EMRFD Message Archive 9666
Message Date From Subject 9666 2014-01-20 03:56:36 Ashhar Farhan ssb out of the raspberry pi is this for real? http://pe1nnz.nl.eu.org/2013/05/direct-ssb-generation-on-pll.htmlbasically, it claims that you read the mic, figure out the frequency and amplitude of the signal and move the PLL and change the amplitude.i can imagine doing this for a single tone. how does it simulate multi-tone modulation? what about the none sinusoidal stuff like the sound of 'rrrr' and 'kkkk'? i spent some years porting voice codecs so my gut feel is that this can't be it. but then, i may be wrong.- f9667 2014-01-20 13:24:48 Corey Minyard Re: ssb out of the raspberry pi 9668 2014-01-20 15:56:35 kb1gmx Re: ssb out of the raspberry pi >>>I've actually been pondering if this could be done. The ARRL homebrew
contest had a winner (David Cripe) that built an amplifier that
extracted the amplitude and frequency separately and used a class E
amplifier to amplify the frequency portion and a audio power transistor
to control the amplitude of the amplifier. If that's possible, it
should be possible to directly synthesize the amplitude and frequency.<<<
While his approach was by far the most interesting I'd seen. There is a
huge gap between detecting amplitude and using that to modulate a
saturated [switch mode] amp and creating SSB on the fly. One is easily
done with simple analog circuits while the other is a true tour de force of
mathematics at high speed.
I've looked at the possibility of using the Raspberry Pi to run the usual baseband
transceiver software to use with something like the Softrock RXTX ensamble.
Its get enough processing power for that and then some. So I'd expect some of
the more aggressive methods are will within the range of the 'Pi.
The little RaspberryPi is a lot of processing power in a small package and price.
Allison/Kb1GMX
9669 2014-01-20 15:56:47 Eamon Egan Re: ssb out of the raspberry pi VE2EGNI never heard that SSB was reducible to an FM modulation.- Eamon
Here is one of the comments.I think there is such a silence because this technique does not work.. sorry. Had a go at coding it myself, then realized you cannot get fundamentally AM sidebands by just FMing a constant carrier, no matter how cleverly.. anyone else had a go?
Hugh G6AIG9670 2014-01-20 17:16:59 Ashhar Farhan Re: ssb out of the raspberry pi There was a very brief mention of this simultaneous envelop and frequency modulation of carrier to generate SSB in the EMRFD. The citation is unfortunately behind a paywall.- f9671 2014-01-20 18:00:22 iq_rx Re: ssb out of the raspberry pi The technique of generating an SSB signal, either electrical or mathematical, separating it into envelope and phase modulated components, amplifying the phase modulated component with a saturated (perhaps class C) amplifier and then putting the envelope back on with a high level modulator has been widely known since the early 1950s. The best known amateur radio example is the 8 watt linear mode B transponder in Oscar 7, launched in 1974, designed and built by Karl Meinzer DJ4ZC.
I have built a number of experimental models on the bench, and friends have built large commercial versions. The technique simulates beautifully using Matlab.
As Allison mentioned, the block diagram is compelling and simple, but implementation is difficult--requiring fluency with the both afore mentioned analog signal processing mathematics and the subtleties of envelope modulation--both rare these days, among my graduate students at least.
A philosophical difficulty is that the bandwidth of both the envelope and phase modulation must be considerably wider than the actual signal you would like to amplify. The resulting broadband spectral products magically disappear in the mathematics and simulations, but are not as easily suppressed in practice--particularly when efficiency is required.
As with phasing SSB generation (and for similar reasons) it is relatively easy to generate a two-tone SSB output signal that has all the undesired outputs 20 dB down from either of the two tones. 30 dB down requires more care, and 40 dB indicates a carefully engineered, highly evolved system. Some of the accuracy needed for 40 dB suppression of wideband distortion products requires burning current, and one might be better off with a conventional linear amplifier. That has often been the conclusion for nearly 6 decades. Some modern modulation techniques are more suitable than SSB for separating the envelope and phase and recombining them at the final or penultimate stage.
