E
easyarm
need digital radio transmitter schematics that will work with
microcontrollers.
THANKS
microcontrollers.
THANKS
easyarm said:need digital radio transmitter schematics that will work with
microcontrollers.
greeting,Android Cat said:More information would be good.
What data rate? Short range or long range? Point-to-point, digipeated,
or what? One-way or two-way? Full duplex or half? What frequency and
what power level? Licencing? Cost per unit? Parts or off-the-shelf?
In short, what's the application? (And would a handful of R/C modules
make you happy?)
--
need digital radio transmitter schematics
that will work with microcontrollers.
Rod Speed said:There's allegedly one in the Nov Silicon Chip.
http://www.siliconchip.com.au/html/conts-nov-03.htm
Howard Long said:That describes (amoungst other things) the 9600 scrambler technique in an
attempt to remove the DC component when modulating an FM transmitter and
then decoding it back using an FM receiver. It uses a maximum length
feedback shift register to randomise and then unrandomise the bits. You
never need more bits than the length of the shift register to resync. This
bi-state technology is quite old now, and I know that it has been
implemented in a PIC. I have two of the original designs made out of CMOS
4000 series logic, and I still use them today for satellite comms with some
of the older satellites still in operation. It has also been used for
terrestrial comms, but 9600 is so slow these days!
More recently, this 9600 modem has been implemented using DSP techniques and
PC sound cards.
Latterly, the use of phase and amplitude modulation has been implemented in
an attempt to get more bandwidth out of a high signal to noise channels such
as telephone modems. This is how you get 33.6kbps out of a 3kHz bandwidth
phone line.
For satellites, generating anything more than four states becomes
inefficient due to the need to use linear amplifiers which are inherently
less power efficient than their non linear class C counterparts. Four states
may be implemented by flipping between four phase states (-45, +45, -135
+135 degrees) by only changing phase, not amplitude. This is called offset
QPSK.
Anyway, that doesn't help what you are trying to achieve. The 9600 scrambler
technique is proven and does work quite well over radio, but you need to
consider some means of error detection and correction. In its simplest form,
this would be a retransmission, although these days there's all sorts of
techniques.
For the RF side...
If you are in Europe there is a project on an RS-232 radio transceiver in
the December 2003 Elektor.
I have used the RF Solutions devices with a lot of success
(http://www.rfsolutions.co.uk) in particular the ones based on the
Radiometrix devices (http://www.radiometrix.co.uk).
One thing to note - if you need full duplex things become a bit more
complicated. It's normally more cost effective to simulate it in software,
but for some realtime applications it's not possible and you will have to
operate on two different frequencies, probably in different bands to avoid
in-band desense.
Regards, Howard
I am at least 13 hours of flight from you. no way to get that magazine.
can u post it up? please.
Phil Allison said:** The project is sold as a series of kits by the author - programmed
PICs are involved.
Is 433.92 MHz clear and legal for such use where you are ??
easyarm said:
too many restricted, no way we can advance in research.
I am at least 13 hours of flight from you. no way to get that magazine.
can u post it up? please.
The project is sold as a series of kits by the
author - programmed PICs are involved.
Rod Speed said:Is there a url ? Nothing obvious turned up with his rather uncommon name.
Hmm, I don't think I agree with this. In satellite work bandwidth is at aHoward Long said:That describes (amoungst other things) the 9600 scrambler technique in an
attempt to remove the DC component when modulating an FM transmitter and
then decoding it back using an FM receiver. It uses a maximum length
feedback shift register to randomise and then unrandomise the bits. You
never need more bits than the length of the shift register to resync. This
bi-state technology is quite old now, and I know that it has been
implemented in a PIC. I have two of the original designs made out of CMOS
4000 series logic, and I still use them today for satellite comms with some
of the older satellites still in operation. It has also been used for
terrestrial comms, but 9600 is so slow these days!
More recently, this 9600 modem has been implemented using DSP techniques and
PC sound cards.
Latterly, the use of phase and amplitude modulation has been implemented in
an attempt to get more bandwidth out of a high signal to noise channels such
as telephone modems. This is how you get 33.6kbps out of a 3kHz bandwidth
phone line.
For satellites, generating anything more than four states becomes
inefficient due to the need to use linear amplifiers which are inherently
less power efficient than their non linear class C counterparts. Four states
may be implemented by flipping between four phase states (-45, +45, -135
+135 degrees) by only changing phase, not amplitude. This is called offset
QPSK.
There's allegedly one in the Nov Silicon Chip.
http://www.siliconchip.com.au/html/conts-nov-03.htm
Hmm, I don't think I agree with this. In satellite work bandwidth is at a
higher premium than power (usually) so if you can conserve bandwidth by
using 8 or 16-QAM then so much the better. These, along with better coding
techniques, are becoming the norm now. However that's just detail - nice
post.
You dont need to do any fancy encoding to transmit digital data. Iseasyarm said:need digital radio transmitter schematics that will work with
microcontrollers.
THANKS
Hi Howard.Howard Long said:Hi Ken
On the uplink this is a non-issue - we've got the advantage of plenty of
power down here on Earth.
For the tiny LEO birds I deal with generally a class C PA is used for
digital comms, but sadly I am talking about power budgets of a few watts.
I don't have any technical experience of dealing with many other digital
satellite systems, certainly none using QAM, although I had always assumed,
perhaps incorrectly, that anything other than class C was inefficient. As an
example, I was of the impression that almost all DBS TV is done using QPSK,
although as I only have a peripheral interest in this (as a user!), I am
referring to a single six year old text ("Issues in Advanced Television
Technology", S Merrill Weiss, Focal Press).
Of course, as you suggest if the application has limited spectrum and
sufficient power, then there is nothing wrong in using QAM. I just wish that
the satellites I use had that luxury!
I wonder which applications of satellites lend themselves to using QAM on
their downlinks?
Kind Regards, Howard