Search found 17 matches

by artm
Tue Jul 30, 2019 1:10 pm
Forum: Troubleshooting Help
Topic: Direct sampling interference vs upconverter
Replies: 9
Views: 2813

Re: Direct sampling interference vs upconverter

I use always 2.4Mhz, dongle is V3. I bought another dongle and it behave just same. Both from rtl-sdr-blog ebay store and both date stamp 2018-9-13 on pcb.

I have only dc-spike (6.001.05Mhz)and -35dB both side. Same at 12 and 24Mhz, but more spikes around.
by artm
Mon Jul 08, 2019 5:58 am
Forum: Troubleshooting Help
Topic: Direct sampling interference vs upconverter
Replies: 9
Views: 2813

Re: Direct sampling interference vs upconverter

I thought is it actually IMD? It behaves strange when its so wide (whole band), occurs so low level, way below blocking level. Spike at other side of carrier is much lower. This not seen on normal IF-mode. Some way it is mixing product with "dc-spike"... I watch videos on youtube and hard to say, th...
by artm
Mon Jul 08, 2019 5:41 am
Forum: Other SDR Devices
Topic: MSi.SDR sound crackle pulses and spurs
Replies: 20
Views: 6365

Re: MSi.SDR sound crackle pulses and spurs

Do you have noise floor abt S9+30 when turning gain to full, GR=0? I tested more again and found 24Mhz and other spurs are on screen even the adjacent input pins are shorted. Level measured at ant. connector then decreases, as it should. So, these must come from chip itself? not direct from xtal etc...
by artm
Sun Jul 07, 2019 4:14 am
Forum: Troubleshooting Help
Topic: Direct sampling interference vs upconverter
Replies: 9
Views: 2813

Re: Direct sampling interference vs upconverter

These spurs are receiver IMD distortions. RTLSDR has IMD about 50-60 dB, so these spurs will appears 50-60 dB below strong signal. Well, I found it can tolerate only less than 40dB in direct sampling mode. Signal level abt. -85dBm at bottom. DC spike is quite high. imd_direct.JPG In up-converter mo...
by artm
Sat Jul 06, 2019 11:58 am
Forum: Troubleshooting Help
Topic: Direct sampling interference vs upconverter
Replies: 9
Views: 2813

Re: Direct sampling interference vs upconverter

Addition info, when LO is same as oscillator, no wide spurs (upper in picture). Within 1Hz and noise floor pumping. 2kHz offset and spurs are wider (bottom in picture). More offset more wider spurs. If using other freq, same happens any frequency if sdr LO is same as input signal.. :shock: test1.JPG
by artm
Sat Jul 06, 2019 11:07 am
Forum: Troubleshooting Help
Topic: Direct sampling interference vs upconverter
Replies: 9
Views: 2813

Re: Direct sampling interference vs upconverter

I don't have such spurs around 6 MHz on directsampling mode with open input. If it appears when you connect high level 6 MHz source, then this is intermodulation distortions. This is known issue of any receiver. Smaller level of these spurs means better IMD performance of the receiver. I have clean...
by artm
Sat Jul 06, 2019 5:19 am
Forum: Troubleshooting Help
Topic: Direct sampling interference vs upconverter
Replies: 9
Views: 2813

Direct sampling interference vs upconverter

Wondering what cause this. Rtl-sdr V3 On direct sampling mode and feeding it 6Mhz xtal oscillator there is lot spikes around and tuning causes these spikes move wildly. Signals are well below overload and decreasing level (w/ext. attenuator) may cause spikes grow a bit as seen on picture. 14Mhz LP f...
by artm
Tue Jul 02, 2019 11:55 am
Forum: Other SDR Devices
Topic: MSi.SDR sound crackle pulses and spurs
Replies: 20
Views: 6365

Re: MSi.SDR sound crackle pulses and spurs

One possibility that most spurs are 24Mhz and it's harmonic products?
Msi's spektrum looks terrible. Bottom rtl v3 own spurs. Scale is near dBm, not calibrated. 10dB attenuator between dongles.
msi_rtl spurs.jpg
msi_rtl spurs.jpg (52.31 KiB) Viewed 2334 times
For comparison, I also test that your 30Mhz test.
compare2.JPG
compare2.JPG (40.02 KiB) Viewed 2334 times
by artm
Tue Jul 02, 2019 5:48 am
Forum: Other SDR Devices
Topic: MSi.SDR sound crackle pulses and spurs
Replies: 20
Views: 6365

Re: MSi.SDR sound crackle pulses and spurs

no, I don't agree. With low-IF there are a lot of images (mirrors from borders of the Nyquist zones). And most of spurs are present in both modes, you can test it on wideband spur at 30 MHz. According to my tests, zero-IF almost always works better and gives you more control. Probably low-IF mode w...
by artm
Tue Jul 02, 2019 3:38 am
Forum: Other SDR Devices
Topic: MSi.SDR sound crackle pulses and spurs
Replies: 20
Views: 6365

Re: MSi.SDR sound crackle pulses and spurs

We need to know better these chip's histoy, if they are defectives maybe faulty mixers inside.. etc. I noticed too usb cable and ferrites wont help, no difference when pcb is in case or not. in my case there is no 1 kHz interference when LO=600'001'000. Tried LO=600'000'001, and there is also no 1 k...