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Radio Recycling. By Nicolas - M1HOG Introduction. Disclaimer - Nothing in the talk is warranted as accurate, optimal or indeed sensible. Objective – Encourage people to recycle a CB as a way of learning about radio systems and producing a useful and unusual radio.

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radio recycling

Radio Recycling

By Nicolas - M1HOG

  • Disclaimer - Nothing in the talk is warranted as accurate, optimal or indeed sensible.
  • Objective – Encourage people to recycle a CB as a way of learning about radio systems and producing a useful and unusual radio.
  • Practical - High level talk through of the process and issues.
why recycle
Why Recycle
  • Ready made framework
  • Accessible - discreet components, no surface mount, freely available circuit diagrams
  • Brings back an old radio to use (on legal bands)
  • Learning experience, Low cost
  • Low monetary cost - but you will need some time!Create a unique radio?
what to recycle
What to recycle?
  • CB Radios - 11m (27Mhz) was once an amateur frequency now between our 10 and 12 bands!
  • Potential for easy conversion to 10M
  • Inspirations - T4TT series of articles in PW by G4CFY (Spectrum communications)
  • Older AM CB’s are cheap!
am fm
  • AM varies the strength of the transmitted signal in relation to the sound be sent.
  • FM varies the frequency of the transmitted signal in relation to the sound sent.
colpitts oscillator
Colpitts Oscillator
  • A basic oscillator design
  • Built from a kit, then reproduced using perf board.
voltage controlled oscillator
Voltage Controlled Oscillator
  • A voltage-controlled oscillator (VCO) is an oscillator designed to be controlled in frequency by a voltage input. The frequency of oscillation is varied by the applied DC voltage.
  • Used in conjuction with the phase locked loop.
  • This example uses varicap – a diode whose capacitance is controlled by a voltage from the PLL.
phase locked loop
Phase Locked Loop
  • Enables a frequency which can be changed in steps, to be locked against a fixed crystal reference frequency. Provides a variable freqency output with the stablity of the fixed crystal reference frequency.
  • Using CBSIM to help understand the PLL.
basic types of pll found in cb s
Basic types of PLL found in CB’s
  • Discreet – Only the comparator is on the chip / everything else (divide by inputs etc) can be changed.
  • External Loop – The control loop can be easily accessed / altered.
  • Monolithic – All functions are locked within the chip, no easy frequency change is possible.
  • Due to the PLL chip used, it turns out the very first radio I used, back in 1982 can be put on the air again..
jaws mk2 overview
Jaws MK2 - Overview
  • A PLL controlled 27Mhz AM dual conversion 10.240Mhz / 455Khz Superhet transceiver, similar principles to the BITX 20 discussed in Martins talks.
  • PLL - The control loop can be easily accessed / altered.
  • Discreet components, published circuit diagrams.
  • Jaw Mk2 CB – There was no MK 1!
  • Neat mobile rig with classic red LED display.
  • Popular AM CB of the 80’s.
conversion overview
Conversion Overview
  • Move the frequency to 10M - 29.00 to 29.100 with original 10Khz channel spacing.
  • AM operation only.
  • Provide a new offset frequency for the VCO.Down mix into the PLL remains the same.
  • Ensure the PLL locks across the new range.
  • Tune up the RX and TX.
offset frequency
Offset Frequency

Original Frequency

New Frequency

new offset frequency
New Offset Frequency
  • Provide a higher Offset Frequency for the VCO 17.055mhz replacing 15Mhz.
  • Crystals - Quartz Lab
  • Colpitts Crystal Oscillator Kit and reproduction using perf board
offset frequency1
Offset Frequency

Original Frequency

New Frequency

increasing the vco frequency
Increasing the VCO frequency
  • The VCO now has to operate about 2Mhz higher than before.
  • Either - Reduce the capacitance or the inductance.
  • Inductance - Only 5 turns! So one turn would probably be too much.
  • Capacitance – Removed the tiny capacitor in the base of the coil. Added a small 1-28pf trimmer across the coil pins, set it to a few pf and centered the coil slug. Measured the output of the mixer while clicking through all the channels - perfect lock on RX and TX across the whole range and a cleaner signal.
learning points
Learning Points
  • Understand, test and measure the donor rig thoroughly before taking it apart.
  • Rig up a PLL lock LED to indicate if the PLL has "lost grip".
  • Try and avoid getting bogged down in why one detail does not work. It will still be there later.
  • Even a 10x probe can squash things.
  • 4 watts of RF will get everywhere.
  • Highlighted the need for a proper power meter and signal generator, although you can successfully improvise.
  • Jaws 2 Information
  • My Jaws 2 conversion Blog – M1HOG
  • Scratchy Volume Controls - Greg OH2FFY
  • Explanation of Jaws PLL operation - Greg OH2FFY
  • Data Sheets
  • LC7120 - Jaws 2 PLL.
  • TA 7310P - Mixer for PLL.
  • TA 7205AP - Audio Power Amp.
  • LC7131 - Jaws 2A PLL – Cannot be modified.
  • General Information
  • CB2HAM Yahoo Group - Lots of helpful advice, schematics for the MK 2 / MK 2a and a host of other conversion information. Thanks Greg.
  • Double Balanced Mixer
  • List of PLL modifications
  • Roger Lapthorn's 10m page
  • Spectrum Communications
  • Explanation of PLL pin functions
  • RF power meter
  • Modulation meter
  • Tutorials and articles from NA5N - includes a great introduction to scopes
thank you
Thank you !

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