[Music] what is the sides behind how far these walkie-talkies uh traverse so I'll tell you a
quick story I was up at about 1500 feet so that's four or five hundred meters really up
high using one of these and I got in contact with someone all I did is I just shouted my name hello
in uh wherever I was Clay Hill can anybody hear me and this guy came back and I think he was
in Norfolk which is you know two three hundred miles away or something so it's
quite remarkable so they can have a large range but I want to do the science behind
why in the main they don't go very far so let's just explain how this works here so
we've got the body of a I mean this is a retrovis rb639 in fact they sent me these uh for a little
review I'll I'll talk about them in a minute but it could be any walkie-talkie right most
sort of consumer walkie-talkies are in the UHF range which is like in the UK it's 446 megahertz
and USA you've got gmrs and also the Family Radio Service FRS which is also right up there on the
UHF Spectrum now 450-ish megahertz the wavelength that is about 70 centimeters all right a quarter
wave so the perfect antenna for a walkie-talkie for this would be about 15 centimeters long so
it'd be kind of up here right where it's not that so inside this I mean without taking it
apart and cutting it open it'll be a little coil so it's actually extremely inefficient the way
it's working so I've drawn here with some modeling just to show you you don't have to get involved in
all this or anything else just to show you that the bottom half of this element here is kind of
the walkie-talkie bit and then the top half above the Red Dot would be the antenna okay we'll add in
let's say 1.5 meters which is about here okay uh five five something feet and we can see that we've
got some weird patterns on the screen so the one on the left is if I'm holding this perfectly still
like this and I keyed a microphone and you could visually see the RF it looks like a donut from the
top yeah I had a donut with a hole in the middle it looks like that and I can just prove that to
you by clicking this button here and we'll show you what the donut looks like so that's a kind
of a donut shape in this case it's a donut with some extra sprinkles but it's effectively a donut
there you can see the middle of it down there so when you keep the microphone goes boom and
you get this shape of course it's not in colors the one on the right is if we're standing on the
pavement the sidewalk and we cut a slice of this color chart right through the middle right we'll
be able to see what the donut looks like from the side okay and that's it there and then we can do I
mean in science we can measure things all right so we can say at one degree above the Horizon
so your friend is over there and I can run the curse around it'll tell me a little thing up here
it says minus 4.5 DBI Doesn't Matter What minus 4.5 means it's it's all relative to a different
antenna if you built a different one right now that for minus 4.5 is on the basis that it's 15
centimeters 16 centimeters long it's not this is all compact so there'll be some losses what I'm
saying there is that minus four and a half would probably be up about minus 14 and a half okay
just the science there now there's some really cool software called radio mobile
and this is it here and I'm just about to do you a little plot to see the coverage if you're on
a hill at a thousand feet uh which is about 350 meters give or take 300 meters and the underlying
ground under this hill is like a hundred feet or about 35 meters all right so the antenna will be
1.5 meters above the ground the gain we decided would be about a minus 14 say minus 15 DB your
friend he's also going to be holding about head height and that his gain is also going
to be minus 14.5 okay because he's got a matching 14. basically 14 matching one of these will have
about 450 megahertz that doesn't really matter the transmit power on these is I believe 0.5 of a watt
and we won't bother with any transmission losses there's no coaxis that will be soldered directly
onto the to the board then we can hit submit and it will draw us a nice map with like Google Earth
and that sort of thing you'll be able to see roughly how far this signal goes so here we go
so here we go let's zoom into Broadway Tower which is here it's a place called fish Hill fat Broadway
Tower is about there but it thinks something about here and we can't even get into Broadway
we might be able to get to Evesham there's a little place called chipping Norton at about
I can tell you now about 10 miles away something like that so it's actually not a bad coverage for
a tiny walkie-talkie I could prove it to you we could go out we could spend all day doing
this and mapping it all but I'm telling you it'll be about that okay so that's not a bad coverage
I can't don't know a scale on here unfortunately to measure it but I know that road Buckle street
from there to there is about 500 meters okay so that's the sort of scale now we can do the same
again we can modify this coverage our Factories at Holy farm so we can do the same again this
time at Holy Farm which is on a plateau at about 130 meters flat it's just a plateau all right
there's trees around and everything else I did a test actually I never published a video with Carl
and we had a couple of little walkie-talkies and I could get about 500 meters honestly and then I
could hardly hear him incidentally while this plot is is uh is um plotting if your friend is
transmitting that way and you're receiving this way all right you it's going to be some loss there
so if in doubt train your fellow compatriots to if it's ever marginal keep your walkie-talkies
absolutely straight up you'll get a marginally better signal so let's zoom into Holly farm
and have a look at the plot now it's for a start off it's slightly different color it's all a bit
yellowy that's completely flat to here and I can tell you that a lot worse than than the Broadway
Tower so that's that's the science behind it also at UHF trees buildings just like your cell phone
you go into a brick built building you know you've got a perfect signal out here and I've come inside
I can't I haven't got anything well that's on your cell phone be either on a higher frequency again
but you've got to remember the cell towers are on you know 30 meter 100 foot Towers sometimes so
they're looking down on you and they've got very clever antennas and everything tracking where you
are in directional and switching all sorts of stuff in the main if I answer the question for
you 500 meters what's that 600 yards or something will be your Optimum range all right and if you're
over a hill okay the signal can't go over a hill if you've got even a brow of a hill you've got
a radio shadow on the other side so if you're in populated areas cell phones work great all
right use a blooming cell phone but if you just want short quick stab are you there yet yes I am
can you tell me have you cleared the library yes I have you know and you're all in the one Community
or you're under the one business partner that sort of sort of thing these will work fine it
says you're having a cooler person all right so quick short start stabs 500 meters in the
main PMR will work fine all right so I just want to briefly mention these retrovis there's a link
in the description I've got no skin in the game on these and in fact Fred in the shed I'll put a link
in the description he's done a full review of this right it's pointless me doing it all over
again Fred's done it for me yeah he lives down the road as well rb639 right so quickly there
is no control buttons okay so it's you've got a push to talk so you push the talk you go hello
are you there all right that works we've got a menu button volume up and down which
also is the channel up and down and a button on the top so and you can lock it all up and
then you'll be able to give it to someone and say I'll talk to you on this hello can you hear me oh
hello one two three one two three can you hear me
but that's it so pnr446 by the way non-removable antennas are normally little stubby things range
is 500 meters these work fine I like them because they're super slim very very slim and thin
extremely light about 100 grams you can slip them in your pocket there's also a lock function so you
don't accidentally switch it on and there's a cool feature where you could actually send you
know tones but Fred's done a better video than I will ever do uh when it comes to he's got the
patience of going through all the functions and everything and frankly I just can't be bothered
uh walkie-talkies from retrovis no skin in the game I think I'll put them in the box
send them back to them and let them have them back because I'm not really a reviewer but it
was a prompt for me to show you the science behind why pmr446 gmrs and um Family Radio Service is a
very limited range unless you've got some other gear you may have had some fantastic experience
uh using that let me know in the comments mine was about 200 miles maybe you've done better all
right next video is coming up here have a jolly good day thanks for tuning in bye for now [Music]
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