Re: VERTICAL LINES IN WATERFALL #radioastronomy #bestpractice


jdow
 

There is another site worth consulting once you discuss audio. Go find Jim Brown's, K9YC, fine set of articles. (Conveniently it's at "http://k9yc.com/";.) Jim Brown is a retired professional theater audio fellow. One of his main gigs was a theater in the same building in Chicago as a large bunch of high power TV transmitters. Perforce he learned how to properly handle audio in a high RF environment where even 60 Hz hum is a severe enemy.

More or less he points out the same thing I often point out most bluntly with the simple law, "Ground isn't." This means that what you "assume" is a nice ground that unites over there with over here isn't by any means a nice theoretical unipotential ground. It features such things as resistance and inductance within the ground plane and capacitance coupling to adjacent emitters. Every time you forget this it will come up and nail you, again.

{^_^} Joanne

On 2017-11-17 10:29, David Eckhardt wrote:
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@hotmail.com <mailto:normand_fortin@hotmail.com>> 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
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