because of who i am i get a lot of people who think oh i know Callum will know that
one .. I want to talk about adjusting your SWR now this could be for CB or it could be
for any antenna you like but in the main let's just concentrate on quarter waves and dipoles
in the main okay so the rule of thumb is if your um frequency is too low that means it's
too long so low and long they both start with a capital l don't they low and long
that's all we need to remember so if it's too low and it's too long it needs to come up but how much
now i could do some basic maths here right hopefully you'll be able to follow along
but this is a funny old spreadsheet i've just got running there's some stuff at the top here
which we'll cover in a minute but let's just put down a frequency let's just put down let's say uh
what we use we use cb frequencies or hand radio let's use cb radios we've got an antenna that
resonates on 27.1 and we want it on 27.3 well the speed of light is 300 which means if we divide
300 by 27.1 we'll get a wavelength and it says it there let's maximize this
wavelength which is 11.07 now we can divide that by four and that's our quarter wave 2.767
meters whatever that is in feet and by the way you can always translate just use google
convert two seven six seven whatever that is two inches use google and it will come up with the
the formula will actually give you the result so let's say but we actually want 27.2 megahertz or
we can copy all this down now we're looking for uh we want to go from 2.76 to 2.75 so we can minus
that one minus that one and it's too long too low so we need to we know we need to cut in meters
0.01 of a meter which is one centimeter just under half an inch now i've done the hard
work for you here which is on this little spreadsheet here now you can get to this
if you just do a google search for swr calculator m0 mcx you'll come to a page
um with a spreadsheet on it okay easy so far but how does this work now this relies again on a
quarter wave or a dipole leg and it doesn't actually matter what the length right now
is because this is pretty accurate but let's say we'll do the same one again 27.1 and we're aiming
at says resident now 27.1 we're aiming at 27 point i don't know three let's say actually it was 27.2
wasn't it it will give give it the same result it says we need to cut 0.1 at 0.95 a centimeter
one centimeter okay so you can do this for longer frequencies 3.75 let's say is our
80 meter band and we want to lift it up to the dx portion of region 1 which would be 3.3
so 22 centimeters so it's just under a foot look okay and that's how that works
now some of my antennas for instance have got a fold over at the top
that fold over does the tuning so in the main let's say take a three-quarter wave antenna
and we fold over the top now the fold over
is counts for about three times less on your tuning than one of these so in other
words if we were going we had a fold over on the 12 meter band and we were tuning it 24.8
and we wanted 24.9 if it was um centimeters yeah if this was a quarter wave it would be 1.13
just over a centimeter so that's a half an inch however if it's if you're only adjusting the fold
over you need to multiply that by three okay so that would be um inch and a half three three and
a bit centimeters so there we are and that's how to tune elements okay it's kind of easy um
you can hit the play uh the space bar at any point in time to see what maps i've been using here and
it doesn't really matter what the element length is right now if it's a quarter wave and you cut
1.13 centimeters off to go from 28 to 20. 20 24.8 24.9 you will move it proportionally up all right
now i don't mind if you're subscribed or not to this channel anymore uh people in the know used
to remember i had another channel once and i was in the the whole world of how we grow
our subscriber base okay i honestly don't care if you subscribe or not so the only
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you another day on youtube who knows all right i'll see you maybe on the next one bye for now!