hello good evening my name is callum from dx commander and i want to talk about takeoff
angles for receive and transmit uh tonight because i've been basing my computer model
software modelling of my takeoff angles at five degrees of buffer horizon and i've had a couple of
debates or arguments if you like with people who say that i shouldn't be basing my maths at five
degrees it actually doesn't matter as long as you base one antenna at five degrees off the horizon
and the next antenna at five degrees off the horizon then you go all that one's going to be
better than that one in the main now i need to i forgot to find something up here which i've got
to do now so sorry about this this is mma okay and what i need to do is just put z2 at or 5.2
so this is a computer model of a vertical um and i'm just beginning of wire thank
goodness for that nothing off the ground 14 degrees we should get roughly swr that's okay
that was quick wasn't it um so this is a a vertical antenna i can maximize this for your
delight vertical antenna on the screen on average medium ground nothing special not by the sea okay
so the dilemma is a lot of people say why don't you measure the gain
where that red dot is and it says it up the top here 0.9 db at 20 degrees of the horizon well i
could just as easily measure it at 10 degrees oh horizon it says minus 1.7 there but what i found
is getting the really low angle stuff was very hard so i started measuring all my models
at where's it 175 degrees or 5 degrees off the horizon it says they're minus 5.9
sounds not a lot however we have to appreciate and i'll show you a couple of research papers now and
i'm a bit annoyed because there was one research paper which i read a modern paper done in the last
five years where they built this massive array of antennas and actually measured all the signals
and they could tell that the you know the vast majority of this signal is coming in at three
degrees vast majority of that signals coming in at five degrees and so on so on for dx in other words
multiple hop stuff over 1500 miles or 2 000 ish kilometers was coming in between three and eight
degrees of horizon which actually is one of the reasons i swapped to measuring my models
at minus five at five degrees off the horizon because if i built a three element a array in
software or i wanted to measure one thing against another and i'm measuring it up here at 20 degrees
there sometimes wasn't much difference the real grunt is happening lower down okay
so anyway that's a computer model let's just minimize that at the moment because i wouldn't
mind actually building another one in a minute maybe a dipole or something we'll just show you
the difference whatever this is a 1961 paper now unfortunately like a lot of these papers it's
it's uh beautifully done there's a lot of data in here which i'm not going to show you at all
but at the very bottom i put my glasses on it says less than two degrees provided on average signals
nearly 10 db stronger it's interesting that in 1961 they were finding that the long haul stuff
you know between 6 800 and 8 400 kilometers you know so we're looking at five six seven thousand
miles we're coming in at angles of less than two degrees okay so there's an interesting one here
and i'll put these links in the description below you can have a little read if you want
there's this one here which is slightly newer um i think this is an ar rl 2011 here we are qex
so i hope he doesn't mind me doing this this is the graph bottom right i want to focus into so
let's just maximize the screen a bit here so what he's got here is up the side right it says percent
probability just there percent probability 5 10 15 and across the bottom we've got the elevation
angle in degrees for 80 to 10 meters so that's 3.5 megahertz up to 30 megahertz angles of arrival
okay so what it's saying that on let's say three degrees we've got a higher probability of picking
it up and then we have at 20 degrees i mean i think we all know that on the surface most of us
understand that signals come in not straight down they come in at an angle but if you look at from
10 degrees which is across the bottom here down to zero the bulk of our signals are coming in between
you know one and eight and in fact the research paper i read said it was between the bulk of the
and the bulk of the signals coming in on dx is going to be between three and eight that doesn't
just say say that between 10 and 20 degrees you can't receive anything because by the look of
it just looking at the surface area here you know 15 to 20 percent of our signals is coming in at a
higher angle right by the way this is not sporadic e this is traditional hf dx all right which is um
a camera's just stopped who cares and that's why i focus at at five degrees because you're trans you
remember your transmit takeoff angle is probably going to be the same as the same as your receive
tank which uh take off uh receive angle because it's like a mirror isn't it you can't bounce a
signal there and expect it to go along like this tropospheric and sporadic he does a bit of that
he can go up and get lost in being ducked before he comes back down again and the research papers
i was reading later earlier today were suggesting that on the six meter 50 megahertz band sometimes
that can be up as high as 15 degrees certainly not much higher all right so there we are that's why i
base i just think it's a very firm understanding of basing my maths at five degrees and this graph
particularly here bears it out for me anyway because the bulk of the signals are coming
in between about two and ten by the look of it here certainly two and nine right on this one
i think you got a bit of light coming in the camera sorry about it
so people then say oh i've got mountains you know a couple of miles away what do i do
you still get out all right you're just not going to get out as well as the guy who has a flat
take-off angle and by the way some of the research i was reading today is suggesting that horizontal
horizontally polarized transmission antennas can have more loss particularly in the first few
kilometers at very low angles all right they're over vertical vertical polarization i haven't
looked at that much so i don't know but let's untangle this let's get back to mmana because i'm
going to start another instance of this and we'll fire up um won't take me long because you know i'm
quite quick at this so minus 5.2 and 5.2 this is a flat top dipole and we will add the source to the
center of the wire and we'll put it up at 10 meters off the ground which is your average
it really is your average dipole for joe soap all right a bit of an swi here of 1.5 to 1 it
doesn't matter so this is on 20 meter band now flat top not inverted v i'm sure done
if not i will do another video on that let's stick on takeoff angles at the moment
so at i can reduce the size of these so we can probably get a better picture the two
things together on the screen at once hold on a minute let's move that to there and back to there
left is our dipole so at 10 degrees off the horizon it's telling me it's 1.7
10 degrees off the horizon here it's saying minus 1.7 so our what frequency are we on 14.
