VLF Earth Mode: 3.6km DX today with 4W

My earth mode VLF DX increased to 3.6km today using QRSS3 and a PC running Spectran. TX was 4W into 20m separated electrodes in the ground. TX frequency was 838Hz. The 80cm loop and preamp receiver were set up in several places well out of the village in several directions and results well exceeded my expectations. Lots of information on my earth mode webpage including screen shots and sound recordings made using Spectran when out in the field.

This screenshot was from the roadside 2.5km south of the QTH. Signals were so strong (30dB S/N) that the signal was audible when Spectran's BPF in circuit (lots of 50Hz hum without).

More 500kHz weirdness

Today I experimented some more with 500kHz WSPR using earth electrode pair arrangements rather than conventional antennas. In the end I was still getting reports from 210km away when using around 100uW ERP (maybe less) from a loop consisting of an earth rod outside the back door connected to about 7m of wire back to the bedroom with the other connection going to the central heating radiator. Why this works I have no idea! My latest theory is that this small loop is acting as a coupling loop to local overhead phone wires. I can't see otherwise how this "non-antenna" can otherwise work.

Stable audio frequency tone generation (for VLF QRSS)

Next week I want to try QRSS3 with my earth mode VLF system to extend the range. As in the test this week,  Spectran software will be used my PC to filter and decode it. For a stable source I'll use a crystal and divide this down to sub-9kHz. Looking around for a suitable simple circuit I found G4HCL's very simple 1750Hz toneburst circuit which uses a 455kHz ceramic resonator (pulled slightly) and a 4060 IC as a divide by 256. With a crystal instead of the ceramic oscillator this should be perfect if followed by some filtering to produce a decent sine wave output. See M1GUR's page for more details.

Earth electrode loop effective area at 500kHz

From some measurements of my earth electrode "antenna" this evening and some estimates of the ERP calculated from received field strengths 69km away, I've received an estimate of my effective loop area including that part that is within the ground. This was calculated by Rik Strobbe OR7T as 70m^2 in total, suggesting some 20m^2 of the loop was within the ground. These were Rik's calculations:

"Assuming

- 50uW ERP

- antenna is traded as a loop (gain = -0.4dBd)

Due to the negative gain (-0.4dB versus dipole) a loop antenna must "radiate" 55uW to get 50uW ERP.

Since the antenna feeding current is 0.15A the radiation resistance is 2.44 milliOhm (R= P/I^2)

The radiation resistance of a small loop is : Ra = 320xPi^4*A^2/L^4

where A = loop area (m^2) and L = wavelength (m)

For 500kHz Ra = 5*10^(-7)*A^2 or A = 1416*sqrt(Ra)

If Ra = 0.00244 Ohm then effective the loop area is 70m^2"

Diagram of my earth electrode antenna for 500kHz and sub-9kHz

This is a hand drawn diagram of my earth electrode antenna for 500kHz and sub-9kHz. On 500kHz WSPR this has managed to TX a signal as far as G0KTN who is 210kms away when using my 5W QRP transverter. Sub 9kHz my 4W TX is audible by ear at 0.5km range on an 80cm loop.  This is a totally "stealth" antenna that is not visible at all to anyone looking at the property.

Balloon SSTV from 30kms

From the Southgate News page:

Ed M0TEK and James M6JCX bring news of an amateur radio Slow Scan TV transmission on 434.075MHz USB that'll take place from a high altitude balloon at 30km on Thursday, June 17.
In addition to the 434.075MHz USB SSTV transmissions there's another telemetry beacon on 434.650MHz USB.
At high altitude the balloon may be receiveable by stations up to 300 kilometers away.
Ed and James write:
Just to announce that there is going to be a balloon launch Thursday, June 17, from Churchill, Cambridge at ~ 11:00BST. Onboard will be Nova 18 consisting of the CUSF Ferret tracker and a school experiment and also there will be Pegasus VII a SSTV payload. Normal flight profile is expect, burst altitude just over 30km landing just South West of Milton Keynes.

Screengrab of 1.8kHz earthmode transmission today

Today I modified my VLF TX so it could send either a 10 wpm or QRSS3 beacon signal. I also went out into the fields with my loop/preamp and a PC with Spectran to receive it. For the first attempt with a PC I went 0.3km away from home where the 4W signal from the earth electrode "antenna" could clearly be received by ear. With Spectran I could read the 10wpm CW signal with 20dB S/N in a 12Hz bandwidth, if my understanding of the Spectran settings is right. There is an audio recording here so you can judge the S/N yourselves. This suggests that with QRSS3 and really screwing the bandwidth down I should be able to do much better. My problem is knowing how to calibrate the soundcard etc and clearly I need a more stable source than my free running twin-tee audio oscillator.

500kHz WSPR - without an antenna!

Well, I'm amazed. This evening I connected my 500kHz transverter straight to the two connections of my sub-9kHz grounded electrodes and TXed WSPR. No attempt was made to match anything on the assumption that the two electrodes system looked not too far from 50 ohms resistive as measured between 1-9kHz.. Pout from the IRF510 is around 5W. What happened?

Three people copied me - M0BMU, G7NKS and M0JXM with reports between -21 and -28dB S/N. The wire to the furtherest ground rod is at most 20m long and most of the way it is 1.5m above ground. Once again, this must be acting as a pretty effective loop mostly within the ground.  Screen grab of the WSPR log attached.

So, if you live on clunchy chalk soils like me then don't worry too much about big antennas, :-)

Grounded electrode antenna on 500kHz

This evening I tried listening on 500kHz WSPR using the 20m spaced grounded electrode pair "antenna" in the back garden (earth rods 20m apart). To my surprise I decoded G3ZJO and G7NKS. Both stations were using just 1-2mW ERP. I'm tempted to try this "antenna" (actually a loop formed in the earth) on TX to see if anyone can decode me on 500kHz.

WSPR with the X80 and 5W

Well, here is a summary of my (intermittent) QRP WSPR beaconing tests since I erected my X80 vertical at lunchtime today:

• Bands tried 80, 40, 30, 20, 17 and 10m (reports received on all bands tried)
• Reports from 25 different stations in 14 countries and 3 continents
• Best DX 6105km on 17m

So, a reasonable test for the antenna and I believe it is working out pretty well so far.