Mobile on 8.97kHz VLF

Route taken from A to F (about 4km)

Today I did a fascinating experiment on 8.977kHz VLF using my 5W earth mode transmitter and a mag-mounted E-field probe and laptop running Spectran in the car. Basically I did a "drive around" test to see where the signal could and could not be copied.

Signal strength on 4km run between 2 villages

A continuous carrier was transmitted and I continuously monitored the received signal in the car. The drive was from the middle of the next village (Swaffham Prior), out through to the main road, then back along the main road to Burwell, around part of the village and then back home to the TX location. The signal was visible in Swaffham Prior at 5-10dB S/N, then disappears and returns on approaching Burwell where it is up to 40dB/S/N in 0.18Hz bandwidth. Within Burwell it is almost solid copy. The red timing ticks are every 30 seconds.

What I am detecting (I think) is the local E-field from the VLF signal in the ground, no doubt aided by local utilities. What puzzles me is why there is NO copy in between the 2 villages when there are, I think, pipes and cables in the road.

In the coming days this test is worth repeating locally in other directions and further afield. Fascinating to think a 5W VLF signal injected into the ground can be copied on a 19 inch whip on the car roof like this.

Another approach to 472kHz WSPR

An old work colleague Richard G4KPX has been doing more experiments with indoor loop antennas. Recently he has been using an indoor loop for 472kHz with an ERP of around 1mW. I just checked the WSPR database and see he has achieved some amazingly good results with 49 unique spots with best report from Sweden at over 1300km! Well done Richard.

G4KPX's WSPR results over 500km with just an indoor loop TX antenna

Optical NLOS test - next time pack everything!

This evening I set off to my Landwade location where I hoped to check the non line-of-sight (NLOS) signal level from my 481THz, red LED, QRSS3 beacon TXing from home. This time I'd carefully aligned the TX and adjusted the RX optical alignment in daylight, so everything should have been spot on.

481THz RX with iPod Touch 4g running SpectrumView

Then I realised I'd left a vital lead at home that allowed me to connect the optical RX to the laptop. Next time I need a checklist as it is a 10 mile round trip to the test site.

Instead, I tried to copy the signal using the optical RX fed into my iPod Touch with SpectrumView software, but the bandwidth was too wide to allow me to find the weak signal. I hope to repeat the test in the next week (with the laptop and Spectran set to 0.34Hz bandwidth), but this time with EVERYTHING packed for the test.

I was very annoyed with myself for forgetting this audio lead as it prevented a meaningful test being done. I also need to find a different NLOS test site that is less far to drive to but still at about the same distance (3.6km).

The limitations of my cheap tripod are also apparent: I need a much sturdier one that has a compass attached and much smoother pan and tilt.

8.97kHz earth-mode tests with mag-mounted E-field probe

Today I started some tests at 8.97kHz with my mag-mounted E-field probe (EFP) on the car roof. As usual, the transmitter was my 5W QRSS3 beacon feeding the 20m spaced earth-electrode antenna in the garden.

The logical starting point was to drive to my usual "strong" test site 1.6km from home and compare signal levels on the usual 80cm square RX loop with that on the EFP.  For reasons I have yet to understand the signal was NOT copied, even on the loop! What I did see was what looked like an FSK telemetry signal, possibly from overhead power lines close to 8.97kHz. I've never seen this before. Anyone know what it is?

8.97kHz 5W earth-mode signal at 0.4km on E-field probe

I then drove to my new QTH (due to be occupied in about 4-5 months time) which is 0.4km from the TX and sat in the car in the drive with the iPod Touch 4g running SpectrumView software connected to the EFP. The antenna was a short 19 inch whip. Signals were copied quite well (see photo showing "3" from my callsign). The bandwidth on SpectrumView cannot be narrowed enough to optimally receive QRSS3 and results would be better with the PC set to 0.34Hz bandwidth.

Tomorrow I'll have to find out why I couldn't see my earth-mode signal at the usual test site on either antenna. I'm also going to do some /M reception at 8.97kHz using the E-field probe and laptop with Spectran set to 0.34Hz or 0.17Hz bandwidth. With a continuous signal I'll be able to log the signal level as I drive around the village and nearby.

What IS amateur radio?

This is a question I keep asking myself. It clearly means different things to different people, but I am saddened by the trend to cheque book amateur radio.

In its early days the hobby was clearly about experimental radio: making receivers and transmitters that communicated over short distances, with many/most of the parts being hand-made, even down to the variable "condensers". Over the years this has changed for many (most?) amateurs and now one could be forgiven for thinking all that matters is how expensive ones new HF radio or antenna is, so one can boast about how wonderful ones station is to others on HF.

