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DK7FC Germany flag Germany

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Radio amateur since 1999. Started as DO4FX and DD5FX on 2m/70cm. In 2000 i became DK7FC and moved lower and lower in frequency. Since 2002 i'm predominant QRV in CW. I prefer realQSOs, not that 5nntu stuff. Since 2009 i'm experimenting with kite antennas. Started building vertical Zepp antennas for 80m and 160m, later i came back to the LF 137 kHz band. In 2010 i started experiments below 9 kHz. Detailed informations and the ongoing progress in 2010 can be found below. Since 2010, 95% of my activity is on 472 kHz, 137 kHz, 8.97 kHz, 6.47 kHz and 5.17 kHz. If you hear my callsign in SSB: It´s a pirate!

Special interests:Experimenting with verticalkite antennas up to 300m! (have a special permission by the German air traffic control).Building and using class D, E transmitters (DC...33km, 2200m, 630m, 160m, 80m, 40m, 30m, 17m, 10m), antennas, antenna tuners and the rest you need to be QRV.

Since 2010 preferred bands: 58km, 46km, 33km, 2200m, 630m

Normally QRV as DK7FC/p, sometimes DK7FC/m, from hills, out of my car or great places of nature! Since 2011 i'm using a 30m high and 70m long inv-L antenna for MF, LF and VLF operation.

Join the LF group:

To get in contact with a worldwide group of radio amateurs who operate on the real low bands below 1 MHz (630m and 2200m band as well as the VLF bands on 33km), you may join to a simple email reflector to exchange informations like skeds and building equipment, discussion propagation phenomena and much more. This reflector is an essential part of coordination for the small group of amateurs acting in that very exciting range of the spectrum.

To join this group you need to send an email to Majordomo@blacksheep.org. Leave the subject field blank and type

subscribe rsgb_lf_group in the first row. Then type end in the second row in the message field. Ensure that no other text is written in the message field. To unsubscribe, type "unsubscribe rsgb_lf_group" in a similar email.

I'm looking forward to welcome you there.



Fascinated by:

  • QRQ, QRO, QRP :-)
  • RIGs: Elecraft K2 (10W; 160m module), ICOM 706MK2G; different Antennas (dipoles, loops, verticals, J-Antennas); homemade paddles

Member of: DARC (F42), HSC (#1805)

Not member of eqsl!

I am offering a MF,two LF and a VLF Grabber (websites showing captures of spectrograms as received in Heidelberg, JN49IK):

http://www.iup.uni-heidelberg.de/schaefer_vlf/DK7FC_MF_Grabber.htmlfor 472...479 kHz (630m band)

http://www.iup.uni-heidelberg.de/schaefer_vlf/DK7FC_VLF_Grabber.html for 8.97 kHz (33km band)

http://www.iup.uni-heidelberg.de/schaefer_vlf/DK7FC_LF_Grabber.htmlfor 137 kHz (2200m band)

http://www.iup.uni-heidelberg.de/schaefer_vlf/DK7FC_LF_DX_Grabber.htmlfor 137 kHz (2200m band, very slow modes)

Latest activities:

June 2012: After the permission for German radio amateurs to operate on the new 630m band, i'm quite often on air. It seems to turn out that the center frequency of CW activity is 472.5 kHz. My activity is focused on CW mainly. In summer the band opens arround 23 PM local time. My best DX so far is EI0CF in a range of about 1500km.

July 2012: I've tested a full size dipole antenna on the 630m amateur radio band, i.e. the range of 472 kHz to 479 kHz. A report can be found here: https://dl.dropbox.com/u/19882028/MF/A%20full%20size%20dipole%20for%20the%20630%20m%20band.pdf


2010: Exploring the VLF bands below 9 kHz like the "Dreamers-band", 33 km wavelength. On August, 1st 2010 first time exploring the 46 km band,. Later in October 2010 my a transmission on 5.17 kHz took place and was received in 904 km distance.! Except the kite experiments i am tryingto reach some distance with earth electrode antennas (49.6 km on the 33 km band so far). For an introduction on the work of radio amateurs below 9 kHz, see the excellent page of Roger/G3XBM at https://sites.google.com/site/sub9khz/

Below you can find find detailed informations and photos of the development of my work below 9 kHz.

