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Wicen R4D5 Co-ordinator


matt at vk3smb dot com
Even Poorer Mans Spectrum Anal
This will boggle your mind with the simplicity of the thing, and how effective it is.

Parts Needed

  • An old Analog TV tuner module (variactor tuned version). (grab one as they end up at the tip).
  • An old AM CB. not important as so long as the receiver works.
  • An old CRO. It has to be a Cathode ray scope as we need the horizontal deflection voltage.
  • A stable power supply capable of supplying the voltage needed to tune the TV tuner to its highest range.
  • A hand full of Good quality Potentiometers.
  • A wideband pre-amp kit from Jaycar if you want to get fancy and see the band noise increase at 50Mhz when there is inversion around.
Building it
Every version of this will be different as there is so many varients of tuners kicking around. I will draw a diagram of my unit when I get time but basically it is assembled like this:
  • Modify the CRO, bring the Horizontal deflection voltage out via about a 50k resistor (a plug on the back is a good idea, keep in mind this is a high voltage). The value of the resistor will depend on the voltage of the horizontal deflection and the voltage needed for the tuner.
  • You want to set up the tuner with the power supply so you can activate the different bands. newer ones are continious from DC to daylight almost.
  • Plumb the power supply into the varicap pin via a 100kish pot so you can get the tuning from near 0v to maximum voltage for your tuner.
  • Via another pot, shove the horizontal deflection voltage onto this pin also. This means we are varying the voltage of the varicaps in time with the horizontal deflection. (starting to see where I'm going with this??).
  • get the IF out from the tuner and stuff it into the antenna socket of the CB.
  • open the CB up and grab the 455khz IF. hack into it before any caps get in your way and remove the DC from the signal.
  • Plumb the IF out and shove it back into the CRO's Y input.
Thats about the it. From here you can add a speaker out so you can hear as well as see the whats going on, add calibration to your dials, fine tune it, add attenuators or pre-amps etc etc.

Before someone asks why we are using a CB in there, here is why:
The IF output from the tuner is a broad as a barn door and no good. The CB is mearly a front end for the thing to narrow down the samples to about 15khz or better depending on the CB.

Mine worked great for years untill the power supply in the cro gave up.

A diagram of mine will be added when I re-draw it so people other than me can read it.

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