Radio Recycling

Slide 1:Radio Recycling

By Nicolas - M1HOG www.M1HOG.com

Slide 2: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.

Slide 3: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?

Slide 4: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!

Slide 5: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.

Slide 6:Colpitts Oscillator

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

Slide 7: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.

Slide 8: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.

Slide 9:Phase Locked Loop

Slide 10: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..

Slide 11:Introducing the Jaws MK2

Slide 12: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.

Slide 13:Inside the Jaws MK2

Slide 14: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.

Slide 15:Offset Frequency

Original Frequency New Frequency

Slide 16: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

Slide 17:Installing the new offset frequency

Slide 18:Offset Frequency

Original Frequency New Frequency

Slide 19:The VCO coil

Slide 20: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.

Slide 21:Tuning up the Jaws MK2

Slide 22: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.

Slide 23:Links

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

Slide 24:Thank you !

This presentation is available at www.SADARS.org Nicolas www.M1HOG.com