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

Bob Camp kb8tq at n1k.org
Thu Jul 16 18:23:06 EDT 2015


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



> On Jul 16, 2015, at 9:57 AM, Dr. David Kirkby (Kirkby Microwave Ltd) <drkirkby at kirkbymicrowave.co.uk> wrote:
> 
> ZOn 15 Jul 2015 22:18, "Poul-Henning Kamp" <phk at phk.freebsd.dk> wrote:
>> 
>> --------
>> David Kirkby - Kirkby
>> Microwave Ltd " writes:
>> 
>>> What's the best sort of antenna for these?
>> 
>> I use a $20 loop antenna I have rigged up myself, it lives in my attic:
>> 
>>        http://phk.freebsd.dk/loran-c/Antenna/
> 
> Hi,
> Thank you for that. But it is a bit short of information.  I appreciate
> your use of "the nearest bent nail" principles, but roughly how many turns
> were there on the coil? Do you have a circuit for the amplifier? The AD797
> data sheet you link to is broken, but the error message is quite funny. I
> found the data sheet on the AD797 and see it is a very low noise op-amp.
> 
> I must admit to knowing next to nothing about antennas at the Loran 100 kHz
> (+/- a lot) frequency. How does one go about testing the antennas? I'm
> about to place an order for an FS700, but will not have an antenna when it
> arrives. I have a short period of right of return, and I'd like to get
> something in place so I can quickly test this.
> 
> I have an HP 4284A precision LCR meter which works at more than 8000
> discrete frequencies between 20 Hz & 1 MHz. Those frequencies include 60,
> 80, 100, 120 and 150 kHz.  That's the only thing I have got that measures
> impedance as low as 100 kHz.
> 
> There's a description of the active antenna for the FS700 in the manual,
> but with no circuit diagram, it is a bit tricky to understand. I assume
> that the FS700 has some sort of bias-T to pass DC up the cable to power the
> amplifier - is that so? If so, do you know the voltage?
> 
> No doubt all these things will be revealed when I get the FS700, but I'd
> like to be ready to test it when it arrives.
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