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QDX-M 80m
#80m
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Hi All,
I have a plan to build a QDX-M for 80 metre FSQ activities. The QDX-M appears to be ideal for this with it's clever non SSB method of producing the tones required. However, the web page shop only lists 10,11,12 metre bands at the moment. After looking at the circuits for the QDX and QDX-M the changes for 80 metres would seem to be: 1. Use the low pass filter design for 80 m from the QDX. i.e change the inductors and capacitors in the QDX-M to be the same as the 80 m filter in the QDX. 2. Change the inductor in the QDX-M (L12) so that it resonates with the 56 pF capacitor at 3.6 MHz. 3. It looks like L14 remains the same for all bands. So my question is: Has anyone done this and are there any steps I've missed, and can I buy a QDX-M kit with all the appropriate toroids, inductors, and capacitors? I'd like to buy one QDX-M for 80 metres and one extra set of components to change the unbuilt 10 metre QDX-M I have to 80 metres. Apologies for the long and involved post. Best Regards Richard Katsch VK2EIK |
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On 22/04/2025 23:39, Richard Katsch via groups.io wrote:
I have a plan to build a QDX-M for 80 metre FSQ activities. The QDX-M appears to be ideal for this with it's clever non SSB method of producing the tones required. However, the web page shop only lists 10,11,12 metre bands at the moment. After looking at the circuits for the QDX and QDX-M the changes for 80 metres would seem to be:Richard, The QDX-M has not featured much in this group. I guess it is for more specialised users, the QDM came out soon after and little has been added to the QDX pages. I bought one because the diode switching is omitted, theoretically giving a little more gain on high frequencies, and the possibility of use at LF. I'd think the standard QDX is better for general use being multiband and band variations better documented. You could miss out some unwanted bands. The QDM LPF will not be much different than the QDX ones but maybe the RX filters will vary. The multiband QDX RX filters are adjusted because of stray capacitances and other interactions. 73 Alan G4ZFQ |
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Hello Richard My original aim for the QDX-M was to make versions for 160, 630 and 2200m, which are not suitable for the QDX because of the difficulties with PIN diode switching such low frequencies. However I got sidetracked by many other projects which is why I still did not go through the process of building and documenting one for each band. So at the moment it would be an experimental thing for you. The filters will not differ much from the 80m filter in the QDX 80-20m version, and this would provide a good starting point. The firmware only needs adjustment of the Band Configuration screen for the desired band.? 73 Hans G0UPL On Wed, Apr 23, 2025 at 2:39?AM Richard Katsch via <rkatsch=[email protected]> wrote: Hi All, |
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Hello Allan & Hans
Thank you for taking the time to reply. I can see from the group messages that you have a few other irons in the fire! My interest in the QDX-M is in building a few for our radio group to allow (encourage) experimentation with the FSQ protocol and NVIS propagation. The QDX-M makes an ideal, cheap, dedicated radio, which together with a laptop computer make an ideal field station. I understand that some experimentation might be necessary to set up the band/low pass filters and I have some equipment here to do that sort of thing. My understanding of band selection is that it is done in firmware after getting the radio going. So my crunch point is: Can I order a QDX-M with two sets of toroids, caps, and wire etc to proceed with the build? I can source them locally but it would be neater to get one box with all the bits. We're well out in the "bush" and everything happens by on-line order anyway. Thanks again and I hope all is progressing well with the SSB project. Best regards Richard VK2EIK QF69al |
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