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Old 23-03-2008, 08:06   #1
df9rb
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Perseus SDR and DRM

Hi all,

since last week I own the Perseus SDR. This is a fantastic radio for analogue reception but I had a lot of troubles to use it for DRM. To help others and to exchange informations I started this thread. Here my informations gathered the last days:
The demo version of Virtual Adio Cable (VAC) adds every 5 to 10 seconds the word "trial" into the datastream which influences Dream badly - only the full version works.
The best settings of VAC I found until now can be seen in the attachment
With this settings the input spectrum in dream (start parameter -c 3) is very clear and DRM-decoding is stable with a SNR better than 30 dB.
With these settings the SNR below 20 dB is a little better compared to my DRT1, above 20 dB SNR the DRT1 is up to 5 dB better.

Bernd, DF9RB
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Old 23-03-2008, 11:10   #2
maxpower
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Hi Bernd!

Thats great to hear!

Most of the guys owning a perseus by now don't like DRM and so there wheren't very much infos about perseus performance on drm. Please keep us informed.

Stephan
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Old 25-03-2008, 15:14   #3
df9rb
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Hello,

until two days ago I thought transfering data digitally from (nearly) the antenna to the loudspeaker output is the best way to decode DRM. Now I know this is a wishful thinking concerning I/Q-signals. The Perseus receiver delivers has SR (sampling rate) of 31250, Dream works with SR of 48000. VAC transferes and resamples the data stream from the Perseus to Dream. When I configure VAC with a SR from 31250 to 48000 the Input Spectrum in Dream shows a nearly unsuppressed mirror image (see 31250_48000.png), and the SNR is not better than 26 dB. With these settings resyncs of Dream only happen when I produce a high CPU-load (average CPU-load approx. 30 % when running Perseus and Dream). When I force Perseus or Dream to an other SR by VAC the mirror image is much better suppressed (48000_62500.png) or perfect suppressed (62500_62500.png). The SNR is up to 33 dB then - but Dream resyncs every 5 to 20 minutes even when there was no high CPU-load!!!!!

Has anybody ideas what to try for solving this problem???

Bernd, DF9RB
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Old 25-03-2008, 16:00   #4
simone
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Hi Bernd,
what version of Dream are you using, do you get the resyncs also with 1.9.6 and older or only with the latest version?
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Old 25-03-2008, 20:05   #5
df9rb
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Hello Simone,

I tested mostly with 1.10.7 but I did also some tests with older versions and
I had the resyncs also with older versions of Dream. I often run Dream (also version 1.10.7) with the DRT1 in parallel to identify possible TX-failures or propagation problems. With the DRT1 I had no resyncs over an hour from DW Sines but more than 5 with the Perseus.... I presume the problem are the different sampling rates of Perseus and Dream.

Bernd
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Old 27-03-2008, 11:47   #6
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DRM, Perseus, Technical Overkill?

Hallo,

I am very interested in the discussion. The receiver seems to be a marvellous progress. But till now, I did not buy one. Probably I will do it.

The problems related to DRM are downsampling of an audio stream to 48 kHz, the normal working frequency of DRM. To be forced to use as an example VAC by the owner and have experiences seems for me not to be the right way of presenting and developping a receiver.

There should be ? by hardware an output for quite right downsampled audio-streams for as an example DRM. Waiting for DRM+ says too, that there will be a new sampling frequency for this purpose. ... and one should be able, to have an down-sampled output with the possibility to down-regulate (or absolute ) the sample rate.

A lot of users will have a second problem too connected with special demodulations programms, which need an additional (second) output.

I like VAC and WAVECLONE. But PERSEUS should at some time be ready and not a test-bed for the profi.

Wolfgang Hartmann, Nürnberg, 49N28, 11E03
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Old 27-03-2008, 15:55   #7
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Hello,

after many hours of testing I found out a setting of VAC, in Perseus and my computer which produces less resyncs together with Dream.
- I disabled "cool and quiet" in BIOS of my computer
- setting the parameters in VAC according to the attachment
- I increased the sampling rate in Perseus from 125 kS/s to 500 kS/s
With these settings I have resyncs between 30 minutes and 1 hour
The "cool and quiet" function adapts the PC-clock according to the CPU-load.
Presumable every clock-change affect the resampler badly. The sampling rate of the Perseus should have no influence to the datastream to DRM but only change the visible frequency range - but how knows?
Wolfgang the Perseus has a SR of 31250 in the mode "User" (I found this in a description) and seems to have the same SR in DRM mode. When I configure a SR range from 11025 to 48000 VAC displays 31250 when I start Perseus.
Perhaps a SR of 48000 from Perseus could solve my problem.
I observed everything concerning the Persus SDR in internet for weeks before I ordered one. And one reson to order was the continuous improvents done by the developers. So I am quite confident that also the DRM mode will work in some weeks.