December, 4th 2010: (9th experiment). This 12 hour experiment was done in a snowy landscape but in clear blue sky. The transmissions took place on 8.97 / 6.47 / 5.17 kHz. Wind was strong during the whole time, so the angle of the kite was quite high. The antenna currents were 950 / 850 / 530 mA. The first time a 300m vertical antenna was used to transmit on 8.97 kHz. The achieved ERP was up to 58 mW.

See an image of the 300m vertical antenna at https://dl.dropboxusercontent.com/u/19882028/VLF/300m%20VLF%20kite%20vertical%20by%20DK7FC.jpg

During the experiment a interested hobby photographer crossed the way and took some photos. He even wrote a report. See: http://mkorbit.de/2010/12/05/weltrekord-signalubertragung-auf-einer-langstwelle-vlf/

Due to increasing interest by amateurs on VLF, more and more RX stations come up now. 23 stations in 9 countries in 2 continents successfully received my transmissions. A new distance world record was achieved once again. Chris/4X1RF received my signal in 2873 km distance, well visible for all interested people on his VLF grabber: http://qsl.net/4x1rf/vlf/vlfgrabber.htm

One of the goals for the next experiment is to reach the very new VLF grabber of Halldór/TF3HZ in Iceland: http://simnet.is/halldorgudmunds/

A map of the locations of successful receptions of my transmissions can be found here: UK and north west EU (above 200 km) and Overall receptions. See the updated list below.

October, 23th: (8th experiment) The first time i used a 300 m vertical antenna! A transmission at 5.17 kHz, the 58 km band, was successfully received by 6 stations, ODX is Jacek/SQ5BPF in 904 km! On 8.97 kHz the wire height was 200m, antenna current up to 1 A. The first time, a 1000 km distance in DFCW-600 was exceeded by amateurs on VLF! John/EI8JK received the signal clearly in 1310 km in Ireland. Furthermorei used SpecLaband a GPS module for transmitting a GPS-"locked" signal with an accuracy of about 1E-8.

October, 2nd: (7th experiment) In this experiment the wind was strong and the ground wet, so optimal conds. The first time i used a 200 m vertical antenna on 8.97 kHz. The big loading coil has a tap now at 50 % of its maximum L to resonate on the Dreamers band again. Due to the reduced coil/earth losses i reached the 1 A antenna current limit and due to the lower Z of the antenna, the voltage at 1 A is now just 16 kV rms.Since the wire/kitewas in a high angle mostly (> 70 deg.), the ERP was up to 27 mW. Just about 350 W was applied to get 1 A!

First time reached the 1 A antenna current limitFirst time reached the 1A antenna current limit

Tap for 200m/8.97 kHz at the center top of the coilTap for 200m/8.97 kHz at the center top of the coil

This strongest signal i ever radiated was received by several stations in Germany, France, Italy, UK, Poland, Netherlands and Austria. A new VLF reception world record by amateurs (RX/TX) was achieved by Jacek/SQ5BPF, 904 km!

Also see the reports of this experiment of Jacek: http://www.lipkowski.org/~sq5bpf/dk7fc_20101002/index_en.html

and of Paul Nicholson: http://abelian.org/vlf/ss101002/

For the 8th experiment, a switch was applied to extend the range of the amperemeter to 2 A! :-) CU in the 8th experiment, maybe even with a 300 m vertical wire on 5.17 kHz! New records will be made by radio amateurs :-)


August, 1st: (6th experiment) The first time a used a 200m kite antenna after achieving a special permit by the german authorities for kites up to 300m above GND. Theloading coil's Lwas not reduced in this first test so i came out on the 46km band! I found that i can resonate from 6,4...6,6 kHz and started a transmission on 6470,00 Hz. Due to some poor wind the kite went down several times so there was no real "message" sent but just some carriers.

This carrier was received by at least 7 stations in Germany, France and the UK although there was heavy QRN during this transmission. Transmitted some hours earlier in the morning it could habe been 14 dB more above noise! Anyway the best distances are 264km (DL4YHF), 460km (F5WK) and 857km (Paul Nicholson).

