Saturday, 17 November 2012

MRM-30 goes QRO

One of my first Manhattan style construction projects was a RockMite 30 circuit. I had upgraded my RockMite 20 with a Hamgadgets memory keyer chip, this left me with a spare keyer chip. I thought a great way to use the spare chip was to build a RockMite 30. I had seen pictures of other home brew RockMites on the Internet and I thought it would be something I would be able to do.
I wanted to make an 'ultimate' RockMite, so I put in a VXO circuit and also the output PA transformer modification promoted on the Yahoo RockMite Group. I used a 2N3866 transistor for the PA. I was hoping for about 800mW of RF, but I was disappointed that the rig would only put out 520mW. I then upgraded the output filter, this promotes a super clean transmit signal from the rig, but it introduced another 20mW of loss, I was now only getting 500mW from 12 volts.
I was still pleased with my efforts though, it was the first home brew transceiver that I had attempted and it did work. My local radio club put on a camping and amateur radio weekend in July 2011 and I tried out the newly completed using an inverted vee dipole. I was pleased to work HB9UH with some very shaky QRS CW! It turns out that Hans, HB9UH, is a member of the Helvetia Telegraphy Club, a group dedicated to promoting the use and teaching of Morse Code.
The QSO with Hans remains my only contact with the rig. My CW has improved a bit since then, I have been using another Manhattan style RockMite 30 rig which I built to take part in LA1KHA's PP3 challenge and also an MTR by KD1JV for my SOTA activations this year. The MTR is my favourite rig, I rate it above everything else, so my other rigs have been gathering dust! I decided that I need to try to use my other home built radios.
I was always disappointed with the low power output from the home brew RockMite 30 - (MRM-30), I thought it would be more useful for SOTA if it could put out a bit more power. A couple of watts on 30m should be very useful.
I looked in to a design for a 5 Watt RockMite 80 on the Yahoo group, the design used a CB PA output transistor, a 2SC2166. I thought that I could use a similar scheme for my rig. I managed to locate an Eleflow 2SC2166 at a reasonable price on Ebay.
I replaced the 2N3866 output transistor on my rig with a 2N2222A and I used an adapted version of the 1.5W PA circuit from the Small Wonder Labs SW-30+. I knew that the circuit would be capable of a couple of watts at 10MHz. I built the circuit in to the RockMite this week and I was pleased to measure the output at around 2 watts, I'm well pleased with that! I could probably get a lot more out of the circuit, but I happy to stick at the 2 watt level. The signal still looks very clean, so I'm really happy.
I hope to try the rig from a SOTA summit soon, Winter Bonus is only a couple of weeks away!:-)
I haven't added any RX filtering yet, I'm going to see how bad it is without first!
New 2 watt output stage squeezed in (right hand, middle)

Friday, 16 November 2012

Buckden Pike - Remembrance Sunday

For this years Remembrance day, I decided to go to the Buckden Pike War Memorial to do the two minutes silence at 11am.

A Wellington bomber crashed on Buckden Pike in January 1942, killing all but one of it's crew. The survivor erected a memorial cross at the crash site to pay tribute to his fellow servicemen.

Buckden Pike, 2303ft, is classified as a 'Marilyn', so it is included in the SOTA scheme (G/NP-009), being worth 6 points. My plan was to operate my radio from near to the trig point and claim the SOTA points, before moving on to the War Memorial, something like 1km away.

I parked in the public car at Buckden and set off walking along the bridle path at about 0745utc. I was pleasantly surprised to find that the once boggy path had been properly surfaced and was now easy to walk on.

I gained the summit at just after 0900utc, it had taken around 80 minutes from the car park to the trig point, much faster than previous occasions.
I'd taken along my MTR (Mountain Topper), a little two band CW rig, built into an Altoids tin. Using a 1000mAh LiPo battery, I was on the air on 7.032MHz at about 0925utc with about 2.5W. I was amazed at the pile up that quickly developed! I found after about 20 minutes of operating, my brain got a bit fried and I started making a lot of mistakes. I took a 5 minute break from the pile up, but upon asking 'QRL?', I was greeted with another wall of chasers! I moved on to 14.058MHz, again I was met with a big pile up after only a few minutes. My time soon unfortunately run out, so after working Barry N1EU in Delmar, NY, at 1040utc, I had to leave the chasers and tear down the station. 34 QSO's were in the log, so the little MTR had done a great job, I'm sure I could have worked many more stations given a lot more time. I had actually operated a little too long really, it was 1050utc by the time I left for the memorial, and it was about 1km away!
Unfortunately, the route to the memorial is very boggy indeed! I simply didn't have the time to carefully pick my way through the bogs, I just had to run like mad! I reached the memorial at 1058utc, I'd just made it and I was quite soggy too! There was quite a mixed gathering of people at the memorial, and we all fell silent for two minutes at 11am. I was persuaded to pose for a group photograph, although I didn't know any of the other people there! For once, the photos should turn out OK, the weather was actually very nice, usually the visibility is very poor at that time of year, with thick fog being the normally expected conditions. My camera didn't record the memorial pictures properly, so I don't have any pictures of the people at the cross :-(
As you see, the weather was fantastic -
73 de Colin, M0CGH