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Interference from PC?
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Marsh Parker
--- In softrock40@..., "observer35" <rein0zn@i...> wrote:
Hi all,Not me. Either with the SoftRock or my other rigs. I elected to put a 78L05 in place of Q1 so I can't comment on that. Marsh, NC7V
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kb9yig
Hi Rein,
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I have built about 25 of the v4.0 SoftRock40 receivers and find the PC noise does not cause much of a problem. When the receiver is calibrated to S9, (-73 dBM, 50 uV RMS), the baseline is around -135 dBm with 10-15 dB spikes riding on the baseline every 1 kHz or so. Also at the LO frequency, around 7.054-7.056 MHz there is a large broad spike associated with the LO and the fact that the soundcard contributes lots of noise near zero frequency. I will be quite interested in the experience of SoftRock40 builders as they finish their kits. If I can help with problems in getting the little receive running, I would be happy to do so. 73, Tony KB9YIG --- In softrock40@..., "observer35" <rein0zn@i...> wrote:
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Hi Tony,
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Thanks for your reply. From looking to the picture on one off the softrock pages I got the idea that the board was directly plugged into an USB connector of the computer. Looking more careful it seems the board is running from an USB cable connector? My question was more in general, not softrock specific. I was surprised to see an unshielded front-end that close to a PC I have been playing quite a bit with Linrad Spectran dspblaster etc just running off a TS 850 at least 30 ft from the PC and I get all kinds of stuff from the computer. In fact it means that I will have to put the computer in a second box with all inputs and outputs well decoupled I think. This is just monitoring basically antenna noise. I am expecting a board shortly and will let you know, using the Delta44 sound card. 73 Rein W6/PA0ZN kb9yig wrote: Hi Rein, |
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leon_heller
--- In softrock40@..., "Marsh Parker" <nc7v@e...> wrote:
--- In softrock40@..., "observer35" <rein0zn@i...> wrote:The supply from the USB connector is 5V. Are you using a separate powerHi all,Not me. Either with the SoftRock or my other rigs. supply? Leon |
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kb9yig
Hi Rein,
Actually I just plug my SoftRock into the USB socket on the front of my Dell 2400 machine. The little receiver plays quite nicely that way and others have had the same results with various computers. As I write this, I have a SoftRock playing on the same PC. Forty meters this morning at my QTH shows a flexuating base noise level of about -122 dBm and the peaks of the soundcard related spikes are visible to about -118 dBm. S5 signals are at about -110 dBm. Tuning around I find an S3 signal that is still good copy. I continue to be amazed at how well PowerSDR software and a simple receiver circuit work together to make a nice little receiver. 73, Tony KB9YIG --- In softrock40@..., "Rein A. Smit" <rein0zn@i...> wrote: Hi Tony,connector of thean USB cable connector?surprised to see an unshieldedetc just running off a TS 850 at leastIn fact it means that I will have toDelta44 sound card.the PC 135noise does not cause much of a problem. When the receiver is so.dBm with 10-15 dB spikes riding on the baseline every 1 kHz or soundcardAlso at the LO frequency, around 7.054-7.056 MHz there is a large builders ascontributes lots of noise near zero frequency. thethey finish their kits. If I can help with problems in getting wrote:little receive running, I would be happy to do so. -------Hi all, subject=Unsubscribe>YAHOO! GROUPS LINKS of -------Service <>. |
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KY1K
I'm brand spankin' new to the group so didn't see the original thread.
