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Matlab code needed for SSB demodulation

Started by Rick Lyons June 30, 2012
On 12.5.17 00:44, danielot@gmail.com wrote:
> On Thursday, May 11, 2017 at 3:19:51 PM UTC-3, Steve Pope wrote: >> >> Yes, if you have the Hilbert transformer at baseband, then you have >> additional difficulties in recovering components near DC, relative >> to having the Hilbert transformer at IF (as described in my last pair >> of posts). > > I finally made my code working! But then I realized it only works for baseband. I'm just wondering now how would it be possible to do the Hilbert transformer at IF as you said. > > I have the impression the Fig. 5 of the AARL paper you shared is still describing a baseband Hilbert transformer, which had to be implemented as a BPF due to physical limitations. I think it would be impossible to design a LPF with +90 deg at DC+ frequencies and -90 deg at DC- frequencies. > > Does it look right? > >> >> Generally -- if you're actually building a receiver -- you need >> an architecture and a frequency plan, and therefore face a decision >> between direct conversion and low-IF, ahead of your ADC. For the >> SSB case these two choices correspond to the two possible placements >> for the Hilbert transformer described above. >> >> If you're just doing a simulation for a proof of concept, then it may >> not matter yet, and you can simulate it either way. But if you're >> pretty sure which way the final design will go, then save yourself >> some work and go in that direction now. > > Thanks for the advice. > > We have designed a receiver. By undersampling our 500 MHz carrier at ~221 MHz sampling rate (RF/864*383) we get the IF at 56.7 MHz (RF/864*98)). Then we downconvert to baseband digitally in a FPGA using standard AM demodulation using complex NCO. That's the point where I wanted to improve and use SSB demod. > > This is the project: http://www.ohwr.org/projects/bpm/wiki > > Daniel >
A question: What kind of filtering do you have in the RF front end before sampling? -- -TV
On 12.5.17 12:55, Tauno Voipio wrote:
> On 12.5.17 00:44, danielot@gmail.com wrote
> A question: What kind of filtering do you have in the RF front end > before sampling?
I made a quick image response calculation. You have image responses in addition to the desired 500 MHz: 164.9 MHz, 278.4 MHz, 386.6 MHz, 608.2 MHz, 721.6 MHz, 886.6 MHz, 829.7 MHz, 943.3 MHz, and many others, including direct pass-through of 56.7 MHz. In digital signal processing, the images can also be called aliases. If there is any energy in any, some or all of the images, it will come to the ADC output indistinguishable from the desired 500 MHz. -- -TV
On Friday, May 12, 2017 at 8:22:46 AM UTC-3, Tauno Voipio wrote:
> On 12.5.17 12:55, Tauno Voipio wrote: > > On 12.5.17 00:44, danielot@gmail.com wrote > > > A question: What kind of filtering do you have in the RF front end > > before sampling? > > I made a quick image response calculation. You have image > responses in addition to the desired 500 MHz: > > 164.9 MHz, 278.4 MHz, 386.6 MHz, 608.2 MHz, > 721.6 MHz, 886.6 MHz, 829.7 MHz, 943.3 MHz, > > and many others, including direct pass-through of 56.7 MHz. > > In digital signal processing, the images can also be called > aliases. > > If there is any energy in any, some or all of the images, > it will come to the ADC output indistinguishable from the > desired 500 MHz.
Thanks. The RF front-end is basically the following sequence of components: LPF: Minicircuits LFCN-530+ 2x2 switch: RFMD RFSW6223 BPF: TAI-SAW TA1114 Amp: Minicircuits TAMP-72LN Attenuator: Minicircuits DAT-31R5-SP+ LPF: Minicircuits LFCN-530+ Amp: Minicircuits TAMP-72LN LPF: Minicircuits LFCN-530+ The signal coming in is composed of very short pulses (aprox. 10 ps Gaussian profile) with considerable energy going up to a few tens GHz. And also we have all harmonics starting from 500 MHz / 864 = ~580 kHz. This is called the revolution frequency, which is the repetition rate of the electron bunches train circuliating inside the vacuum tube, whilst the 500 MHz comes from the 2 ns spacing between the bunches (or pulses, from the signal's point of view). We've made similar analysis to yours to cope with aliased frequencies. We're happy with the lowpass performance but just recently we discovered the attenuation provided below 400 MHz by the BPF (55 dB) could be slightly better and make a positive impact in noise performance. We may want to add a coaxial HPF module between the RFFE and the ADC when we'll be deploying, maybe Minicircuits SHP-500+. An unbalance of 0.001 dB between channels means ~1.5 um beam position measurement. Our spec is < 80 nm RMS in 0.1 Hz - 1 kHz bandwidth.