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Diskussions- und Newsboard des DARC-Ortsverbandes I40  |  allgemeine Kategorie  |  Selbstbauprojekte (Moderator: DF8OE)  |  Topic: DDC Module2 <- zurück vorwärts ->
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DF8OE
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Re:DDC Module2
« Reply #15 on: 04. September 2020, 14:49:25 »

If this is done at both I2S and all three I2S lines: the solution will not work. When WM is published and you add DDC/DUC you short-circuit the outputs of the busses. That MAY work for the inputs - but definitly not for the outputs of WM and module. There may be problems at the inputs, too because of the load will be critical at higher bus frequencies (and DUC/DDC will use higher frequencies). So it would be mandatory to put one 0R resistor in each line to WM which can be removed easily. Module does not need 0R - you can unplug it 

vy 73
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Re:DDC Module2
« Reply #16 on: 21. September 2020, 05:57:06 »

Hello, people.
I am here and I am ready to answer all the your questions.
I am doing the Sparrow 4 N7DDC Edition and this is first of all my own vision how it should have been a power delivery system of modern HAM transceiver with battaries power.
I have changed pinout for CPU because I will need to change the firmware in any way.
The RF board will have everithing needed to use 4 LiFePo elements, balanse and charger and also MCU-companion, wich will to control of power and to send for DSP-MCU all the meassured parameters from buid-in ADC. So board to board connector has mainly I2C bus to connect them each other.
I don't know exactly, who knows, probably Artur's version would be more interested for other people, I just realise myself in this project and obviously doing what I want to have personally.
I am ready to change the firmware of DDC Module 2 if anyone wants to use it in his own projects.
At this time I have assembled the CPU board and working on firmware.
 IMG_20200909_215739.jpg
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N7DDC
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Re:DDC Module2
« Reply #17 on: 21. September 2020, 05:57:39 »

other side
 IMG_20200909_215753.jpg
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Re:DDC Module2
« Reply #18 on: 21. September 2020, 07:32:02 »

Hello David,
welcome to our forum, glad to see you here. Can you present the list of pinout changes for STM?
You mention on cqham.ru you need to change the UHSDR code to zero IF, can you explain why do you need this?
« Last Edit: 21. September 2020, 10:34:28 by SP9BSL » Logged

73 Slawek
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Re:DDC Module2
« Reply #19 on: 21. September 2020, 15:37:09 »

Hi.
The header with the pinout you can find here
I need to see the filter on the center of panorama because I can do this using DDC.
Output IQ signals dont have a flicker noise on zero freq unlike signals from audio codec.
 UHSDR_UI_ovi40_config.zip
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DF8OE
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Re:DDC Module2
« Reply #20 on: 21. September 2020, 15:45:03 »

But as long as I understand it is impossible to work in FM or AM in zero-IF-mode because you are crossing a division by zero point... Maybe you can get it work in RX but not in TX.

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Re:DDC Module2
« Reply #21 on: 21. September 2020, 17:11:00 »

Hello, Andreas.
All the known SDR progs on PC work in Zero-If and able to work even with variable IF, other words they are able to slide a filter by panorama including zero freq too.
I have noticed one time using QUISK when the 1000kHz domestic AM station is on the center of panorama and the filter tuned on 1000kHz too, the quality of sound is getting very bad. But it is enough to tune the filter even on 1 Herz, the quality is returning back.
 
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Re:DDC Module2
« Reply #22 on: 21. September 2020, 17:19:00 »

FM demodulating code which is used in external software needs so much horse power what is not a problem in a modern PC. If you use zero IF that cannot be realized in an embedded systems same way. To get FM realized we need a "tricky" solution (developed by KA7OEI) which uses much lower horse power but depends on a no-zero crossing signal. So if you switch to zero-if in UHSDR FM is disabled. If you enable it by removing the disabling UHSDR crashes immediately (some ms) after switching to FM because of there are divisions by zero...

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Re:DDC Module2
« Reply #23 on: 21. September 2020, 17:36:39 »

Is this possible to use IF = 1 Hz or ZeroIF can not to be inside the filter ?
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Re:DDC Module2
« Reply #24 on: 21. September 2020, 17:58:28 »

You must shift it so that no wanted products are crossing the zero line. In SSB or CW you can use zero if without problems. In AM you cannot - you will get distortions These are gigantic if the carrier is exactly at zero. If you move it a little bit away the distortions are in the audio signal bandwidth. You can demodulate signal - but it is slightly distorted. In FM you cannot work at zero if in systems which use simplified demodulation routines (like in embedded systems). If your if is too near to zero so that component of your signal are crossing zero you will get gigantic distortions which mostly make from a "Q5 signal" a "Q1 signal". Therefore 6KHz if is a little bit to near to zero. If you are working with low deviation signal may sound ok. But if you increase it your signal bandwidth will cross the zero. So we decided to move to 12KHz which always give a comfortable space between end of signal and zero... But it is not a problem to work in non-zero if mode. You can throw away signal spectrum by cutting the asymmetric spectrum at one side. The only proof is "a symmetrical view". I by myself do not see any sense to do so.

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« Last Edit: 21. September 2020, 17:59:26 by DF8OE » Logged

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Re:DDC Module2
« Reply #25 on: 21. September 2020, 21:46:58 »

HI, Andreas
I think you are not right.
I remember that time 20 years ago when PowerSDR worked with 12kHz IF, but now all known progs can work on zero freq.

The most important advantage is not only symmetrical view, it is the possibility to tune the filter when the panorama and waterfall are motionless.
I will ask somebody who has a lot experience with this and come back soon.
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Re:DDC Module2
« Reply #26 on: 21. September 2020, 21:57:44 »

Quote from: N7DDC on 21. September 2020, 21:46:58
The most important advantage is not only symmetrical view, it is the possibility to tune the filter when the panorama and waterfall are motionless.
Hi David,
this feature is already implemented in the code from very beginning. So far we're not using it because of small display and high overhead for F4 core.

Quote:
I will ask somebody who has a lot experience with this and come back soon.
Please do it, there is problem with FM in UHSDR at zero IF, I know because I also have working DDC solution with UHSDR (see SParkle threads).
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73 Slawek
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Re:DDC Module2
« Reply #27 on: 22. September 2020, 05:13:44 »

I have asked George RX9CIM, autor of SDR Tulipan, Visair and Malachit. He confirmed that all the modulation including FM work perfect with zero IF and variable IF.
With sound codec IQ this is impossible.

Tulipan is using STM32F407ZGT6, we have H743 . Should to work !
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Re:DDC Module2
« Reply #28 on: 22. September 2020, 05:24:01 »

I by myself do not have the skill to do this. I am happy that I understand the maths in pieces when we are working in time or in frequency domain. But definitely no chance to code this. And I have not yet seen any Open Source project using small horse power as on embedded systems where I can learn how this can be done. Telling "it is possible" does not help. Existing projects where it works but that are Closed Source does not help, too. If you (or anyone) knows someone who can code this and is able to share his knowledge or contribute in a collaboration and versioning system (GitHub): invite her/him. Open Source lives from sharing, contributing and learning from each other.

EDIT:
Because of technical discussion started fast and with many informations I totally forgot - please excuse me:
Welcome to our discussion group David! We want to improve the existing project and extend capabilities - and therefore we are happy that you are present here now.

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« Last Edit: 22. September 2020, 05:28:59 by DF8OE » Logged

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Re:DDC Module2
« Reply #29 on: 22. September 2020, 05:39:38 »

Hi, Andreas
Thank you

I think you have to try the current DSP code with IQ from DDC. Just remove amplitude and phase balansing, DC removing and try.
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