VLF Amateur News 2014

Paul Nicholson <vlf0403@abelian.org>

to rsgb_lf_group

A spectrum from the natural radio receiver at Sebring Florida

27.516N,81.517W range 869.4 km run by Joel Gonzalez,

http://abelian.org/vlf/tmp/141204b.png

S/N is 12.6 dB in 55.5 uHz.

The noise level there is often quite high both natural and man

made. A rough spectrogram shows quite a good nighttime S/N

http://abelian.org/vlf/tmp/141204a.png

but only for a while. A summer daytime test might do better

on that path with less background to compete with.

For comparison, here is W4DEX at Hawley Texas in similar

bandwidth during the day on 2nd June, range to Hawley is 1816km.

http://abelian.org/vlf/tmp/w4dex_140603b.gif

Jim AA5BW wrote:

> I can run 10uW ERP at 8820 Hz for ~ 12 hour periods;

> oscillator stability may be ~100uHz.

I think you would need another 7 to 10dB ERP increase and

stability of order 10uHz to have a chance.

If you can't manage so much power but can do long transmissions,

it might just be worth trying the summer daytime T/A path.

It is long and stable and although attenuation is higher,

the background noise is lower. Might just be detectable in

something like 25uHz bandwidth for a full day carrier.

But your 10uW ought to reach Forest VA 37.344N,79.288W without

difficulty. Markus DF6NM achieves over 1000km with 10uW or

less, over a mostly land path - and gets across 14 character

messages at that ERP and distance.

For converting fT to uV and vice versa, on distant signals

I just assume free space impedance and use

fT = uV * 3.333

and

uV = ft / 3.333

The 3.333 is just 1/c combined with some powers of 10

to convert the micro and femto units.

Paul Nicholson

Nov 18th 2014

Hello VLF!

Mine VLF-grabber 8270 Hz is now active and will work one or two weeks. Unfortunately there NO Internet therefore all reports will be "manually" ) (47 uHz and 1 mHz window, sync'd to GBZ)

Pse ur tx! :)

73 de RN3AUS/Alex

Nov 15th 2014

Uwe, DJ8WX, has been intermittently ("when the sky is blue") testing on 8.27kHz recently and has been copied by Paul Nicholson in the UK and by Stefan DK7FC.

Oct 9th 2014

Stefan is busy again:

Hi ELF,

This afternoon i'm attempting to transmit on my INV-L on 136.172 Hz (not kHz!). Just preparing my H bridge VLF PA and i intend to use an old 10 kV transformer which i got from an old furnance (to inflame the oil stream), see https://dl.dropboxusercontent.com/u/19882028/VLF/10kV%20Trafo.jpg

Will that work on 2.4 km distance? It's well inside the near field. Which mode could be possible? QRSS-3? CW? The 2200000 m band, or 2.2 Mm band :-) A near field of 350 km !! I hope i can apply 10 kV to the antenna. It will not be resonated. And maybe i will see harmonics as well, because the input is rectangular...

73, Stefan/DK7FC

Sept 22nd 2014

I made spectrograms of W4DEX at 8971.1 Hz,

Signal/Noise ratio

http://abelian.org/vlf/tmp/w4dex_140605a.gif

Amplitude

http://abelian.org/vlf/tmp/w4dex_140605b.gif

The amplitude scale is approximately fT. There's enough signal to send about 12 to 18 bits (2 or 3 characters) during the short night window, and maybe nearly the same again but slower over the weaker daytime path.

Paul Nicholson

July21st 2014

http://rn3aus.narod.ru/VLF/vlf.html

For pictures and sound clips.

July 11th 2014

See http://abelian.org/vlf/tmp/w4dex_140603a.gif

Hello VLF!

Trace on my grabber on 8270.

http://rn3aus.narod.ru/VLF/vlf-8270-trace11072014.bmp

Grabber http://rn3aus.narod.ru/VLF/index.html

Alex RN3AUS

June 22nd 2014

Dear Group, (sent to RSGB LF group)

I tried again to get an LOA for VLF. This time, the response from Industry Canada was favourable: 10 mW 8.0-8.3 kHz. Yesterday, after a few slight rf burns, and thanks to PA0RDT's miniwhip design and DL4YHF's Spectrum Lab and advice, VLF sigs on 8.277 kHz were heard at 200m from the 100m wire aerial. This was a reception outside my back yard! 10 watts from an 1970's keyboard amp (volume control set on 3) were stepped up with an xfmr to a lossy 500 ohm tuning coil peaked with a ferrite rod for maximum squeal at L=0.35 H.

