chirt05
Newbie level 3
ssb filter ne5532
Hi all
Perhaps my question is stupid, but I am momentary at the end of my ideas. What the heck is the demodulation of AM if I have a I/Q signal ?
My homebrew HDR-2005 (= HardwareDefinedRadio 2005 Wink is a mixture between QRP2001, SDR-1000 and other concepts. It sounds great in SSB.
I demodulate LSB, USB or both but not AM. Yes, yes I know M = srt(I^2 + Q^2), but how I do it in hardware ! Up to now all my trials with AM ended in much distortion.
Does anybody knows how I produce a clear AM from I and Q with (analog) hardware?
Best regards
Chris
---snipped from https://groups.yahoo.com/group/soft_radio/message/
Many Thanks for Your suggestions !
Before I post yesterday my question, I experimenting much hours and
nights (my XYL damned me ;-).
But also Your different answers show me that this simple "problem" is
not so clear as it seems...
> Try using only one of your I/Q channels;
> for example, take the I channel, and ignore the
> Q channel. Then use a simple detector circuit to
> demodulate the signal from the carrier.
and
> ...but I thought that the I and Q signals were identical
> except they were out of phase with each other. o for
> AM detection you could use either one by itself and the
> result would be the same.
Firstly I think so too, but practiclay I had no succes
(distortions) and
> How about envelope detecting both the I and Q signal
> independently (perhaps with a simple diode and RC filter)
> and them summing the resulting audio signals? Perhaps
> not an optimal solution, but it should work.
Why not optimal ?
> Or you could emulate what Alberto does in the SDRadio
> ECCS demodulator where you could have a pair of SSB
> demods (one for LSB and one for USB) fed from the IQ
> channels. Then sum the audio outputs from the demods.
> The gotcha' on that approach is that you need to
> assure that you are always in zero beat unless you
> don't mind annoying heterodyne whistles in your audio.
> This would require some sort of feedback to form a
> frequency control loop……
Very interesting, I look at ECCS demodulator...
Theoreticaly I thought this technique some days before,
but I dont build it practicaly so far.
Its important where I took the I/Q signals. After the QSD
or after the Polyphase-Filter befor sum or diff the signal
to LSB/USB.
> ...compute sqrt(I^2 + Q^2) in hardware, apart from using
> a look-up table programmed in a ROM... maybe someone
> else will stand up and suggest a simpler way.
and
> Cordic has been implemented in VHDL, IIRC (Opencores).
Yes I know the Cordic algorithm, but my HDR-2005 is
analog hardware....
(FST3253, INA 163, NE5532, ..... )
O.K. I think about Your suggestions and goes on
my work-bench....
73
Chris
Hi all
Perhaps my question is stupid, but I am momentary at the end of my ideas. What the heck is the demodulation of AM if I have a I/Q signal ?
My homebrew HDR-2005 (= HardwareDefinedRadio 2005 Wink is a mixture between QRP2001, SDR-1000 and other concepts. It sounds great in SSB.
I demodulate LSB, USB or both but not AM. Yes, yes I know M = srt(I^2 + Q^2), but how I do it in hardware ! Up to now all my trials with AM ended in much distortion.
Does anybody knows how I produce a clear AM from I and Q with (analog) hardware?
Best regards
Chris
---snipped from https://groups.yahoo.com/group/soft_radio/message/
Many Thanks for Your suggestions !
Before I post yesterday my question, I experimenting much hours and
nights (my XYL damned me ;-).
But also Your different answers show me that this simple "problem" is
not so clear as it seems...
> Try using only one of your I/Q channels;
> for example, take the I channel, and ignore the
> Q channel. Then use a simple detector circuit to
> demodulate the signal from the carrier.
and
> ...but I thought that the I and Q signals were identical
> except they were out of phase with each other. o for
> AM detection you could use either one by itself and the
> result would be the same.
Firstly I think so too, but practiclay I had no succes
(distortions) and
> How about envelope detecting both the I and Q signal
> independently (perhaps with a simple diode and RC filter)
> and them summing the resulting audio signals? Perhaps
> not an optimal solution, but it should work.
Why not optimal ?
> Or you could emulate what Alberto does in the SDRadio
> ECCS demodulator where you could have a pair of SSB
> demods (one for LSB and one for USB) fed from the IQ
> channels. Then sum the audio outputs from the demods.
> The gotcha' on that approach is that you need to
> assure that you are always in zero beat unless you
> don't mind annoying heterodyne whistles in your audio.
> This would require some sort of feedback to form a
> frequency control loop……
Very interesting, I look at ECCS demodulator...
Theoreticaly I thought this technique some days before,
but I dont build it practicaly so far.
Its important where I took the I/Q signals. After the QSD
or after the Polyphase-Filter befor sum or diff the signal
to LSB/USB.
> ...compute sqrt(I^2 + Q^2) in hardware, apart from using
> a look-up table programmed in a ROM... maybe someone
> else will stand up and suggest a simpler way.
and
> Cordic has been implemented in VHDL, IIRC (Opencores).
Yes I know the Cordic algorithm, but my HDR-2005 is
analog hardware....
(FST3253, INA 163, NE5532, ..... )
O.K. I think about Your suggestions and goes on
my work-bench....
73
Chris