very good day everybody to be honest there's a lot of baloney about cb antennas i i mean there is
they all do a job and then the main within a couple of db i can't see why one is going to be so
blooming different to the other now that i've built myself hundreds of of antennas you know
and i think it's because in the cb world um you've only got the one frequency you know
and we're comparing things like the line of sight because on the one hand we want to speak to
joe our friend up the road five miles away line of sight that's different to speaking to uh fred
in cyprus or whatever else because actually you need a bit of elevation tiny bit of elevation
you know we need five six seven eight nine ten degrees off the horizon they're two different
things but anyway that's a discussion for experience and you know build a couple yourself
a couple of dipoles maybe and whatever else but i was talking to mike months ago about
this antenna and it used to be called the cb well it's still called it actually the cb
antenna i've just it's called it a star duster and you remember this one it's this looking
thing here basically what we've got is a feed point at the bottom
and then these three radials which which do that each one of these is a quarter of a wavelength
long okay so if we're looking down on the top now that's the element coming straight up and
then at 120 degrees we've got these things coming out now there is something right at the top here
which to be honest just looks i can't quite see see those little things at the top oh here we are
i said a better picture of it what is that for i mean i've played i mean i just i don't know
means you can charge more means that people don't know i don't know what
it is i don't know what it is no idea there's a really old one look starduster
okay so i thought we'd build one and if we get enough um shut that down if we get enough
interest there we are i'll physically build this because we do dx come on i've got an 80 meter pole
so i could we could quite easily build this out of wire and put it at i don't know 16 meters off
the ground it should be at that height should be fantastic so i thought what would do i might
come back to the book in a bit but what we could do is quickly model it all right and have a look
now there's some people here going to say yeah but how does that compare to an imax 2000 or a
whatever i don't know probably roughly at the same height probably not a lot in it
actually but anyway or the um android 99 probably about the same xantron 99
because this is in effect a center if we think about this this is a center fed dipole there's the
coax coming in here now it just so happens we've probably got a better match because these radials
are are coming out at an angle aren't they at 45 degrees ish not quite so the center of the coax
is effectively by the way if you didn't notice going straight up here and the braid of the coax
is effectively going to these radials elevated radials so we're getting into the vhf world
we really are it's a quarter wave vhf antenna it is for hf so we'll build this for say 27 28
megahertz because there's a handband at 28 and some of us some amateur radio operators use cb
antennas for 10 meters because they work fine why has my cross become enormous well whatever i don't
know so i'll show you i mean you can follow along with this just download mma gal by the way it will
be german you'll have to go set up language and set english that's the only difference
free download mma gal you'll work it out so i'm going to start with this button here i'm going
to go to my let me think about this i want to look at the side of it so we'll have um x here
zed ahead of us and i'm gonna over over spec it i'm gonna build it too big to start with so i can
see what i'm doing i'm just looking over the head that has 20 meters that's far too big let's build
it as a 10 meter so this should tune actually on the 1480 band and just get the zoom about right
so we've got two points there i did a test earlier on hold on i might shut up when i do this
okay that says 9.8 so what i'm going to do is i'm going to rotate it that's one big square and
two small squares just going to rotate this by 120 degrees and do the same thing again
so with any luck there it is with 120 degree legs this one here we need to put
some coax to so why one at the bottom or the base i want to get little red dots there now
so this is far too enormous so what i need to do is scale this to 0.25 a quarter of this
so that is now two and a half meters long now we don't need to
to tune this we don't need to change that length and all these lengths okay
we just need to change this oh [ __ ] draw an arrow we just need to draw that length there
change that length there and that's what i'm gonna do all right so
2.5 i know for a fact it's going to be in software about 2.7 meters long and in reality if you were
building this it would be about 2.65 but i'm gonna well if there's enough uh consensus on
the channel here or if you're watching this i'll build this and put it up about six meters sixteen
fifteen sixteen meters high because i've got eighteen minute eighteen meter telescopic poles
we call them the nebula 18 meters 2.7 this is gonna be at 27. i don't know three five
uh most of the people here let's it doesn't really matter let's let's go for 28 and a half
and tell this it's actually 2.6 there we are 28 and a half 16 meters it's remembered that
good copper wire because i built one before is start swr is 1.36 to 1 i can go to swr hit the
resonance button 28 dead all right well let's just have it at 28. 28 megahertz will be fine
so we're getting a perfect almost a perfect match on sw but what does it look like okay
so if you've never seen a plot like this before on the left hand side this is it as if we're flying
