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QMX + LF / ELF use
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Hi all
I have recently built a QMX Plus which is working well & I am pleased & impressed with it.Good job Hans !
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My intention for the QMX Plus I have is to drive a transverter so I can access the LF/VLF bands (I am interested in ELF/VLF from the? Dreamers band 8.7 - 9.1 KHz through to 472-479KHz).? Mainly slow data / slow CW type of contacts. My plan was to drive a home brew transverter runnng at 10MHz.
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However examining the software and the hardware architecture I am wonderng if I could directly access the ELF / VLF bands from a QMX Plus ? Certainly the filtering will need modifying (and I guess may even need to be external filters so requireing modifications beyond simply swapping filters & reconfiguring the architecture by changing the software set up).? Anyhow, has anyone tried this ? The QMX Plus looks to be an ideal candidate as a prime mover for a transverter as it is, but direct access would be ideal. Another QMX Plus purchase ?
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Thoughts anyone ?
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Adrian M1LCR |
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On 07/10/2024 19:19, Adrian Rees (M1LCR) via groups.io wrote:
from the? Dreamers band 8.7 - 9.1 KHz through to 472-479KHz).Adrian, Hans knows all about the Si5351, it is specified from 8KHz up but from what frequency does it work in quadrature? It is possible on 160m but will it go lower? Then dropping everything to those frequencies would make a right mess. Filter switching would not work. I suggest something proven unless you are up to a real challenge. 73 Alan G4ZFQ |
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Hi? Adrian, Alan The '5351 can produce output down to 2kHz (not 8kHz, that was in very early datasheet revisions, which were incorrect).? Quadrature mode by the original method I devised, where the phase offset register is set to the same even? integer number as the MultiSynth divider, limits the divider to a maximum value of 126 (because the phase offset is 7-bit). The lowest frequency that can be attained by this method?is 3.2 MHz.? QCX/QDX has a mechanism explained on this page: (Japanese but Google translate does a good job) and this allows QCX/QDX to operate on 160m (QCX) and on bands 160, 630, 2200 (QDX). At the current time it has not yet been implemented on QMX and this is why the image rejection on 160m on a QMX+ is currently not? working properly: there isn't the correct phase shift of the oscillator. So that is high on the list to fix once I get SSB done. I would see no reason not to make the 90-degree phase shift trick work for 630 and 2200m too. You would not be able to simply substitute filter components for 630m and 2200m directly into a QMX+, because the PIN diode switching will not work at such low frequencies nor will the PA (higher permeability ferrite is probably needed). So there may be a host of modification work needed but - the QMX+ should in the end at least be capable of receiving and transmitting low level at the 630m and 2200m bands; and amplifying this up to a few watts is probably an easier project than a transverter. 73 Hans G0UPL On Tue, Oct 8, 2024 at 9:00?AM Alan G4ZFQ via <alan4alan=[email protected]> wrote: On 07/10/2024 19:19, Adrian Rees (M1LCR) via wrote: |
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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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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:
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