[Amps] Incidental intermodulation was Rectifier equilization?

[John G3UUT]

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 at contesting.com] on behalf of Hardy Landskov [n7rt at cox.net]
> Sent: Friday, September 13, 2013 12:28 PM
> To: amps at 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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