over as a bumblebee for the top and we can see the rf spreading out and on the right hand side
as if we could slice through we're standing on the sidewalk or the pavement and we could physically
see the rf we're taking a slice right through the middle i'll show you this in color in a minute
and then we can hover our mouse you see it it'll tell us various things
there's a couple if you've if you're new to the channel you won't know that i very often baseline
things antennas that is at five degrees off horizon so i'm concentrating on this bit at the
top of this screen which says 175 degrees now any quarter wave vertical as long as a quarter wave
so first of all the 40 meter band it would be about 10 meters long i'm on the 10 meter band
about two and a half meters long give or take that number there would say depending on the ground
that number there would say about minus five anywhere between about minus four point six to
minus six depending on the ground the quality of the ground we're elevating this up now we've made
our own ground with these three radials and this is saying minus 2.9 so it's getting on for 9 db
more than a ground mounted quarter wave now if you followed my live stream this morning we were doing
10 meter contacts now 9 db is nearly 10 times the power so my 200 watts let's say is the equivalent
of um on this antenna is if i compared it to a straight vertical it's not quite 10
times the power but nearly but it's like all of a sudden if i said from 200 watts to my vertical
and i clicked to this one which it says 2.9 not minus 2.9 or anything it's it's like me putting
on a nearly a 2000 watt amplifier okay so the numbers don't sound a lot but every three db
is doubling okay so this is a smear this is a substantial uh difference it's quite interesting
and if i show you the 3d far field plot i have to do a couple of things here why can't i get oh okay
um this is it in in far field and i said it was showing it in colors so you got to
remember that they if your line of sight okay you want the lowest you can get to the horizon
you'll be doing very well you'll be doing very well indeed um you know but i just want to imagine
what this would be like on a 18 meter pole you see because i've got a funny feeling it's gonna be
three to six db better than your average imax and what's that going to cost us well that's about 200
pounds of the pole a bit of wire all right because literally it's a bit of wire now i could actually
sell you the bits i've worked it out just need a little bit of aluminium a little bit of plastic
to fit on that pole and you could have one of these gigantic by the way 18 meters is huge right
it's kind of getting on for 60 feet and by the way it's you it says here by looking at this plot
what is happening underneath this all right now we've got experience of this because
a couple of years ago paul carl and i we went up to the hills
at 1500 feet and james copied us s9 we're running a v2000 which is a stacked a pair of
two or three 5 8 antennas for the two meter band 145 megahertz or so
he's a copy does you know s9 the whole way from his house in basically staffordshire all the
way to some place about 50 miles away and when he got to the village underneath where we were
we disappeared completely disappeared because the takeoff of things like this is such that
underneath the antenna there's not much happening you probably wet so if you're too high sometimes
you better off just with a straight quarter wave because there's too much gain on things like this
so anyway give us your thoughts if you want to dare me to build this and have some fun my only
problem is if i build this i won't be able to have a hf antenna for my regular friday so we'd
have to just do 10 meters all right i did think of multibanding this right but that'd be difficult
the construction method by the way would be if i've got the this this pole which i'll do in blue
we'll do black the construction method is is that basically these uh blue pieces i'd put a little
egg connector on they would just carry on down to ground there would be the guys all right i'll put
more guys in here just to hold because 80 meter telescopic pole is pretty um well wibbly wobbly i
think it's the is the answer before we go i think it'd be interesting to see what would happen if we
change this to 14 megahertz the 20 meter band but we're gonna have to change some things
here because clearly that line there is now five meters high and if i've got a pole which is 17.5
meters long minus five meters the feed points gonna have to be 12.5 meters so this point here
where the ground is we'll have to add 12.5 maximum okay that's the height so it'd be
interesting to see what sort of game we could get 80 meter pole with a star duster is that
what we called it the star something anyway on 20 meter band let's have a look minus five
okay there's three db in it i'd get another three db but i'd get another three db all the way around
so you would need an enormous tower if you wanted to you know i mean let's just have a
bit of a laugh you know you've got a 100 foot tower right you put one of these on the top
well it's gonna do roughly the same as what we had a minute ago
it is two point four for the twenty meter bang there and i get out final 20 meters at -5 whatever
it is dbi interesting though isn't it if you fancy me building it let me know in the comments
if this has been any value at all give me a thumbs up whatever who knows let's not sweat
about that the important thing is we've had a good time tonight or today rather
and it's my weekend now so i'm going to shut down and i'll edit this another day
all right in the meantime from calum here in the bunker all the best now bye for now