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DF8OE
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Re:DDC Module2
« Reply #30 on: 22. September 2020, 08:30:23 »

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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Re:DDC Module2
« Reply #31 on: 27. September 2020, 01:45:52 »

Hello, Artur
Set the amplificator in settings to see the noise with no antenna.
Later I will correct the bitwise shift.
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Re:DDC Module2
« Reply #32 on: 27. September 2020, 05:48:22 »

Hi Artur,

at this stage I do not care about any currents and do not measure anything here. There is enough to do at the software integration in a clean way. But I like the currents you posted - very nice for a direct conversion!

vy 73
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Re:DDC Module2
« Reply #33 on: 27. September 2020, 07:27:03 »

Just set the RX codec gain to 0 and you will see the noise floor. This is not a bug, known behaviour. We will adjust the AGC for spectrum later.
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Re:DDC Module2
« Reply #34 on: 28. September 2020, 10:23:22 »

Hi

I am trying to follow this discussion, strictly from a user perspective (always building a new and BETTER transceivers). Saying that I have to admit that I am not qualified to make comments about the current developments (Sparkle, N7DCC approach, ...). I love to solder and use home transceivers while I am not too much knowledgeable about the "magic behind" each TRX.

I used Google extensively (hi) trying to better understand why adding N7DDC module would made future TRX home made projects even better - in performance of course.

However I would be grateful if someone can explain in easy language why it is better (or not) to include DDC module vs. "traditional" approach (with WM sound ICs) such as OVI40 UI PCB. I guess this kind of information would be good (and educational) for other forum followers as well.

Thank you in advance

Janez, S58J
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Re:DDC Module2
« Reply #35 on: 28. September 2020, 10:32:25 »

OVI40 UI can be used for direct sampling, too. My RF approach uses direct sampling, too.

You do not have
  • phase errors so no IQ-adjustment needed in TX and RX
  • oscillator coupling to the output in TX
  • to generate CW by DSP - you simply can generate a very clear output signal without hum or distortion
  • spectrum/wf limits to 48KHz. Using OVI40 you will have 196KHz guaranteed, possibly 384KHz, too
  • to use bandpass filters at all. Only lowpass filters for TX
Additionally full duplex is possible - following predistortion can be realized. Signal generating can be done without gaps down to a few KHz.

vy 73
Andreas
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Re:DDC Module2
« Reply #36 on: 28. September 2020, 12:13:52 »

Hi Andreas

Thank you for your quick reply. Just to be shure, when you list those bullets under "You do not have" you are talking about the simplicity/benefits of using OVI40 UI, am I right?

In terms of quality of each TRX I have two indicators: quality of RX and clean TX output. OK, the list goes on (frequency stability, filtering capabilities ...) but those two just listed are the major concerns for me. 

If this DDC thread doesn't bring much to the table in the RX and TX area then we are coming back to the old philosophy: simpler is better. I'll stick to my OVI40 UI, hi.

Please take this as my own opinion, a person keen on HF contesting (high power), QRP operation (where I use only home made QRPs) and hunting DX on 50MHz. Others, more technical and development oriented persons, for shure might think differently.

Looking forward to your reply.

Janez, S58J
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Re:DDC Module2
« Reply #37 on: 28. September 2020, 12:44:44 »

OVI40 UI is just its name tells: it is an user interface. Today you can only add mcHF RF board which does not have good signal quality in TX and other restrictions / issues which are related to the RF signal processing.

Using a "DUC" (Direct up Converter) for TX and a "DDC" (Direct down Converter) for RX you do not need any mixing by analog signals. You directly digitalize incoming RF by a fast ADC and you get yor TX signal by direct producing it with a fast DAC. We already have had designed OVI40 to use this much more modern system. You only have to remove 4 100R resistors and add 4 wires to get direct connection from DUC/DDC to STM32 without walking through TX/RX audio codec.

Everything you already know (and hopefully love) on UHSDR will be present when running with DUC/DDC, too. But you get a much better signal quality, and if you want you can use your tube (or LDMOS) PA with >= 1KW without any doubts. For CW TX quality is universes better than from mixing concepts like mcHF.

vy 73
Andreas
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Re:DDC Module2
« Reply #38 on: 28. September 2020, 15:20:42 »

Quote from: SP3OSJ on 28. September 2020, 13:39:36
The DDC receiver is better

Hi Artur,
There is something wrong with your receiver based on mcHF: the picture with -101dBm is at least 10dB higher than usual mcHF does, on the other side with DDC you show -133dBm which is too low. Did you calibrated the s-meter?
« Last Edit: 28. September 2020, 16:02:30 by SP9BSL » Logged

73 Slawek
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Re:DDC Module2
« Reply #39 on: 28. September 2020, 17:31:46 »

Hi!

this looks like a very interesting development. However, I have not yet understood how/whether it can be used with existing OV I40 UI PCBs. Is this possible?

Or would it be better to build a Sparrow UI (is there anything called like this?) which has a possibility to plugin the DDC module?

Is there a place where I can read more about this project?

73 Frank DD4WH
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Re:DDC Module2
« Reply #40 on: 28. September 2020, 19:19:35 »

Quote from: SP3OSJ on 28. September 2020, 16:43:41
For the Gain RX ->AUTO< setting (correct s-metr >0<), the DSP chip is as shown in the photo. OK?

if you like then ok... 
Leaving the codec gain to AUTO you add 24dB, sometimes less - it depends on AGC algorithm. In codec there is volume control but in fpga you haven't such thing. This is simple codec not a DSP.

A picture is better than thousand of words. The rx path is calibrated to S9 signal - as it should be, amplifier/attenuator are off and the shields are open. Antenna input left floating (same settings for both pictures):
 codec_gain.jpg
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Re:DDC Module2
« Reply #41 on: 29. September 2020, 03:48:25 »

Hi Frank,

as I already wrote: no need to build a Sparrow. You can use OVI40 UI PCB for driving DUCDDC. Just inject I2S directly to STM32 by cutting the four resistors R8/R20/R26/R27 from audio codec and solder 4 wires there to connect to RF board. Output of DUCDDC behaves like the output of Audio codec and can be treated in software like this. But you do not have any of the disadvantages of mixing concept.

vy 73
Andreas
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Re:DDC Module2
« Reply #42 on: 29. September 2020, 08:39:40 »

Hi Andreas,

thanks for your explanations!

It is very hard for me to get an idea about this project, because there is virtually no information available (schematics, block diagram).

So, I understand that its still experimental and the DDC/DUC plugin does substitute the codec and the QSD and QSE.

Thanks again for the info!

73 Frank DD4WH
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Re:DDC Module2
« Reply #43 on: 29. September 2020, 15:05:25 »

There are noch schematics at this stage. But a schematic does not help for understanding - only for hardware bug-hunting... For understanding theory I attach a block diagrams

This is for RX
 RX-fpga.png
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Re:DDC Module2
« Reply #44 on: 29. September 2020, 15:11:57 »

...and this is for TX

Everything regarding I/Q processing is done on digital domain. Antenna is connected to an ADC in RX mode and to an DAC in TX mode. Data is feeded digital from a FPGA which does all the things QSD mixers and codec does.

I forgot:
In block diagram you see "Xilinx Core". Please replace this with FPGA core because of it is not fixed to Xilinx.

vy 73
Andreas
 TX-fpga.png
« Last Edit: 29. September 2020, 15:13:37 by DF8OE »
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