Is it possible for someone who is not especially enthralled by winding a mile of 0.7mm wire to use an iron core to make a VLF tuning coil?

Joe VO1NA

June 4th 2014

Transatlantic 8.971kHz

In recent weeks there have been successful transatlantic tests on 8.971kHz which have been copied in Europe by Paul Nicholson (and others?). Dex W4DEX has been transmitting a long, stable carrier. See http://w4dex.com/vlf/8971Hz/ .

May 23rd 2014

Coherent BPSK at 8270 from DF6NM

Marcus DF6NM, Paul Nicholson and others have been experimenting with coherent BPSK at 8.270kHz with very good results.

As Paul says, "In combination with coherent signalling and Viterbi list decoding, a circa 10uW ERP signal is decoded with 95% reliability at a range of over 1000km and achieves 85% of the Shannon capacity."

May 3rd 2014

"Since 10:32 I am on air again with a straight carrier on 8270.000 Hz, same power as in earlier tests (0.3 A current or about 10 to 15 uW ERP). There seems to be a small peak on the DK7FC grabber, and I hope that some of the currently dormant VLF grabbers (eg. OK2BVG, PA1SDB) may be coming online again.

Interestingly my VLF grabber http://www.df6nm.de/vlf/vlfgrabber.htm which is currently in RDF mode on the loops is not being overloaded, other than showing some noise increase.

Best 73,

Markus (DF6NM)"

April 27th 2014

http://www.home.pon.net/785/equipment/transmitting/VLF_transmit_2.htm

VLF radio enthusiasts are not limited to listening, some are sending out signals using home built equipment. The samples here are from an experiment to find out if VLF can be used for amateur communications. It was done in the Sierra Nevada Mountains in California. The transmitter sent out an intermittent CW (continuous wave) signal at one mile from the receiver, then again at two miles. The frequency used was 1.8 Kilohertz, well within the VLF range.

Sample 1 (650 Kb) Low power (one-half watt) at one mile

Sample 2 (650 Kb) High power (100 watts) at one mile

Sample 3 (650 Kb) High power (100 watts) at two miles

The above information comes from Laurence Kramer

March 24th 2014

Today I received an update from Harry Woodhouse, G3MFW on recent earth-mode tests near Truro in Cornwall. With 41W Harry has covered 18km by utilities assisted earth-mode. A very good distance. I am adding Harry's paper as a page attachment (see bottom of page called: 8.97kHz_underground.doc).

March 14th 2014

Great news from IK7FMO in Italy!

Hi all, this past night my signal, from SE Italy, was visible to the Grabber OK2BVG.

Issued but not yet stable.

Frequency: 8269.993

Time: 07:00 - 08:00 GMT

Marconi antenna - 70 W 0ut. QRB: 866Km.

'73 from Richard - IK7FMO - JN80OX

Feb 28th 2014

Eddie G3ZJO and Henny have been busy copying Russian ZEVS (submarine) signals around 82Hz. More activity is reported recently - Ukraine related maybe?

Feb 25th 2014

At last I have received an official response from OFCOM re sub-8.3kHz operation in the UK. See http://g3xbm-qrp.blogspot.co.uk/ .

Also DJ8WX announces operation tonight Feb 25th:

"Hi Rodger and Eddie,

so I do announce herewith that the TX will stay on the air the coming night

with 5000sec/dashes forming a castle mode letter.

If the TX will be switched off during that time the reason would be bad WX / rain.

Uwe/dj8wx

GL"

Feb 23rd 2014

Apparently Uwe DL8WX has been active again in recent days. Only those with grabbers already running will have seen him. PLEASE may we have prior warning? It maximises chances of being spotted!

Feb 2nd 2014

Another obscure comment "I can Cee Uuu" from PA1SDB timed at 15:34 today would appear to refer to a signal on 8270.005Hz which may be from DL8WX, if it is Uwe he normally leaves his TX on overnight.

73 Eddie G3ZJO

Feb 18th 2014

More news from Stefan DK7FC:

Markus, VLF,

Am 01.02.2014 20:34, schrieb Markus Vester:

Stefan,

>running two 478 µHz "6000" windows centered on 5755 Hz (on the grabber, but much QRM here) and also 17265 Hz (offline) which seems more quiet. So hoping for a long carrier...

