The 472 - 137 KHZ antenna placed between the two towers. Consists from 3 wires 28,00m long spaced 50cm each other. The antenna is a Marconi "T" type. The left side is at 30m height and the right side at 20m height. The center wire 40m long come directly to the shack. Ground system consists of about 150m wire with 4 poles in the ground and then connected to old galvanize tube water supply pipes.
The antenna on 137KHz has efficiency 1,77% and gain -17,50dbi. On 472 KHz has efficiency 17,7% and gain -7,50 dbi.
LOADING COIL AND VARIOMETER
The loading coil for 137KHz has a diameter 40cm, with 70 turns,coil lenght 20cm and about 100m wire 1,5mm2. The variometer consists of 2 coils. The external coil has diameter 16cm and the internal 5cm. Needed inductance for this type and size of antenna for 472KHz is 175 μH and for 137KHz 3mH. Both variometer coils give a tunning range between 270 to 390 μH.Using as transmitter YUMA TX136KHz I have in the output 50w. To test the antenna current I build a RF-ameter with a toroid coil 25:1 and a 100mA full scale meter. With 50w I can read 60mA in the RF-ameter. The antenna tunned on 137KHz has SWR 1,1:1.
TXing on 137.710KHz QRSS-10 cw I can see very often my signal in some EU's grabbers.
1) YO/4X1RF grabber : http://qsl.net/4x1rf/yo/lfgrabber.htm
2) DK7FC grabber : http://www.iup.uni-heidelberg.de/schaefer_vlf/DK7FC_LF_Grabber.html
Finished so far 2 QSOs in 137.710 KHz in QRSS-10 CW mode.
1) 27/01/2013 at 19:11z YO2IS QRSS-10 CW.
2) 27/01/2013 at 19:40 UW8SM QRSS-10 CW.
3) Heard DK7FC (wspr-15 strong) - DF6NM (wspr-15) - IK1HSS (wspr and qrss-10) - G8HUH (wspr-15) - UW8SM (wspr-15).
My first transmitions captured by my local radioamateurs neihbors SV8DOU (50m !!!) - SV8RX (8 KM) - SV8YM (12 KM).
Here is my QRSS-10 CW signal captured by YO/4X1RF grabber in Bucharest 03 Feb 2013 at 18:20z on 137.710 KHz.
In the R7NT DXCC 136 KHz list you can see GREECE for first time on 136 number DXCC country 50.
I would like to thanks Stefan, DK7FC - Marco IK1HSS for big help and ON7YD for his nice LF web page : http://www.strobbe.org/on7yd/136ant/
I hope to see you on LF band soon. For skeds or reports please e-mail me : sv8cs at otenet dot gr