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Re: LF: lf andnoise and offshore.

To: [email protected]
Subject: Re: LF: lf andnoise and offshore.
From: "Peter van Daalen" <[email protected]>
Date: Wed, 14 Jan 2004 18:37:06 +0100
Reply-to: [email protected]
Sender: <[email protected]>


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






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