The procedure for tuning the Alexloop antenna recommended by its designer, Alex PY1AHD, is “by ear”, i.e., using the background noise in the audio to select the capacitance that allows for maximum noise. However, on occasions the noise is difficult to hear and/or its maximum, difficult to establish. Also, often the SWR thus selected does not correspond to the lowest SWR and its value remains higher than 2:1.
Pressing TUNE in the KX3, in addition to transmitting a standing signal causes the SWR to be prominently shown on the display together with the transmitting power. See the following picture showing an SWR of 1.5-1 after TUNE was pressed with transmitting power set to 1.0 W:
When TUNE is pressed the signal sent is at the power at which the KX3 is set to transmit, not the power at which it is set to tune. Hence, in order to use this feature to tune the Alexloop, first the transmitting power needs to be reduced (i.e., to 1W), then, using MENU, the internal ATU needs to be bypassed, pressing TUNE the Alexloop can then be tuned to the minimum SWR value. After this is done the power can be restored to 5W, and again using MENU, the ATU can be reset to AUTO and used to further reduce the SWR reaching the transceiver. Although all this can be achieved manually, this is not too practical. However, this task can be significantly simplified with the use of the following two KX3 macros:
Using the KX3 Utility these macros can be written and transferred to the KX3 and subsequently assigned (using the MACRO option in the KX3 menu) to the two programmable function switches in the KX3 (PF1 and PF2). Once this is done, the Alexloop tuning procedure is as follows:
- Press PF1 (bypass the internal tuner and set the transmitting power to 1W),
- press TUNE (send a steady 1W signal),
- tune the Alexloop to minimal SWR using the variable capacitor at the antenna and the SWR numeric value in the KX3 display,
- touch on XMIT (cancel the signal being sent by TUNE),
- press PF2 (revert to 5W of transmitting power and re-activate the internal tuner) and
- touch on ATU to further minimize the SWR reaching the transceiver.
Although developed primarily for the Alexloop, these macros and procedure can be used to tune any tunable antenna (i.e., Buddipole or Buddistick, to select the coil tap and/or to adjust the whip length).
Note: an obvious improvement would have been to append the pressing of TUNE at the end of the first macro and the touching of ATU in the second. However these two steps are ignored when included in the macros. I have been unable to resolve this, and prefer to keep these steps independent from the macros.