locked Re: Understanding USB and PC noise

smswk
 

Maybe i am wrong but:

i have never seen any discussions like that when talking
about any other software defined radio.

The number of spikes where they do not have to be
or the extreme efforts of USB filtering seem to be an exclusive HF+
problem.

The HF+ has a very good shielded case.
Terminate your antenna inputs and use the best USB cables you can get.
What will you see ?
Unwanted spikes and unwanted noise.

And you can go fürther with filtering. Using ferrit cores,
trying it with RC Circuits for theUSB shield, external linear PSU,
special D+ / D- Data Line Filters etc.

It is possible to reduce the problems above but they are still there.

Don`t get me wrong. I really like the HF+ and it is maybe the best and most sensitive
SDR you can get for just a few bucks.

When your antenna inputs are terminated and you add filters like you have never done
before in your life and the prolems are still there:
Stop to spend money on trying external improvements.
In my opinion prior to firmware upgrades almost every week a solution for this has to be found.

vy73`s
Stefan






-----Ursprüngliche Mitteilung-----
Von: jdow <jdow@...>
An: main <main@airspy.groups.io>
Verschickt: Di, 17. Apr 2018 10:28
Betreff: Re: [airspy] USB cable noise and Airspy HF+

I have a very large number of spikes. Many are from the APC Matrix 5000 UPSs we
have to ride out brownouts. Others trace from the 100 kW (peak) solar array we
have. Other noise is telco DSL leakage and powerline insulator leakage. Making
it quiet around here will take a lot of work. Distance isolation will help. But
that will lead to a lot of transmission line. Win some, lose some. In an urban
or very dense suburban environment "Noise is." In fact a LOT of "noise is."

{O.O} I wanna cry.

On 20180417 00:53, Patrick wrote:
Thanks for these precious tips.
I have hundreds of spikes on VHF/FM I don't manage to suppress ... I added
several ferrites, purchased a quality USB cable, put the HF+ "away" from the
desktop (2m), no improvement at all. I suddendly realize that I did not add a
ferrite clamp on the monitor cable (a jack connector for audio), not sure it
could help but I'll give it a try.

I also noticed that the number of spikes increases / reduces according the the
yagi azimut. Maybe the problem comes from the outside only ... (I live in a
buidling)

Have a nice day,
Patrick



2018-04-17 9:25 GMT+02:00 jdow <jdow@... <mailto:jdow@...>>:

Normally speaking the distance from a noise source reduces signal by the
square of the distance. For the near field, next to your computer, for
example, signal strength reduces with the cube of the distance. You need a
well shielded computer - in and out. Ferrites on the power cord should not
be ruled out. Ferrites on all audio and video cables should not be ruled
out. Ferrites on any other I/O cables should not be ruled out. These may
include pairs of ferrite beads, one big one with several wraps of the cable
through a 3/8" hole and one smaller that works well for UHF and above. The
idea is to prevent radiation from escaping the computer, monitor, or other
peripherals. Make the cables high impedances for RF. Then at the antenna
make sure it is "balanced" even if you use coax. A set of ferrite beads or
transformer and beads can keep the cable's common mode impedance high to
reduce pickup. But, hey, why take just my word for it. Visit Jim Browns
excellent write-ups. Jim, K9YC, fought some REALLY high EMI environments as
a professional audio engineer in a building in Chicago with several very
high power transmitters on top. I'd say he figured out a thing or two worthy
of attention, "http://audiosystemsgroup.com/RFI-Ham.pdf
<http://audiosystemsgroup.com/RFI-Ham.pdf>". Good judicious grounding and
good EMI isolation can make your life a lot better with regards to sources
you control. There is not much people can do about a neighbor's plasma TV or
the like unless they are on (very) good terms with their neighbor. Sometimes
you can get the FCC in the US to act.

{^_^}

On 20180416 23:43, Patrick wrote:

Hi there !

Assuming one use quality USB cables and / or ferrites, is it necessary
to keep the HF+ far from the computer or does it make no difference if
they are side by side ?

Thanks
Patrick

2018-04-17 4:32 GMT+02:00 jdow <jdow@...
<mailto:jdow@...> <mailto:jdow@...
<mailto:jdow@...>>>:


    Oh, another is "Conductors radiate". There is no conductor possible
that
    does not radiate with the possible exception of the center
conductor of a
    piece of superconducting coax. Even dummy loads radiate. (They can
reach the
    LA area from the Seattle area, as a matter of fact, if you feed
them enough
    power. "Gee, your signal's weak tonight!" was the consensus of the
group
    nattering with Art Bell on ham radio after his show one evening.
That was a
    fun group while it lasted. Art and his humongous loop antenna were
a long
    time source of discussion on that on the air gathering of hams. It
certainly
    was not a net or a formalized rag chew. It was fun shooting the
breeze more
    and less technically until some bozos destroyed it by jamming us.
And the
    FCC STILL has not removed the creeps from the air.)

    {^_^}

    On 20180416 18:18, Joe M. wrote:

        Is there a list of "Joanne's Laws"?

        Joe M.

        On 4/16/2018 8:51 PM, jdow wrote:

            You have not been listening. "Ground is not ground." That
is one of
            Joanne's Laws. It simply means you are deluded if you think
the ground
            over there is the same as the ground over here even if the
distance
            between here and there is in fractions of an inch.

            In a word, no. Ground isn't ground. And data does not like
to be
            bypassed to ground giving it round edges and reduced amplitude.

            {^_^}

            On 20180416 16:17, Bryon NF6M wrote:

                I wonder, as far as RFI coming in on the USB cable
itself, would it
                help to add some RF bypass capacitors from the USB
data/power
                lines to
                ground within the HF+?

                It seems like that would essentially short any stray RF
to ground at
                the connector, while allowing DC signals and power to
remain
                unaffected.

                Or would that distort the rise/fall of DC transitions
on the
                data lines?





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FM RFI.JPG

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