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Re: QMX + LF / ELF use

 

Hello Ian

QDX has been tested on 160, 630 and 2200m and works well (firmware does, anyway). The PIN diode band switching doesn't work on such low frequencies so it's necessary to use the single band QDX-M. The low pass and band pass filter design, and the transformer all need to be suitable for such low frequencies.?

There's no technical reason why the QDX receiver and transmitter couldn't be made to work for lower frequencies than 2200m. The lowest frequency the '5351 can handle is 2.5kHz. but I believe currently I only coded it to work down to 2200m band.?

On QMX+ even 160m receive doesn't work correctly because the 90¡ã phase shift isn't set up correctly. QMX+ on VLF bands would also be feasible in firmware - leaving it to the constructor to somehow experiment with the output transformer, BPF and LPF as well as suitable band-switching involving relays not the supplied PIN diodes.?

When I've finished the SSB project I'll work on these things.?

73 Hans G0UPL


On Sat, Oct 26, 2024, 07:21 Ian via <drumli=[email protected]> wrote:
Hello Adrian, Alan and Hans,
I can add to this discussion about direct use of the QDX-M at very low frequencies, based on some tests I have done with my QDX-M units built to operate in the 2200m band. These units have been working successfully, exchanging text messages using THOR and OLIVIA. They are REV 5M boards loaded with 1_10 firmware. (for an example see ).
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To test the lowest frequency that they might work, I shorted across the Band Pass filter ( L12 and C28), adjusted the Band configuration values, and ran the RF Filter test. The tests produced OK graphs down to 85 kHz. Below that frequency there was simply no data produced, so my conclusion was that 85 kHz is currently the lowest possible frequency that the QDX-M might function.
I setup the unit for 88.5 kHz USB and ran all the Terminal tests, including the "Transmitter Test". All tests were OK. I then tried transmitting a THOR message (generated by running the RadioMsg app in an Android phone) and all looked OK, including the slow flash LED indicating a successful Tx on the QDX-M. Unfortunately no power was being delivered to the dummy load. The unit returned to normal operation when I returned all values to those used on the 2200m band (phew!) and I currently think that the firmware prevents Tx outside the 2200m band limits.?
I do note that there is a difference between the QDX firmware and QMX firmware, in that the QDX offers only an option to "Enable/Disable" Japanese Band Limits, whereas the QMX software offers a selection of "ITU Region 2, Japan, or None". It would be nice to be able to access such a selection in the QDX world.
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Using the QDX-M units to access the 2200m band has been marvellous.?
Thank you Hans, for making these units available, and in particular for the super-clear documentation.
Ian
VE6IXD?
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