MST400 SSB QRP Transceiver

The weather was miserable yesterday, so spent some time stuffing components into MST400 transceiver boards in the workshop.  ozQRP in NSW make this kit, and it looked nice and cleverly designed to use commonly available parts , for example 10MHz crystals for the SSB filter and 10.7 style IF transformers etc. for the front end.  At 5W out it would make a nice portable radio for SOTA mountain topping.

I am surprised that the kit is not more popular.   I chose to built the 7MHz variant.  There are only a few band critical components anyway.

The short form kit is very reasonably priced and was able to get most of the other rats and mice components at Jaycar yesterday.  After about 3 hours most of the parts were loaded,  Jaycar were out of a few things, so will have to try another store.  The LCD display is an Ebay item for about $2.80 delivered, so will be a wait on that.

Documentation for the build is excellent.  The plan is to try the transceiver kit out on a SOTA activation.

With a DDS VFO it should be a fine radio if it all works, there is a tuning rotary encoder included with push control for frequency steps.   The power supply current should be reasonable at about 80mA (VFO) +70mA (transceiver).  The VFO is a bit thirsty as expected, maybe a switching regulator with appropriate filtering will make a big improvement there as a linear reg takes the supply down to 5V.  Thinking about an all aluminium case rather than the plastic case recommended.

I plan to experiment with the final amp as 10W would be nice, the IRFZ24 device will be worth trying as lots on hand.  Here is progress so far:

MST400 boards

2012-10-06: Haven’t had a lot of time to work on the MST lately, but have managed to obtain the last missing components from Altronics.  For the time being I will use the plastic box recommended in the instructions for a housing.  This is probably the fastest way to get it up and running.

Waiting for the LCD display now from Ebay. I have one or two in projects in the workshop, so might rob one for the short term.

Next job is some metalwork for the front and rear of the plastic case, the panels that came with the case are plastic.  Really not that much to do after that.

2012-10-09: Had some time to do a bit more, its pretty well complete now except for the LCD display and that could still be a week off.  The front and rear panels are aluminium with etch primer and flat black paint (they look plastic in the photo).

Getting there!

Wondering about replacing the 4 pin mic connector with an RJ-45 socket so that I can use an FT817 microphone or one of the several commercial fist mics that I have on hand.  It turned out that I had soldered the rotary encoder to the wrong side of the PCB.  As I was originally soldering it, was thinking, gee, I would have a hard time removing this due to the size of solder lugs and thermal sinking of the copper pads on the ground plane.  Of course, Murphys law prevailed and I had to remove it and resolder it on the other side of the board, which took some time and effort.

2012-10-13   It works!   The LCD display arrived a little earlier than I thought it would so connected it up, mounted the VFO pcb and terminated the last few connectors

and mounted the speaker.  I found an old Pye microphone that checked out OK and put a connector on it.

Put some power on it with current limit set on power supply and the LCD lit up with frequency and voltage.  The alignment procedure was very straight forward, everything tuned as it was supposed to.  It seems reasonably sensitive and transmit power output is a little over 5 Watts as specified.  There weren’t any signs of instability or birdies when tuning or varying power supply volts.   Now to try it out on air!

Update: With the MST connected to an offset centre feed dipole, it was receiving a QRP SOTA activation from the Victorian high country very nicely (VK3WAM).  I gave Wayne a call and he answered straight back with a good signal report.  A VK1 and a VK5 also chimed in and gave nice signal reports, with 5×8 in VK1.  So it certainly works well!

Update 2012-11-15:  A software update was posted on OzQRP for the MST400 recently that gives the ability to save the last frequency and tuning step through a power cycle.  The update was requested by email and promptly received (V1.1).  To program the software I used this programmer hardware wired to a 6 pin female ISP connector to match the VFO board (which looks to be wired as a standard).
With the interface connected to Com1 on the PC, I used AVRDude as the programmer (which is part of WinAVR).  AVRDude is command line based but pretty easy to use once you get used to it.
The command line for programming the new VFO software to read the old software and save it just in case is:
avrdude -c ponyser -p m8 -P com1 -U flash:r:\user_data\readfile.hex:i
where the current software is saved in readfile.hex.

To write the new file the command line is:
avrdude -c ponyser -p m8 -P com1 -U flash:w:\user_data\DDSVFO.hex

The new software loaded fine, although at first it didnt look like it was saving the old frequency on power down, but this turned out to be me not setting the option to save in the VFO configuration.

