[Premium-Rx] RF-590 Front Panel RFI

[Ahmet Gundes]

RF-590 Front panel is full of Noise sources, including the vacuum florescent display power supply and the microcontroller oscillators.  i think they could
have done a better job in reducing EMI / RFI on the front panel. in one of the
590's, display power supply was leaking out noise into the DC supply which
ended up getting into the AGC driver IC and thru this into the IF Section.
Capacitors and Inductors used to isolate and reduce the RFI before they enter various stages of the receiver are not very effective. Higher values of capacitor and inductors substantially reduces noise which travels throughout the circuitry and in a way uses the pcb traces as an antenna.  i think designers at Harris are much more exposed these interferance issues and i would have expected to see a better design and definitely a self encased front panel.

NRD-535 also has a similar Display Noise issue, but is a consumer grade receiver.

Noise coming out of the front panel can easily be picked up with a scanner radio revealing the frequencies and their harmonics if these are crystal oscillator rfi.

Ahmet Gundes
 
> I was able to get rid of that display noise completely by converting the
> display switching power supply to an analog design using 60 Hz AC and DC.  I
> had to add one small power supply in the power supply module to do this.
> 
> If someone is interested in making the 590 better on VLF, I can give you
> some pointers on doing this.  Also MiniCircuits has a mixer that should work
> better for VLF.  It is the RAY-6U, rated from .01 to 100 MHz.  The downside
> to this is you lose about 5 dB in dynamic range with this mixer.
> 
> John Reed
> 
> 
> 
> > After some careful listening today I noticed the RF-590 does have some
> > fluorescent display noise at about 15.6KHz with a rough audible 
> > broad 3rd harmonic
> > around 46-47KHz and this can drift in frequency a bit. The fundamental at
> > 15.6KHz is audible even with the antenna disconnected, I would 
> > say about an S-1
> > signal level. Interesting that this fluorescent display noise 
> > frequency is very
> > close to the standard horiz. osc frequencies used in standard TV 
> > sets. Using an
> > outboard upconverter with a 4MHz LO the noise can be just about eliminated
> > with the receiver tuned to 4015.6KHz and using shielded antenna 
> > connections to
> > an outside antenna. Display noise on VLF would still be a problem if using a
> > loop antenna or any antenna in close proximity to the receiver 
> > though. 73 Todd
> > WD4NGG
> >
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