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Expecting a sensitive receiver to operate just inches away from a wideband noise source is optimistic (IMHO). For best results, it needs shielding just like any other receiver and or transmitter does. Computer noise might not show up as clean carriers or be identifiable by tuning across the band. It appears as an elevated noise floor most of the time, which sounds like background noise. I'm sure many people have interference from their own computers and most don't even realize it's there because it sounds rather like normal atmospheric noise. For absolute best results, shield it. For casual listening on a crowded band, don't worry about it and run it as supplied. My softrock-40 is going on LF when I get it and it will be located away from the computer and shielded. Switching supplies, florescent lamps and computer interference is pretty severe at 190 kHz and I want to have good reception. I'm even considering magnetic shielding due to the nature of the interference at these frequencies. Regards, Art The supply from the USB connector is 5V. Are you using a separate power --
No virus found in this outgoing message. Checked by AVG Anti-Virus. Version: 7.0.344 / Virus Database: 267.11.1/104 - Release Date: 9/16/2005 |
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Jim Sheldon
I have my softrock 40 running. It's plugged into an external USB hub for
power, and hooked up to my B & W broadband folded dipole. I can find no birdies within it's limited tuning range - 7.030 to 7.080 as specified in the AMQRP info. It is extremely sensitive, and copies signals within that range as well as my K2 does, and that's saying something. The K2 has by far the best receiver of any rig I've ever owned. All this talk about computer birdies and pc noise is pretty much unfounded. There is NO noise apparent with the scope on the DC voltage line coming from the USB port. The computer is a Dell Dimension 8100, Pentium IV @ 1.4GHz and even with the covers off, I still cannot find any birds attributable to the computer. I AM using just the bare-bones, unsupported SoundBlaster PCI sound card that's built into the Dell's motherboard. It performs adequately for the Soft Rock 40, but I would presume to say that if one had an SDR-1000, this card would definitely be struggling. My sampling rate is only 48 KHz, and it still does very well. Maybe this will allay some of the fears I see expressed here on the reflector. What the heck do you expect for $23 bucks a full blown SDR-1000? Jeez, lighten up and experiment with the thing! It works as advertised, and maybe even better considering the low end sound card I'm using. Jim - W0EB |
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KY1K
OK, this person has experience, my views are different and contrary to this persons real life observations.
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Apparently there is no interference when operating the softrock-40 without shielding. Congrats to the designers of the softrock-40, they've managed to do something never before done in the history of receiver design. However, I've never seen a high quality receiver made available in a plastic enclosure.............. GL to all. Art At 12:47 PM 9/18/2005, you wrote:
I have my softrock 40 running. It's plugged into an external USB hub for --
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Jim Sheldon
Art and all,
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You missed the point I was making - there are no birdies noted within the limited tuning range provided. This thing, as built will ONLY tune from 7.030 to 7.080. It was not designed as a complete receiver that covers the entire band. I'm absolutely certain there would be junk received outside of that range were it able to tune there. Plastic enclosure? What enclosure. Mine is operating on the desk as a bare, unshielded board. The only shielding involved is the coax to the antenna and the shielded audio cable from the I-Q output on the board to the Line input on the sound card. The enclosure is not supplied with this simple kit. If you want to put it in an altoids can or any other metallic enclosure, this is easily done, subject to whatever your imagination can devise. I'm merely stating that it OPERATES AS ADVERTISED by the designer. W0EB -----Original Message----- |
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kd5nwa
I bought a 16 foot USB extension in case I needed it, and I have matching long audio cables.
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The monitor is the culprit most of the time, but just in case I have a Industrial PC that they were throwing out at work, It's fully encased in metal including a grounded cover for the CD/Floppy drive area. With it came a 15.1" LCD monitor that I hope will be quieter that the regular monitors I have. I still have not received my SR-40. When it was first available I stayed late and bought some, then next day I was 8th on the list, with the current list I'm down to 50 or lower. And people all around me have received theirs. It's a conspiracy, I should have worn my aluminium hat! I'm brand spankin' new to the group so didn't see the original thread. --
Cecil KD5NWA <www.qrpradio.com> I fail to see why doing the same thing over and over and getting the same results every time is insanity: I've almost proved it isn't; only a few more tests now and I'm sure results will differ this time ... |
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Stan Rife
开云体育???Tony, one thing I noticed, when just playing around
with the SDR software, was the?600 Hz?tone that comes from the
soundcard (?) at the 7.056 freq.?after the Fixed HW oscilator is set up per
the instructions. This is, of course, without the SoftRock hardware installed,
as I do not even have my kit YET. (boo hoo).
??? Is this oscilator tone, at that freq., something that will
always be there? I saw a procedure in the manual that said something about going
above 7.056, as much as the test oscilator is below 7.056 and adjusting for a
null. I am not quite clear on all of this. I do have an XG-1, and I assume that
is what this is refering to.
