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')
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.
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) !