[time-nuts] Firmware and antenna for Stanford Research FS700 Loran C frequency standard

paul swed paulswedb at gmail.com
Fri Jul 17 16:42:17 UTC 2015


I had not been paying attention to the thread but it has evolved into an
area I had a question about. Typical LORAN C systems are the vlf preamp and
whip.
You never see anything about larger antennas such as might be used from the
US to receive Europe stations.

For WWVB 60 KHz I built a large loop 10' X 10' and 800' of wire tuned with
preamp.
The gain was dramatic to say the least.

So I have been interested in building a large loop for LORAN C. But never
really found any detail. From this thread it may be actually useful. I
would build the same size loop but not make it sharply tuned because of the
large signal bandwidth +- 10Khz.

With the whip on winter nights I do get occasional lock of the European
signals.
Granted this will be an over the summer project.
Regards
Paul
WB8TSL


On Fri, Jul 17, 2015 at 8:31 AM, Dr. David Kirkby (Kirkby Microwave Ltd) <
drkirkby at kirkbymicrowave.co.uk> wrote:

> On 16 July 2015 at 23:23, Bob Camp <kb8tq at n1k.org> wrote:
>
> > Hi
> >
> > Quick and simple:
> >
> > 1) Signal power is proportional to the area of the loop. Bigger is
> better.
> > 2) Inductance is proportional to the turns squared. Turns do not directly
> > affect signal to noise.
> > 3) Inductance may be resonated with a capacitor. This gives a bandpass
> > function.
> > 4) The coil shapes are very common. The many inductance calculators on
> the
> > web will give you an inductance estimate.
> > 5) If the inductance is resonated, the system Q (and thus bandwidth) is a
> > function of the coil losses and the amplifier’s input impedance.
> > 6) More turns gives a power match into a higher impedance ( more
> voltage).
> > 7) *Practical* matching of the amplifier to the antenna will give you an
> > reasonable target number of turns.
> >
> > Bob
> >
>
> It's interesting that
>
> http://www.vlf.it/feletti2/idealloop.html
>
> says that sensitivity is set by the mass of copper used. To quote
>
> "A single turn square loop, 1m side, made with 1kg copper has the same
> sensitivity of a 1000 turns square loop made with 1kg copper and  same
> dimensions. In this context, the sensitivity limit is represented only by
> loop thermal noise:
>
> noise floor (nV/sqrt(Hz)) = 4 sqrt(R in kOhm)"
>
> It is not immediately obvious where that equation comes from, but
> re-arranging the equation for thermal noise power
>
> P=k T B
>
> (P in watts, k= Boltzmann contant, B is bandwidth in Hz)
>
> and assuming a temperature T of 300 Kelvin, k = 1.38 x 10^-23 J/K, one
> finds the constant is 4.06, so the 4 in that equation is fairly accurate at
> 300 Kelvin.
>
> I'd much rather wind a loop with a few turns than a few hundred turns!  But
> obviously the voltage rises with the number of turns, so requires less
> gain.
>
> Dave
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