10m AM Net in S.London (Wednesdays)

A 10m AM net has been started in South London, UK by Gary G7IRG. It meets on 29.05MHz (AM mode) on Wednesdays at 9pm local time. Last week the net had 3 people on: G7IRG, G0KRT and M0GPG. If you live in this area, or indeed anywhere, why not see if you can hear the net and give them a call?

When 10m is wide open, as it will be in a couple of years time, the band between 29.00 and 29.1 MHz will be filled with AM stations from around the world.

6m when the band is quiet

6m is a band ripe for exploitation when there is no DX around. When there is sporadic-E or F2 DX about, people use the band in thousands and some have worked DXCC. However, when conditions are not good, it is left to a few dedicated enthusiasts to work random MS and tropo and ionospheric scatter mode QSOs using QRO with modes like JT6m. The amount of LOCAL 6m activity, at least here in the UK, is very low indeed.

We have 2MHz of band in the UK (4MHz in the USA) and it is a pity more use is not made of this fine band for local QSOs using simple QRP homebrewed equipment. It is an ideal band for QSOs up to around 20 miles or so and much quieter than 160m or 80m, which can be very noisy these days.

3 transistor SSB transceiver

http://www.intio.or.jp/jf10zl/3trssb.htm

The website of Kazuhiro Sunamura JF1OZL is magic and contains some superb ideas for QRP enthusiasts. Every time I return to this site I find something to enjoy and to inspire me. Take for instance the 3 transistor 6m transceiver he describes: it is wonderful. Kazuhiro San, if you read this THANK YOU for your great ideas.

10m or 6m QRP DSB ideas

Having finished my SixBox 6m AM transceiver, my mind is now turning to ideas for either a 10m or 6m QRP DSB transceiver. I have already breadboarded a 10m version in separate sections (RX based on the Neophyte RX, a DSB TX based on a single balanced diode mixer), but I have still to breadboard a mixer-VFO based on the NE602 which would be useful for either band. Actually a fundamental crystal x2 would give around 25-30kHz shift on 28MHz and around 50kHz on 50MHz, so this may be a simpler, and adaquate, route. However crystals "to order" are expensive these days, although the spec (temperature, cut frequency accuracy, etc) would be very low.

Today I noticed another 6m DSB schematic from a Japanese ham. There are plenty of good ideas from JA land where, despite commercial rigs, homebrewing is still in strong. See http://www6.plala.or.jp/jr8dag/micro6dsb/mi6dsb02.htm for JR8DAG's schematic. In my view, this is a rather complex schematic and I am sure it could be simplified.

SixBox 6m AM QRP rig now boxed

Today I complete this project and put the 50mW AM transceiver into a small diecast aluminium box. Using a 9V battery inside the box the rig puts out about 20mW. From an external supply it is about 50mW. The polyvaricon tuning capacitor works very well and the RX tunes from around 45MHz to 70MHz. Already it has been useful as an indicator of Band 1 activity.

Overall, I am pleased with this little transceiver. It was all done with the most basic of test equipment and is a circuit that should be easy to copy. Now to try to get some local 6m AM activity going! It would be very nice to make a PCB for this project. I'm thinking about it....

My next project is either the long intended 10m DSB rig or a DSB version of this 6m AM rig. However, to be useful this would need VXO control and a 3rd overtone xtal will not pull very far.

SixBox QRP 6m AM rig closer to completion

Today I did a full rebuild of the 6m QRP AM transceiver on a much smaller (dead bug style) board so that it will fit in a small diecast (or aluminium) box. In the course of the rebuild I tried out the RX varicap tuning idea which works, but I was unable to move the frequency more than 1-2MHz before the superregen stopped oscillating. I tried a 1N4007 and the collector-base junction of a 2N3904 as varicaps. In the end I decided to use a low cost polyvaricon tuning cap in series with 22pF and this covered 6m plus a few MHz either side. I also ran the PA stage in class C and this seems to improve the modulation. Here is a picture of the SixBox after rebuilding, but before I started the testing. Because of family commitments I shall not be able to finish this now for a few weeks but I am looking forward to some local "DXing" with this around the Cambridge area. It is funny but working local stations with this is (almost) as much fun as working real DX with a proper radio!

SixBox 6m AM QSO

A solid QSO this evening with G6ALB (2 miles away) on 6m AM using the 50mW SixBox rig with vertical antennas at each end. In the other direction, using the super-regen RX at my end, we did some sensitivity tests with Andrew putting a signal generator on and gradually dropping his AM modulated carrier. I was able to copy his signal when it was reduced to 0.5mW.

I also tried to receive a 7dBm carrier from Andy on 70.26MHz AM using the retuned super-regen RX, but was unable to hear it, although we were both using 6m antennas which were not resonant on 4m.

Currently I am putting a rebuilt SixBox in a real box. Later, I will make a breadboarded DSB version.

More details on the SixBox page of my website.

G3XBM webpages have moved

Today I switched my webspace from NTL to Google Sites. I've been having issues with FTP connection to the NTL webspace for weeks and the Virgin Media "help" has been anything but. I do so HATE having to press button 1 for this, 2 for that etc and in the end getting connected to someone who doesn't have a clue. No problem with the help centre being in India, but I would like to get help in the end. No joy.

So, I decided Google Sites would be a better bet. Google Sites is free, allows 100M of webspace and pages can be edited without HTML. There is also good feedback on site visit statistics using Google Analytics. The downside is the page formatting I can use is less complex, less fancy, but this is no big deal.

If you go to http://www.g3xbm.co.uk you will be directed to the right place.

In praise of the Asus EEE Netbook PC

For over a year I've used a little 7 inch screen Asus PC701 Netbook PC running the preloaded Linux operating system "as is" as my main PC. It has never crashed, always boots up in seconds, does 95% of what I ever need from a PC and is inexpensive. It went with me to New Zealand on holiday (allowing me to do a daily blog from hotel rooms and to video Skype our sons) and fits easily in the hand luggage. Today in the UK the version ships with 8GB of solid state memory (mine just has the 4GB) from around £151 brand new.

If you want simple, low cost and effective computing you'd be hard pressed to beat this little beauty. Of course there is now a lot of choice in netbooks with larger screens, XP etc, but for me the original Asus EEE is hard to fault.

SixBox 6m AM (improvements)

Been doing some more work on the SixBox AM transceiver and have come up with a simpler and better TX lineup. I abandoned the osc/multiplier in one stage and went instead for a 3rd overtone xtal followed by a modulated buffer and PA. The third overtone oscillator values shown ensure the crystal reliably oscillates on its 3rd overtone.

The little PA and buffer work well with just T37-6's as (untuned) chokes in the collectors of the buffer and PA followed by a low pass filter. This arrangement is very stable and simpler than before. Modulation is clean and deep. As it stands it produces 50mW of AM on 6m. A further single stage linear PA would take this to around 1W of AM, but I will leave this to others.