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todd_terry
18-05-2009, 20:04
Hi all,

I've modified my receiver according to the german pdf document hosted by drmrx.org. I think I've done everything fine, but the SNR is really weak (see attached files).
I use a sat-schneider downmixer with the 462kHz crystal.
Did anybody else made this mod too on the ATS-909?

simone
18-05-2009, 20:23
Hi todd_terry,
can you please post the SNR plot, did you also try on other transmissions/ frequencies? What´s your soundcard, is this on a laptop maybe with power supply connected?
Simone

todd_terry
19-05-2009, 04:57
Hi simone,

I've finnaly found the source of my problem: it's the receiver's AC adapter.
The problem disappears if the receiver is powered with batteries.

Thanks for your help.

mvs sarma
19-05-2009, 13:05
Hi simone,

I've finnaly found the source of my problem: it's the receiver's AC adapter.
The problem disappears if the reveiver is powered with batteries.

Thanks for your help.
It might be better to use linear power supply than any SMPS type at least for radio reception and Dxing

mitajohn
19-05-2009, 17:17
Hi,

If you search for old threads this forum you will find a lot of info about all measures to minimize noise to/from RX/pc & psu, I don't know if these old threads exist any more. For example wind the audio cable from the down-mixer to the soundcard, around a toroidal ferrite, as in the pic (I filed it from the forum years ago, introduced by the member Bernd, If I'm not wrong) it will block noise from pc to RX.

EDIT: Well I was mistaken, the pic was introduced by dk8cb, sorry for any inconvenience.

Siber
20-05-2009, 11:35
If quality of grounding of a computer is bad, rings and the network filter will not help. The most effective in the situation is an optical insulator. I have developed the simple scheme of such device. Here look.

Instead of the specified transistor can be used BC847, 2SC945 or BC107BP.
Using the jack "Mic In" is obligatory.

todd_terry
20-05-2009, 17:15
Hi,

thank you all for your help. The noise from the computer is not my main problem because I already have quite good SNRs.
The most important thing right now is the PSU. I'd be grateful if anyone could tell me where to find a schematic of PSU filtering (something that really works) because none of mine give good result.

mitajohn
20-05-2009, 17:20
Hi,

Yes, the opto-isolator is an option, but it will introduce noise and you need two isolated psu (the one in your case is the soundcard's mic input, in some MB there are 5 DCV there). Most simpler is a 1:1 audio transformer and a ~1uF cap in series with the secondary, connected to the mic or line input which depends on the output signal level.
As for the RX psu, buy a linear one (not an smps) or diy one with an LM317 or similar regulator, do a google search and you will find a lot of schematics....

Siber
21-05-2009, 00:37
Hi all!
to mitajohn:
1.The audiotransformer will not protect the receiver from high-frequency noise.
2.You should provide a level of a signal which air noise will exceed optron noise.That way the optron noise did not affect to reception.


If for supply of your device 4,8 voltage is enough , this schema will allow to exclude fluctuations from work of the PC processor on USB. There should be the germanium diode.

mitajohn
21-05-2009, 07:28
Hi all,

@Sider,
I'm not intending to start a debate here, any solution depends on the particular circumstances. The fact is that I have been tested both solutions, opto and trafo, in my case the best was a small 1:1, 600 ohms Bourns audio trafo which I'm using for about 3 years...and in test, it produced a SNR > 48 dB.

Siber
21-05-2009, 08:18
Dear mitajohn
I have tested these schemes too but in conditions of bad grounding a computer. Now if someone who did not do that we have made can read through our correspondence and not search for the road
:)
_________________
Regards, Vladimir.

mitajohn
21-05-2009, 17:17
Hi all,

@Sider,
No doubt about that !

dadalbinder
22-05-2009, 17:52
Hallo,

we have a lot of groundings commonly in our systems.

1. Grounding of the antenna should be separated from the grounding of the receiver.

2. Grounding of the computer with our equipment has two components. One the grounding to the soundcard. The other one between DRM-mixer in the receiver or outside with the computer.

3. Because of that, we should avoid technically multiple groundings in our systems.

4. There could be a third grounding problem with an audio-amplifier following the soundcard output.

Sometimes it could be usefull, to turn the plug in the mainline for 180 degrees, to get a better result. But it depends from the system, You use.

It is wise, even in conventional circuits to avoid mulitple grounding "loops" or to have a circuit wiht one main grounding line through the whole thing in a unique way.

One factor for not so good SNRs could be based on the AGC-factors and time components of the used receiver. These factors should be relatively low and not fast. Every DRM signal contains a lot of carriers within this signal. If AGC is too fast, it will reduce the reachable SNR.

Wolfgang Hartmann, Nürnberg

Siber
23-05-2009, 04:00
Hi all!
In conditions of an usual city apartment you cannot provide good grounding of devices. Therefore I have decided to fulfil system of reception DRM without use of grounding. The symmetric input for the aerial and optical or acoustic isolation of a computer and the receiver is used. It looks here so.

Vladimir