Re: LF: Ferrite wideband antennas?

[Daniele Tincani <danieletincani@yahoo.com>]

Hello Ha-Jo,

 

thank you for your reply, which contains many interesting information.

 

However, please note that my question was specifically about the possibility to realize wideband rx antennas on ferrite cores.

 

Best regards

Danile

From: "hajo.brandt.dj1zb@t-online.de" <hajo.brandt.dj1zb@t-online.de>
To: rsgb_lf_group@blacksheep.org
Sent: Friday, August 19, 2011 11:58 PM
Subject: Re: LF: Ferrite wideband antennas?

Dear Daniele,

At my locaton in eastern Bavaria I am using such a vertical broadband loop pointing north from 10 kHz to 500 kHz since several years and have also made experiments with a horizontal loop covering 1,8 to 30 MHz.

Their principle is as follows:

A broadband transformer is needed between the loop and the cable going into the shack.
Without such a transformer the loop inductivity has to be so high when feeding usual cable impedances that a ferrite core will be needed to realize the inductivity needed for broadband performance. I have used wire loops only so far.

The inductive reactance of the secondary of this transformer should be 4 times the cable impedance (3.2 mH for 10 kHz). The loop circumference should be low in length compared to a quarter of the highest frequency (for VLF to MF usually no problem, for HF the circumference had been 2 meters).

The inductivity of the primary of the broadband transformer should be equal to the inductivity of the loop (in my case 30uH and 17 meters circumference for 10 to 500 kHz).

When meeting these conditions, the inductive reactance of the loop itself will always be higher by a factor of 4 at least compared to the cable impedance transformed down by the turns ratio. This is the condition for the loop to operate broadband.

But the problem for the receiver may come in the shack: It must be capable of taking all the power delivered by the broadband loop, including the power received by broadcast transmitters! Otherwise the receiver may be overloaded and may need a more linear frontend or has to be equipped with a good front end selectivity.   

AT VLF to MF a long cable into the shack usually will be no problem because of its low attenuation at low frequencies, therefore all additional selectivity I can provide in the shack. For HF and higher the situation is different of course and may need at least part of selectivity and preamplification already at the loop output.

For the time being however, I have problems using my loop for the reception of SAQ, since a solar panel had been installed on a roof two houses from here, in autumn 2010. Obviously the chopper of this installation is generating a strong 300 Hz spectrum up to 20 kHz in my loop. As I could clear interference into my active antenna completely the interfering field should be inductive. It seems to come from several directions (including the wiring of three houses because the installation is feeding three phase current into the mains)!  

OK?

73 Ha-Jo, DJ1ZB  


"Daniele Tincani" <danieletincani@yahoo.com> schrieb:

Hello LF,

 

a very interesting discussion is in progress on the reflector on ferrite rx antennas. My understanding however is that until now we have been talking about narrow-band antennas. May I ask the experts if a wide-band ferrite antenna could be feasible, able to (partially) match the "panoramic" approach of SDR receivers, at least in the LF/NDB and/or MW bands? Such an "ideal" antenna would combine some advantages of air-cored loops with a reduced size (uhm... too "ideal" to be real :-))

 

Regards

Daniele