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:
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).
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
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.