Earth mode VLF tests with E-field probe RX on car

As an experiment today I rigged up an E-field probe on the car to try to do something similar to LA3EQ's earth mode tests of the last few days. Instead of WSPR I used QRSS3 on 8.76kHz putting my usual 5W into the earth electrodes (one connection to the copper pipe ground and one at the bottom of the garden 20m away). The E-field probe consisted of my 1.5m long whip into an MPF102 source follower feeding a 2N3904 emitter follower with roughly the same arrangement as the PA0RDT E-field probe. The probe was attached at the top of a 2m long PVC pipe poking out of the rear window vertically. The actual E-field probe was powered by an internal 9V battery and was mounted about 1m above the car roof.

With the laptop PC running Spectran on the front passenger seat I was able to drive around and glance at the screen whilst moving. In the village there was a reasonable copy of the signal but outside of the village I only managed to get a couple of places 1km apart where the signal was strong enough to copy. One was at 2km and another at 2.1km. Compared with a loop on the ground at the same spots last year the signal was at least 10-20dB weaker. Although I am getting reasonable copy of the 11905Hz Alpha beacon the signal level is around 10dB down on the level on the 80m sq loop at home. So, maybe the E-field probe can be improved still.

In summary, with utilities assisted earth mode, for that is what the propagation is, the car mounted E-field probe is, as yet, nothing like as effective as a loop for RX.

I'd like to rig up some way of driving along with a horizontal loop attached to the rear of the car about 0.5m above the ground. This way I could drive around the local area and log where copy is possible. Presently I have to get out of the car with the loop to take a measurement when doing earth mode tests.

So, a useful test even though the results were not outstanding, or even good :-)

WSPR at VLF

Seeing Jan LA3EQ's recent 4km earth mode tests with WSPR at VLF I must pass on something I'd forgotten about.

WSPR software is able to transmit a WSPR signal at least to 22kHz just by selecting the TX frequency to the chosen frequency. For example, if you want to send WSPR at 8.970kHz just select the band as "other", set the dial frequency to 0.000kHz and set TX frequency to 0.00897kHz. Listening to the tone it definitely is at the frequency stated.

What I haven't determined yet is how high the WSPR software will decode at. When I tried WSPR some time ago on 8.97kHz I used my up-converter and FT817 as the receiver. When I tried to decode directly at 8.97kHz today (setting the RX PC's dial frequency to 7.470kHz) it did not decode.

Bank bonuses - direct action Dutch style

Being really VERY annoyed with the size of totally unjustified bank bonuses in the UK, I was amused to read this article which proves that peaceful and non-violent "people power" can work. No need to spray paint on banks (pointless and unhelpful), just threaten, en mass to withdraw your money.

http://www.guardian.co.uk/business/2011/mar/27/dutch-bankers-bonuses-axed-by-people-power

A 100W PA for VLF use

BK Electronics in the UK make a range of MOSFET PA units with built-in toroidal power supplies. They have a 100W unit for £53, which is very reasonable for a built and tested unit. I believe these units work to 137kHz with a small modification and they would be ideal for 8.97kHz VLF use. There are versions up to 1kW, but these are quite expensive.

See http://www.bkelec.com/Modules/Amplifiers.htm

Easy mistakes

On Monday night I was looking for Uwe DJ8WX again on 8.97022kHz.  To my great surprise I copied nothing when G3ZJO and M0BMU were getting good copy. I'd copied Uwe several times before. After suspecting my PC sound card was faulty, I found out why I copied nothing tonight: on Sunday I'd retuned my loop ATU to copy M0BMU on 500kHz and I'd forgotten to retune it back to 8.97kHz. Although Spectrum Lab locked onto GBZ OK, the sensitivity was about 20dB down! We learn by our mistakes.

G3XIZ a good signal on 8.976662kHz VLF today

Chris G3XIZ has just started TXing again and is a decent signal here in 424uHz bandwidth with the signal up to 20dB over the noise (see picture). Eddie G3ZJO was also getting a good signal. At 1530z Chris dropped the power 10dB but unfortunatley I was unable to copy at this QRP level, whereas G3ZJO was still able to.

Back from holiday

There have been no posts this last week as I have been away on holiday in Devon in SW England staying at my brother's cottage. For once the weather was excellent with wall-to-wall sunshine every day. I did not take any radio gear with me this time but plan to take the FT817 when I go next time to do some pedestrian portable cliff-top QRP DXing. Last May I worked some excellent European DX on 6m with just the FT817 handheld.

Loop TX antennas at VLF

At first sight the idea of a 10m x 10m wire loop as a TX antenna at 8.97kHz VLF sounds a non-starter as a way of radiating any useful power. Having tossed the idea around with others though it appears that, although very inefficient, it would not be that much worse than a smallish Marconi vertical because these antennas need very large (and lossy) loading coils, height and good grounds to be effective. With 100W to such a small loop around 0.45uW could be radiated. Already G3XIZ has spanned 218km with just 2uW to his vertical, so for small gardens the VLF TX loop is worth a look.

G3XIZ and DJ8WX on 8.97kHz

The Spectrum Lab plot showing reception here again of these two stations around 8.97kHz VLF. Both were using back garden antennas. DJ8WX is around 645km away. G3XIZ about 45km.

GPS cannot always be relied upon

As if to remind us of the vulnerability of modern technology yet again:

The MoD has informed OFCOM of the following GPS jamming exercise

Dates: 19 – 26 May 2011.

Times: limited periods between 0700z 19 May to 100z 2 May 2011. 

Location:  The ground based radar jamming events will take place in the SW approaches against the remote radar head at Portreath 21-22 May, undertaken by F-18 Growler aircraft. Additionally there will be radar jamming against deployed targets in South West Wales throughout the period 19-26 May. Communications and airborne radar jamming will take place throughout the same period on the East Coast with aircraft operating within the North Sea Military Danger Areas. Communications and maritime unit radar jamming will take place in the SW approaches and Bristol Channel. Falcon aircraft will operate from Sea Level to FL240 unless jamming AEW aircraft where they may operate above FL245.

Note: Safety of life operations will take precedence over exercise activities at all times.