Форум радиолюбителей ДВ

Here are results from the post-processing of yesterdays transmission at
5.17 kHz. RX sites at DK7FC (tree) in 57.6 km distance and DL0AO in 283
km distance. Mixing the two orthogonal loops at DL0AO allowed to steer
the resulting software rotatable loop into and angle where the SNR
became as good as it can be for that day and time. Now the message is
completely readable in 283 km distance (4.8 wavelengths). Two versions
of the result at DL0AO are shown, one from DK7FC.

TX site: 1130m spaced ground electrodes in JN39WI | 1.7 A antenna
current at 370 W TX power (higher losses due to dry soil, thus less
power from the given antenna voltage at the PA)

73, Stefan

Am 03.08.2019 18:08, schrieb DK7FC:

    Свернуть
     BTW today i transmitted "73" in QRSS-240 at 5.17 kHz, starting 08:30
     UTC. There was a team from a TV channel (Bayerischer Rundfunk) at the
     VLF RX site of DL0AO and they followed the QRSS coming in on the
     spectrogram. I hope they will report about it then...
     Unfortunately it took 1.5 hours to fix two broken wires of the
     antenna. Afterwards the QRN already set in, so half the message was
     lost in the noise... Anyway, the 7 is quite doubtless.

     73, Stefan

MT-Hell Standalone

G8HAJ has designed a standalone MT Hellschreiber interface that uses a small 14 pin 16F1615 PIC device.  It can be used either to send a beacon message or inreal time QSO mode using RS232 interface from a terminal.

The speed / bandwidth is made continuously variable from a few 100Hz down to fractions of a Hz using a pot to control the settings.  Which makes it useable at LF

The downside is that it uses a hybrid SMT/CMT which he calls Pol yPhase or PP/MT-Hell type of modulation that does require a linear transmitter - so no high power with a switch mode Tx   

More details and a full description and PIC firmware download at Graham's web site  http://g8haj.uk/    or specifically   http://g8haj.uk/?page_id=288


Four of us using that module recently had a simultaneous full-quadplex (4 way version of duplex :-)  QSO on the QO100 satellite.    A few screen dumps of the QSO underway showing all four stations can be seen here :
http://www.g4jnt.com/DropF/new14.tif
http://www.g4jnt.com/DropF/new18.tif
http://www.g4jnt.com/DropF/new27.jpg
http://www.g4jnt.com/DropF/new29.jpg




Andy
www.g4jnt.com

http://forums.qrz.com/index.php?threads/novel-compact-antenna-for-vlf.654054/

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

Технических деталей что-то не видно, а жаль...

Удачная конструкция.

Широкополосный трансформатор 8.27 кГц-136 кГц-472 кГц 1:1, 1:4, 1:9, 1:16 и 1:25. 1:36

UPD - на всякий случай дискуссия по сему поводу из рсгб:

Hi All
Transformer is ready.
https://klubnl.pl/wpr/en/index.php/artykuly/uniwersalny-nadawczy-autotransformator-antenowy-na-pasma-827khz-136khz-i-472khz/
73! Marcin SQ2BXI

-----Original Message-----
From:
Sent: Friday, February 15, 2019 5:56 AM
To: rsgb_lf_group@blacksheep.org
Subject: RE: R: Re: VLF: in VK?

Hello VLF!
The primary coil of the transformer is ready. 10 turns (diameter 2mm) give 9.62mH which gives about xl=500Ohms at 8.27kHz. It is a good idea!

73! Marcin SQ2BXI

-----Original Message-----
From:
Sent: Monday, February 11, 2019 4:55 PM
To: rsgb_lf_group@blacksheep.org
Subject: RE: R: Re: VLF: in VK?

Hello Stefan!

