Maker Pro
Maker Pro

Long range (high power?) 433MHz, 916MHz, 2.4GHz transceiver for data comm

S

Sam Acme

How much RF power required for more than 600Km line of sight (say from a
satellite to earth) data communication?

Is there any off the shelf solution (or home made) for such a system?
(Transceiver on the satellite must be small, light weight, low power-high
efficient, while we do not have such restrictions on the other transceiver
to be used on earth)

Do we need special license to use transceivers at these frequencies?
 
P

Paul Burke

Sam said:
How much RF power required for more than 600Km line of sight (say from a
satellite to earth) data communication?

Is there any off the shelf solution (or home made) for such a system?
(Transceiver on the satellite must be small, light weight, low power-high
efficient, while we do not have such restrictions on the other transceiver
to be used on earth)

Do we need special license to use transceivers at these frequencies


The tragedy of the commons. The open bands are usable because the power
is limited. Then people start cheating, and increasing the power, making
these frequencies unusable for those who stick to the rules. So they
have to increase thir power- a classic arms race. The limit (for 433 in
the UK) is 10mW.

If you can afford a satellite, you don't need to use these frequencies!

Paul Burke
 
J

John Jardine

Sam Acme said:
How much RF power required for more than 600Km line of sight (say from a
satellite to earth) data communication?

Is there any off the shelf solution (or home made) for such a system?
(Transceiver on the satellite must be small, light weight, low power-high
efficient, while we do not have such restrictions on the other transceiver
to be used on earth)

Do we need special license to use transceivers at these frequencies?
If you've got a 1mtr^2 aerial/dish picking up the signal and generating 1uV
in a 50ohm load and the satellite is illuminating a spot on the Earths
surface about 800km across then ohms law and the area of a circle suggest
you only need an 11mW transmitter on the satellite (assuming absolutely no
losses).
I've honestly no idea if this is true. It was just a passing thought :)
regards
john
 
D

Dave VanHorn

one of the first lunar probe transmitters was 0.1w at 108 mhz.
 
D

Dave VanHorn

Richard Crowley said:
-

Yeah, and to receive it, they used steerable dishes that were
as big (and likely cost as much) as your whole neighborhood!

i don't know that to be true, but i have the schematics for the transmitter.

moonbounce is done by hams all the time, on the 2 meter band.
given that the moon is a really lousy reflector, and also the wrong shape,
it seems entirely reasonable to me that a low noise receiver, with a
reasonable antenna, could pick up a tenth of a watt from that distance.
 
A

Andreas Schmidt

Dave said:
i don't know that to be true, but i have the schematics for the transmitter.

Are those available for download somewhere?

Cheers,

Andi
 
D

Dave VanHorn

\
The photo of one guy's receiving antenna on the front of the magazine
("QST"?) shows the dish as big as his house. And "steered" with
two junker car chassis running on a circular track. I'm sure most
hams use more modest receiving antennas, but only by means of
blasting the moon with hundreds (thousands?) of watts.

here's the seti league's antenna. this is probably about 8' across and about
3' high.
http://www.setileague.org/eme/emeant2.jpg
four antennas transmit, and the other four receive. notice that the antennas
are wound in different directions. when the signal reflects, it is changed
to the other rotation direction.

here, they describe the system.
http://www.setileague.org/eme/emepix1.htm
power up the pipe is 150 watts.

given the large path loss, the signal coming off the moon will certainly be
much less than 100mw
 
D

Dave VanHorn

Richard Crowley said:
here's the seti league's [EME] antenna. this is
probably about 8' across and about 3' high.
http://www.setileague.org/eme/emeant2.jpg

Thanks for the reference, Dave.
I couldn't figure out what interest SETI had in the
moon (which most of us believe to be uninhabited!)
Until I read further that it is a "reference standard"
for radio-astronomy calibration. Ingenious!

big kind of awful reflector in the sky.
 
M

Michael Black

Richard Crowley" ([email protected]) said:
...

The photo of one guy's receiving antenna on the front of the magazine
("QST"?) shows the dish as big as his house. And "steered" with
two junker car chassis running on a circular track. I'm sure most
hams use more modest receiving antennas, but only by means of
blasting the moon with hundreds (thousands?) of watts.
The date of the photo might be crucial.

The first amateur moonbounce took place in 1953 (the first moonbounce
ever, by the US Signal Corp, was in 1946), though they never tried
to contact anyone (obviously); they just hear their own signal back
from the moon.

That was before parametric amplifiers (Sam Harris is credited with
making the first practical paramp, he was a ham and did moonbounce),
and transistors. They had to use either fairly noisy diode mixers
(I forget what frequency they used) or fairly noisy tubes in the front
end. I suspect the transmitters were fairly effective, but still
they likely needed every bit of ERP they could get.

And large antennas had to be the norm in the old days. Not many doing
moonbounce, and still not so great receivers. I'm not sure how many put
their equipment right at the antenna, rather than facing the losses
of the feedline.

But once enough got on with those big antennas, and other factors improved,
it became easier for others to do it. A guy in Australia did it
in the sixties from Australia, and they had something like a 150watt power
limit. But, he had a lot of space on the farm, and he had big rhombics.
I thought he had a section to allow some directing, but basically he
could only do moonbounce when the moon was in the right place for
the antenna.

When Sam Harris started working at Arecibo, he worked it so they
used the antenna for moonbounce one or two times in 1964 or so.
That thing had so much gain that it made moonbounce feasible for
a lot of people during the brief time it was tried.

So there's a balance. The guys with the big arrays enable people
with much smaller systems to do moonbounce.

Along the way, the receivers got better. First, they used
paramps, and then solid state devices started getting better.
I remember one review of a fairly early FET converter, and
the writer said it compared well with his 416 (or was it a 417?)
converter, and the 416 was considered basically the best front
end tube for VHF/UHF at the time. He admitted that it meant
his tube converter needed adjusting, but considering there was
no finicky adjustment of the FET converter, it bode well for
the future.

So if someone wants to hear their own echo at this point, they may
find they still need a fairly good system. But because there
people with good systems, others can get by with less.

Michael
 
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