Re: VERTICAL LINES IN WATERFALL #radioastronomy #bestpractice


jdow
 

Ground is simply another circuit element. Those who think otherwise or don't
understand that circuit element are doomed to interesting failures. When
considering antennas ground becomes a most interesting and LARGE circuit
element. Distributed Ls and Cs, even Rs, behave in very strange unexpected ways.
A distributed circuit triangle of resistive material over a dielectric over ground can show such interesting things as a 3 dB/octave attenuation slope. Happy nightmares! (When I ran across that analysis I suddenly understood what happens in real transmission lines a little better. After all, they are distributed RLC circuits, too.)

{^_-}

On 2017-11-17 14:01, David Eckhardt wrote:
Thanks, Joanne!! You nailed it ! ! ! ! *When it comes to RF, there is NO
GROUND.* However, there is a 'return' for RF fields. I often point out
that the Crab Nebula doesn't need a 'ground' to fill the known universe with
copious amounts of RF energy. The ISS doesn't need a 'ground' to communicate
with earth from LEO. Our Voyager probes which have left the influence of our
Sun don't need 'ground' to communicate with the big dishes on earth.
Communications through amateur repeaters using hanke-talkies doesn't require
a 'ground'. Someday, maybe, just maybe, before I push up daisies, people will
realize 'ground' isn't what they envision it is. Grounding or earthing for
safety is quite well founded in sound theory and engineering practices.
However, 'grounding' to alleviate 'RF in the shack' is quite bogus in both
theory and good engineering practices. The latest ARRL publication titled
"_Grounding and Bonding for the Radio Amateur_" finally got it correct after
decades of bad information from that organization regarding the subject. I
STRONGLY recommend it to anyone having trouble with the subject. The Brits
got it right: they 'earth' for safety, NOT for RF RETURN. How can we ever,
in our life times, get this fact across???????
Dave - WØLEV
On Fri, Nov 17, 2017 at 5:19 PM, jdow <jdow@earthlink.net <mailto:jdow@earthlink.net>> wrote:
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> <mailto: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 * */Just Let Darwin Work/*
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