Very tiny VLF TX antenna?

Just possibly this research could lead to compact (inches only length) VLF transmitting antennae. This link was sent to me by Jay W5OLF, who designed my 10m WSPR beacon, which is still working fine.

See https://phys.org/news/2019-04-slac-compact-antenna-radios.html

Successful amateur VLF TX tests from Poland

Transmissions from Poland at 8.27kHz VLF have been received in the UK. The antenna used was a long baseline earth-electrode "antenna".  From my own experiments with far shorter baselines, I know such structures work.

See https://klubnl.pl/wpr/en/index.php/2019/03/03/nadawcze-proby-z-dipolem-ziemnym-w-zakresie-vlf/

Earth-mode VLF

Yesterday, I mentioned amateur VLF experiments below 9kHz. A very accessible introduction is earth-mode communications, especially utilities assisted earth mode. Using the latter mode, 6km has been spanned,  with just 5W, although much further should be possible. With much higher power and larger baselines at the TX end, I expect the small radiated power will be detectable hundreds of km away, although this is not going to be earth-mode.

An example of a typical earth-mode VLF transmitter is shown at the link.

Amateur VLF website

Quite a bit of activity is happening below 9kHz for amateurs. Although I sometimes fail, I try to report what is happening on the Sub-9kHz Amateur Radio website. If you are interested, take a look. For RX and earth-mode you do not need complicated equipment or big antennas. This is one of the real frontiers and great fun.

Amateur VLF

Recently, there have been up to 4 stations active around 8.27kHz VLF. This is the excellent spectrogram at Paul Nicholson's station in Todmorden, UK. Such levels of activity are rare.

SAQ VLF transmission missed

Earlier today there was a CW transmission from SAQ on 17.2kHz. This uses an alternator TX and broadcasts heritage transmissions a few times a year. Years ago, I received a QSL card from SAQ for one of their transmissions. If, like me, you missed today's transmission you may like to look at this video of today's transmission.

See https://youtu.be/shqi43EV07c .

VLF upconverter

Amateur VLF transmissions demand very narrow bandwidths, high stability, long integration times and special (free) software. By contrast, commercial or government VLF signals are often strong. These stations usually have high power and very big antennas.

To receive commercial or government broadcasters a simple upconverter is fine. An example of one is my design.

For amateur VLF signals this is almost certainly not suitable. Most amateur VLF signals are seen on a PC screen rather than heard.

VLF earth-mode transmitter

Before my 2013 stroke I enjoyed experimenting with VLF. Quite a few European amateurs were copied. This required special software, very narrow bandwidths and very long integration time. Casual listening does not work with very weak amateur signals!

In TX I was restricted, but did some useful experiments with VLF earth-mode. Best DX with 5W QRSS was 6km.

See https://sites.google.com/site/g3xbmqrp3/vlf/8-97khz-earth-mode-transmitter

More amateur VLF transmissions

Riccardo  IW4DXW has been doing more 8.27kHz VLF TX tests, but most stations in Europe have failed to decode him. 

Inspired by DK7FC, Stefan, he hopes to do some "guard rail" loop tests soon.

See https://sites.google.com/site/sub9khz/

More VLF experiments

Stefan DK7FC is planning more VLF tests at 17.47kHz:

"Hi VLF,

For this week, i'm planning to start with new experiments on 17.47 kHz,
where i have a (renewed) special permission to transmit.

So far the best results were a prooved carrier detection as well as a 1
character EbNaut decode by Edgar from Tasmania (VK7).

The first goal will be to determine the best time (start time and
length) on the path for this season. We have a usable path for about 2
months centered on our autun/spring time (21st SEP).

The Signal will be exported by SpecLab to simple txt files containing
the FFT data. This allows stacking, which will be required to get some
S/N at all. A reasonable stable path is essential during the
transmission time. All this will be determined by running some carrier
transmissions, a few hours per day, starting about 16 UTC.

When knowing the time to try we will attempt to transfer a 2 character
message and then even longer messages. 5 characters would be realistic i
think, with some luck and good propagation and low QRN on the RX site...

More soon.

73, Stefan"

VLF DX tests with earth-electrode antennas

Stefan DK7FC is transmitting 75W into an earth-electrode "antenna" and seeing if he leaves a trace on the RX at Todmorden in the UK.

"Hi VLF,

I'm sitting in my car while writing this email. I'm in JN39WI96GX and i transmit on 8270.000 Hz with a GPS locked signal generator into an about 450 m long earth antenna using two guide rails as the earth electrodes on both ends. On each end there are 16 (18) massive T-T poles holding the guide rail, providing a super good earth coupling. I measured that they are connected to each other.
The transmitter is on the air since 9:08 UTC running 550 mA with just 75 W DC inout power into my hand warm lossy linear mode VLF PA!