Below you see some of the achieved screenshots of this transmission showing a carrier at 6469,97 Hz (due to the frequency offset of my DDS VFO of abt -30 mHz):

Overall carrier received at the DK7FC VLF grabber in HeidelbergOverall carrier received at the DK7FC VLF grabber in Heidelberg, 40 km distance

Reception at DD7PCReception at DD7PC, 53 km distance

Reception at DL4YHFReception at DL4YHF, 264 km distance

8,1m^2 kite in abt 200m height8,1m^2 kite in abt 200m height

Maximum antenna currentMaximum antenna current: 920 mA (voltage range here not valid)

In this experiment, the radiated ERP was up to 11 mW ante the antenna voltage up to about 20 kV rms!

Now i know where to make a tap on the coil to resonate at 8,97 kHz with the 200m vertical, about 275 mH! Then, the signal could become about 7 dB stronger compared to a 100m vertical antenna. This will be checked in the 7th experiment that may be in september.

The remarkable signal levels at the different locations give some questions about the propagation on the 46km band! Further tests will be done on this!

Also, see the final report of Paul Nicholsons scientific work on this experiment at http://abelian.org/vlf/ss100801/

CU in the 7th experiment?


May, 16th: The 5th experiment was a great success although there was no reception of my signal above 300km due to strong QRN that is typical for the summer period. But there was a lot of new equipment parts that were to test and that performed very well at once! A new analog amperemeter was integrated into the loading coil. It allows very good resonating the system and shows how the antenna current changes due to the kite movement.

New amperemeternew amperemeter


In this test the wind was a little unstable but anyway the kite was in a high angle mostly. The average current was about 800mA, 900mA peak. 900mA causes about 28kV (rms) at the antenna wire! This is the level were audible PD begin to occurr. So, with an antenna efficiency of 0,00059 % the ERP was up to 5,4mW, my best radiated signal so far...

Furthermore a new PA was tested successfully. It rectifies the mains at its input. The primary C of 2000µF has thus a voltage of abt 300V. Those are switched by a H bridge and feeds the primary winding of the loading coil. The PA system has partly mains potential. Thus, the primary winding has to be insulated from the VLF earth. The PTT and VFO signals are supplied byfiber optic cables, so perfectly decoupled. The PA gets not even hand warmduring running a 40min carrier at > 500W! Also it can handle pretty much reactive power. There are no problems when the wind falls out so that the wire lays on the ground and the antenna is out of resonance! This PA will also handle 1,5kW i suppose :-)

New VLF PA with a H bridgeNew VLF PA

Finally i could check some additional earth rods with gret success. One rod of 1m length and a second with just 20 cm decreased the earth losses from 450 Ohm to 300 Ohm. Here, i plan to achieve even better results in the upcoming tests....

The first time there was areception of a ham radio generated signal on my grabber. I transmitted DFCW-600 in the early morning ("FC"). This signal appeared up to 25 dB above noise. Later i transmitted DFCW-60 while the QRN came up and reduced the SNR.

DFCW-600 reception in 40km distanceDFCW-600 reception in 40km distance


In the next tests i will reach the 1A / 31kV antenna limit! :-) Additionally i plan to transmit a signal that allows me to compare a second VLF grabber at a different location. This helps improving those RXs. All in all it is a work that prepares the RX / TX system for the autumn/winter period where new world records will be done (by me?) :-)


April, 15th:Since today, my new VLF grabber is QRV. Here you can take a look tothe VLF activity in south Germany. The distance to my /p QTH is40 km.


The grabber is still in test mode and fed with a battery. The optimal configuration will be found in the next weeks.

March, 21th, 2010: 3rd activity! Now there are 10 stations who received my signal! A summary of their screenshots can be found at: http://abelian.org/vlf/ss100321/ The program was to transmit 2x the letter "K" in DFCW 600 mode. Such a "K" takes 30 minutes to be transmitted!! After that, i sent "DK7FC/P 73" in DFCW 120. This was nicely copied by DF8ZR (16km), Michael Oexner (72km) and DF6NM (180km). Others saw the message as well but not really readable. The first time, the signal crossed the alps and was nicely received at IK1QFK (544km). In UK the signal was detected by M0BMU (655km). The ODX is still Paul Nicholson (859km). Congrats to all Receivers!!