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Stan Rife
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Stan Rife
开云体育??? Keep us posted, Art, and let us know how it works out.
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Stan Rife
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Hello All,
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I am afraid that I started the discussion on computer noise in receivers. This was more a general question and not about this particular setup. The question was not about noise within the freq range of this particular design. Nor did I specify antennas in use, band active etc or not. Nor is it in anyway to criticize the design or whether the costs of this board or too high or to low. Besides that I hope that we can accept questions like this one and discuss the subjects in a rational way as radio amateurs interested in home brew and/or new technology and in each others experiences and views. 73 Rein W6/PA0ZN Stan Rife wrote: Tony, one thing I noticed, when just playing around with the SDR software, was the 600 Hz tone that comes from the soundcard (?) at the 7.056 freq. after the Fixed HW oscilator is set up per the instructions. This is, of course, without the SoftRock hardware installed, as I do not even have my kit YET. (boo hoo). |
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Stan Rife
开云体育??? I don't know too much about all this, but I personally
have experienced noise generated from some of the clones I have built in the
past. Some of the cheaper Motherboards seem to have this problem. I am running
an ASUS MB at this time and have not noticed any noise problems problems, so
far. I hope I have similar results to yours, Jim.
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Stan Rife
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kb9yig
Hi Stan,
Yes, the tone at 7.056 MHz (or what ever frequency you set in as the fixed oscillator frequency) is always there. One of the software guys who has worked on SDR-1000 software thinks something can be done to reduce that large noise spike. The source for that tone when no SoftRock is connected is still not well understood, at least not by me. The thought is that the sound card adds more noise at near zero frequency as well as 60 Hz noise pickup. I have notice when a SSB signal spectrum was centered on that frequency, the SSB signal was still quite readable. When the SoftRock is connected, then that noise at 7.056 MHz also contains a LO signal. The use of the XG1 is for S9 calibration at -73 dBm, receiver sensitivity check and image null at (7.056 -7.04) above 7.056 MHz. Hope this helps Stan 73, Tony KB9YIG --- In softrock40@..., "Stan Rife" <srife@s...> wrote: Tony, one thing I noticed, when just playing around with the SDRthe 7.056 freq. after the Fixed HW oscilator is set up per the instructions.This is, of course, without the SoftRock hardware installed, as I do noteven have my kit YET. (boo hoo).always be there? I saw a procedure in the manual that said something aboutgoing above 7.056, as much as the test oscilator is below 7.056 and adjustingfor a null. I am not quite clear on all of this. I do have an XG-1, andI assume that is what this is refering to.[mailto:softrock40@...] On Behalf Of kb9yigthe PC noise does not cause much of a problem. When the receiver is135 dBm with 10-15 dB spikes riding on the baseline every 1 kHz orso. Also at the LO frequency, around 7.054-7.056 MHz there is a largebuilders as they finish their kits. If I can help with problems in gettingthe little receive running, I would be happy to do so.wrote: subject=Unsubscribe>Hi all, Service <> . |
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Bill Tracey
I believe the gunk you see near the center frequency with or w/o hardware attached is an artifact of the signal processing architecture, and noise near DC on the audio input (ie 60 hz hum,. etc)
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How the software tuning works is by having a software mixer fed with the local oscillator to dowconvert the signal of interest. In the case of the SoftRock, you have the hardware QSD downconverting and quadrature sampling a 48 khz swath of RF centered on 7.056 Mhz. To listen to a signal at 7.060 MHz, the software mixer is set to run with a local oscillator at 4 khz to mix down the 7.056 Mhz centered signal. As you tune closer to the center frequency, the freq of the software local oscillator gets lower and lower. Very near the center frequency, the local osc will be in the 100's of hz, Mixed with 60 hz (and harmonics) hum this will tend to product responses at 60Hz (and harmonics) +/- SoftwareLO etc -- thereby getting you the gunk around the center frequency. I will have to admit that my understanding of this phenomenon is not as crisp as I would like it to be. As Tony said in a prior post, there's some hope that some of this can be eliminated with DSP magic. One approach would be to record and characterize the