Q&A – Elektor Academy AVR Defined Software
Can you program mash dividers in your signal generator?
Answer:
I have not considered the MASH technique up to now.
It certainly would be interesting to realize that on the AVR.
What is the highest freq for the receiver? Can you do band scann?
Answer:
Highest frequency is about 600kHz. Since the selectivity is only due
to the selective antenna, a band scan offer a wide frequency range is not possible.
I would like to understand I/Q modulation better. Can you suggest any reading
material or other sources that is not too mathematical?
Answer:
I would suggest the ARRL Handbook 2012, My older version already has a complete
chapter about DSP and SDR.
Can you show what is on the display when receiving for example BBC on 198
kHz?
Answer:
In the course there will be a picture showing that. The two scope traces show
amplitude and phase. The amplitude trace is nearly constant. The phase-trace
clearly shows the modulation of the data-stream.
Would you comment on high speed ADC?
Answer:
To digitize higher frequency signals an external fast ADC would be necessary. But that
would also require a faster CPU. So for an SDR based on the AVR will faster ADC will not
make sense.
Would you be able to give some guidance at some time in the future to the demodulation of time code signals here in North America. CHU in Canada or
WWVB in the US?
Answer:
The CHU signal has a too high frequency for direct application of our concept.
After some down conversion it should be possible to demodulate the Signal.
I think WWVB at 60kHz should be easy with our concept by changing the frontends
sample rate and adjusting the demodulation software.
What sort of CPU do you need for wide band SDR baseband?
Answer:
The CPU must be fast enough to handle the bandwidth of the baseband signals.
So for basebands above 100kHz you certainly should use a DSP.
What is the sensitivity of the receiver?
Answer:
Due to enough gain I thank the sensitivity will be in the 20 to 50uF range. But the
selectivity is only determined by the selective ferrite antenna, so the bandwidth is small
and strong nearby jamming signals will reduce the SNR.
Suggest good textbooks?
Answer:
See above:
I would suggest the ARRL Handbook 2012, My older version already has a complete
chapter about DSP and SDR.
"Digital Communications " by Proakis
"RF and Baseband Techniques for Software Defined Radio" by Peter B. Kenington
Could you offer a dev board that would a low a designer to test high speed
ADC?
Answer:
I think you should look up the application notes of Analog Device, Linear Technology
and others and then also look at their dev-boards..
Are the microprocessors used here DSP type or regular microprocessors? Do
we need DSP processors for SDR?
Answer:
I use a regular CPU. Treating only relatively low frequency signals that is possible.
For "real" SDR in the HF region a DSP with AMC(Multiply Accumulate-) instructions is
necessary.
I will like to build an Audio/Video TX/RX device for max 3 km distance. do you
have any idea of this type of design?
Answer:
The problem is, that you have to fulfil the legislations. So I would suggest using readymade RX and TX boards.