okay everybody my name's callum from dx commander and here i am looking at my whisper plots
transmit plots for m0xxt you can do that as well just go to
wspr.aprsinfo.com and you can see how well it's been performing but we'll do the whisper
plots another day and how well this antenna has been transmitting because when we launched the
signature 12.4 a couple of weeks ago i wasn't guaranteeing 30 meters i said i probably had
a trick and indeed the trick worked out so let's untangle this and go back to the to the beginning
so what we've got is about a 12.4 meter pole so that's 40 something feet telescopic bomb
now that's supported by three guy wires and then we've got seven elements wire elements starting at
the base so we've got something called a driven plate supported underneath that by something
called a ground plate and we put our radials on there and then these seven elements come up
and how does it work so we've got each element is terminated with the fork connector and goes
onto the driven plate so the center of our coax effectively is going to that driven plate now
similar to a fan dipole a fan vertical which is kind of what how the dx commander was born
has a num these number of elements going up and when our in the simplest terms when
our wigglys come along flying down the coax it will see one of the elements as
being just the right size for it and it will go shooting up it okay that's it
it'll see the right impedance fundamentally now easy so far so on like a 10 meter pole 30
something feet bolt it's very easy to get 40 30 20 all the way down to 10 meters on six elements
because the 40 meter element we can fold over at the top with a little bit of trickery all right
and we can get 15 meters on that so six elements will give us all the bands from 40 meters to 10.
now with a bigger pole we got an option to get down to 30 meters okay so what we've done is we've
put a center element in the middle of the plates and we helically go up one turn every six feet
roughly to the top of the pole but fairly near the top of the pole we've got this coil and that's
what i want to talk about today because i've done searches on the internet and i can't find
anyone that talks about the placement of a coil and the harmonic it gives out so originally when
we built this pole we had a coil just over halfway up and our resonant frequency uh it was fine on 80
meters but we had this harmonic which is fine i was expecting a harmonic somewhere between i
don't know 10 megahertz and 30 megahertz i didn't know where the harmonic was going to be happened
to be 14.6 now we had an option then we could have tuned that coil but we didn't know how at the time
to force it to deliver um a tune at let's say 14.2 megahertz but i didn't know what the losses were
going to be and everything else i wanted to remove the harmonic completely from anywhere near the 20
meter band and we discovered by moving this coil i mean you don't just move it you have to unwind
it all and wipe it all back on by moving the coil up the pole so what was happening is that
the frequency was going down so we went from 14.6 and we moved the coil a bit and ended up at 12.3
and finally after a lot of shuffling around we got it resonant at 10.1 so we've got this 80 meter
element we just got 100 turns about an inch and a quarter roughly at 28 feet something like that and
that's giving us our next harmonic which is at um on the 30 meter band 10.1 megahertz it so happens
so by lifting that up an inch also we could have gone down to from 10 we could have gone to 9.9
9.8 or by moving the coil down a bit we could have gone up in frequency you know maybe it could have
ended up on the 20 meter bank and maybe that's an experiment we do because what is happening
i think is that we've now got a loaded 5 8 for the 30 meter band all right now i know coils
typically have a little bit of um a little bit of loss but it's okay we often use coils
don't we in our in our hobby and not terribly lossy particularly if it's high up the pole
so we've got these aluminium plates at the bottom and then we've got it's all these spreader plates
okay they're made of something called ultra high molecular weight polyethylene all right or uhmwpe
sometimes known as pe all right eight mil so just over a quarter inch thick they're quite
quite chunky and heavy big size of dinner plates because we wanted to get all the elements away
from each other so the swr curves really nice and they are but that's for another video the point of
this though is do you know why moving that coil up and down the harmonic moves okay now a lot of
people go oh i know why that is it's a trap you've made a trap unfortunately we haven't
because when we started this experiment the 20 meter band if you had a trap what would happen is
that would need to be about five just under five meters long so that it that when 20 meters the
