31 Jan 2013

More Ferrite Rod TX DXing

This evening I fired up the FT817 and the small 15mm diameter ferrite rod tuned with a 365pF air-spaced variable and have been spotted on WSPR even further away. This time a couple of spots from Norway, the best being LA9JO 2096km away. As someone pointed out, I may be coupling into local wiring and this might help, but the ferrite rod behaves just like a loop with good directivity and matching just as you would expect i.e. a very low impedance tap point is needed for a good match and tuning is extremely sharp. Personally I believe the radiation is all coming from the ferrite rod and nowhere else.
WSPR reports with a ferrite rod TX antenna on 40m (5W into rod)


Anonymous said...

The directivity effect would have to be shown to be evident on TX only and
the right direction to the distant receiver for your idea to be right!!

Roger G3XBM said...

Tony, surely not. With a small ferrite loaded loop I would expect the same directivity on both RX and TX.

Anonymous said...

Roger - Yes they are the same of course but it's a subtle one.
You have to think about it.

Put it another way, you would have to show that the DX receiver loses the signal if you point the end of the rod toward the station, if he doesnt lose your signal you could still be coupling into local wiring.
Do you get it?!

Roger G3XBM said...

Agreed Tony. I now understand and will confirm.

TiƩgui said...

Hello Roger,
you can be sure, your loop is not radiating. I have yet made experiments around that... and get nearly no radiation.

The near field from the ferrite is actually coupling to your house wires, this is in fact your antenna ! But not the loop.

73, from Thierry.

Klaus, DJ7OO said...

Roger, did you find the 73 Magazine article on ferrite rod transmitting?
( It's hard to find without knowing year and month of issue )

Wouldn't it be interesting making similar tests also on 10 MHz and maybe on 475 KHz?

Anonymous said...

Hi there,

Have you conducted any more HF tests on your ferrite transmitting antenna to confirm that it's actually the ferrite and not the house wiring that is transmitting?

I live in a concrete building and have constructed some traditional magnetic loops mounted on a concrete balcony, but I'm constantly intrigued by the possibility of the small ferrite transmitting antenna. In particular, if the ferrite truly is radiating, then this would allow the ferrite radiator to be placed at the end of a long stick and out in the clear beyond the walls of the concrete building, improving radiation by moving the radiator away from the lossy concrete.

But again, the key question is: is it really the ferrite that is radiating, and not the house wiring and/or the feedline?

Would love to hear your latest thoughts on this.

P.S. I commented a year or so ago on your previous ferrite rod article: http://g3xbm-qrp.blogspot.jp/2009/10/ferrite-rods-as-transmitting-antennas.html . I'm glad to see you are still experimenting in this area!