Now, some additional Photos of the recent activity for the VLF ham enthusiasts:

All in allAll in all

Keying the PA by DFCW by fiber optic cablesKeying the PA and DFCW by fiber optic cables

coil at extended placecoil at extended place

300W PA, still rather a prototype...300W PA, still rather a prototype...

VFO frontVFO front (f is divided by 2 (CMOS 4013)in the PA to get exact 50% duty cycle)

VFO back, with added DFCW switching circuitVFO back, with added DFCW switching circuit

View out of the shack ;-)View out of the shack ;-)


March, 15th, 2010: 2nd activity was a total success. A new ham world record in VLF transmitting and receiving was reached: 858,7km at 8,9700kHz. Paul Nicholson in the UK received my transmission! Detailed informations about that will follow here. Also Markus/DF6NM received my signal at his VLF grabber in 180km distance, congrats to the RXers!

Just some details on the Equipment: 100m Vertical wire antenna, coil/antenna voltage was abt 15kV rms, average antenna current about 480mA, giving up to 1,7mW ERP. Applied power was up to 250W.

Now some pictures of the 2nd experiment. The 3rd will be even more improved, i know what to optimise next...

Lifting up the kiteLifting up the kite

Adjusting to resonanceAdjusting to resonance

Building up the equipment

Building up the equipment

Watching voltage wave formWatching voltage wave form

Measuring antenna currentMeasuring antenna current

Taking some photos during transmitting ;-)

Taking some photos during transmitting ;-)

Resulting line in a distance of 180km at DF6NM's VLF grabber (15mHz FFT resolution)Resulting line in a distance of 180km at DF6NM's VLF grabber (15mHz FFT resolution)

So, the next experiment will be in the next weeks, most probably in the morning on saturday or sunday!


Before March, 15th 2010:In a first test i built a class D PA with about 130W out of 12V. The coil was not very suitable, 100mH with Q=28. So a parallel C of abt 3,2nF was needed for resonance. With this arrangement the antenna voltage was just 1,6kVrms, abt 23dB less than needed. 20kVrms is planned. This will give an antenna current of abt 0,65A into the 580pF 100m vertical wire. The listening station was in a distance of 16km but got nothing. But his RX wasn't suitable in this moment, as seen later. So, still optimistic! Markus/DF6NM reached 12,1km @ 8,97kHz with an ERP of 1,3µW, the new ham record in the "Dreamers-band", congrats! Dreamers band shall be the name for the 33km band since those hams who were optimistic to get successful reception in the far field were titled as dreamers, and they are! :-) So, with proper equipped RX stns and my new coil the ERP will be about 2,7mW when TX power is 200W!

Here a picture of the new coil, just finished before a few hours:

new VLF TX loading coil, on a 200 liter water barrel

Technical and mechanical data: L=553mH, Q=82, R(DC)=283 Ohm; 0,4mm diameter enameled copper wire, about 1200 turns! Average diameter 0,55m, height abt 0,5m. So, about 2000m wire! :-)

A 30mH variometer part and a current meter (1A full range) will be added before the next test. The next TX test will be in March @ 8,9700 kHz! Since yesterday (07.MAR10) Markus is offering his new VLF grabber: http://www.mydarc.de/df6nm/vlf/vlfgrabber.htm

cu there down!



LF section of this site below:

In the following there will be writtenthe latest of my 137 kHz activities that i do in theese weeks...It is due tothe interest, fascinationand euphoria that is inevitably achieved by being acitve in this band!

general discription of the setup:

Kite (Mega-Power Sled 36 (90% needed) and Mega-Power Sled 81(10% needed))supported vertical, 100m up, giving a C = 580 pF, so L = 2,3mH. Coil losses 8...13 Ohm. Overall resistance about 25...30 Ohm. Radiation resistance = 0,83 Ohm (antenna @ 90deg), so antenna efficiency about 3% (!!). RX: Elecraft K2with additional Converter by GW4ALG, receiving in the 30m band. RX antenna(s): TX antenna with a 6...34dB attenuator or a activeE-fieldantenna with signal transmission via a optic fiber cable (to avoid coupling of local QRM by a coax). The E-field antenna (30cm wire) has better SNR than the 100m vertical!. PA is a class E 1kW PA (running at lower power). QRV in CW, DFCW3. CW is preferred, if possible. Additional parts: Generator (650W), homemade paddles and keyer for CW, homemade power supply for the 12V car system voltage and PA voltage (adjustable), tuning-meter (to determine the phase/resonance and the Z), sequencer for CW (semi-bk) or DFCW/QRSS, 3 VFOs (DDS, analog and xtal). Secondary class E PA (12Vin, 40W/120W out).

