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. Practical - High level talk through of the process and issues.

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? 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)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 A basic oscillator design Built from a kit, then reproduced using perf board.

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 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.CBSIM

Phase Locked Loop

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..

Introducing the Jaws MK2

Jaws MK2 - Overview A PLL controlled 27Mhz AM dual conversion Mhz / 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.

Inside the Jaws MK2

Conversion Overview Move the frequency to 10M to 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 Original FrequencyNew Frequency

New Offset Frequency Provide a higher Offset Frequency for the VCO mhz replacing 15Mhz. Crystals - Quartz LabQuartz Lab Colpitts Crystal Oscillator Kit and reproduction using perf boardColpitts Crystal Oscillator

Installing the new offset frequency

Offset Frequency Original FrequencyNew Frequency

The VCO coil

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.

Tuning up the Jaws MK2

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.

Links Jaws 2 Information My Jaws 2 conversion Blog – M1HOGMy Jaws 2 conversion Blog Scratchy Volume Controls - Greg OH2FFYScratchy Volume Controls Explanation of Jaws PLL operation - Greg OH2FFYExplanation of Jaws PLL operation Data Sheets LC Jaws 2 PLL.LC7120 TA 7310P - Mixer for PLL.TA 7310P TA 7205AP - Audio Power Amp.TA 7205AP LC Jaws 2A PLL – Cannot be modified.LC7131 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.CB2HAM Yahoo Group 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 ! This presentation is available at Nicolas