The technique has been given many names, the oldest and arguably most respected is the Envelope Elimination and Restoration or EER technique. More recently, Polar Modulation has been applied. To read more, Google EER, Frederick Raab, Leonard Kahn, and follow the links.
Phase modulation is relatively easy, but it is quite amusing to design and build high quality envelope modulation systems, and a challenge to get beautiful pictures on the scope. I suspect that some of the modern AM crowd is having an awful lot of fun, and students who understand envelope modulation are in high demand in some wireless circles.
Incidently, the recent QST article that compares the effectiveness of various modes in dB contradicts 6 decades of very careful amateur and professional communications theory and measurements, much of which was reported in QST in an earlier era. I wonder how it got past the reviewers.
Best Regards,
Rick KK7B
9673 2014-01-21 03:00:41 Stephen Farthing Re: ssb out of the raspberry pi Hi guys,Yes, it is for real. I have received Guido's RPi SSB signals on 40 meters transmitted from his shack in the Netherlands here in the UK on my K2. Also my good friends Jan, G0BBL and Alan M0PUB have carried out many experiments with SSB on the Pi using Guido's code.The Pi is an interesting platform for radio work. The big problem is the lack of documentation for the processor. As I recall this is a policy decision by Broadcomm to protect their secret smoke.I have copied Guido in on this. Hopefully he will join the group and share his wisdom with us.Regards, Steve G0XAR9674 2014-01-21 10:08:11 Russ Ramirez Re: ssb out of the raspberry pi I enjoyed your reply Rick, in particular the opening paragraph, and the fourth (which I guess speaks volumes about your application knowledge).re: QST, I think ARRL has lost some technical edge anyway IMO.RussK0WFS9675 2014-01-21 10:40:21 johnsorj666 Re: ssb out of the raspberry pi Hi All
If you have interest in using Phase Modulation, you may want to look up the background information on the RCA Ampliphase system used by AM broadcasters. My local AM station, KSTP 1500, used such a transmitter at the 50kW level---please note that this was 40 years ago when I toured their transmitter site so I am not sure if it is still widely used....
Interesting concept though....
ray johnson
WB0EBG / KE3QY
EN35la9677 2014-01-22 08:59:03 Don Hackler Re: ssb out of the raspberry pi The RCA Ampliphase system hasn't been used by AM broadcasters for quite a while. It was basically a Doherty amplifier system, modified slightly to get around Western Electric patents. It was an interesting concept, but difficult to keep adjusted properly in routine operation. RCA also used special tubes that have not been manufactured for a long time. Most 50Kw stations are digitally modulated solid state rigs now, as they are less expensive to operate. The savings on the power bill paid for the newer technologies quickly.
On Jan 21, 2014 10:40 AM, <johnsorj@aol.com> wrote:Hi All
If you have interest in using Phase Modulation, you may want to look up the background information on the RCA Ampliphase system used by AM broadcasters. My local AM station, KSTP 1500, used such a transmitter at the 50kW level---please note that this was 40 years ago when I toured their transmitter site so I am not sure if it is still widely used....
Interesting concept though....
ray johnson
WB0EBG / KE3QY
EN35la9688 2014-02-02 09:28:45 drmail377 Re: ssb out of the raspberry pi This may be a bit OT, but the RTL_FM demod lib has just been updated (as of my post time) faster-better is claimed. Can do AM, FM, USB, DSB with a low footprint and resources. This may be a nice candidate for the RPi. Haven't tried a cross compile as of post time, but there should be a binary out there soon. With a bit of work RTL-FM may be adopted for Tx as well as Rx with the proper hardware, I remember seeing it done somewhere (sorry no links folks).RTL_FM UPdated
http://www.rtl-sdr.com/rtl_fm-updated/
http://kmkeen.com/rtl-demod-guide/