05.12.09: Now i built my receiving loop for 137kHz. It has 44 turns and a diameter of 85cm (must be so small to be /p). I need abt 380pF for resonating on 137,7. The 3dB Bandwidth is less than 1kHz (measured in a lossy environment). Let's see which SNR can be achieved in the field... :-)

137kHz RX Ant, 44 turns

25.12.09: In this /p activity i got 3 new QSOs in about 7 hours of operation. First in CW, later in QFCW3. Tnx to Andrej/EW6GB, G3XIZ and IK1HSS. Wind was good the whole time but with some short breakdowns that caused strong QSB to my signal, as EW6GB remarked. Here a pic of the shack in the car in JN49IS...

/p LF Shack.../p shack in my car on the hill without local QRM :-)

During the QSOs the whole signals at the argo monitor had strong QSB (as if someone is playing with the AF-volume) and i thought there is a loose contact in the arrangement but later i noticed that my active antenna (which is completely separated to the whole equipment by afiber optic cable and battery supply) is strongly influenced by the TX-antenna. The following pic shows the dimension of the influence:

antenna tests

The screenshot of the argo monitor was in "visual gain HIGH" mode with the active antenna receiving and the TX ant wire disconnected of the loading coil. In the middle i connected the wire to the coil. In the right part i turned the argo mode to "visual gain low", that was the case during all the QSOs! I saw that the SNR is much better in the left part (sure, QRM is less but wanted signal also!) But anyway the SNR is better left, as i saw in the second half of the QSO with IK1HSS. That means, that the active antenna with a 30cm rx wire in 2m up has a better SNR than the 100m vertical TX antenna!

For the next activity i have to built a device that decouples the wire during RXing. I will try a relais (or perhaps even 2 antiparallel diodes?) between the lower end of the coil and ground...

03.01.2010 I started at 6UTC and was qrv at 9UTC. There was very much snow, also between the radias and ground. So the variometer has to be tuned to maximum L since there was an additional series capacity due to the snow. Wind was not very strong and became even weaker in the afternoon. Later i cahnged my kite from 3,6m^2 to 8,1m^2, giving 2 more hours of operation until the wind got down totally. I participated to the best activity for me. Mni stns in CW and QRSS. Tnx for QSOs to DF6NM, DK8ND, M0BMU and DD7PC. I got my best dx rx rprt ever:Ed, RU6LA sent me a screenshot of my DFCW3 signal out of 2233km :-)

my DFCW3 in 2233km

C Q D K 7 F C

Good copy although i had at least 3db less power then else. There is not even 1km of sea water between Ed and me so a transatlantic QSO could be possible? Naive? Optimistic but still no QSO partners from USA...

If you want to do a QSO, please contact me :-) I am not only interested in new dx records or new countries, each QSO has its own value and i'll be happy about it :-) Do not think that we cannot reach what wasn't reached yet.

Finally the car and the radials were covered by snow so i got afraid to be not able to leave the field any more ;-) The activity took abt 12hrs with a lot of fascination and motivation for the next improvements...

3. Jan 2010 @ -10°C 12hrs activity

The coil was covered by a trash bag for water shielding... Next improvements will be the reducing of coil losses by lifting the coil about 0,5m so the the magnetic field is not reaching the lossy ground. In lab measurements the R decreased from 13 Ohm to 8 Ohm!

Some older pics to get impressions...

Loading coil, wire, kiteloading coil 2,3mH with amperemeter and kite antenna

Tuningmeter, Kitetuning meter and antenna, view out of the car during QSO

ground plate and loading coil

CU next in /p...

Actual QSO ODXs in /p: CW:804km (G3KEV), QRSS3/DFCW3:1804km(RA3YO)

Actual cfmd RX-RPRTs ODXs in /p: CW:2038km(RN3AGC), QRSS3/DFCW3:2233km(RU6LA)

cu on the bands!

gl es 73s de Stefan / DK7FC














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