Message-ID: <014001c3dac5$075aceb0$f89a8418@Peter>
From: "Peter van Daalen" <peter@vandaalen.demon.nl>
To: rsgb_lf_group@blacksheep.org
Date: Wed, 14 Jan 2004 18:37:06 +0100
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Subject: Re: LF: lf andnoise and offshore.
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 Good afternoon Rik, James and all.

 Your responses were very encouraging.
 I decided to try LF this spring.
 I got enthusiastic about the idea to try LF on /MM.

 I have two frequency standards ( better than 1e11 tau 1000 secs ), so very
very  QRSS will be an attractive option for me.
I guess that very narrow FFT bins and very long integrating times should be
possible.
What is the longest sec/dot size that is used on amateur LF ?
I noted that Rik's QRS program offers up to 60 sec per dot.
Are there programs with much longer sec/dot times out there ?

 But before going /MM I have to build a LF station from scratch......
Therefore I need some help of your community.

 Do the various cheap car audio amps ( OP up to 600 W rms ) do a reasonable
job on 137 Khz ( after possibly removing audio filters etc. )  or is the
frequency roll-off disqualifying ?

 If disqualifying, does someone have a suggestion c.q. reference for me to
build a Tx ?
In the junkbox I have lots of Fairchild Power MOSFETS 75345P 55V 75 A ( ex
various 24>220 V AC ships power sinus converters ) mounted on heavy alu
cooling blocks.
So, if I have to build the Tx PA myself, I prefer to use these FETS.
Has someone a suggestion for a possibly suitable circuit diagram ?

 With an aerial effenciency that low, I guess the heat dissipation in the PA
OP stage will be tremendous.
Where is most of the heat dissipated ?
Though I don't know as yet what outputstages are used on LF, I guess this
will be in the tank/pi coil (?) and therefore I would welcome references to
information as to minimizing dissipation loss in coils ( or wherever else
the dissipation losses appear ).
( As I said before, I am an absolute virgin, at least on LF... :-)

 If advantageously, onboard I could build a very big multiturn loop aerial.
Does big multiturn LF loop aerials have an advantage over straight wire
aerials ?

 Is the maximum E(I?)RP still restricted to 1 W ?
Is this restriction applicable to /MM offshore as well  ( say midway on the
North Sea between G and PA  )?

Thanks for your thoughts.

 73, Peter PE1ECM


> > Hi Peter,
> >
> > At open sea QRM (man made noise) levels are likely to be low (apart from
> > what you generate on your vessel). So I wouldn't worry about QRM.
> > But the main advantage of /MM operation is that the loss resistance (the
> > main factor that determines antenna efficiency at LF) is extremely low
> > By using the steel vessel as counterweight the loss can be less than a
few
> > Ohms, at land it is in the range of 30 ... 150 Ohm at 136 kHz.
> > Your main problem might be to make a low loss loading coil, as the loss
of
> > a typical loading coil (on 136 kHz) is in the range of 5 to 20 Ohm.
> >
> > 73, Rik  ON7YD
>
>