Propeller grunt and DSP/Modulation?
rwgast_logicdesign
Posts: 1,464
in Propeller 1
So I haven't posted here in a looongg time, looks like the forums are quite different! I pretty much got hooked on software defined radio, and started using cypress PSOC chips as my main beefy platform. Iv'e been basically doing electronics repair, electrical, and some consulting for PLC systems the last two years so I could watch my daughter since I have 100% custody. I was got really tired of fixing T.Vs ALL THE TIME, and was happy to take a fixing up a tanning salon who needed repairs done to the capacitor banks in a few beds, there PLC had bad caps, and there computer system had never been scanned! It was a pretty nice change of pace until the lady kept giving me more work and did't like that I wanted more money so she fired me. So I finally sat down and started desinging products to start on tindie. It is all RF gear BroadBand Low Noise Amps, hairpin filters on rogers pcb, and im working on an 8 port antenna diversty array controller that has broad compatibility from a scanner or baofeng to an rtl-sdr or ettus usrp! As soon as I got all my parts and PCBs delivered I got picked up by a local wireless ISP that has fiber drops all over and base stations with sector antenna arrays (like a cell tower) that the customers point are dishes at. It is pretty cool playing in two server rooms a few block from each other over a 100gig bit wireless link. Anyways none of this has much to do with my question just thought I would drop an update to anyone reading who may remember me always working on my robot, it is actually finished now, hardware wise. There are a few more things I want to add to the guy before I start writing the real code, #1 is a phased radar system, half the reason I got so sucked in to RF.
So I have been kicking around writing some PC software for people that reverse engineer signals with an SDR. The issue is beyond understanding I/Q and how to build a quadrature transceiver I dont know much about DSP. I thought maybe I would start by building a packet modem on a micro controller. Now there is a project called micromodem which does ASK1200 baud using an arduino, and I know Phil wrote an ASK Bell Modem for the propeller, these are nice options for APRS some amsat stuff etc etc, but there slow and I would say the only saving grace of a Bell ASK modem would be it wide spread standardization for many packet radio protocols. I want to make a decent speed (56k?) long distance link, my thinking is to use to 70cm transcievers probably one of these, Dorji Modules that come in 2M and 70cm versions. They seem like an easy way to get on a legal frequency and I can stick them anywhere with a modem and not worry about loosing a handheld. From what I can tell there highly configurable, so much so some guys have used two with a micro to make repeaters, but there about as clean as a baofeng so I guess the need filtering if your going to put them in to serious full time use, unless you wanna be that guy spreading barley legal harmonics for all us SDR users to see.
So why QAM? Well I was cleaning the garage found a ton of old 56k ISA USR "hardware" modems (as in cheap not v.92 modems that used your cpu) and wondered could I either connect a transciever to one of these guys, or even better just desoldier the demodulation chip eleminating the matching network and use that. Then I saw an Instructable and found out there is a program called J-QAM that can modulate data in to QAM64 (same as a 56k modem) then play it out the sound card, this can buy you a theoretical 400kbps connection and the guy who wrote the instructable used J QAM to push files encoded in QAM64 in to a little commercial band FM transmitter, the kind you use in your car if you dont have aux or bluetooth for whatever media device you use. On the other side there was a PC with an FM stereo connected to line in. According to the instructable he was able to get a 60k link this way.
I just happen to have been given a set of really nice commercial Larid brand gold anodized 70cm Yagis. I figure I could run a low speed link 20 to 30 miles away, especially since my house sits at the base of a mountain higher than most of my surrounding rural dessert area, and use TCP over Slip to bridge my network with a buddys. Also this is a good project im betting if I learn to modulate/demod QAM64 I will be able to handle most any thing I find on the spectrum. Secondly just like when this stuff was over the phone lines I can screw with DSP effects like echo cancellation etc, in order to improve signal quality. The propeller came to mind QAM64... it can be broken down by 8 per core,,, the prop can generate audio with an rc filter... and hell you could even add an SD card that stores other modulations and modes, loads them in to SRAM and then you have kind of a multi mode universal modem.
My problem at this point is I only know enough to know how it all works and be a bit dangerous, so I have no idea if a prop would be able to handle QAM, and DSP to help impove the quality, not to mention sound. I thought it would be really awesome to put a little TFT on the thing with an FFT of the signal!
P.S Sorry if the "Short Story" was annoying to anyone, im just excited about life right now, and have wild dreams of being able to make a living doing electronics I want to do down the road. SDR is still bleeding edge and every day more people are getting in to, not to mention as the price on quality SDR comes down there will be no need for analog radios.... so I feel like I am sort of in the right place at the right time, like sparkfun during the "make" movement. Im just not sure how many people will want my SATCOM and Radio Astronomy Gear, gotta be pretty Geeky or at an Engineering school to be in to that stuff.
