digital radio transmitter schematics

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?)

greeting,

I would to built radio transceiver so that everyone can do the remote sensing.

is this a right choice ?

There's allegedly one in the Nov Silicon Chip.

I am at least 13 hours of flight from you. no way to get that magazine.

can u post it up? please.

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

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

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

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

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scrambler

form,

very informative.

the oz radio modem is more like a kid's toy.

Is 433.92 MHz clear and legal for such use where you are ??

........... Phil

is this one better?

too many restricted, no way we can advance in research.

programmed

If they refuse to say what the application is then I assume it is all three.

......... Phil

Dont have it myself.

Someone mentioned it in here, the local papershop had sent theirs back the day I rang, literally.

Havent gotten around to doing anything about it myself.

Is there a url ? Nothing obvious turned up with his rather uncommon name.

The UHF modules are by Laipac as sold by :

......... Phil

"Phil Allison" wrote:

"Niels Damsgaard-Sørensen" <

"Phil Allison" <

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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.

Ken

scrambler

form,

Only 1200bps sinngle duplex though 8-(

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

You dont need to do any fancy encoding to transmit digital data. Is this anything like what you are trying to do???

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Hi Howard.

Not sure what's up with my brain lately - that should indeed have been "PSK", not "QAM". Sorry.

You're certainly right about efficiency with the class-C and all that - I hadn't thought of the microsatellite application. I deal with bigger birds but with the general limitation of restricted bandwidth. Horses for courses, which I think we can safely assume we both knew but didn't think of off-hand. :-)

I see you're (probably) in UK - are you at Surrey? Are you actually working in uSatellites??

Cheers.

Ken