Today, the ferrite cores B64290L82X830 came to me. I'm building a transformer 1:1/1:4/1:9/1:16 and 1/25 on the VLF. I'll check if it works soon.
73! Marcin SQ2BXI

-----Original Message-----
From:
Sent: Monday, February 11, 2019 2:50 PM
To: rsgb_lf_group@blacksheep.org
Subject: Re: R: Re: VLF: in VK?

Hi Dimitris, VLF,

Am 11.02.2019 01:07, schrieb Dimitrios

    Свернуть
     I have an idea about impedance transformation and that is to use high
     power 70V/100V audio distribution transformers at both ends. I don't
     have to go to 50 ohm as I don't use the coaxial cable as a
     transmission line (it's only a tiny percentage of the wavelength!), so
     I could use a 4 ohm to 400 ohm transformer or similar. I think in
     general the impedance transformation ratio goes down as the power
     rating goes up and we can live with that. THe audio transformer should
     work fine on the higher frequency but that will have to be tested.
     Perhaps something like this but not at that price!!

     https://www.altronics.com.au/p/m1160-300w-100v-line-pa-transformer/

     Another option is to get a PA amplifier of suitable power output that
     has a 70V or 100V output. You only need one transformer at the antenna
     end to get down to 4 ohm to reduce losses. I have a 50 W amp with such
     output but that's not enough power.

These high power audio transformers are interesting. I wonder how well they work below 1 kHz. But they are to expensive, as you say. You don't need them. For any impedance transformation above 1 kHz i use ordinary
N30 ferrite toroids. There may be slightly better core materials but i'm getting very good results and they are not expensive and you can find them at many distributors (min quantity = 1, not 50000000000000000000000000). Especially at VLF they are well suitable and not expensive.
One of my preferred cores is that one:
https://www.buerklin.com/en/ring-core-outer--x-inner--x-height--63-x-38-x-25-mm-n30/p/84d258
It works easily for a few hundret watts on all VLF frequencies.

Yes you don't need to match the cable impedance but the losses on your cable are caused by the current and resistance of the wire and so, if you transform from 4 Ohm to 50 Ohm, then your losses drop by 92 %, regardless if it is necessary to match the cable impedance.

    Свернуть
     I can easily try the ground loop on the 120m long antenna as I do have
     ground rods at both ends. It would be interesting to compare the
     signal strength in both cases. THat's why I am building a network of
     VLF stations by giving away the large ferrite rods to interested
     amateurs! They can help doing comparisons like this.

Yes, sure. Good luck in getting people motivated to build up a permanent VLF RX station. It would also be good to have someone building up a grabber site or maybe even providing a stream. Your activity can cause a world wide motivation for people who are principally interested in VLF reception and/or transmission, even if they won't be able to receive you from so far away.

    Свернуть
     The ground is very rocky and there is almost no soil at the top.
     Typical Australian native vegetation is the only thing that can
     survive on it. I have thought about the dipole on the ground and I
     have the perfect spot for it which is putting the feed point at the
     top of the hill therefore making an inverted-V :-) Only concern with
     that is the high voltage at the end of the dipole wires and the
     possibility of a bush fire ignition. Definitely a project for winter!
     I have tried to tune my ~120 metre wire to VLF in the past with mixed
     results. Worth revisiting this. The wire basically starts at my house
     and follows the hill resulting in the top of the wire being maybe 20
     metres higher than the bottom.

I'm taking part in your experiments by imagining that i would be in your position :-) My latest thought is that a few (wooden?) poles of 10m height or so would be ideal. One is close to the house, and then two more in 100m distance from the house, e.g. here:
http://k7fry.com/grid/?qth=QF44OX00PV&from=QF44OX00LN
The 2x 100m dipole could be connected using a good HF ladder line down to the shack.
Aluminium wire is light weight and cheap and the lower conductivity could be compensated by using a higher diameter, something like this,
https://www.amazon.de/dp/B004UA7XT2
This antenna would have the advantage that you can use it from MF to DC and the kangaroos would not be able to destroy the antenna.
For VLF experiments, the ends of the wire can be grounded, just by adding another 100m of wire at the ends and let them slope down, maybe with another pole at 4m height.


