[time-nuts] Totally unrelated, but..

Charles Steinmetz csteinmetz at yandex.com
Thu Dec 8 10:58:21 EST 2016


Ed wrote:

> It would be helpful to give some specific info about the circuit and
> regulators used for these experiments, such as operating voltage,
> load current, and regulator type.

I concur.  It would also be helpful to have more detail about the 
phenomenon you are observing (see below).

Also, consider the possibility that what you are hearing and concluding 
is RF interference may be noise generated elsewhere, for example in the 
audio section of the rx. If the audio section is quasi-stable, it could 
be sensitive to the absolute power supply voltage, or to the output 
impedance of the regulator. The same could happen in the AGC circuit, or 
the local oscillator.

Can you see the noise on the signal strength monitor or on the AGC line? 
  (If the rx doesn't have a SS monitor, you may need to add one for 
troubleshooting.)

Over what range of frequencies is the interference/noise produced? 
Listen for it on a wideband receiver (which has much greater sensitivity 
above noise than a S/A).  To do this, make a test antenna by stripping a 
couple of feet of shield off a length of coax and forming the insulated 
center conductor into a solenoid with several turns.  Feed this into the 
50 ohm receiver input, then "sniff around" the misbehaving circuit. 
Tune the wideband rx up and down to gauge the extent of the noise band.

Is there anything about the rx that could cause unusual behavior (for 
example, is it a direct-conversion rx, or is there something unusual 
about the LO)?

Best regards,

Charles




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