Re: LF: Coupling a LF resonant ferrite rx antenna

[Daniele Tincani <danieletincani@yahoo.com>]

Hello Stefan, your hand-sketched schematics (and also the way you built the antenna, etc.) look just like my idea of the final result I would like to obtain. BTW I still have some BF862s from my experiments with your VLF E-probe :-) I think I would try to replicate your example.

73

Daniele IZ5WWB

Da: Stefan Schäfer <Stefan.Schaefer@iup.uni-heidelberg.de>
A: rsgb_lf_group@blacksheep.org
Inviato: Giovedì 28 Giugno 2012 17:22
Oggetto: Re: LF: Coupling a LF resonant ferrite rx antenna

PS: For a 50 Ohm output, just 2 or 3 turns on the out-coupling winding was the best choice for my ferrite antenna.

Am 28.06.2012 16:54, schrieb Stefan Schäfer:

Hi Daniele.

If your RX is successful enough, maybe a simple transformer works well.

Apply a test signal by using a loop, say 20cm diameter, inductively coupling to the ferrite. Then use a secondary winding which goes directly to the coax of the RX. Use a 50 Ohm resistor or an oscilloscope with a 50 Ohm input directly. Adjust the number of turns to get a maximum signal voltage on the scope. The match also strongly depends on the position of this secondary winding on the coil. The impedance becomes lower when you come closer to the center of the rod.

The will affect the Q of the resonated system. So you may build an arrangement which allows you to move and fix the secondary coil on the rod. If the signal is strong enough, maybe from a nearby BCD station, you can reduce the "gain" a bit. I have done it similarly with my active ferrite antenna, see https://dl.dropbox.com/u/19882028/LF/DK7FC_LF_p_active_ferrite_antenna.JPG

73, Stefan/DK7FC


Am 28.06.2012 16:14, schrieb Daniele Tincani:

Hello LF,

 

it seems I managed to build a pretty good ferrite coil (abot 80 turns of Litz wire over a bundle of seven 20cmx1cm rods). Nulling and peaking seem acceptable for my purposes. With current var cap, tuning range is about 160-650 kHz and could easily be moved to lower frequencies by adding a parallel fixed capacitor. Until now I have only made some quick tests by inductively coupling the coil with the internal ferrite of a portable radio. I would like now to make the antenna suitable also for direct connection with a 50 ohm input. What do you suggest: to add for example a transformer or a buffer amplifier (or both :-))? If a transformer is recommended, is it advisable to use the main coil as the primary winding?

 

73

Daniele IZ5WWB