Bernd, DF9RB
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Old 03-04-2008, 09:27   #8
dadalbinder
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DRM Samplerates and Perseus

Hallo Bernd,

I have the impression, that one needs for DRM decoding a sample rate of 48 kHz normally. There is no profit to use 96 kHz or 192 kHz.

To have a different samplerate, You derive the signal for DRM decoding in programms as DREAM, SoDirRa and others, it is a special calculating to achieve this task. This could be done - I think easily - if one has to DOWN-sample from higher samplerates. The other side: UP-sampling is connected with a lot of work (cpu and programming) and possibly with a lot of minor mistakes.

All these factors are connected with I/Q-working, a very special demodulation type, which is very sensible to amplitude and phase-differences.

The Perseus should because of this factors, use generally downsampling for DRM. ... and: have an output for this purpose!

Thinking further: DRM+ will be coming with a samplerate of 100 kHz - maybee-. For this case, one would need an output samplerate of 100 kHz.

And: The overall question is the procedure to optimize amplitude and phase of a soundstream. Phase and amplitude are changing not only by means of VFO but also from outside signal coming in. As far as I see with experiments with the RxDis Software, they are changing during receiving.

The marvellous Perseus - as far as I see the receiver - has to improve soft- and hardware - to optimize all features of receiving.

Interesting times coming!

Wolfgang
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Old 03-04-2008, 19:50   #9
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WoW!!!

Today I tried WindRad 1.31 for DRM with the Perseus receiver - and what shall I say: it works perfect!!!! As long as I observe now no resyncs of Dream and better SNR than with the DRT1. Logs will follow.

Bernd, DF9RB
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Old 03-04-2008, 20:14   #10
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That's a very promising undertaking, Bernd !
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Old 04-04-2008, 03:25   #11
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Winrad wow!

Bernd-
I look forward to see what settings you are using. I assume that VAC is still required?

73,
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Old 04-04-2008, 14:19   #12
df9rb
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Perseus and Winrad

Hi all,

here a short log of the Perseus-receiver with Winrad vs DRT1 (DW from Sines with an excellent signal). The SNR from the Perseus moves a little up and down as I switched off the AGC which gives a little higher SNR at optimized level settings. To answer Alan´s question: yes also Winrad needs VAC. The big difference to the original Perseus-software is that SR from Winrad is 24000 instead of 31250 from the Perseus-software which seems to fit much better to the 48000 with which Dream works. Settings in Winrad are: Input: Perseus HF-receiver, Output: Virtual Audio Cable, Mode: DRM - That´s it! Now for an excellent receiver an excellent software exists!

Bernd, DF9RB
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Old 05-04-2008, 11:41   #13
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Hi Bernd!

I've got a question: In Winrad I've got to calibrate Phase and Amplitude on I/Q by myself and its optimized for just one frequency in the spectrum.

As far as I know the perseus (and his software) optimizes aliases by himself. Is it done by the Software (PC Software) ore more hardwareside (Perseus CPU)?

If it would be first methode, the Pereus would behave itself in Winrad like a standard I/Q Receiver (Optimized only at one Frequency, Images appear besides Optimum-Frequency).

If optimizing is done in the Perseus itsself, it would behave like a very wideband non-I/Q Receiver (without any images in the spectrum).


Greetings,

Stephan
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Old 05-04-2008, 13:42   #14
df9rb
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Hi Stefan,

I am not a specialist for I/Q-receivers but I presume that the Perseus-hardware optimizes aliasis itself. When I change amplitude, phase or delay in Channel Skew Calibartion in Winrad I see images in the spectrum. The optimum is always amplitude = 1, Phase/Delay = 0 between MW and 15 MHz where I tried. In "Input Spectrum" in Dream is a image but it seems not to influence Dream (see attachment).

Bernd, DF9RB
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Old 17-04-2008, 11:21   #15
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Winrad 1.31. version 10 and DRM

Hello,

an information by Alberto says:

"when Winrad is set to DRM, it changes its output sampling rate to 24 kHz, so to be able to transfer a band of 12 kHz
to the output. The program DreaM is perfectly capable to use this sampling rate, both directly, using a second audio
card (as I do), or via VAC (Virtual Audio Cable), which I have and have experimented with."

I think resampling from the Perseus sampler rate of 31,.. kHz to 48 kHz is much more unsafe then to give the 24 kHz directly to a decoding program as DREAM or SoDiRa.

So far the good news about the new Winrad version related to DRM has its answer from programming skills of Alberto.

Wolfgang Hartmann, Nürnberg
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