Do you measure your hand-wound toroidal inductors with an LCR? How often do you get the numbers indicated by the schematic or online calculator?
My inductors for the RFBitBanger measure 1.5-2.5X the value predicted by toroids.info for the LCR's frequency. Maybe they'd be OK wound around 330º, but the physical design calls for 180º. #HamRadio #RFBitBanger
I'd like to avoid playing an RFBitBanger equivalent of the (tr)uSDX RF tuning game, which goes kinda like this:
For each filter coil:
• measure 2nd harmonic notch with VNA
• squeeze and expand turns
• de-solder
• drop a turn
• re-solder
• repeat
For each serial resonance coil:
• measure output power curve vs frequency
• squeeze and expand turns
• disassemble
• de-solder
• drop a turn
• re-solder
• re-assemble
• repeat
For 4–5 bands, it's a bit much. #HamRadio #RFBitBanger #truSDX
I think I’ve got most of the (tr)uSDX / RFBitBanger band slot adjustment technique, now? To reduce how often you need to re-solder and re-assemble…
- try the instructions‘ turn count
- adjust spread and turn count until measurement OK
- THEN solder
- short out the pi filter
- adjust spread of serial resonance coil to move S11 resonance
- remove short
- adjust spread of pi filter coil to move notch on S21 log mag
- THEN plug into radio
- check power and efficiency #HamRadio #RFBitBanger #truSDX
Winding half a dozen inductors or more? Measure one of each type across the range of turn counts so you can correct the instructions.
Worked example for the RFBitBanger batch 2 T50-6 toroids, 40m band L2:
• find 12 on the X axis
• read up to the predicted line
• read across to the measured line
• read down to 9 on the Y axis
You might end up needing 8 turns, or 10, but either way 9 is going to waste less of your time than 12. #HamRadio #RFBitBanger #truSDX
VK2TTY he/him
F4JWJ, Pierre