this is the next video for the bonus
series where we want to build a ground
station for a geostationary satellite
and contact a station in Antarctica I
will not repeat the content of the
previous video so it is highly
recommended to watch it first if not
already done but first I have to thank
you
I asked if I should continue with the
series and you responded the video got
four times the amount of comments than
my other videos and most were positive
or even enthusiastic so let's continue
with a bonus series pretty youtubers
here is the guy with the Swiss accent
with a new episode and fresh ideas
around sensors and microcontrollers
remember if you subscribe you will
always sit in the first row last time we
got an overview of the needed components
today we will build and test the first
part a 2.4 gigahertz transmitter with an
output of 20 watts or 43 DBM this is
quite a lot if we compare it with a 100
milli watt maximal power of a Laure
transceiver of course you need a ham
radio license to operate such a
transceiver here in Switzerland you even
need a special license I have a ham
license since 1977 and to get this
special license was of course in the
first step so from a legal point of view
we are cleared and the additional
license was free of charge and delivered
in only one day during corona lockdown
maybe another Swiss world record some of
my viewers wrote that 20 watts would not
be needed this would be great because
this power amplifier is the most
expensive part of the project this one
with 8 watts is 5 times less expensive
but as many other things from China it's
on its way
not yet derived as shown in the last
video I will use an ad on Pluto SDR as a
transmitter so we first have to measure
it
put power then we can calculate the
needed gain of course we can use a
spectrum analyzer to measure its output
power not a cheap solution later I will
show you a cheap one because the
spectrum analyzer is very expensive I do
not want to destroy it
this is why we have to know its
limitations they are here 30 DBM max
with an exclamation mark we paid a stay
way below that anyway it's good practice
to add an attenuator I have here one 420
DP and 2 watts so no problem for the
Pluto measurements for sure an issue for
the 20 watts of the amplifier later on
to find the exact frequency for our
purpose we consult a band plan of the qo
100 the uplink is on these frequencies
so we choose the middle for the test to
for 250 I use the SDR console software
to create a tone which is the name used
by RF engineers for a single frequency
here I can adjust the power the maximum
power is around minus 19 DBM of course
we have to add the 20 DB of the
attenuator the instrument can do that
calculation automatically and now it
shows around 1 DBM or 1 milli watt not a
lot here is a good point to talk about
TP and DBM 0 DBM or 1 milli watt is the
reference so DBM is the measurement for
power other than what it is logarithmic
1 what is 30 DBM and 20 watts is 43 DBM
TP is just a logarithmic multiplier for
power 10 DB is a factor of 10 30 DB is
1,000 why do we use DB and DBM because
we are lazy DB and TBM can be added and
we can avoid a more complicated
multiplication
the calculation is easy the Pluto
delivers 1 DBM and our 20 watts are 43
DBM so we need an amplification of 42 DB
looking at the signal at full power on
the Pluto we see that we not only get
the primary signal we also get unwanted
signals around the courier not perfect
for the moment I do not know where it
comes from
I already modified my Pluto for an
external reference signal but I did not
get the GPS do so I use this ADF 4351
board so let's check it again
when I got my GPS do if we reduce the
power to minus 15 DBM these frequencies
are still there so it seems that they
come from the deep soul of the Pluto and
not from any over driven amplifier
I mentioned that I got a 20 watt
amplifier as the last step before the
antenna according its datasheet its gain
is 37 DB its price is more than $200
which is a lot for Aliexpress so I
assume you want to see what's inside
actually not a lot first we see that I
have version 2 of the board and as a
driver we find the Chinese YP 2 2 3 3 w
it has 26 DB gain and can deliver
already 3040 BM or 2.5 watts the final
stage is a YP 0 2 2 7 185 I did not find
a datasheet but these transistors are
quite expensive and die fast if you do
not pay attention the rest is a boost
converter which boosts the 12 volts
input to 28 volts we can calculate the
input power needed to reach the 20 Watts
43 DBM - 37 DB equals 6 DBM
so we search for an amplifier with a
gain of at least 60 B M minus 1 DB M
equals 5 DB and an output power of 6 DB
M here I have one with 20 dB
and 10 DBM output power it runs on 12
volts which is anyway needed for the
last stage cool so let's connect this
amplifier between the Pluto and the
spectrum analyzer and here is the place
for some tips about working with radio
frequencies all RF components used in
this project have 50 ohm connectors
which is the de facto standard in most
applications never leave connectors open
if not used at least not if power is
involved because it fast can become
expensive why power only can be
transported to the next step if the
cable or the next device has a 50 ohm
input otherwise parts or even the whole
power is reflected if you leave a
connector open it is very similar to if
you would short-circuit it the power
cannot leave the device and is
completely reflected our F power
transistors already become hot during
regular operation when they can deliver
all power to the next stage if they get
it back they easily overheat and die an
expensive death so never leave
connectors open and if you have no other
device to connect you can connect a 50
ohm load then this load dissipates the
heat and your amplifier is happy next
avoid turning male connectors inside
female connectors because they lose the
valuable plating over time this is
especially true for instruments where
you often connect and disconnect cables
and third if you want to do it right you
have to use such a tool to fasten the
connectors
and really we can drive the output to 15
DBM at the required six DBM the spurious
elements stay 35 DB below similar to
without the amplifier so we are good to
go let's come back to my promise from
the beginning of the video I promised
you a cheaper way to measure power this
is a power meter for around $30 it
ranges from 1 megahertz to 8 gigahertz
incredible but pay attention it's only
specified up to minus 5 DBM and please
adjust the frequency otherwise your
readings are not accurate also here I
use a 20 DB attenuator and it shows 9.5
DBM which is 3 DB away from the $3,000
spectrum analyzer keep in mind my setup
is not exactly the same so the results
are not completely comparable but
frequent viewer know that I'm not known
as a fetishist for exact measurements I
want to talk to the Antarctic and 1 DBM
measuring difference will not prevent me
from doing so an additional goodie of
the cheap power meter you get a software
with it for your PC of course it is not
really comparable with a spectrum
analyzer because you do not see the
spectrum and would not discover if your
setup emits unwanted frequencies but
it's good to check power levels now
comes the last step adding the power
amplifier
now the - what attenuator is no more
sufficient we need more fortunately I
have this one for 50 watts I connected
in addition to the 20 DB attenuator I do
not want to risk my spectrum analyzer it
was already hard to convince the wife to
get the permission to buy this one after
we connected the second attenuator and
the amplifier we can start it on the
minimum power of the Pluto I get 10 DBM
output or 100 milli watt we can drive it
up to around 41 DBM or 12 watts then it
stops the case get
quite warm after these short tests I
assume it has to be cooled if I want to
talk for a long time so the setup works
and delivers nearly the 43 DBM peak
power now I can't reveal another secret
at least for the non ham operators I
told you in the last video that I will
use single sideband modulation SSB was
invented because of its power efficiency
I show you what this means my
transmitter is switched on but we see no
signal only if I start the talk we see
asymmetry but it is only high if I speak
loud so the average power is much
smaller than P 3 and we will hardly ever
get the 20 watts out so the power
dissipation will not be as high as with
a constant tone and the chance that my
amplifier survives is a little bit
better that's all for today we
successfully reached nearly 20 watts on
2.4 gigahertz which will be way too much
if I believe some of my viewers but as a
biker I know this placement can only be
replaced by more displacement next week
we will go on with the receiving part
set up the dish antenna and hopefully
hear the first signals from far in this
space as always you find all relevant
links in the description I hope this
video was useful or at least interesting
for you if true please consider
supporting the channel to secure its
future existence thank you bye