I know what it's like CK I was about 9 when Aus changed. Best idea is just use metric and stop trying to convert it all the time, thats when most confuse themselves.
Tell that to Myanmar (Burma), Liberia, and the USA.
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homerb.b.
- Thread starter hotrod
- Start date
Tell that to Myanmar (Burma), Liberia, and the USA.
metric may as well be dutch to Americans lol
metric calculations since we are in the cb section i will use the frequency of 27.000mhz as a example
1 wavelength in meters
300 divided by freq (300 divided by 27.0 (freq)= 11.11m in free space (full wave length)
1/2 wave length in meters
150 divided by freq (150 divided by 27.0 (freq)= 5.555m in free space (1/2 wave length)
1/4 wavelength in meters
75 by freq (75 divided by 27.0 (freq)= 2.775m in free space (1/4 wave length)
1/8 wavelength in meters
37.5 divided by freq (37.5 divided by 27.0 (freq)= 1.390m in free space (1/8 wave length)
5/8 wavelength in meters
for 5 x 1.390m (5x 1/8 wavelength) = 6.95m
all this does not take in account of velocity factor of radiator as vkrules said
all above measurements in meters are rounded up to nearest 5mm
(0.19685 of a inch in old world speak)
Hows it going Dave. Maybe we should call it the 12 yard band to accommodate.
not dave ..its mike
dave has his own account here i believe (no idea of the username )
dead boring ...band is dead and i am off the air "(last storm killed my vert) ..guess its time to put the shockwave up http://www.shockwaveantenna.com/
Velocity factor when discussing antenna length measurements?
The velocity factor when measuring the length an antenna element is essentially 1. You don't need to calculate for it. The only time you have to consider a velocity factor is when the RF is being transmitted through a medium other than air, such as the dielectric in a coax transmission line, where the velocity factor is based on the dielectric material and not air...
The DB
The velocity factor when measuring the length an antenna element is essentially 1. You don't need to calculate for it. The only time you have to consider a velocity factor is when the RF is being transmitted through a medium other than air, such as the dielectric in a coax transmission line, where the velocity factor is based on the dielectric material and not air...
The DB
tank you to all that replied. im not very good in math and metric is greek to me..lol. with winter coming here in pa im starting to think bout inside projects/hobbys. im not sure
if ill make a antenna ..especially a 5/8. maybe a 1/4 wave seems it dont need a matching system.. the fourmla i mentioned i found on utube by a ham op. has several for many different designs
if ill make a antenna ..especially a 5/8. maybe a 1/4 wave seems it dont need a matching system.. the fourmla i mentioned i found on utube by a ham op. has several for many different designs
I use 11778 divided by frequency in mhz ( = wavelength in inches x .9979, VF of aluminum in air) and I believe 'end effect' only comes into play on 1/4 waves, but it's been decades since I researched it and could be mistaken, though the Penetrator calcs out perfectly w/o using it. I also deduct the average circumference from the calc'd length, a .64 for 27.185 ends up being 22" 11".
I'll give you my simple answer.
I use an online antenna calculator. I build the antenna, then use the MFJ-259b analyzer to tune it. As for the matching network, for a 5/8 wave I use a tapped inductor (coil) to achieve the impedance transformation I need.
Does the online calculator get me the exact length I need? No more so than the formulas offered. I achieve the length to the exact measurements I need as I tune the antenna with the analyzer. When X=0 on the frequency i am tuning to (usually 27.385), or as near zero as I can get it, I have achieved resonance for the tuning frequency.
If I were to use the 27MHz length of 36.08 feet offered above (instead of 27.385) to get to a 5/8 wave antenna I'd divide it by 8 and then multiply it by 5.
36.08/8=4.51
4.51x5=22.55'
or 22.55/36.08
Or, multiply 36.08 by .625
36.08x.625=22.55'
if inches are what you want (instead of decimals), then just multiply your answer by 12, as in a foot.
22.55x12=270.6, or 270-5/8" Then I make them too long so I can shorten them as needed.
Not much science here, but I get the antenna up and get on the air . . .
I use an online antenna calculator. I build the antenna, then use the MFJ-259b analyzer to tune it. As for the matching network, for a 5/8 wave I use a tapped inductor (coil) to achieve the impedance transformation I need.
Does the online calculator get me the exact length I need? No more so than the formulas offered. I achieve the length to the exact measurements I need as I tune the antenna with the analyzer. When X=0 on the frequency i am tuning to (usually 27.385), or as near zero as I can get it, I have achieved resonance for the tuning frequency.
If I were to use the 27MHz length of 36.08 feet offered above (instead of 27.385) to get to a 5/8 wave antenna I'd divide it by 8 and then multiply it by 5.
36.08/8=4.51
4.51x5=22.55'
or 22.55/36.08
Or, multiply 36.08 by .625
36.08x.625=22.55'
if inches are what you want (instead of decimals), then just multiply your answer by 12, as in a foot.
22.55x12=270.6, or 270-5/8" Then I make them too long so I can shorten them as needed.
Not much science here, but I get the antenna up and get on the air . . .
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