ozQRP MST400

Here are some (very poor quality) photos of the current project. An ozQRP, MST400 the MST standing for “Minimalist Sideband Transceiver”. Available as a partial kit in two versions, 40m and 80m. I’m building the 40m version designated MST400. The kit comes with the PCB and optionally some hard to find parts. You source the rest of the parts yourself. The parts sourcing issue elevates this kit to an intermediate level of difficulty. This is not a beginners kit.

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Front view. Plastic box (finding good, cheap metal boxes is so hard – sigh). Metal front and rear plates. Silver knobs from a very old defunct crystal CB radio (Yeah, I know, never use metal knobs!). The fact that the two smaller knobs don’t line up properly shows up in the photo! It’s not so noticeable when your holding the radio. I’ll have to do something about that. The misalignment is due to the way I mounted the pots (more on that in a minute). The signal strength meter is from the same discarded CB radio.

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Top view. Speaker grill is a sink drain filter. Not sure if I like the look or not. But it’s functional. Next time I might just use it as a template and drill holes in the plastic. The construction manual is alongside. The manual is absolutely excellent! Not quite the Elecraft “step-by-step” gold standard but very good for the intended audience.

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I had a roll of aluminium foil (flashing) with adhesive backing. Available from hardware stores and used for insulation. I used it to insulate the box from RF. I mounted the DDS VFO, a separate but matching kit (you can supply your own VFO if you prefer) and the controls to a PCB set rearwards from the front panel. Rather than mounting them directly to the front panel. This makes it easier to keep the front panel looking neat and builds a RF shield between the DDS VFO and the main transceiver PCB. Probably not required but it seemed like a good idea.

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Another shot of the case top cover. Showing speaker, sink drain speaker grill and aluminium insulation.

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Front panel and DDS control board. Upside down. Not only can I not take in-focus pictures I get them upside down as well! I’ll fix it later.

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Here is the cause of the pot alignment problem. Because of the pot shaft length that I had on hand I decided to try and solder the pot body directly to the PCB. It works. But the precise alignment is quite difficult without building an alignment jig to hold the pots in place while soldering. And if you build that jig, out of say PCB material, then you may as well make it permanent! Ah, well, live and learn.

6 thoughts on “ozQRP MST400

  1. HI Steve We all live and learn. Well I’m the one who suggested using the sink Drain. Well it works great if you drill the small holes especially in plastic. Works without drill press but practice on something and maybe clamp. Metal will need drill press and sharp bits. Also best metal cases and thick and cheap from tentec. T series. I can give you several more places if interested. See one of my cases from China on the yahoo site for the MST400. Nice precut vent holes and speaker holes. 73 Ron WD4GWK pics on QRZ.com

    • Hi Ron,

      The sink drain is a great idea! At the time I had some speaker grill mesh I was going to use across a round hole. But when I drilled the hole the ~=3mm plastic lip back inside to the speaker grill mounted inside the case didn’t look any good. So with a large round hole what do you do? I mounted the actual sink drain in it. In hindsight it would have been better to simply use the drain as a template and drill the holes. Later I might get around to replacing the radio case top and do exactly this. But for the moment I’m off playing with building various portable antennas. Radio works a treat. 73, Steve.

  2. Can you give me an idea of the circuit you used to run the signal meter? I’m thinking of the same sort of thing with mine… Cheers and nice build by the way

    • Hi Josh,

      From memory it was called “Audio Derived S-Meter” and originally it came from Doug DeMaw’s “W1FB’s QRP Notebook” published by the ARRL, page 57. Although I ran across a reproduction of the circuit in some online BitX stuff. This was about the third circuit that I played around with and none of them were even remotely close to providing the correct meter response. But after the 3rd attempt I left it alone as this circuit worked at least as well or better than the others I had tried. I made a mental note to come back and solve the problem properly another day. So I calibrated my meter for S9 and anything much above or below that point is hopelessly misleading. Which pretty much makes it the same as most other S-Meters 🙂

      It wiggles around and looks pretty.

      I should mention that Leon, VK2DOB of ozQRP does offer the LED S-Meter add on kit for the MST which uses a micro processor. Which goes a long way towards solving the difficult problem of converting the large dynamic range logarithmic signal into a more sensible closer to linear signal for driving an S-Meter. Or in the case of Leon’s kit a bunch of LED’s. I did buy this kit and build it. Works a treat. So if you want something somewhat meaningful you might consider this add-on.

      I just liked the look of a real meter.

      73, Steve.

      • Thanks for the reply. I too like the idea of a real meter. I guess I will have to do some homework. I guess my next question would be, how to you find the radio performs? Are you happy with it?

        • The radio performs really well. Simple but well thought out and engineered. The only issue I have with mine is the lack of any easy way to generate a carrier tone so that you can tune an external ATU. But the Mark-II version of the kit addresses this issue and a bunch of others besides. So mine needs to be retro fitted with a simple code tone oscillator. Which would also allow you to send Morse code at a pinch. Not that I’m much of a code person (yet…). All in all, I’d happilly recommend this radio kit as a great portable QRP rig for field work. Which is what I use it for. 73, Steve.

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