and at 5 degrees off the horizon minus three point eight five degrees of horizon it says
minus five didn't wasn't expecting these numbers actually ten degree ten okay so in fact
our flat top dipole at 10 meters 30 something feet would beat on transmit in these two planes
right you gotta remember that five degrees from there to there 6.9 so in two directions
it will be better than this our vertical and then for
all of this it'd be worse unless you could rotate it that would be why wouldn't it
but bearing in mind that's 10 meters if you just brought it down to eight meters above the ground
forget the fact it says low loss no loss there doesn't matter this is now eight meters off the
horizon at five degrees wait minus six point six so you can see every every meter counts doesn't it
so that's interesting what about at nine then nine meters off the ground
right we would beat just i would have thought 75 so we're more or less equal between the dipole on
the left in two directions only and this one here which is uh minus 5.9 interesting um we
should we inverted v it now just for the hell of it while we're doing this hold on then x y
divided wire into two pieces okay
and so now we'll just start there and that needs to be about five point converted
typical inverted v configuration all right we need to move that
wire one
beginning i'm just guessing no it's the end
wire one and
now they're gonna leave need to leave these bottom bits off the ground because it said here zed
two and a half so we're two and a half meters down off the ground anyway
so we need to lift the center up two and a half now we're on the
bottom of the ground so then we'll add another 7.5 so we'll make it 10 meters
to the top so let's have a think about this this point here is now going to be 10 meters
off the ground yes all right average average big tree all right so let's see what this plot does
and i can cheat here i can just say show me elevation at five degrees and
i can run around here now so in fact your inverted v um in two directions
minus 5.4 it says there and over here we are if you remember minus 5.5.9 so your inverted v at 10
meters off the ground um it's just average i mean you know look let's just think about this 3 db
you are hardly going to notice the difference it's like going from 50 watts to 100 all right
6 db you can detect by the way that is an s point and there's just a little bit more i mean you can
detect 3 db i can certainly on ssb because there's just a little bit more torque power it's just
it's just they've gone from eight to nine you know on the volume control it's just a little bit thing
six db you can definitely hear that the voice level comes up there's more of a smack to it so
you know sometimes we look at these dbs and we we we start to worry ourselves a
little bit too much i think and that's the other thing is these antenna manufacturers
i mean i know i'm an antenna manufacturer but i'm kind of an odd one out they'll tell you if this
was a pretend aerial you know they would tell you that this has gone it says it here 6.1 dbi
they would advertise that as an antenna giving you 6.1 6.2 db gain maximum you know wouldn't tell you
it's at 32 33 degrees off the horizon which by the way is good for about a thousand miles all right
that's particularly 40 meters rest the time as we saw in the previous graphs nobody's going
to hear you on that gain so it's back to 3 to eight db three to eight degrees it's down here
somewhere which is at minus five because if we do everything at five we can then baseline everything
so i can't remember who it was now but there was one guy over on josh's discord
who just couldn't quite grasp why i was doing everything at five degrees because he's telling
me that yeah but the signal is coming in at 12. there's signals coming in at 20
but the majority of the dx and the thing is as you can see on the um vertical here on the
right hand side if it's coming in on the on you know if i can squeeze a little bit more out at
five degrees off the horizon i don't think we're going to lose much up here which is 25 degrees
you know it it'll it'll always be about you know one two three four db up there all right unless
you do something a bit weird so it's not like we're going to lose all the top end right even
if you measure like a 5 8 or a three quarter wave there's still some pretty good gain there
you'll never just by doing a b switches it's like these people who do a b comparisons on cb aerials
there's gonna be next to nothing of it i promise you unless you've got something very drastic going
on in fact i think we're gonna do that i think we're gonna get um we'll build we'll take my
imax and get a game master and we'll do a side by side i just want to dig into the cb argument
that one aerial or antenna is better than another we'll do a ground mounted as well because for dx
point of point to point you need literally zero degrees off the horizon because you're
talking to a trucker five miles up the road there's no skip involved in that
we need to now get line of sight okay and a ground mounted vertical isn't this isn't going to be
as good for line of sight we need a bit of height to get down to him however for dx you might find
in sporadic e and stuff that your ground mounted 10 meter quarter wave
outperforms all the fancy and gay masters in imax 2000s and silver rods and all that
listen this channel is all about demystifying and giving you little bits of knowledge
i am not a professor and this is not a lesson in takeoff angles this is you that you now understand
a little bit more that you can go away do your own research and things make a bit more sense
all right that's what this channel is all about when i do the serious stuff like this we've got
a lot of fun stuff we do as well all right and as usual if you like all this below neither i
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project that i'm working on so we'll come up with that soon alright see you next time bye for now
you