Tuning T-Match Tuner

finished kit finished kit

Read about the T-match

Using the T-Match

There are various ways of tuning the T-match. Some are more lossy than others.

Traditional mid-C procedure

The procedure:

  • Tune to the desired frequency.
  • Start with inductor at minimum, transceiver cap and antenna cap at MID position.
  • Adjust inductor for maximum noise.
  • Start with antenna side cap adjusting for maximum noise, then transceiver side.
  • Flip the Tune/Transmit switch to Tune.
  • Key the transceiver and adjust capacitors to the dimmest LED showing possible.
    • DO NOT switch the inductor setting while transmitting.
  • Stop transmitting. If you were not able to get a good match try reducing or increasing inductance and repeat the tuning procedure.
  • Once you are satisfied, return the Tune/Transmit switch to Transmit.

max-C procedure

The procedure:

  • Tune to the desired frequency.
  • Start with inductor at minimum, transceiver cap and antenna cap at MAXIMUMUM position.
  • Adjust inductor for maximum noise.
  • Start with antenna side cap adjusting for maximum noise, then transceiver side. TODO: which side to adjust first?
  • Flip the Tune/Transmit switch to Tune.
  • Key the transceiver and adjust capacitors to the dimmest LED showing possible.
    • DO NOT switch the inductor setting while transmitting.
  • Stop transmitting. If you were not able to get a good match try reducing or increasing inductance and repeat the tuning procedure.
  • Once you are satisfied, return the Tune/Transmit switch to Transmit.

min-C procedure

The procedure:

  • Tune to the desired frequency.
  • Start with inductor at minimum, transceiver cap and antenna cap at MINIMUM position.
  • Adjust inductor for maximum noise.
  • Start with antenna side cap adjusting for maximum noise, then transceiver side.
  • Flip the Tune/Transmit switch to Tune.
  • Key the transceiver and adjust capacitors to the dimmest LED showing possible.
    • DO NOT switch the inductor setting while transmitting.
  • Stop transmitting. If you were not able to get a good match try reducing or increasing inductance and repeat the tuning procedure.
  • Once you are satisfied, return the Tune/Transmit switch to Transmit.

1/4-c procedure

With the min-C and max-C approaches I often found that when it came to fine tuning I was stuck since the other control was either at a minimum or maximum.

The procedure:

  • Tune to the desired frequency.
  • Start with inductor at minimum, transceiver cap and antenna cap at one quarter C position.
    • This is halfway between min-C and mid-C starting points.
  • Adjust inductor for maximum noise.
  • Start with antenna side cap adjusting for maximum noise, then transceiver side.
  • Flip the Tune/Transmit switch to Tune.
  • Key the transceiver and adjust capacitors to the dimmest LED showing possible.
    • DO NOT switch the inductor setting while transmitting.
  • Stop transmitting. If you were not able to get a good match try reducing or increasing inductance and repeat the tuning procedure.
  • Once you are satisfied, return the Tune/Transmit switch to Transmit.

Testing Procedure

  • Set up a NanoVNA with s11 set to SWR and s21 set to log mag (insertion loss).
  • Calibrate NanoVNA.
  • NanoVNA CH0 connected to TXVR jack of T-Match.
  • NanoVNA CH1 connected to ANT jack of T-Match.

Select a frequency, then tune for a match using the various procedures.

Frequency Procedure SWR Log Mag dB Notes
28.060 MHz min-C 1.115 -3.42
28.060 MHz 1/4-C 1.014 -2.92
28.060 MHz mid-C 1.034 -2.82
28.060 MHz max-C 1.28 -13.16
14.060 MHz min-C 1.361 -1.05 all inductor – no C added
14.060 MHz 1/4-C 1.349 -1.10 mostly the same
14.060 MHz mid-C 1.041 -4.13
14.060 MHz max-C 1.036 -8.75
7.1 MHz min-C 1.290 -1.29 all inductor – no C added
7.1 MHz 1/4-C 1.108 -1.99
7.1 MHz mid-C 1.062 -4.48
7.1 MHz max-C 1.051 -13.12 C2 at max
3.58 MHz min-C 1.142 -3.79
3.58 MHz 1/4-C 1.089 -4.42
3.58 MHz mid-C 1.48 -5.35
3.58 MHz max-C 1.393 -14.9

Conclusions

  • Least amount of loss was observed when using traditional mid-C or 1/4-C starting position for C.
  • Further research with a real-world antenna needs to be done.
    • Set up a test fixture and observe Power In and Power Out of T-Match.
    • This would still not account for loss in a 9:1 transformer after the matching unit.
  • All of the observed loss points to why a QRP station should utilize a resonant antenna to achieve maximum radiated RF energy.

Also, check out this nice video from @TheSmokinApe on insertion loss.