A CAT5 fed PA9RDT antenna for VLF

This blog has reported on the excellent work by Roelof, PA0RDT on active antennas. In a note earlier in the year Roelof reports on an other variant of the design.

"Michael Oexner has had good results with a mini-whip E-field probe I build for him. The circuit diagram is below. The feedline is CAT5 network cable.

"Note that the RF-isolating transformers in the signal path are not correct. I have used MCL TT 1-6 parts, rated for 0.004 - 300 MHz at the -3 dB points. The common mode chokes are not optimum, as I used the parts I had on hand. Type 75 or 77 ferrite should be better.

"Michael used a PERSEUS SDR, which has a noise figure of about 25 dB at 9 kHz. This is due to the fact that there is also a RF-isolating transformer in the signal path.

"It is amazing that with this not optimized set up it was possible to have good reception over a 72 km path. The actual capture area of the antenna is 30 x 40 mm single sided copper clad PCB.

There are quite a few people around with a PERSEUS SDR, who are probably interested in receiving Stefan's (DK7FC) signal on 8790Hz (ed- yes Hertz). So a simple antenna design might help. "



Stewart/G3YSX