This effect is interesting and explains something I've been aware of for
some while ie. that the quality of a local oscillator or your own
transmission sometimes appears to be bad when listened to by pick up of
RF in the shack rather than by a direct connection through a sniffer or
attenuator. A related effect I've noticed in particular is that the
bench fluorescent light in my shack causes this problem and what's worse
actually causes intermodulation of the VHF RF signals it picks up
directly or on the wiring. This effect being caused by the extremely
non-linear characteristics of the lamp, the unstable characteristics of
the discharge and the fact that the mains sinewave is sweeping it
through the full range of the non-linearity. So be careful of this when
monitoring or doing two tone and other signal quality tests.
Having worked on SDRs professionally I can well understand that they are
particularly susceptible to these effects.
73 John G3UUT
On 13/09/2013 19:40, Fuqua, Bill L wrote:
When using direct conversion receivers or Zero IF frequency SDR receivers it
is important to have capacitors across
all rectifiers in all the power supplies if possible.
Sometimes Local Oscillator leakage thru the power line coupled to the power
line by some other means, gets is
modulated by the changing impedance of the diodes at a 120 Hz rate and you will
hear a constant buzzing sound.
The signal introduced by the local oscillator to the power line is amplitude
modulated by the diodes switching on and
off and picked up again by the receiver. The AM signal is at the same exact
frequency the receiver is tuned to and
the sidebands are demodulated.
This same effect is sometimes noted when you tune in your own transmitted
signal, lets say a CW signal, and you hear
a hum on the carrier which is not heard at the far end. The RF in the shack is
being modulated in the same way. The hum
is only noticed in the shack but not on the signal going out the antenna.
73
Bill wa4lav
________________________________________
From: Amps [amps-bounces@contesting.com] on behalf of Hardy Landskov
[n7rt@cox.net]
Sent: Friday, September 13, 2013 12:28 PM
To: amps@contesting.com
Subject: [Amps] Rectifier equilization?
I have just rejoined the amp list after a few years and am wondering if the
diode equalization question was ever resolved.
I am building a new bridge HV PS and it uses 12 diodes per leg. Rich Measures says
using a .01 & 470K across each diode is no longer needed due to improvements in
semiconductor manf. processes.
I have 100 1N5408's that came off the same reel so I feel they should be
matched fairly close.
I would like to hear a few opinions.
Thanks
73 Hardy N7RT
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