Well, i hope that 16 hours key down were long enough ;-)

>On which of the two frequencies would you expect to radiate more power?

I don't know. But the harmonic signal is very weak and cannot cause interferences for JXN or HWU or SAQ or GBZ...

I've done measurements at home, 950m distance, of that 5.755 kHz transmission and saw that the signal was very weak, see attachment. Just 50 dB SNR in 4.5 mHz at 3HD. The TX power was just 15W at the end. Also the frequency response of the active antenna + soundcard is attached.

The experiments are very interesting here and i like to do the measurements. Despite rain the coil was on the top of the building and on air. It was just covered by a trash bag. The voltages are very small...

I just hang out a 30cm long wire connected to a probe of the oscilloscope and so the voltage waveform of the antenna wire. It nearly looks as expected :-)

Now i got another idea. There is a 2.2 uF WIMA MKP-10 capacitor in series to the output of the H bridge, just to protect it against damage in case of a DC output. Now i've disconnected the antenna and tuned for the series resonance of this C and the L of the primary winding of the loading coil. The resonance is at 1.77 kHz. This allowed me to calculate a much smaller additional series C which helps to attenuate unwanted frequency components, i.e. makes the spectrum cleaner and provides a lower impedance on the wanted frequency :-)

There is really no alternative to that H bride PA which works from 10 Hz to 100 kHz :-)

in a few minutes i will be on air again for a longer time, hopefully with a much stronger signal.

Maybe you can detect something of that 5.755 kHz transmission.

73,GL, Stefan/DK7FC

Jan 30th

Hi VLF friends,

For those how could be interested in local VLF experiments, i'm now transmitting on the 70m long 30m high antenna with the LOPT transformer. TX power is just 3W. Mode is QRSS-400. The transmit frequency is 5.756666 kHz, GPS "locked" in SpecLab.

Last night i've done a first local test on that frequency, 30m distance. The signal was visible in the grabber window, as well as a weak 3rd harmonic was detected (3HD) at 17.27 kHz.

Now, with the todays experiment i'm trying to receive that weak signal on 5.75666 kHz from my home QTH in nearly 1 km distance. If successful, a few /p receive tests will be done. And, in previous tests, "the big coil" will be used.

73 and gl with your own projects :-)

Stefan/DK7FC

Jan 29th 2014

OK2BVG's excellent reception of DJ8WX on 8.270kHz recently.

Jan 21st 2014

"Uwe is again producing very good traces on the European grabbers. Even in my noisy location I am now getting a nice peak in the 42 uHz FFT (slightly higher due to an uncorrected 0.25 mHz error in my frequency readout).

Uwe, do you intend to stay on longer tonight?

Best 73,

Markus (DF6NM)"

Jan 13th 2014

There has been almost too much VLF activity recently to keep abreast of around 8.270kHz from DJ8WX, PA1SDB,DK7FC/P and OK1 and W. Great to see such renewed interest.

A reminder that to successfully copy VLF amateur stations at any distance it is necessary to use Spectrum Lab in locked mode with the dsplay ative and slowly scrolling for HOURS and with very narrow bandwidths (typically 42uHz or 420uHz). The exception is VLF earth-mode that I have copied at nearly 6km with relatively wide QRSS3 bandwidths (0.34Hz) . For example, DJ8WX leaves a good trace here but it takes days before this is clear on the screen as a few solid lines. If you can't look yourself,check the various grabbers now active.

Jan 3rd 2014

From DJ8WX

OK. OK. dreamers, the TX is on the air since 1309UTC.

QRG: 8270.000Hz.

WX: continuous rain but not so strong.

when ever the order comes, I can switch to Op-4H.

Uwe/dj8wx

VLF. If I did configure my RX PC well, then I'm now (Saturday Jan 4 - 11h UTC) RX ing in OPDS 4H on 8270 Hz. No time to setup a dropbox, but will do that next week. Not much free radio hobby time this weekend...

73's, Peter - PA1SDB

And from the USA....

Hi All,

I just finished measuring the results of the coil I wound today. Antenna current is 0.400 Ma as measured with a Fluke T5-100 clamp on amp meter. Maybe my 1500 foot loop will TX a signal now. I would like to give it a test run tonight if anyone will be able to listen for me. Let me know if you can.

I plan to wind another coil and see if I can increase the antenna current and one more idea to try this weekend.

Rich

WD4RBX

EM84nn