Message-ID: <4B9FE483.8020806@abelian.org>
Date: Tue, 16 Mar 2010 20:05:23 +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: <000001cac47a$f4ba1350$0202a8c0@laptopcore2> <E2DAF94B7561449DA86210B16A68F704@JimPC> <38A51B74B884D74083D7950AD0DD85E82A1B57@File-Server-HST.hst.e-technik.tu-darmstadt.de> <4B9F82C9.3000301@abelian.org> <4B9FB3F5.6030707@iup.uni-heidelberg.de>
In-Reply-To: <4B9FB3F5.6030707@iup.uni-heidelberg.de>
Subject: Re: LF: DK7FC's 2nd VLF TX test...
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


Stefan schrieb:
 > Paul, do you have ideas to even improve your RX or are
 > you at the limit? :-)

I have already used every trick possible - the rx sensitivity at
9kHz is as good as it can be.  I can think of no electronics
or signal processing that will make further significant
improvement.  It is just fine tuning now...

The only way forward is to combine the outputs of multiple
receivers.   For example, a fellow VLF enthusiast lives just
over a wavelength south of me.  By combining coherently
the outputs of the two receivers, a narrower beam can
be synthesised.  Adding further receivers into the network
gains further.  This would have to be the next step.

Thanks for the info on the DDS VFO, now I recall you mentioned
it in an earlier post.   I wondered whether it would do FSK.
The QRSS mode is very poor, a most inefficient use of the
channel capacity - literally a waste of time.  Dual frequency
Morse code would be much better, but better still an efficiently
encoded digital signal sent with UT synchronous FSK.

Probably Spectrum Lab already has everything you need for
this, including the ability to sync the carrier frequency to
an external frequency standard.

 > i plan to get the permission for a 300m vertical antenna!

Yes, it is much better to go higher than to go wider.  By going
higher, you increase both the antenna capacitance and the
effective height, the product of which is the dipole moment
per volt.  If you increase height by a factor N, the dipole
moment increases by N^2 and the ERP is proportional to the
square of the dipole moment!   If you put up 300m you will
be probably be detectable at 5000km or more.  Lets see, 20mW
at 5000km, that's about 6fT if 1/sqrt(r) holds out.  Kein Problem!

With some efficient message encoding, you will get your callsign
across the Atlantic in reasonable time - in both senses.

Oh, I will make a web page as you requested.
--
Paul Nicholson
--