hi welcome back my name's callum from dx commander in the last video we had a bit of a muck up trying
to get a 40 meter element working with the 10 meter element and the 40 meter was linear loaded
and harmonics on linear loaded antennas are different to straight antennas yes whatever
the wigley's got a different place to go so i think it was mike m0msn and james m0yom said
well a quick dirty way out of this is to put a coil in it since this is a fiberglass tube
we don't need a form or anything we could just wrap a little coil around so we did the math
and we worked out we needed 13 or 14 turns around the pole to bring in 40 meters and and it worked
the placing of where the elements should be if you are going to build say a home brew
you want to nest this up a tree or something that seems to be important as well so this is
i had just streamed the field and didn't realize it would come out so badly on the on the picture
but anyway that's the base plate and the grab the driven plate and the ground plate
of the dx commander rapid so starting at the on the left hand side the so239
we've got the elements in order 15 17 12 20 then we've got 40 which we're going to focus on in a
minute and then 10. now 10's right next to 40. so last night i thought it was a brilliant idea
to swap 12 and 10 over i didn't realize it was so close i thought that difference of
separation will just fix every problem i've got under the sun actually it made it worse
but whatever let's uh see what else what other footage we've got so this is the coil driven
element as you can see and this is one two three four five six seven eight nine ten eleven twelve
thirteen fourteen so you can see on the right hand side at the bottom we've got the 40 meter element
comes up to a little ghibli jobley jubilee clip that goes actually to the guide plate which i'll
show you in a minute and then it goes around in a coil and it turns out that each time we go around
it's about 200 kilohertz actually it's 220 kilohertz going around once
then we just come out of that now i haven't intentionally
i haven't made this exactly very pretty i just this is kind of my prototype but you could do
that really nicely with like cable ties or shrink wrap or whatever you want we haven't smoke tested
this yet tom is coming to see me tomorrow which is thursday and we're going to run
a few watts down here and see if we can get it smoking but and i have a little infrared
temperature gun you know that should be a laugh and then the element goes straight up to the top
so let me just tell you the spec if you wanted to build this if you wanted usa which is kind of
settled at sort of two 7.25 so you get all the way from 7.2 to 7.3 ish you need 13 turns all the way
around all the way to the top and then back down to the upper spreader by about six inches and
that's it you get a perfect chain and i'll give you the cut chart in a minute for in fact i'll
put the cut chart in the description all right rather than me reeling out a load of figures here
if you want uk which is centered around kind of 7.1 ish then add a turn but instead of
coming all the way back down from the top to the upper spread that go about halfway and
you can tune that depending exactly where you want it i've got mine at seven point one five one two
well one point two to one or something and that's fine slightly sharper than a regular vertical
in other words the swr curve on this because it's got a coil on it it's just slightly sharper
a full quarter wave be slightly wider that's all let me run through some swr charts oh before we
go anywhere let me give you a little tip here this here is i think i can zoom in some people
go up we've got a little metal eyelet at the top of most dx commander poles not the expedition
so if you don't want to go through the eyelet i supply a little bit of this pvc tubing
you slip that over the end and honestly it holds it forever it's absolutely fine
and that's how you do it within expedition which you're out of stock of anyway so here we are
oh okay i'm i'm bottomed out to about seven one two five that whole screen is a hundred
kilohertz from left to right so you can see i'm about one point two one point three on the left
hand side about one point four on the right hand side over 100 kilohertz so that's pretty good
um we haven't got the 30 meter element because we've replaced the 30 with this 40 you see
that's 500k wide here and i'm in the field i'm about 10 meters away with something
called westflex 103 very high quality coax to the stick here so 500 kilohertz centered at 14 195
and port 20 meters is absolutely fine this one's a little bit blurred i'm sorry 18.1
is 1.23 to 1 and that's a 250 kilohertz graph but um 17 meter bands pretty narrow anyway so
it's fine best i can get on 21 at 21.1 as it so happens and that's tuna but it's his own elements
you can cut and shorten it whatever it's 1.97 i can't do any better no matter what i do it's tough
uh 12 i didn't have a problem with okay this is centered at 24.990 so i need to add about half
an inch one centimeter just to send it back down 1.18 best i can get is 1.79 on the 10 meter band
but you can see that's a 500 kilohertz that's out of focus we got a better shot of that no
um 1.791 across 500 kilohertz now if you've got a longer length of coax
you will find due to the loss of the coax these swr numbers will be better
and also coax acts sometimes as a transformer as a whole a whole other video right
you see the thing is impedance repeats every half wavelength so if you've got 62 ohms at the feed
point and you've got a half wavelength of coax that's the velocity factor and you plug your meter
in there you'll get an accurate meeting from the feed point okay what's happening is that impedance
is traveling down the line at odd places so if you cut it at the wrong place you could actually
end up having a much better match if you know to me but i love it it works tremendously at the rig
end you see i'm getting like one point three to one across all the bands because i'm running 50
meters and that's 160 foot of coax good cold quality coax but it settles all the swr curves
so i can't really do the testing at the rig end i've got to get out in the field which is what
you can see here the next piece of r d will be the 12 meter signature and that will have a coil
driven 80 meter element um look forward to that next video is this one have a great day everybody
we're off to bude in cornwall very sort shortly and uh i'm gonna have a week off there's a few
videos i've done that are in stock you can enjoy them when i'm away all the best now