Inactive week radiowise

This week I've been very inactive on the radio because we have had our grandson's 3rd birthday party here with his French grandparents (neither of whom speak English) staying along with his mum and dad. Still, a lovely time was had and he got lots of nice presents. By the way, he now knows the difference between square waves and sine waves and loves going "oo oo", which means fiddling with the audio oscillator and scope.

Looking for G3XIZ on 8.9719kHz VLF

Looking for G3XIZ on 8.9719kHz - maybe a faint trace??

Between 2000 and 2200z this evening G3XIZ has been transmitting on 8.9719kHz VLF with his Marconi vertical and about 20W RF into it. I've been monitoring with my earth electrode antenna, a preamp/filter and a PC running Spectran on 0.17Hz resolution, but don't think I've seen any sign of him.

Real QRP on 8.760kHz today

Weak trace at 1.5km from the 320mW TX by earth mode

320mW 8.760kHz QRSS3 transmitter

Having blown up my 4W transmitter yesterday I built a smaller QRSS3 beacon TX today that puts out 320mW into 50 ohms. I connected this to the earth electrode antenna and went out with the loop and E-field probe and PC to see how it performed. The signal was copied weakly but solidly at 1.5km away at the local National Trust carpark (see picture from Spectran showing the XBM part of may callsign). An attempt at 5.1km was unsuccessful although faint traces of the line at 8.760kHz may have been visible.

How to be stupid ...follow me

Just managed to blow up my 8.76kHz TX by putting the supply the wrong way round: took out the 4060, 5-Vreg and several electrolytics.The TDA2002 was also damaged. Rebuilt the keyer and freq gen part OK but now need to source a new audio PA IC or module. Now I have a reverse protection diode across the pins! You learn the hard way.

In the meantime I may try even lower power with my trusty 2N3904/3906 1W PA and see if this can be seen at the NT carpark (1.5km) and at Lord's Ground Farm (5.1km). Also, as this PA is efficient and runs cold for ever I could try 1 day on, 1 day off, QRSSSSS and see if more distant people could copy it using very narrow bandwidth reception as per DK7FC's tests.

QRP at AA1TJ

It's time to remind people of the wonderful circuits and ideas at Mike Rainey AA1TJ's site. Always full of amazingly simple designs that really work. See  http://www.aa1tj.com/radio.html

UK first transmission on the Dreamer's Band (8.760kHz)

Signal received at 5.1km from home QTH on 8.760kHz VLF

This morning 0915-1115 GMT I transmitted a QRSS3 beacon signal on 8.760kHz under the terms of my NoV recently received.  I think this is a first in the UK, legally at least.

8.76kHz TX

TX was 4W from a TDA2002 audio IC matched into earth electrodes 20m apart. The beacon signal was provided by a K1EL keyer chip and the frequency reference by dividing down an HF crystal by 512 times in a 4060 divider IC. Reception was possible 5.1km away from the transmitter location, detecting the signal with an 80cm loop fed into an E-field probe (Hi-Z input) into Spectran running on a WinXP PC. Best reception was always with the loop flat on the ground suggesting the main mode of propagation is utilities assisted earth mode. Comparing results on 8.76kHz with those at 838Hz earlier in the summer, my first impressions are that signal levels are some 6dB weaker, but more careful tests will be needed.

500kHz interference

In the last few days several stations across Western Europe have noticed a strong wideband signal that is severely impacting reception between 498-502kHz. This appears to be a NATO test transmission for a marine data system that may be introduced in the near future.

8.75kHz VLF transmitter ready

My small 4W, crystal stabilised, 8.750kHz VLF transmitter is now ready to test having fitted the crystal and 4060 divider this morning. All being well I'll test this Wednesday or Thursday when I've optimised my soundcard settings on the PC used at the RX end.

Preparations for Dreamer's Band Tests

This evening I modified my loop antenna and VLF preamp to better optimise them for use at 8-9kHz and also modified my E-field probe antenna. So, on the RX side I think I'm ready with the hardware. By Wednesday I hope to have the 4060 divider behind the HF crystal to give me a stable 8.750kHz source for the TX. If the weather is reasonable I should be out testing in the Fens locally by Wednesday or Thursday.

First "Dreamers Band" UK test next week

As is required by my NoV, I asked the Met Office for permission to transmit in the 8.7 - 9.1kHz band next week Tuesday to Friday 0800-1800 GMT and they've confirmed it's OK.

My initial tests will be a repeat of the earth-mode tests done at 838Hz earlier in the summer using the same kit  with 4W to 20m spaced earth electrodes. I'll also test with the 70m sq wire loop antenna used for 136 and 500kHz. The most likely TX frequency will be 8.750kHz (4.480MHz xtal divided by 512). I'll find a means of getting on 8.970kHz later. Modes will be 12wpm CW and QRSS3 initially.

These local tests are not in the same league at all as DK7FC's and I'm only expecting a few kilometres at best. However, it is a start and it allows me to test TX and RX equipment and different PC packages.