73, Stefan

Hi ELF,

Yesterday, a 12 character EbNaut message was transferred over the 3.5 km (0.00027 wavelengths) path at 22.97 Hz.
Higher noise levels caused some unsuccessful attempts but last night was quite good and i increased the symbol length to 30 seconds. The message took 14:24 (hh:mm) to pass over to the tree.
Capture of the signal post-processing chain and message decode attached.

73, Stefan



Am 07.02.2019 17:05, schrieb DK7FC:

    Свернуть
    Hi ELF ;-)

    I'm glad to announce that since 15:46 UTC i am transmitting on ELF (the real ELF, i.e. into the range of 3...30 Hz, ITU radio band 1 ) for the first time ever.

    Here are the parameters:

    TX frequency: 22.970 Hz
    Wavelength of that frequency: 13060 km
    Antenna voltage: 4.8 kV rms (+ a DC component of 7.5 kV)
    Antenna current: 325 uA
    ERP: 600 aW, or 6E-16 W

    Call it QRP!
    The goal is to detect the signal on my 3.5 km distant tree grabber, whose E field is now working again. Since the E field probe is not to far above the tree, the effective height is not as much as it should ideally be, at this frequency, so the RX is somewhat deaf. Anyway i can see the Schumann resonances and the 60 Hz power grid. So i hope it will work.

    A spectrogram which is centered on the frequency of interest in now shown at http://www.iup.uni-heidelberg.de/schaefer_vlf/DK7FC_VLF_Grabber2.html (3rd window). But maybe 424 uHz FFT bin width is even to optimistic! In a few minutes we'll see more :-) It takes about 40 minutes until a peak could have fully developed...

    73, Stefan

Hello Markus, ULF,

The carrier was stopped after 2 hours (13:17 UTC).
What a great result! Again i did not expect such a S/N in 424 uHz at DL0AO. The QRB is 283 km, http://k7fry.com/grid/?qth=KO02MD&from=JN39WI
With that SNR and dureation, we could have transferred a 50 character EbNaut message on that frequency!
It is the new lowest frequency for DL0AO (amateur signal detection), so congrats to that!
That SNR indicates that even lower frequencies could be detected at DL0AO. Maybe it is worth to try 970 Hz again? So far the best distance on frequencies below 2.97 kHz is the 57.6 km path between here and my tree. At 1/3 of the frequency, do we expect about 10 dB less SNR? What about the local noise situation? 10 dB in 424 uHz, that would be fine.
If i would be even more crazy, i would buy another 120 Ah accu and build a stronger DC/DC converter and then run 1 kW from there. Everything is possible! But there is another idea that i will follow, which can improve the antenna efficiency a lot...

So, thanks to the crew for operating the RX site at DL0AO and the grabber service and these very good results in the end of the year!

73, Stefan

Am 30.12.2018 13:24, schrieb Markus Vester:

     Wow, a 20 dB peak on the DL0AO grabber !!!

    https://vlf.u01.de/
    https://vlf.u01.de/VLFgrabber/vlf5.jpg

    Congratulations to Stefan and the DL0AO crew!

    Best 73,
    Markus

    -----Ursprüngliche Mitteilung-----
    An: rsgb_lf_group <rsgb_lf_group@blacksheep.org>
    Verschickt: So, 30. Dez 2018 12:40
    Betreff: ULF: Carrier on 2970.01 Hz

    Hi ULF,

    The accu is fully recharged and i am on the hill again, transmitting on
    the ground loop antenna. This time, the accu has even more power. The TX
    power is 520 W (!), the DC measurement tells i need just 64 V for 1 A,
    and now, at 2970.01 Hz i am getting a record antenna current of 2.75 A!!
    The carrier ison the air since 11:17 UTC and i intend to run it for 2
    hours again, like yesterday.

    Reports are welcome :-)


    73, Stefan