Re: VERTICAL LINES IN WATERFALL #radioastronomy #bestpractice


David Eckhardt
 

Yes, every touch pad I've had produces voluminous amounts of RF noise, but generally in only the LF and HF regions.  Even turning them off in FW does not stop the RF.  My Toshiba laptop died recently, but I had it pretty much encased on all external surfaces bottom and rear of the display) in aluminum foil which must be commoned to the internal 'ground'.  The backshell of the video connector turned out to work well.  Also, if you use the microphone and/or the line input to the PC or laptop, it is necessary to common the backshell of the audio connector to the internal 'ground' as well.  Virtually all audio inputs and outputs on laptops and PCs float against the chassis or internal 'ground'.  This introduces AC noise into the audio inputs so they must be tied to chassis as above as well.  This helps keep AC noise from entering the circuitry as well as helps reduce radiation from noise generated internal to the PC or laptop.

I have a 27" Dell display on my tower PC (4-banger AMD processor @ 3.6 GHz).  That Dell display, too, produces interference on HF all the way through they Water Hole at 1.42 GHz!  It becomes worse as frequency is increased!  I have completely covered the back of the display with aluminum foil and commoned that to the video connector on the back of the display.  All this added aluminum foil is not so much for classic shielding, but to give the fields closure closer to their points of origin and prevent them from opening (radiating) into free space. 

Another hint:  I was given three older Compaq desktop PC's.  Usually Compaq did better with EMC/RFI than these units.  They all just scream out the line cord from HF through VHF.  In their day, they would NOT have passed regulatory testing for either radiated or conducted emissions.  So be it........  Installation of a standard line filter cured that problem.   Simple installation by Compaq of a common mode choke would likely have brought them into compliance with FCC and international laws.  But, remember, only one unit has to pass testing once (although the suppliers are required to do audits, but typically, no one does) and what ever the contract manufacturer does after that is 'hands off'.  I won't belabor the point further......

Dave - WØLEV   

On Fri, Nov 17, 2017 at 1:18 AM, Normand Fortin <normand_fortin@...> wrote:

Thanks a whole lot David, by the way, i'm doing astronomy too, its a matter of time before i combine both hobbies ;-) 

Thats why i'm putting a lot of effort controlling my R2 in every corner.

On the technical side, i took another step tonight to ensure the cleanest RF environment around the antenna, which i relocated another 30ft from the house, using RG-58/u (i know its lossy but handy to effect some fast testing, the loss serves also as an attenuator for my longwire which is gonna help my quest i think). That helped decrease the lines further, so now, the remaining ones are very probably what the usb cable carries. They are in the 8.5 to 12.5 mhz range mostly, but much fainter. Like you said, very acceptable, although i'm gonna try my best to clean the usb way. I'm reassured that my Airspy is inded ok from what you described.


2 more questions:

Now in my 1st post about it i was describing those fixed lines with all gain sliders down. Can you see that as well in your setup around HF frequencies?

Also does your laptop touchpad produces some ripples in the hf range as well when you put your fingers on it?   I tore the laptop down completely and back up as i thought a faulty ground would cause that. No fix, but the laptop is now faster!!!

At last i get a decent waterfall window where you can read the band activity from a distance.

Back to the bench now, i got to do another ferrite round on this usb thing.


Cheers, Norm

Airpsy R2 + Spyverter

RTL SDR V3  + Ham it up 1.2

Couple basic RTL for generic testing



Le 2017-11-16 à 19:55, David Eckhardt a écrit :
Initially, this was quite a problem with version 1 of the AirSpy.  I opened it up, scraped paint on the inside at both the USB and SMA connectors and copper taped/soldered (where I could) bridges from each connector to the now bare aluminum (no solder there) and from each connector to the PCB ground plane.  I also installed ferrite with two to three turns through each bead on the USB and RF input cables located at the AirSpy, itself.  I found that even the non-ferrited antenna input cable picked up USB noise and coupled it into the AirSpy.  A lot of that has changed with Version 2 which I now have and especially the HF+, but still have trouble with my ISP (Rise Broadband/ Jab Broadband) getting into the receiver.  I have very aggressively (and I do mean aggressively!!) loaded the RiseBroadband cable with large heavy ferrites with multiple turns through each.  When I'm serious about radio astronomy, especially with the ham - it - up, I turn power OFF on the ISP hardware.  My AirSpys have locked as low as 17 MHz.  I believe because I'm pushing that, I get more vertical lines, but I've learned to live with that.  I can comment that the AirSpys are head-over-heals better than the 'competition', SDRPlay which I also have.  It is absolutely miserable for vertical lines, overload, and just 'garbage responses' in the lower frequency ranges and does NOT respond in a dB manner.  I will NOT be spending any more $$$ on the SDRPlay products ! ! !   Besides, I vehemently dislike SDRuno ! ! ! !

I presently have the AirSpy set up on a crude interferometer (two antennas) on 432.050 MHz (for Cygnus A).  Here (and attached) is a screen capture of my present condition with the AirSpy terminated at the AirSpy with a 6 dB pad (12 dB return loss or better than a 2:1 SWR).
Inline image 1
This is an AirSpy 2.  You will also find the density and number of vertical lines is a function of FFT display resolution.  The above and first attachment are at 524288 samples.  If I drop that to 4096, the following results:
 Inline image 2
Outside of the obvious addressing EMC/RFI, play with the settings.  I like the finer results as I'm feeding the output of SDR# to other applications through VBCable for radio astronomy. 

Regarding the USB noise, just be thankful Firewire died.  It was TERRIBLE for radiating RF noise.  

--
Dave - WØLEV
Just Let Darwin Work

Virus-free. www.avg.com




--
Dave - WØLEV
Just Let Darwin Work

Join airspy@groups.io to automatically receive all group messages.