Mini-Whip with CAT5

I have previously reported on the excellent mini-whip design produced by Roelof Bakker (PA0RDT) (http://carconline.blogspot.com/2009/05/pa0rdt-active-antenna-continued.html).

Recent work on the application of the design to VLF reception has enabled the use of CAT5 (Ethernet) cable in place of a coax feed.



As Roelof said in a note to the RSGB LF reflector : "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."

Referring to work on 9KHz he continues "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."

"I have the parts for an optical link active E-field antenna, as suggested by Stefan. Due to other more pressing matters, I have not yet put them to good use."

It looks therefore as if we can expect further developments of this simple but very effective design.

Joze (S52AB) reports on a CAT5 mini-whip http://s52ab.jalbum.net/mw-test-2/ in which he shows a comparison between reports on a CAT5 fed mini-whip and (presumably) the same mini-whip fed with coax. My visual impression from looking at the received signals is that the CAT5 has a higher loss, although it is not clear at what frequency these measurements were taken. For those interested in LF work, Jose's main site (http://lea.hamradio.si/~s52ab/) is worth looking at.

- Stewart/G3YSX