So I have been kicking around writing some PC software for people that reverse engineer signals with an SDR. The issue is beyond understanding I/Q and how to build a quadrature transceiver I dont know much about DSP. I thought maybe I would start by building a packet modem on a micro controller. Now there is a project called micromodem which does ASK1200 baud using an arduino, and I know Phil wrote an ASK Bell Modem for the propeller, these are nice options for APRS some amsat stuff etc etc, but there slow and I would say the only saving grace of a Bell ASK modem would be it wide spread standardization for many packet radio protocols. I want to make a decent speed (56k?) long distance link, my thinking is to use to 70cm transcievers probably one of these, Dorji Modules that come in 2M and 70cm versions. They seem like an easy way to get on a legal frequency and I can stick them anywhere with a modem and not worry about loosing a handheld. From what I can tell there highly configurable, so much so some guys have used two with a micro to make repeaters, but there about as clean as a baofeng so I guess the need filtering if your going to put them in to serious full time use, unless you wanna be that guy spreading barley legal harmonics for all us SDR users to see.
So why QAM? Well I was cleaning the garage found a ton of old 56k ISA USR "hardware" modems (as in cheap not v.92 modems that used your cpu) and wondered could I either connect a transciever to one of these guys, or even better just desoldier the demodulation chip eleminating the matching network and use that. Then I saw an Instructable and found out there is a program called J-QAM that can modulate data in to QAM64 (same as a 56k modem) then play it out the sound card, this can buy you a theoretical 400kbps connection and the guy who wrote the instructable used J QAM to push files encoded in QAM64 in to a little commercial band FM transmitter, the kind you use in your car if you dont have aux or bluetooth for whatever media device you use. On the other side there was a PC with an FM stereo connected to line in. According to the instructable he was able to get a 60k link this way.
I just happen to have been given a set of really nice commercial Larid brand gold anodized 70cm Yagis. I figure I could run a low speed link 20 to 30 miles away, especially since my house sits at the base of a mountain higher than most of my surrounding rural dessert area, and use TCP over Slip to bridge my network with a buddys. Also this is a good project im betting if I learn to modulate/demod QAM64 I will be able to handle most any thing I find on the spectrum. Secondly just like when this stuff was over the phone lines I can screw with DSP effects like echo cancellation etc, in order to improve signal quality. The propeller came to mind QAM64... it can be broken down by 8 per core,,, the prop can generate audio with an rc filter... and hell you could even add an SD card that stores other modulations and modes, loads them in to SRAM and then you have kind of a multi mode universal modem.
My problem at this point is I only know enough to know how it all works and be a bit dangerous, so I have no idea if a prop would be able to handle QAM, and DSP to help impove the quality, not to mention sound. I thought it would be really awesome to put a little TFT on the thing with an FFT of the signal!
P.S Sorry if the "Short Story" was annoying to anyone, im just excited about life right now, and have wild dreams of being able to make a living doing electronics I want to do down the road. SDR is still bleeding edge and every day more people are getting in to, not to mention as the price on quality SDR comes down there will be no need for analog radios.... so I feel like I am sort of in the right place at the right time, like sparkfun during the "make" movement. Im just not sure how many people will want my SATCOM and Radio Astronomy Gear, gotta be pretty Geeky or at an Engineering school to be in to that stuff.
Comments
http://forums.parallax.com/discussion/132977/hilbert-transform-prop-dsp
http://forums.parallax.com/discussion/133173/fir2pasm-automatic-fir-filter-code-generator
http://forums.parallax.com/discussion/115805/real-time-goertzel-algorithm-object-and-dtmf-sensing-demo
-Phil
This is very much off the subject of QAM, but I figure now that I have you looking maybe I can pick your brain. As I said above I want to develop a diversity array system, mostly I want to use it to do beam forming with lots of small antenna elements in the microwave bands. I like Radio Astronomy and SatCom, I currently have two smaller dishes which I use and a C-Band that I cant put up where I am living. Im thinking small planar arrays of things like patches or chip antenna could get really high directional gain and be electronicaly steered while taking up a lot less space. Maybe you make 6 planar patch arrays, and then plug those arrays in to the diversty controller to beam forming and steering.
It seems there are a few people making diversty controls for first person drone video and there using RSSI or image comparison in order to figure out exactly which antennas to flip on and off, phase 90 degrees etc. I want to make my controller for radios though, mostly wide band SDR but scanners work too, even a baofeng whatever... If it were you what variable would you be looking at that would cause you to start doing antenna processing? I mean its not the hydrogen line sends an RSSI signal. Maybe you sweep one antenna on a rotor graphing signal power and then the controller beamforms to that strong spot the single antenna found?