OBSERVATIONS FROM SCOTLAND                            21 Aug 2007                                GM1SXX

The MKARS80 80M QRP SSB Transceiver.

Question.... what costs £44, comes as a complete kit and transmits and receives LSB on 80M?

Answer.... the MKARS80 Transceiver kit.

Nicolas Pike M1HOG put me on to this excellent kit from the Milton Keynes Radio Society. In short. It's a kit transceiver for the 80M band. This is no bare kit, it's a fully featured LSB 5 watt QRP transceiver with a digital display and Huff&Puff VFO stabiliser.

Of course, 80M is not everyone's cup of tea. I'd have much preferred a 20M version, but at the price (8 Fish Suppers-worth), the temptation was way too great and I had to buy one of these radios.

The photo above shows the MKARS80 Transceiver minus it's PIC microcontroller.  The LCD display panel mounts on the track-side of the PCB by means of connecting pins.  Size-wise, it's a bit smaller than a standard Eurocard. It's quite a 'busy' kit with closely packed parts but if you can solder to a decent standard and have some sort of magnifier... I use a cheap (£3) headband type, you should be able to complete this kit.  It definitely helps to have a temperature controlled iron with a small tip. The transceiver is a single conversion superhet design with a 10Mhz IF and a conventional VFO that is further stabilised by a PIC based Huff & Puff stabilisation circuit. The transmit strip uses the ubiquitous IRF510 automotive power-fet in it's PA, a good choice for a 5W 80M radio. The empty socket above takes the PIC microcontroller.  TX/RX switching is included and the user only needs to provide a headset and a cheap electret mic to get this baby on the air.  The PCB is a PTH type with solder-resist mask and I'd personally rate it as the best one I've worked on to date. The component positions are clearly marked in white on the green background and whoever made the PCB's did a first class job of work.

The IF as I've mentioned is 10Mhz... 9.999 really, and uses a simple filter constructed from 4 standard 10Mhz xtals. The circuit as you can see uses a number of small (2802) pig-nose toroids that have to be wound plus four small ring core coils and the output matching transformer which is the large pig-nose in the top left corner of the photo.   The manual makes some good suggestions for winding the trifilar toroids such as twisting the loose wire ends together and soldering them to make winding easier.  Another trick that was not mentioned is that you can use a darning needle to 'stitch' the wire onto the toroids. Unlike other kits I've built, a generous amount of the different wires sizes is supplied.. enough to cope with mistakes!  After I wound the toroids, I dressed the various wires into their correct positions for soldering then epoxied the toroids onto the PCB in the correct places using a trace of epoxy applied with a Q-Tip. This makes it a LOT easier to solder the wires into place.  The Epoxy MUST be applied sparingly of it could get into the holes for the wires... and you DONT want that!  Oh, and don't forget to tin the leads for the toroids before you glue them all in place.  Like most people, I hate winding toroids, but doing the ones for this radio was quite painless really.  The resistors used in this kit are very small wire-ended types and my eyesight is not up to reading the colour bands so I checked both the resistor and capacitor values on my trusty EBay special AVO LCR meter before fitting them. 

This kit was a doddle to build thanks to the absolutely top-class instructions... available as a download at ..

Transceiver Construction Manual

The kit has an option to purchase a suitable metal cabinet for a few pounds extra (less than the cost of a Fish Supper), that is a nice fit and very lightweight. Some 'metal-bashing' is required to cut the aperture for the LCD display and other holes. Alternatively, you could put it in a standard plastic case, but I think the metal one is probably lighter. as well as offering screening.

The PIC microcontroller used is a 16F818 type (flash device) and the source code is available for anyone who wants to personalise their radio or perhaps add a few extra bells & whistles.  The LCD display displays a short 'start-up-message before reverting to showing the frequency, supply voltage and Huf&Puff correction as standard.   Using a PIC and LCD brings a new dimension to this relatively simple radio and I like it a great deal!

 With a trail radio, it's VERY useful to know the battery voltage.

KOKUPS!  Well being me, I had to make one. I accidentally placed and soldered a capacitor in the wrong holes.  Heating gently and rocking freed the leads and I used a solder-sucker to clear the holes of solder.   My fault for being in too much of a hurry and easily remedied.  I was particularly impressed with the really well-written construction manual for this radio which helped keep me on the straight and narrow path.  For me at least, the manual gets 10/10 as does the truly superb PCB.

After completing the kit, I did a quick ohms check of the power supply lines and connected the radio to my variable voltage PSU.  The voltages all seemed acceptable. The radio uses a pair of 100ma rated fixed regulators, type 78L05 and 78L08 and the outputs looked fine to me. There were signs of audio at this stage and a finger applied to the 10Mhz filter produced some output.

I switched off, plugged in the PIC and connected the display and switched the radio back on. Poking a piece of wire into the BNC produced signals but the frequency was too high on the display. I followed the instructions to tune it to the correct range and was rewarded by quite a few stations on 80M. The audio quality is absolutely superb, better than radios costing a LOT more.

The transmit side will have to wait till tomorrow.  10:30PM and I'm off to bed.   I'm a happy bunny.  This is the best radio kit I've built to date. You have to use one of these babies to realise how good a simple single-conversion superhet can be.  The audio quality reminds me of my much loved Yaesu FT200 transceiver and I could listen to this all day without ear-strain.  Rather different from some other radios where it's a bit like listening down a drinking straw.

73 Al.
GM1SXX
PS, we like to use Fish Suppers as a term for financial reckoning.