I was struck by the cost of the hobby, for some, again tonight when visiting http://www.bigskyspaces.com/w7gj/vhf.htm and looking at the massive and very expensive antenna farm at W7GI.  Now this 144MHz antenna, like many, antenna arrays at this amateur's QTH is aimed at reliable EME operation where large antenna gains help. But what I see is 16 very expensive antennas plus an equally expensive support structure, expensive coax and an expensive mast. This is just one antenna for one band. He has another very big array for 50MHz too, plus no doubt a shack full of expensive radios and linears. The rotator to turn this lot will be a very large device indeed.  Yes, successful EME operation needs big antennas and high power, but honestly is this AMATEUR radio still or semi-commercial experimentation?

I can understand why an amateur may want one 100W commercial radio as the "mainstay" radio for the shack, but I see many shacks loaded to the gunnels with very expensive radios that must have cost their owners well over £10k and in some cases well over £20k.  It amazes me how much money some amateurs must invest in their hobby. I had a decent job and a decent salary when I worked, but there is no way I, personally, could justify this sort of expense on my hobby. It's a personal view and I do not want to preach to others on how to enjoy their hobby, but I am fascinated that spending lots of money on radios seems to be the norm.

Are any readers prepared to share (in the comments) how much they spend, on average, a year on their hobby? £10, £100, £1000, £10k, £20k?  Just for the record, I reckon on about £2 a week (a couple of new HF transceivers over 12 years plus the odd accessory and components).  It is possible to really enjoy the hobby and spend less than the cost of a coffee every week.

My question is, what IS amateur radio?

472kHz earth-electrode WSPRing this evening

The 472kHz WSPR beacon has been running this evening using the 20m spaced earth electrode antenna described in my March 2013 RadCom article. A reminder that there is NOTHING in the air at all, just the wires along the grass to the earth rods.

Quite a few reports received and given already.

472kHz unique WSPR reports received so far tonight

The same earth electrode antenna will be used at the TX end of my VLF test with the mag-mount E-field probe RX tomorrow morning.

Stake out on 481THz

481THz RX on tripod with optics.

In the daylight today I went to the RX site used in last night's unsuccessful over-the-horizon (NLOS) optical beaconing test. I've now marked out on the ground (with sticks and stones!) the exact direction to aim my RX in when I return for a second try, hopefully tomorrow night.

Yesterday it was so gloomy that I could hardly work out where to aim, so this now means I can be within a few degrees accuracy on initial set-up. I've also adjusted the aim of the TX beacon optics. Visibility for Thursday night is forecast to be "very good" with cloud cover according to my Met Office app, so let's hope it works OK tomorrow.

The RX and 100mm optics are shown above. Note that the upper tripod extension (below the tilt arm) is rarely extended as the whole thing is then too wobbly. I need a more sturdy tripod. Also, the low cost gunsight scope (bought for just a few pounds off eBay) is of little use at night (too little light) but very useful in daylight.

Mag-mount E-field probe on 8.97kHz

Just as an experiment, this afternoon I modified my mag-mounted FET drain tuned E-field probe to work on 8.97kHz. The last time I rigged an E-field probe on 8.97kHz and went looking for my earth-mode signal results were very disappointing wih just a couple of places within 2km radius where the 5W beacon was copied, but tomorrow morning I'll see how well (or not) it works. To tune the FET drain to 8.97kHz I just substituted the 137kHz tuned circuit with an 83mH Toko potted coil in parallel with 4n7. Tuning is reasonably sharp. Whether the car grounding will make a big difference we'll see in the morning.

Eddystone User Group

If, like me, you owned an Eddystone communications receiver at some point in the past then you may like to look at the Eddystone User Group pages. Here you will find lots of data on old receivers, links to data sheets and service manuals and a lot else too.

In my case I owned a Mk 1 EC10 receiver similar to the one shown here. This was state of the art in the late 1960s when it sold for £48. By modern standards it is a pretty rubbish receiver.

481THz over the horizon test: no success tonight

Weather this evening was not suitable for the tests, although I did try. I set up the QRSS3 beacon pointing out of my bedroom window using the local windmill as the aiming point. This is on the top of our small hill which rises about 15m. I then drove to a spot 3.6km away over the hill to look for the signal with my sensitive RX and 100mm optics using Spectran to display the trace. Unfortunately this time the slight drizzle and murk was just too bad and no signal was copied, although I've had good results in the past at a very similar spot.

In daylight I need to recheck my beam alignment at the RX location as it was sufficiently murky to not see the local landmarks used to help aim the RX last time. Despite panning across 45 degrees of aim nothing at all was copied of my signal. I shall repeat the test in better optical conditions.

For those interested, the 1W 10mm diodes are available from http://www.ebay.co.uk/itm/350347623711.  You get 10 pieces for £9.26 with free postage and they are very BRIGHT.