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20 Responses to MST400 SSB QRP Transceiver

  1. paul owens says:

    Hi you have helped me in knowing I am not loosing my mind …..I have been after finding out what the model number is of the pye microphone you have..I hope you could help….regards paul

  2. Paul Owens says:

    Hi Glenn,cheers buddie for your reply..much appreciated Glenn.Would be great if could get the model number.Would you know also what radio it came with to help in my search,cant believe how few there are about yours is the first i have seen in weeks of looking..haha
    regards Paul

  3. Paul Owens says:

    Hi Glenn did you get chance to get the model number of your pye mic …cheers
    regards paul

    • vk3yy says:

      Hi Paul, I should be able to get back to you mid next week. Cheers, Glenn.

    • vk3yy says:

      Hi Paul,
      Now back at home but cant find the remains of the transceiver that the mic. belonged to. From memory (hazy) it was a VHF AM transceiver that was fairly compact. I will ask a friend that worked at Philips in the next few days if he can identify it.

  4. Paul Owens says:

    Hi Glenn
    thank you very much for all your help…
    kind regards paul

  5. Andy says:

    It looks like the microphone from a Pye Seeker AM transceiver made for the NZ 66-88MHz or 88-102 MHz band (called the A and B bands back in the day i.e Early to mid 70s) They had an excellent audio response. From memory, these were 600 ohm dynamic microphones actually made in Japan by the Merry Corp, and also used (with different labels, of course) on the Tait T196, T198, T199 and T500 FM transceivers.

  6. Leon (the designer) gave a presentation about the MST to the Canberra Radio Club in April or May 2013. The history of the design and the success (about 200 kits sold to dozens of countries) was all very interesting. Yet another kit to buy and build.

  7. Bill Thompson (VK2YKW) says:

    Bill VK2YKW, I’ve built two of these kits, one was the first kit and the other, the series 2,both are excellent builds and work extremely well with great reports, recommended builds. thanks 73

  8. Norm Lee says:

    G’day there,
    Name here is Norm, call is VK5GI. I’ve built the 40 m version & it works very well indeed, currently building up the 80 m version. I used an N3ZI dds vfo in the original rig, but am considering using the one from Leon this time. Just interested what vfo you used on your rig, and any comments on Leons?
    Kind regards
    Norm VK5GI

  9. Dündar Yasa says:

    Hi friend, I checked the shematic, there are 6 IC’s in shematic, but in PCB board, it seems only 5 IC’s. I think the 6 th IC ( U6 ) can not appear.(Which used for transmitter board.)

    • vk3yy says:

      Hi Dundar, in my schematic there are only 5 IC’s, U1-SA612, U2-SA612, U3-NE5534, U4-LM386, U5-SA612. Are you looking at the schematic for the new model MST2 transceiver?

  10. Dündar Yasa says:

    Okay Glenn i guess, i look for the new model MST2 transceiver. Thank you for your answer. 73.

  11. Hi, I have just completed my 40m mst400 and powered it up on Sunday. Worked first time, simple alignment and overall, works very well. Rx is quiet, filter sharp enough, signals on 40m vary across a very wide dynamic range which you can manage by riding the audio gain. The vfo is excellent, the DDS makes a homebrew rig feel like a proper commercial radio. I am also hoping to take it portable in the future. Regards Paul vk3hn.

    • vk3yy says:

      Hi Paul, it is a nice little radio, I assume that yours is the new version MST2? Great to here yours is working well. There must be a few out there now. Regards, Glenn.

      • No, mine is Mk 1, I bought it a year ago and sat on it until the last few months. I have been QSO-ing over the past few weeks since I got the tx going. Last weekend I got 59 from ZL2OK, and *drum roll* 4×4 up to 5×5 from AF6TC in San Diego, both late at night on 40m. Aerial is a 40m dipole. Qrp is great fun when it works!

        I am thinking of replacing the LM386 audio stage with the Mk2 TDA7052, to get the audio AGC. Other than that I am very happy with the Mk1. Experience suggests it will make a fine portable/SOTA radio.

  12. Update, I have now activated three summits with the radio and a dipole, and its suitability is great. Recommended for anyone interested in SOTA or portable work with a home brew radio. Am thinking about what to build next, perhaps a 20m version.

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