14 megahertz frequency comes along it's a trap it stops there and it thinks it's got a quarter wave
all right and nothing gets through unfortunately that was at nearly six meters when we did that
and it was it was um it was resonant at 14.6 so it's not a trap it's definitely just a harmonic
and i think it's sort of 5 8 and there we are so it all works we had we launched on i think
a saturday morning by sunday night we had sold the first 50 on a special deal that was at 3
59 or 369 i can't remember we're still on the deal at 399 so you can now have the confidence
all right to build one of these and take take one home with you so i've currently got this on
a hinge but i've worked out a procedure where you don't need a hinge i mean i've got one because i
want to put a lot of different poles up and down all the time so i've got this hidden charge but
you to invest in a hinge i just think is a bit of a bit of an ask you know it's another 50 60
or 100 or something well you just don't need that so i've worked out a procedure which i'm putting
in the user guide which means you don't need a hinge you'll just be able to lift it up and down
uh by using some short guys about that long into the ground so the pole doesn't go anywhere as you
lift it up so don't worry about spending money on hinges all right if you really want a hinge
go and get one but you don't need one what you do need though is enough room when you drop this over
you're going to need at least 40 feet 12 meters and a bit more so the thing can lie down so just
be careful about power lines people pets and things like that i've currently got this on
three guys okay and only three and i will find a clip that's on my instagram feed
of when we got hit by i think it was 48 or 49 mile an hour gust for a few seconds and if it
went s-shaped certainly but it went fine if you want to storm protect this you're going to have
to guide the one down from where i guide it and the one up from where i got it because i have
left specific holes in the guide plates and the uh wpe stuff for guys but i'm particularly myself
i'm happy with just the three guys remember that is a single point of failure so do go out every
month or so and just check they're not fraying the only thing we don't supply it's your radio
your coax and the guy stakes okay so you're going to have to go and play price tags and i do that
because some people want a concrete block with a bolt in it other people want to hammer hammer like
a scaffolding pole in the ground you could take a ten foot piece of scaffolding put it in a couple
of feet so the scaffolding comes up you know waist height and put an eye bolt there you get your
lawnmower underneath your guide wires things like that and also you remember back in the day i tried
to self-support this with an aluminium pole a long story it didn't work out in fact we were sinking
a lot of our rf straight into the ground it was acting as a big capacitor people going i could use
plastic fiberglass you can use all sorts i'm sure bear in mind right at the base of that antenna
will be some bolts to hold this thing in place and you'll just crush whatever's there unless it's
metal all right personally i think this is a guide system i wouldn't go un-guide once you
start seeing 30 mile an hour wind 50 mile an hour gusts you'll believe me you'll go oh my
goodness what have i done all right so there we are 80 through to 10 no atu required we're
going to do swr curves another another day but it will do six meters with a nudge just a nudge
of the atu all right you can buy it from my shop all right this isn't a sales pitch by the way
i might as well tell you where you can get one from because i'm very interested in this coil
i think this is fantastic that we could do for instance a fan dipole you could have 80 and 30
if you think about this on the same element by just putting this coil
in exactly the right place then you have 80 30 or 40 we could be moving this coil getting to 40
on a harmonic and uh 1840 and one element what a great experiment that would be all right and
then another one for maybe 30 you could do 30 and 20 on one element so we need to work on that this
year and just understand what's happening and how that's working okay so uh we'll do the plots um
in the next few days we'll do the swr curves or you can stay ahead of all this go to my instagram
page dx commander well because i publish all this on the fly oh they'll like this you know
sometimes i just want to you know upload stuff i'm not a big instagrammer but if you want to
stay ahead of the curve go to uh instagram all right that's it for the time being sorry
i haven't been around i have just been absolutely flat out mike m0msn said uh i know you've been
flat out because you phoned me on saturdays and you phoned me on sundays from the antenna
field poor mike's had it in the neck about this coil adios see you next time alright bye for now
you