White Noise (hiss) Problem

[Felix Dudley]

Using a Ten-TEC 350 D reciever, Dell computer, Sound Blaster Live soundcard
I hear a hiss (white noise) when the radio is tuned to a DRM station, and the computer and sound card is on. When I tune away from the DRM station the hiss goes away. The radio is directing connected to the sound card using a short (unshielded) audio cable. When tuned to a DRM station and the DRM Software Radio software is started I hear the hiss and the radio program.
It has been suggested that this is a sound card setup problem. If this is true what settings should be used? Do I need a filter in line between the radio IF jack and the sound card input? Do I need a shielded cable?

[simone]

Hi Felix,
on your sound card settings you need to disable the line-in for playback, see attachment (sorry it is only in German but should look similar on your PC)
Simone

[Felix Dudley]

Hello Simone

Where do you connect the IF input (from the radio) on the sound card when you disable the line input? What control fader is used to adjust the input level? My card is a Sound Blaster Live 5.1....
When I disable the line-in I disconnect the signal from the radio....
Thank you for you assistance.....
Felix

[simone]

Hi Felix,
the attachment in my post above is the volume control for the playback not recording, if you go to the properties of your soundcard there is a similar panel for recording, there you have to select line in as your input, I guess you tried to disable that one. Maybe you can post a similar screenshot what this looks like on your computer.
Simone

[Felix Dudley]

Simone, I found both the 'Record' and 'Play' mixer pannels of my Sound Blaster Live 5.1 sound card. I have been able to reduce the 'hiss' by adjusting the levels. Reception is very poor at the currnet time. Later to the day condtions may improve. I think that some of the 'noise' is being caused by very low SNR. I think that we have different models of the SB sound card (this may account for some of my problem). The SNR level seems to affect the quality of the audio. What can be done to get better SNR? I read where some guy wraped his sound card input cable aronud an iron core (to reduce RF). Is this reducing the IF signal somewhat? Would this possibly improve my audio and SNR? THANK YOU Felix

[simone]

Hi Felix,
can you post some screenshots of your input spectrum? Is the low SNR due to low signal strength or interference or local problems?
Simone

[richard]

What can be done to get better SNR? I read where some guy wraped his sound card input cable aronud an iron core (to reduce RF).

Hello Felix, yes I found I could reduce PC generated noise by using thin 3mm audio cable and rapping it around a ferrite ring a large number of times. In theory this should only attenuate common mode high frequency signals i.e. noise. I find it works anyway.

Richard

[Felix Dudley]

Sample screen images of DRM Software Radio screen as requested are attached..... Felix

[Felix Dudley]

More DRM screen images are attached..... Felix

[Felix Dudley]

Additional screen images are attached.....

Hope these images will give you the information you requested ... Felix

[Felix Dudley]

Simone
I hope that the above screen images where what you needed...
I can have an S9 + 30 or greater signal strength and still have an SNR less than 20. The current antenna is a homemade version of a Barker & Williamson (www.bwantennas.com) 180 foot folded terminated dipole. It has given me the best results to date. See attached logs..... Thank You Felix

[simone]

Hi Felix,
thanks, your examples do not look too bad, except that you need to reduce the IF input level at your sound card, if it is not possible using the mixer panel then try to do it by hardware.
Simone

[dadalbinder]

Hiss problems in general:

In the Record-Menu You choose Line-In or Micro.

You should at the same step deactivate the chosen input in the PLAY-menu. After this You would have no hiss from this entrance on the Playback-side.

At Funkamateur-shop one can buy NF-Trafos for isolating computer and receiver. Be generally aware of different voltages!!! yes! of the grounded several machines, You are using.

Wolfgang Hartmann

[mvs sarma]

Hi,
Can I use the on board sound card with realtech hd driver for drm decoding with DREAM software

sarma

[mvs sarma]

The moment i connect the derived 12KHz to soundcard's line in socket, myradio starts picking more noice.

I wonder whether the radio can be kept away and a possibility of optical coupling of 12KHZ IF signal to the PC-- perhpas we have to find a best suited optocoupler.

Sarma

[mitajohn]

Hi,

Take care of the ground loops ! Use between rx IF output and soundcard input an isolation 1:1 audio transformer also make about 10 turns of the audio cable around a round ferrite. These are the most practical ways to avoid hum and interference from the PC.

PS: My rx picked up RF noise from the SMPS psu of my monitor and now I use a linear one instead !

[mvs sarma]

Thanks John, Linear psu --is ofcourse a good idea-- --but the noice generated by the deflections circuitry-- - the only way appears to be to filter 12KHZ signal thro' the torriodal filter, as you rightly suggested..
Regards, Sarma

[mitajohn]

Use something as in the attached image which a forum member suggested sometime ago.

[mvs sarma]

I got your Idea dear-- let me see. incidentally, if we can explore the possibility of high speed Opto like 6n136 driven suitably, we can successfully isolate the pc electrically.

it is also true that my radio is commercial type for a general cosumer-- no specific shielding etc, (SONY ICF-SW11 japanease version. not the latest ones as made in China)-- with all that i may be landing in stability issues of Local osc.
that too a single conversion type.

did you come acroos a mod for Degen DE1103 for drm

Regards
Sarma

[mitajohn]

the possibility of high speed Opto like 6n136 driven suitably

Yes it will work, but you need two totally seperate psu to power the input and output circuitry and the electronics in the signal path may be will add noise. The transformer is simple and effective look at:
http://www.drmrx.org/forum/showthread.php?t=1545&highlight=isolation

did you come acroos a mod for Degen DE1103 for drm
No, I used some years ago a DRM modified SONY ICF7600DS with moderate results.

[richard]

Hello Sarma, there is some info about modifying the Degen 1103 on this German website:-

http://www.knallfunke.de/drm/mod/index.htm

I also looked at the isolating the radio from the PC using an Opto isolator but came to the same conclusion as John that the power supply problems were not worth solving. Though I suppose you could power one side of the circuit from the PC USB port and the other from the battery for the radio/12KHz mixer.

I found a better solution is to isolate the antenna from noise on the power supply by using a balanced loop or dipole.

Richard

[mvs sarma]

Thanks Richard,

I do understand that it wold rather be impossible to mod de1103-- and this is confirmed in the site mentioned.

i was thinking the power suppy of the Microphone jack (needed for condensor mic) would be just suficient for the tasistor of the opto and that the 455-12 converter could power the diode portion as you already indicated.

meantime, may be i am using an assembled PC- the power supply is really SO noisy that i can't bring my radio anywhere near it. Basically i have to sort out these issues by mounting RFI filters if not aleady available. mmmmmmean time , i was wondering whether SDR schematics help me out to receive DRM ?

one i find as below
http://zao.jp/radio/sft66db2/schematic.JPG

they propose to use rocky software