Preface
While this conversion is easier than the 6 Metre Conversion (PRM80), the same principals apply. There is still Software mods, VCO mods (maybe), Filter changes, Receiver changes and in particular TX filter mods.
Programming
Download 6metres.zip, unzip it and load it into the 2020 Programming software. You need version 2.54 or higher. After loading the file, program it to the radio, however, 'DO NOT' let the program do a check on the settings, or it will fail.
VCO Check
Check the voltage on the VCO control line during TX and RX. Make sure the voltage stays above 2VDC over the entire band.
Low pass filter
There needs to be capacitance added here. Component Changes:
- C339 - add 27p
Winding Coils
You need the following for the coils:
- 0.5mm enamelled copper wire for all coils except L327.
- 0.95mm enamelled copper wire for L327.
Receiver modifications
Change the following components:
- C342 - add 39pF
- L320 - replace with 5.5 turns @ 5mm Dia.
- L101 - replace with 7.5 turns @ 6mm Dia.
Receiver re-alignment
Re-align the 3 RX front end coils. If the front end does not come good after even with the slugs well down into the coils, add a 10Kohm resistor across C116 to reduce the voltage applied to the varicap diodes. You need to see around 1VDC. Repeat the alignment
Transmitter modifications
Replace the following coils:
- L327 - 1.5 turns @ 4mm Dia. (Using the 0.95mm wire)
- L316 - 3.5 turns @ 6mm Dia.
- L301 - 5.5 turns @ 4mm Dia.
- L302 - 4.5 turns @ 5mm Dia.
- L304 - 2.5 turns @ 4mm Dia.
- L307 - 4.5 turns @ 3mm Dia. (Raised above PCB by 1mm).
- L325 - 2.5 turns @ 4mm Dia. (Raised above PCB by 1mm).
- L313 - Spread the turns to maximise output power.
Specifications
You should now have > 25W TX power at around 6A, and a sensitivity ~-125dBm
Real life
I have modified one of these, and it works great. however the unit I modified was a narrow band model, which means all the old school operators with units that deviate almost to 6khz or are off frequency chopped badly. The PRM80 is not as sensitive to this as the T2020, as their front ends are substantially wider… even on the narrow band model.
I'm not going to take credit for this mod….. I have had it written down now for about 7 years and not told anyone.
