[time-nuts] SMD TADD-1 distribution amplifier - seeking comments and suggestions?

Alex Pummer alex at pcscons.com
Fri Dec 18 00:04:00 EST 2015


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 <phk at phk.freebsd.dk> wrote:
>   
>
>   --------
> In message <CAPnVNRVsvdM+xb6rove8zU4sR1RjBLe+tahWcVyDNcWPhPWiMQ at 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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