Saturday 26 January 2019

QRPlabs Si5351A VFO kit


Once again today I have had the pleasure of building one of Hans Summers kits. Hans designs and sells, as QRPlabs, incredibly versatile and high quality radio kits, mostly based around a core Atmel processor control unit. Having previously built a six-band version of his Ultimate 3S QRP WSPR beacon transmitter (which can do so many more modes than that!) and the QLG1 GPS receiver to govern it, and having a need for an effective way to replace crystals in vintage military radios in order to test conversion to amateur bands, I decided to buy the QRPlabs Si5351A based VFO/Sig Gen kit.


The kit comprises a 2x16 backlit LCD module, the Si5351A DDS module, and the QCV control module. This is exactly the same as the U3S, the only difference being the firmware version of the processor chip, and some of the discrete components. The DDS module is capable of working up to at least 150MHz, and in this kit, produces two independent  outputs. One output is fixed frequency, set up in presets in the firmware, the other the VFO output. The above photo shows the PCBs after populating.


This kit comes with a rotary encoder with a push button switch action. This was the only place I went astray during the build, as I managed to mix up one of the encoder lines with one of the switch contacts, resulting in some rather odd things happening when trying to test!

After a good rummage around, I came up with a metal enclosure for it. I had hoped to use a die-cast box, but all my stock were either too small or way too big! But I had this sheet aluminium box kicking about Its a slightly odd enclosure as it has the seams of one half on the outside of the other, rather than hidden inside.

What took most of the build time was the marking out, drilling and cutting of the box.


 Somehow I managed to drill the encoder hole far too wide, but the washer supplied with it covers this error up,


Unfortunately I havent been able to complete the build today, as I discovered that I dont have any panel mount push buttons in stock, nor any suitable stand offs to mount the unit into the case with! Ive now ordered these, but they may take several weeks to arrive!


A quick test showed all to be well. One thing I discovered though which I hadnt expected, was that the firmware includes backlight brightness control. I had already installed the link for full brightness as I didnt expect this feature, which is used in the U3S, to be in this firmware. So, that link was removed and the correct link for processor control of the brightness added.

Im so pleased with how well this has gone together that I decided I just had to build another of Hans' kits! So, since I needed to measure the QLG1 GPS units dimensions (as ive asked a work mate to 3D print me a box for it!) and this meant pulling out the U3S, I decided that what I really need is a touch more power for WSPR ... so now the QRPlabs 5W HF PA kit is on order, along with an upgraded firmware chip for my U3S, which will control the PA and also give me the ability to control an antenna changeover relay. The HF PA kit has the same PCB form factor as the rest of the kits PCBs, so effectively just 'bolts on'.

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