That noise could come also from the environment, even trough ground-loop
with the cox cable [ if the cable is connected between two grounds and
the cable is long enough it will pick up noise since the noise-current
generates voltage drop along the cable's shield, but the same field does
not drives current trough the internal conductor of the cable thus
causes noise voltage difference at the end of the cable between the
shield and the internal connector.
Take a piece of coax cable put a connector[ preferable an N connector]
to one end of the cable, short the internal connector of the cable to
the shield at the other end and touch that connected shield/internal
connector cable end to a larger metal
object, while the N connector end is connected to a spectrum-analyzer
input, set the spectrum-analyzer to high sensitivity and you will see
all the local AM and FM stations "coming out" from a perfectly shielded
coax cable...
Also the power supply of the amplifier needs a good filtering [chokes,
damping resistors damping ferrites, feed trough capacitors with relative
large value up to 0,1microFarad range. and any wire loop works as an
Antenna, therfore twist the power wires and keep close to metal surfaces
The box of the amplifier need to be closed without any small slots
to get good shielding with more than 120dB attenuation is not trivial,
73
KJ6UHN
Alex
On 12/17/2015 7:20 PM, Bruce Griffiths wrote:
Also add
1) BNX002
(attenuates noise in 1MHz to 1GHZ region) between the dc input and the input to:
2) Simple LCR filter - attenuates from 10kHz to 10MHz (see attachment)
Output of which is connected to the regulator input.
3) Like all the so called RF regulators with internal low pass filters your
regulator is exceptionally noisy at low frequencies.
Try substituting something else - a good one should be at least 20dB quieter at
low frequencies
4) Change the input amplifier to something like that depicted in 2nd
attachment. Reduces complexity and effect of residual power supply noise.
Reduce feedback resistor values.
Bruce
On Friday, 18 December 2015 12:08 PM, Poul-Henning Kamp
<p...@phk.freebsd.dk> wrote:
--------
In message
<capnvnrvsvdm+xb6rove8zu4sr1rjble+tahwcvydncwphpw...@mail.gmail.com>, Anders
Wallin writes:
My 'ultra-low-noise DC-supply' in the form of a lead-acid battery improves
things somewhat, but some spurs still remain:
http://www.anderswallin.net/wp-content/uploads/2015/12/2015-12-17_fda_spurs_and_comments.png
interpretations and explanations are welcome!
The board was not enclosed in a metal can for these tests.
Isn't that the explanation ?
Any SMPS in the vicinity is going to show up...
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