they intersect at a 90 degree angle we just found a 1/4 wave!     Now if we go down the line to where the value falls back to 0 we just found a ½ wave.      If we go down to the negative peak and bring a line up to the 0 line at a 90 degree angle we found a 3/4 wave.     If we travel to the next 0 point we just found a full wave!

      Now remember we are talking about rf (radio frequency).      It travels in different stuff.      Example: (it travels in air), (the vacuum of space), (the copper traces on the boards in our radios).      ( It travels in our feedlines and antennas).      It travels at different speeds in all of those things!!!!! WHAT!!!!

HOW CAN THAT BE?      The answer is simple, ‘Resistance’.     In the fastest medium (free space) electrons can change places very fast!!!     In one of the slowest mediums electrons cannot change places as fast due to effects of the {conductor} and {insulation}!!!      That slow medium is of course [[coax]]!!

    Now remember our line.      If the cycle *1 (or wave) is going slower it will travel a shorter distance for all  the neat little points we found!!
 Make sense so far??         Puzzle on this'un for a while 4B.      Drop a line back and tell me if this makes sense to you.      If it does we will do a little math next time!!!
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Offline ozarkhillbilly49

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Re: 2 Meter Band or Dual Band
« Reply #31 on: May 14, 2009, 09:08:53 PM »
sounds like i managed to get the general idea across 4b. i will post a little later in the day on how to mathematically figure how long a wave is for a given frequency. remember we call the 144 to 148 megacycle band the 2 meter band. i got to get a handbook or 2 out and make sure i get the formula's right 4b!!! ( i would ferget my behind iffen it were"nt hooked on to me). check back some in the afternoon. i will try to get a post up. 73's to all( hey leadpot how is that 726 coming along??) aa5ez qrt.

Offline ozarkhillbilly49

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Re: 2 Meter Band or Dual Band
« Reply #32 on: May 22, 2009, 07:57:01 PM »
hi 4b and foggy! sorry to hear about bob having health troubles. i know how he feels. i have some health issues also. any way hear we go on electrical wave lengths!! remember that first point we found when we started down the 0 line. it was at a voltage peak, remember? that gives a 1/4 wave line some nice proprieties that we can use to our advantage.for instance a 1/4 wave section of feedline can be used as a 4to1 impedance transformer. it can also be used to shift the phase angle 90 deg.(useful in phasing a directive array). one of the most useful things you can do with a 1/4 wave is matching. hang a 1/4 wave stub( or bazooka as some old timers call em) from the feed point of an antenna and start attaching the feedline at different points and you will find a match.i give you my word you can match anything with a 1/4 wave stub.the only drawback is you figure and cut the stub for a given frequency and depending on the antenna you can't move more than a few kc's from your design point darn it!!just ain't no way around that!! that don't mean they ain't useful tho!!now that we see some use's for feedlines of a given length lets see how to find out how much feedline we need for a given freq.to find a one wavelength section of a line take 983 divided by freq. in mcs. multiplied by the velocity factor of the line.the velocity factor is that slowing down in a feedline that i mentioned. it is expressed as a percentage of the free space velocity of propagation. i told you how to find a full wave now here is the formula for a 1/4 wave.245.9 divided by freq. in mcs.multiplied by the velocity factor yeilds line length in feet.example( 1/4 wave line for 7.1 mcs. using rg-8 solid dielectric .66 velocity factor.)245.9 divided by 7.1=34.633. 34.633 x .66=22.857 ft!!! hope i haven't blew you r mind and confused you totally!! best wishes to all!! 73's.aa5ez

Offline Hodr

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Re: 2 Meter Band or Dual Band
« Reply #33 on: May 22, 2009, 09:00:12 PM »
In what forum of GBO could I list a ICOM wr2a for trade ?
blindhari
TANSTAAFL

Offline FourBee

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Re: 2 Meter Band or Dual Band
« Reply #34 on: May 23, 2009, 04:46:29 AM »
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In what forum of GBO could I list a ICOM wr2a for trade ?
blindhari

Not sure blindhari; but go up to the 'General Classified's' and start there.

ozarkhillbilly49; Oops, I hit the wrong button.  
                    Anyway, your example formula is pretty much straight forward.    I had to do a little ciphering between the kcs.,(kilocycles same as kilohertz kHz)terminology (which is what I grew up with too) .  Regarding the Coaxial RG-8 example; I assume the 'velocity factor' is a given number depending on the type of coax?  
                      I'll get the hang of it.  Just need to do some studying on it.  Thanks aa5ez
4B
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Offline ozarkhillbilly49

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Re: 2 Meter Band or Dual Band
« Reply #35 on: May 23, 2009, 07:10:19 AM »
yep your right on the velocity factor thing. i dug out my newest antenna handbook and looked up the coax and velocity factor of the feedline!!handbooks are very handy dandy tools!! want to take a look at i/2 wave lines? they got some good proprieties to!! drop a line back!!! 73's aa5ez

Offline Lead pot

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Re: 2 Meter Band or Dual Band
« Reply #36 on: May 23, 2009, 02:55:53 PM »
I like to use 2808/frequency in mhz. that gets me right on.

2808/146.52=19.16
Dont go were the path leads,go were there is no path and leave a trail.

Offline Lead pot

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Re: 2 Meter Band or Dual Band
« Reply #37 on: May 23, 2009, 03:13:54 PM »
I might add.

When taking the test and the antenna formula comes up the official formulas for 1/2 wave and 1/4 wave ,
492/freq in mhz for the 1/2 wave
432/freq in mhz for the 1/4
or 300,000/freq in mhz for the full wave but than you have to convert mtrs into inches.
But what always got me wondering is.
You take the 492/freq in mhz for the 1/2 wave.
Well common sense would tell you that 492+492=984/4=245 for the 1/4 wave instead of 432/freq.
Dont go were the path leads,go were there is no path and leave a trail.

Offline FourBee

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Re: 2 Meter Band or Dual Band
« Reply #38 on: May 23, 2009, 04:03:42 PM »
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But what always got me wondering is
Yeah; I know .   Why they want to start out with Meters and end up with feet is beyond me.  With One Wave, then Three Quarter Waves, followed by Half Waves to  Quarter Waves.  Enough to make you sea-sick.  ;D
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Offline Rustyinfla

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Re: 2 Meter Band or Dual Band
« Reply #39 on: May 24, 2009, 10:26:35 AM »


   Because most people don't use a metric tape measure when they lay out an antenna.
If you're gonna be stupid ya gotta be tuff

Offline ozarkhillbilly49

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Re: 2 Meter Band or Dual Band
« Reply #40 on: May 24, 2009, 10:32:07 AM »
i know what you mean rusty!! i'm an s.a.e. man myself. i picked up some russian pulse tubes with 65mm. coolers. what a pain in the butt to deal with!! oh well it is my own darn fault for buying the darn things to  begin with.73's aa5ez