Re: LF: Ferrite RX antennas

[Daniele Tincani <danieletincani@yahoo.com>]

Just to complete the picture about LF-enabled antennas, recently Claudio Re I1RFQ has introduced his so-called MaxiWhip design (as "opposite" to the MiniWhip :-)). If my understanding is correct, it basically consists of a vertical element (9 m tall, supported by a fishing rod for example) and a special 32:1 balun (probably un-un). The report at following link (by Angelo Brunero IK1QLD) is in Italian, but shows interesting results in a direct comparison with the MiniWhip: http://www.brunero.it/ik1qld/antenna/.

 

Personally, I prefer to work with small wideband or tuned loops. In my particular, unfortunate condition (very noisy urban area around my QTH), it seems to me that loops offer more predictable results. In my modest opinion, E-probes tend to be more subject to external, environmental factors than loops, so are more suitable for open areas with a good distance from noise sources, metal structures, etc.. Difficult to obtain with a decent predictability in my personal case.

 

Best regards

Daniele

From: Stefan Schäfer <Stefan.Schaefer@iup.uni-heidelberg.de>
To: rsgb_lf_group@blacksheep.org
Sent: Monday, August 15, 2011 7:26 PM
Subject: Re: LF: Ferrite RX antennas

Hello Wolf,

Thanks to the link to your nice to read article. I just found it a hour before your mail and already read it ;-)

Well, i also prefer the usual configuration instead of that sleeve antenna. Also i have to keep the focus on my actual goal: Making a handy antenna for amateur LF / p operation without a car! And the 16 rods i will get (14 cm long, 8mm diameter) will be best in a 2x7 config. i think. Or do you rather suggest 3x5 or even 4x4?
2x7 is then about 30 cm long which is very fine for a backpack and should be robust enough.
I would use the same double side bonding tape, this is very useful to get a first fixed arrangement. Then putting all that in a PVC tube, 2mm thickness and add the turns above the tube.
Would you recommend litz wire or standard 0.5 mm enamelled wire?
As an E field shield i would use aluminium bonding tape, without making a shutcut turn of course.

So the newcomers should not think that this antenna is the best what one can use for LF. Just in that special case of /p i see advantages. Otherwise a well designed loop (+ preamp or a very sensitive RX, if a samll loop is used) or E field antenna such as the PA0RDT should be preferred, as Alan already pointed out.

Looking forward to a direct comparison of the DCF39 SNR that can be achieved and to the first amateur signal received with that antenna in /p...

73, Stefan/DK7FC




Am 15.08.2011 18:33, schrieb wolf_dl4yhf:

Hi Stefan,
The rods were found in Friedrichshafen for a bargain price. I later discovered (most likely after the topic had been discussed here, or in the VLF group) that these rods are used for inductive welding (google("Ferrite Impeder Rod"). Here's a bundle of them:

http://www.qsl.net/dl4yhf/vlf_rdf/vlf_rdf_loop.html

They are 20 cm long.

The most effective use (to "catch the magnetic field from a distant transmitter") is NOT to connect them 'parallel' in a bundle, but to connect them in series (up to a certain point). This is much in contrast to the esoteric sleeve thingy seen somewhere on the web.

73,
   Wolf .



Am 14.08.2011 23:43, schrieb Stefan Schäfer:

Wolf,

Which dimensions has your ferrite rod had?

Never thought i will find a source for rods that are longer than 10 cm but see: http://www.box73.de/catalog/product_info.php?products_id=1422&osCsid=rqlpfme957i65d7etjil1ntru5

even an official distributor..

Any better links?

73, Stefan/DK7FC

Am 14.08.2011 22:27, schrieb wolf_dl4yhf:

Ferrite RX antennas.. been there when 136 kHz started.
Not as good as a larger air-core loop, possibly noise caused by the Barkhausen effect or similar effects, nonlinearities, etc.
Also beware the ferrite is a semiconductor so you will need some E-field screening, otherwise the ferrite material will couple noise into the windings. But it's not as bad as this may sound; actually I used a ferrite antenna for reception for some years until I discovered I had to disconnect the ...errr... RF counterpoise from the main antenna from the mains "ground", and only use an earthstake during receive, at DF0WD.

On the other hand, it's compact, relatively light-weight, and (in a resonant configuration) gives a nice preselector.
I remember when I connected a ferrite antenna to a tiny receiver with SA612 "gilbert cell mixer", the first signal I heard was G3KEV calling cq in CW.  Q5 in SSB bandwidth.
Such a receiver is extremely handy to go /p for reception, and compare different sites.

73,
   Wolf DL4YHF.


Am 14.08.2011 21:43, schrieb Minto Witteveen:

I haven’t thought about ferrite RX antenna for LF….My guess is that it is not going to work – not without an external antenna coupled to the ferrite, and then what’s the point?
DCF77 clocks often have trouble locking indoors or in the neighborhood of ‘QRM’ generators like PC’s, and look what power DCF77 is using…
I could be entirely wrong of course…

73’ Minto pa3bca

 

From: Stefan Schäfer

Sent: Sunday, August 14, 2011 20:03

To: rsgb_lf_group@blacksheep.org

Subject: Re: LF: Re: 137 grabbers

 

<snip>
BTW what do you think about a ferrite RX antenna for LF? Now i'm opening an older discussion i expect ;-)

73, Stefan/DK7FC