7S6SAJ LF operation from Karlsborg 05 Feb 2000

- SM6BBM, SM6LKM, SM6PXJ -

In February 5-6 2000 we had the opportunity to use the old long wave antenna in Kraak, near Karlsborg, on the 136 kHz amateur radio band. We received a special permission from PTS to use 1 kW emrp.
The antenna system can be described as two T-antennas, each approx. 200 m high, in parallel. A model of the antenna is shown in the photo below. All pictures are clickable.

At our visit the antenna system was tuned to 49 kHz. Even though it was possible to tune it to 136 kHz by changing the existing tuner circuitry, we decided to keep it intact and instead connect directly to the antenna feeder. At the site office we found an old document telling the behaviour of the antenna at different frequencies. At 136 kHz we could expect an impedance of 14,7-j100 ohm for one T-antenna. In practice we found the impedance to be approx. 8-j100 ohm for the both antennas in parallel.

One of the two variometers in the ATU house.

A copper bar on top of the variometer (on the corona-ring) connects the both variometers in parallel. This bar was our connection point. A bamboo pole with a "snap-on" connector was available for this purpose.

The antenna was resonated on 136 kHz by means of a small variometer in series and a 1:5 impedance transformer to get 50 ohm to the TX. An SWR-meter and a HF amp meter was used as tuning aid. Finally we could get some 10 amps in the antenna. This would mean an ERP of approx. 700W.

     Yet another use for a clothes hanger.

After a few hours of preparations, we were ready for the first QSO. Strong signals in the RX but also relatively high noise level which made reception difficult some times. Occasionally we suffered from a local SSB TX a few MHz up.
Received signal reports indicated that the radiated signal was something extra.

SM6LKM adjusting the Skanti RX

Frequency counter, Standard Radio CR304, Skanti R5001

One half (50V) of the 100VDC/10A supply.

The TX was a 1kW class D, 4xIRFP450 with an external PC-controlled
DDS VFO. An Icom IC-725 with a low height dipole was used for X-band QSO:s on 80m.



A total of 58 QSO:s was achieved. That includes 4 QRSS contacts and 31 x-band QSO:s. Contacts were made with 13 different countries. The complete log can be found below. The primary goal for the operation was not to make as many QSO:s as possible, but just having a little fun and making a new experience. Between 00-04 UTC we sent QRSS (slow CW with 5 sec dot length) with the hope that someone on the other side of the Atlantic would detect our signals. Unfortunately we were unsuccessful this time.

A few links

The complete log and listener reports

The event generated some activity on the RSGB LF Reflector

recording by OK1FIG
recording by OM2TW
recording by IK1HSS
A write-up by SM6CJJ
SM6LKM's website include some pics from Kr�k
About Karlsborgs radiostation (Swedish)
Karlsborgs radio on Wikipedia (Swedish)

Last edited 2016-JAN-24 SM6PXJ