I'm amazed about the low losses! At DC i got 447 mA at 50.9 V. The wire is 0.4 mm diameter so it has 63 Ohm. That means the ground loss is just 50 Ohm !!!! Amazing! And i have no efforts to build up a ground connection here, i just need to connect the wire. Since the wire losses are higher than the ground losses, i can get maybe 2 dB more signal when buying some better wire. I already found a source that offers 0.75 mm^2 100 m loudspeaker cable (i.e. 200m wire)for just 13 EUR....

BTW i even have an ugly old scope here which is battery powered. I can see that the phase of voltage and current is slightly inductive, maybe 30 deg or so. So i could series resonate the antenna with some C. This is for the next experiment...

The signal becomes visible on my grabber now, in 424 uHz and also some bright pixels in the 3.8 mHz window.

I'm going to stop the carrier at 10:08 UTC, after 1 hour. Then i'll continue on 5.17 kHz!
BTW the antenna , if it works like a real loop, is beaming directly to Paul Nicholson ;-)

73, Stefan"

SAQ (VLF) transmission today

An earlier transmission on 17.2kHz CW from the historic Alexanderson transmitter at Grimeton, Sweden was well received in Italy. I cannot remember if there is another transmission later.

SAQ (17.2kHz CW) transmissions July 1st 2018

To celebrate Alexanderson Day on July 1st 2018, there will be several transmissions from the historic radio station SAQ (VLF) on that day. There will also be special event stations active on several amateur bands. I think QSL cards will be available. I have one from many years ago.

See http://alexander.n.se/the-radio-station-saq-grimeton/saq-transmissions/?lang=en

Success on VLF

Riccardo IW4DXW's EbNaut transmissions from Italy on VLF (8270.003Hz) have been decoded in Germany.

EbNaut tests from IW4DXW on VLF

Riccardo is busy again with VLF transmissions.

"Hi Stefan, Lubos, Paul, VLF

Ok Stefan :-), here we go!

I'm starting a series of EbNaut transmissions, from 0800 UTC (9 May) every 8 hours. Then 3 messages per day (0000, 0800, 1600 UTC). 

QRG: 8270.003

2 ch.

30 sec./sym.

coding 16K21A

CRC 28

duration: 8h 00'

antenna current: 600 mA

many thanks for reports"

Yet more amateur VLF TXing from Italy

Near 8.27kHz is the frontier these days! News has come in of yet more tests from Italy close to this frequency by Riccardo. BTW Lubos is in the Czech Republic.

"Lubos,

many thanks for your report!

I'm testing the coil for long transmissions; I have observed, for my first time, that atmospheric conditions affects antenna current: for example, today it's been a sunny and dry morning, in fact I reach 625mA; in the afternoon the sky was so cloudy and I have measured only 570mA. Now the value is stabilized around 590mA (relative humidity's still high: 86%).

I'm preparing an EbNaut setup for next days: I will announce details soon."

Amateur VLF DX from Italy

A test signal on VLF from Italy has been copied in the UK, Germany and the Czech Republic. Some years ago the refrain was, "you won't get over the garden wall". Oh yeh?

This was from Paul Nicholson (Todmorden, UK) a few days ago:

"A very nice signal this morning,
http://78.46.38.217/fbins3.html#p=1524736800&b=130&s=sp&m=cardioid&w=r&h=62&z1=0.34&z2=0.64&c=1&mb=643,121,724,224,1
Bearing 126.9, great circle is 127.8.

Paul Nicholson"

SAQ (17.2kHz VLF CW) on air May 1st 2018

Apparently, the historic alternator CW VLF station SAQ Grimeton, Sweden, is being fired up on May 1st. This is the first time since 2016. I have a QSL card from them, which came many years ago.

See http://alexander.n.se/?lang=en

Sub 9kHz amateur radio

At one time, I was fit and well and did quite a bit at VLF.  Apart from receiving several EU stations at VLF, I used earth-mode and could detect my own signals at 6km. Further would have been possible. 

Others, using radiated signals, have covered some quite remarkable distances from amateur gardens with modest powers. At one time people said we'd be lucky to get "over the garden fence".  How very wrong they were!

I still maintain the Sub-9kHz Amateur Radio website. Quite a bit is happening and, contrary to popular belief, big antennas are not needed for VLF RX. What is needed on TX are very stable signals and very long times. Luckily, free software allows VLF MSK commercial stations to be used as stable signals to achieve lock.

New EbNaut decoder for VLF amateur DX

Paul Nicholson, a very good UK VLF SWL, has created some new software:

"Updated EbNaut decoder for Windows, now at version 0.8

 http://abelian.org/ebnaut/software_ms.shtml

This version does 16K23A which is a useful polynomial
for short messages combined with a large CRC.

The Linux program is up to version 0.9 now.

 http://abelian.org/ebnaut/software_linux.shtml

The only significant change is the use of DSW re-balancing
of the list decoder stack.  This may reduce decode time
a little when using very large list lengths.  It is most
useful when measuring the distance spectrum of a polynomial
where a degenerate tree often develops.
--
Paul Nicholson"