DF0WD/DL4YHF's Longwave Overview

last updated: March 20th, 2001

General Longwave Information

Amateur radio operation on long wave is allowed in Germany in a small segment between 135.7 and 137.8kHz. The following "inofficial" band-plan is used by most amateurs in Europe :

  135.7 to 135.8: QRSS ('visual CW')
  135.7 to 136.0: TX tests & beacons
  136.0 to 137.4: Normal ('conventional') CW.
  137.4 to 137.6: Data modes
  137.6 to 137.8: QRSS ('visual CW')

See the links page for more information about amateur radio activities on longwave. At the present time, I prefer normal CW operation if possible (to be precise, I didn't have a QRSS CW QSO up to now :-). Tests with PSK31 and other (slower) binary phase shift keying modes (BPSK) are planned.

Summary of the LF activities at DF0WD

To start on LF shortly after the new allocation in DL, a simple 20-watt CW transmitter was built with a conventional LC-VFO divided down to 136kHz (to prevent "pulling" the VFO). The receiver was a Kenwood TS850 with narrow-bandwidth CW filter (270Hz).

In April 2000, the old CW transmitter was replaced by a homemade linear transverter with a maximum output of 100 watts. An old Icom IC706 is used on 10.137 MHz to transmit and receive on 137kHz.

My antenna tuner looks a bit like a tesla coil. It is used to transform the 50 ohms from the transverter into the complex impedance of the antenna.

The longwave antenna we are using here is a 200 meter wire held by the light-masts of a football-field where DF0WD is located. The mean height above ground is roughly 10 meters. Though 200 meters sounds like a "long wire" it definitely is not (in terms of wavelength). The efficiency of that antenna is still very low (see comments on the EIRP below).

Countries worked by DF0WD/DL4YHF in normal (conventional or "fast") CW on 136kHz are DL, F, G, GI, GM,GU, GW, HB9, HB0, LX, OE, OH, OK, OM, ON, OZ, PA, SM (still looking for CT, EI, LA/LG, a "complete 2-way" QSO with Italy and whoever has an LF allocation!).

Effective Radiated Power (or: "the problem with TX antennas")

The main problem on LF is that our TX antenna is always too small.. considering the wavelength of about 2.2 km. There is a lot of formulas for calculating the efficiency of an antenna, but they usually fail because of unknown ground properties (ground conductivity etc). The efficiency of most amateur LF antennas is usually much less than one percent.
The only way to find out the effective radiated power (in "EIRP" or one of its flavours) seems to measure it. You'll be lucky because there are some radio amateurs out there to help you with this.
The following estimate is based on an E-mail posted to the RSGB LF Group from Dick, PA0SE, who measured a field strength of 10 uV/meter for DF0WD in a distance of 266 km. Here is Dick's formula and a few explanations:
Assuming perfect ground over the whole radio path it is possible to calculate what the EIRP at least must have been by using the formula:
P = 1.11 * 10^-8 * (E * d)^2 in which:
P = EIRP in W
E = field strength in µV/m
d = distance between the stations in km.
Because the path is not perfect the actual EIRP must be greater than the value so calculated.

So the EIRP of DF0WD's LF antenna must have been somewhere about 80 milliwatts (with wet trees also affecting the efficiency, antenna current only 1.5 A) !

In Germany, we are still waiting for a (general) regulation which limits the power to 1 Watt(!) ERP like in most European countries.

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