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22. September 2020, 11:51:39


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 1   allgemeine Kategorie / Selbstbauprojekte / Re:DDC Module2  on: Today at 08:30:23 
Started by SP9BSL | Last post by DF8OE
That is not the problem and it is crystal clear. Never was any problem! I got it running in RX out-of-the-box. This week I do not have much time to try TX - this will follow next.

What I am talking about is working with zero IF in AM / FM RX and TX without getting signal quality issues. All this is already working flawlessly in 12KHz IF - in narrow band FM with 6KHz, too - but not in zero IF. And I am not able to code zero IF parts. Maybe this a complete different DSP signal path, switching / moving time <--> frequency domain. But as I already told: my DSP knowledges are not big enough to work on this.

vy 73
Andreas
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 2   allgemeine Kategorie / Selbstbauprojekte / Re:DDC Module2  on: Today at 05:39:38 
Started by SP9BSL | Last post by N7DDC
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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 3   allgemeine Kategorie / Selbstbauprojekte / Re:DDC Module2  on: Today at 05:24:01 
Started by SP9BSL | Last post by DF8OE
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.

vy 73
Andreas
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 4   allgemeine Kategorie / Selbstbauprojekte / Re:DDC Module2  on: Today at 05:13:44 
Started by SP9BSL | Last post by N7DDC
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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 5   allgemeine Kategorie / Selbstbauprojekte / Re:DDC Module2  on: 21. September 2020, 21:57:44 
Started by SP9BSL | Last post by SP9BSL
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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 6   allgemeine Kategorie / Selbstbauprojekte / Re:DDC Module2  on: 21. September 2020, 21:46:58 
Started by SP9BSL | Last post by N7DDC
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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 7   allgemeine Kategorie / Selbstbauprojekte / Re:DDC Module2  on: 21. September 2020, 17:58:28 
Started by SP9BSL | Last post by DF8OE
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.

vy 73
Andreas
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 8   allgemeine Kategorie / Selbstbauprojekte / Re:DDC Module2  on: 21. September 2020, 17:36:39 
Started by SP9BSL | Last post by N7DDC
Is this possible to use IF = 1 Hz or ZeroIF can not to be inside the filter ?
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 9   allgemeine Kategorie / Selbstbauprojekte / Re:DDC Module2  on: 21. September 2020, 17:19:00 
Started by SP9BSL | Last post by DF8OE
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...

vy 73
Andreas
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 10   allgemeine Kategorie / Selbstbauprojekte / Re:DDC Module2  on: 21. September 2020, 17:11:00 
Started by SP9BSL | Last post by N7DDC
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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