Message-ID: <4BA0C110.8030806@abelian.org>
Date: Wed, 17 Mar 2010 11:46:24 +0000
From: Paul Nicholson <vlf0308@abelian.org>
User-Agent: Thunderbird 2.0.0.14 (X11/20080421)
MIME-Version: 1.0
To: rsgb_lf_group@blacksheep.org
References: <910844.27140.qm@web86505.mail.ird.yahoo.com> <4B9FDFA7.7090208@gmx.com> <38A51B74B884D74083D7950AD0DD85E82A1B60@File-Server-HST.hst.e-technik.tu-darmstadt.de>
In-Reply-To: <38A51B74B884D74083D7950AD0DD85E82A1B60@File-Server-HST.hst.e-technik.tu-darmstadt.de>
Subject: Re: AW: LF: 8.97kHz antennas
Content-Type: text/plain; charset=ISO-8859-1; format=flowed
Content-Transfer-Encoding: 7bit
Sender: owner-rsgb_lf_group@blacksheep.org
Precedence: bulk
Reply-To: rsgb_lf_group@blacksheep.org


After my post yesterday I realised there is one more thing
I can do here to the rx.  I have an E-field rx running too,
if this was combined coherently with the loop antenna,
some further directivity might be obtained.   But as yet,
I have not found a suitable device amongst the studio grade
soundcards to handle more than 2 channels at 192k/sec 24 bits
with non-proprietary drivers.

Stefan schrieb:
 > I cannot imagine that we get an improvement at even lower
 > frequencies.

Maybe not.  We should do some arithmetic first before wasting
time during tests.   The noise and attenuation are both lower,
but so is the ERP.   At very long range a lower frequency may
turn out to have the edge.

It is worth noting that, in geometrical terms, there is as
much spectrum to experiment with at VLF as the whole of
short-wave.

 > Is it possible to built a loop that has even more gain, such
 > as e.g. a 4ele cubical quad on HF?

No the element separations required are too great.  To obtain
more directivity, the incident wave must be sampled at points
separated by some significant part of a wavelength.   Actually,
arrival direction can be determined by quite short separation
if phase difference can be measured precisely, but S/N ratio
needs to be high and this doesn't provide genuine directivity.

 > You told us you have a RX antenna out of  2 loops, coupled
 > in a special way.

They are connected (in software) to produce omni-directional
response to horizontally polarised signals, as in a turnstile
antenna with 90 deg phase shift of one loop.   This is good for
whistler reception, as whistlers are theoretically circularly
polarised and the combined loop polarisation in the vertical
direction is circular.  Also the loops are combined in-phase
to produce the steerable figure-8 response for horizontal
directivity.   In software of course, both loop connections
can be done at the same time...

 > And makes it sense to try to receive with the 100m vertical?

Maybe.  Avoid rx overload at all costs (sferics, 50Hz, MF/HF
intermod).  What will the static noise be like?   A thin wire in
a strong wind... triboelectric hiss and static collected from
dust, pollen, etc.  A smaller antenna should give enough S/N,
larger than necessary can introduce these other problems.
Loop antennas avoid many of the problems and provide directivity
to null some of the background (without this directivity,
your signal would not have been reliably detected here).

--
Paul Nicholson
--