Radio Recycling By Nicolas - M1HOG .
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Transcript of Radio Recycling By Nicolas - M1HOG .
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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.
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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?
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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!
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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.
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Colpitts Oscillator
• A basic oscillator design
• Built from a kit, then reproduced using perf board.
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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.
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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.
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Phase Locked Loop
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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..
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Introducing the Jaws MK2
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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.
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Inside the Jaws MK2
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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.
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Offset Frequency
Original Frequency New Frequency
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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
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Installing the new offset frequency
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Offset Frequency
Original Frequency New Frequency
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The VCO coil
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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.
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Tuning up the Jaws MK2
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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.
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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
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Thank you !
This presentation is available at
www.SADARS.org
Nicolas
www.M1HOG.com