10m DSB rig progress (some)

Today I spent a little time on the transmit strip of my 10m DSB transceiver project. I started with the single balanced mixer using a T50-6 (yellow) toroid tuned to 10m, with LO injection from a signal generator and LF via a small audio preamp from an audio generator. For now I used a 1kHz tone to ensure drive levels were OK. Output is currently 20mW pep with 2 small 2N3904 linear stages following the mixer. To reach a useful RF level I therefore need another 20-23dB, easily done in two more stages. This would take me to around 2-3W pep.

HE3OM on 137.7kHz this evening

HE3OM (Switzerland) is currently active during February using an old broadcast antenna 125m long vertical. Signals in Europe are very strong despite an ERP of just a few watts. This was the QRSS3 copy this evening using Spectran and receiving on a pair of untuned earth electrodes 20m apart directly into the FT817 which is deaf at 136-137kHz, i.e. no matching and no preamps.

70.210MHz test with M0AFJ

M0AFJ's 4m CW at 75km tonight

This evening I did a test with M0AFJ in Milton Keynes about 75km west of me on 70.210MHz SSB and CW. Tim was using 80W to a 5el and I was using about 800mW into my loft dipole. M0AFJ was quite reasonable copy at times (see Spectran image of his CW - about 20dB over the noise) but Tim thinks, at best, he just copied the odd fragment of my transmission. With 20dB difference between us the result was not unexpected. I appreciated Tim trying though as I have now copied 3 stations on the band G6ALB (3km), GB3BAA (89km) and M0AFJ (75km).

4m transverter schematic

70MHz (4m) 1W pep transverter

The schematic of my QRP transverter for 4m (70MHz) is attached here and is also available on my website. Can't promise there are no errors but this is close to the real circuit as implemented. If anyone fancies having a go at this please remember this is a starting point and some optimisation of components and tuned circuit values may be needed with spreads in parts etc. As far as I am concerned this project is now complete and I have taken it as far as I want to for now.

My first 4m QSO this evening

Using my 70MHz homebrew transverter I managed my first ever 4m QSO using my own callsign this evening. I worked G6ALB on 70.2MHz SSB first and then we QSYed to 70.26MHz for an AM and an FM QSO. Reports both ways over our 3km path were fine even though we were cross-polarised. We invited others to join us, but no-one else was about. Years ago (1968) I did work ZB2VHF on 70.26MHz AM when running 4W from our university club station G3OUL.

Signs of springtime

My wife Lis with the snowdrops and aconites

Today my wife and I went for a walk to a quiet spot not far from here where we go every year about this time. At last there are signs of spring in the air with masses of white snowdrops and yellow aconite flowers. Winter is nearly done.

Look at those sunspots!!!

This morning the sunspot count is at 84 with a solar flux level 107, the first time I've seen these figures in very many years. Already PA0O is being spotted by VK2KRR on the 10m band using WSPR. If numbers like these start to become more common, as they should  during the climb up cycle 24, then 10m will be back to its old form with worldwide DX almost every day. Yippee!

Simple Sideband QRP 10m transceiver started

A long overdue project of mine is a QRP 10m simple sideband (DSB) transceiver. Having got the 4m transverter working (circuit to follow) I'm now starting work on this project in time for the summer sporadic-E season. A website to track progress on this has been started. See a Simple Sideband 10m Transceiver. With any luck this will be breadboarded by mid-March. I have included lots of links to other 10m designs from which ideas will be (or have already been) gleaned.

New record on 30m WSPR

For a change this evening I put my 5W WSPR beacon on 30m (10MHz). To my surprise I got a report from VK7DIK at a distance of 17169km. This is a new distance record for my WSPR exploits. Others have, I know, managed this sort of DX with mW powers, something that I will have to try at some point.

4m transverter boxed and finished (for now)

G3XBM 4m transverter - finished (for now) with 2-3W pep

Another good day today saw the 4m transverter completed and even boxed. I also did the FT817 DC switching mod  to put 5V DC on the antenna pins when on TX. It was easy to do, with care, and made the transverter switching so much easier. Don't understand why it was not there as standard for the sake of 1 capacitor and 1 resistor. The limitations with the current design are:

• IF breakthrough rejection at 28MHz is not brilliant, as one would expect from a single tuned circuit on the NE602 input. I can change the input to a top coupled pair to help, but will see how it behaves on-air first.
  
• LPF on the PA is just a single 3 component Butterworth. At some point I should add another section, but as the drivers/PA are linear all the way through, the 2nd/3rd harmonics should be reasonable already.



GB3BAA 4m as received

• The TX strip has DC power on it even on RX. I need to arrange to switch this off later, but I am not worried that there is another 50mA or so when on RX at the moment.

This evening I have rigged up a horizontal dipole for 70MHz in the loft and am ready to find some locals to work. So far just the 70.016MHz GB3BAA beacon 89km away visible well with Spectran (20dB S/N).