noise characteristics with no input and then try and remove them with DSP magic when fed with a real signal. One could do this in either the time domain or frequency domain, although I'm not sure how one would maintain sync with the noise signal in the time domain. My DSP skills are not strong enough (yet) to really know how feasible such an approach would be. Another (potentially naive) approach might be to try a different tuning approach. If one is interested in a sig at 7.060, I'd think one could take an FFT of the input signal, zero the FFT bins outside the passband of interest, shift the spectrum over by 4 khz and then IFFT the result to recover the signal of interest. I think this should work, but not having tried it really can't say for sure. Also not too clear in my mind if this would be better than the software mixing approach currently used as you get closer to DC. One thing to be aware of -- in a more complete SDR with a frequency agile downconverter, you typically don't tune in software down near DC. For example, on the SDR 1000, the tuning is always such that you're approximately 11khz above DC for software tuning. The reason for this being approximate is that the DDS tuning is limited to tuning to freqs where the DDS generates a minimum of spurs. I will be the first to admit I'm somewhat of a neophyte with DSP. SDR is an area rich with opportunities for learning and experimenting, and we've now got hardware and software accessible to the amateur community to experiment with. Hoping folks get in there and do some experimenting and learning. Cheers, Bill (kd5tfd) At 01:25 PM 9/18/2005, Stan Rife wrote:
Tony, one thing I noticed, when just playing around with the SDR software, was the 600 Hz tone that comes from the soundcard (?) at the 7.056 freq. after the Fixed HW oscilator is set up per the instructions. This is, of course, without the SoftRock hardware installed, as I do not even have my kit YET. (boo hoo). |
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Stan Rife
开云体育??? Good deal, Tony, Bill. Well, Bill, I'm afraid I'll
just have to be one of those that reaps the benefits of the experimentation done
by others. I am new to most of this. I'll be the first to admit, I need to get
more involved in this kind of stuff so I'll learn more about it. I'm kind of
starting to head in that direction, though. I am trying to find some beginners
documentation on programing Pic Microcontrollers. Won't really know what to do
with it once I learn (applications), but I'll at least have a working knowledge
of what some of the guys are talking about when discussing Pics and firmware.
??? I am not sure if I asked the question the right way, and so
I am not sure if you guys are talking about the same signal that I am refering
to at 7.056. The 600Hz tone I hear is -75 dbm. Are we talking about the same
thing?
??? Also, I noticed that when I start Power SDR, the volume for
the soundcard is turned up to Maximum. Is there a way to have it initialize to
the previous setting on start up? I may be missing something
here.
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Stan Rife
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--- In softrock40@..., Bill Tracey <kd5tfd@a...> wrote:
...the gunk you see near the center frequency with or w/o hardwarenoise near DC on the audio input (ie 60 hz hum,. etc)...Exactly, and this is one tough sucker to get rid of. The soundcard is one of the most vulnerable spots for letting in spurious signals. Most soundards get around the problem by rolling off the frequency response below 100Hz or so. Rolling off is not the same as eliminating, however, and when you can mix the residual spurious signals up into the center of the passband, they're conspicuous weak signals just like anything else would be. It is possible through DSP magic to subtract out the gunk, but you pay for it with a higher MDS. Preferable on the whole to use a better soundcard. 73 Frank AB2KT |
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KY1K
Frank and the group.
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Until recently, the sound card has been thought of as a secondary accessory. By that I mean it plays the windows warning sound, or an mp3 or wav file and allows one to listen to sound effects when playing computer games..... Only recently has anyone though of using it for serious work, although there are a few exceptions. Even on todays best sound cards, there is no shielding despite having 16 bit sensitivity on the inputs and being mounted inside a big noise generator, esp[ecially bad for magnetic interference. Nothing surprises me when it comes to sound cards, they use dimestore time bases and are far from what they could/should be. However, they're cheap and plentiful and give us a taste of what we can do when better sound cards become more common place. Regards, Art The soundcard is one of the most vulnerable spots for letting in --
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