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

[Dr. David Kirkby (Kirkby Microwave Ltd)]

On 16 July 2015 at 08:05, Ole Stender Nielsen <olstni at mail.tele.dk> wrote:

> I use a home-made untuned loop antenna with 4 windings of 2.5 mm2
> insulated wire on a 80 x 80 cm wooden frame, and with a grounded base
> pre-amplifier mounted on the antenna frame. A schematic is enclosed for you
> to copy.
>

Thank you. I will build one of those. I have most of the parts here, but
not the transistors.



> The pre-amplifier is powered through the cable, and loads the FS700 input
> as required.
> I live about 290 km from the island of Sylt, and get nice noise margin
> figures from the FS700, normally about 40 dB, often up to 46 dB.
>

It's odd that http://www.loran-history.info/sylt/sylt.htm shows Sylt as
closing in 2006. Did Sylt ever close and then re-open, and that web site
just out of date?

I'm a little further than you (321 km vs your 290 km) from my nearest
transmitter. I'm located in Althorne, Chelmsford, Essex, UK (51.6517913 N,
0.7752657 E) and I *believe* my nearest Loran-C transmitters are

1) Lessay, France, power = 250 kW, distance = 321 km, bearing = 211 degrees.
2) Anthorn, England, power =- 250 kW, distance = 419 km, bearing 331
degrees.
3) Sylt, Germany, power =  250 kW, distance = 611 km, bearing = 52 degrees.
4) Soustons, France, power = 250 kW, distance = 896 km, bearing 191 degrees
5) Edja, Fraoe islands, power = 400 kW, distance = 1274 km, bearing = 341
degrees.


> For larger distances to the transmitter site, you may need to insert
> additional amplification between the grounded base pre-amplifier and the
> FS700, and that requires that you provide power to the pre-amplifier
> through a bias Tee, and that you load the FS700 input to keep it happy. A
> while after I installed the antenna in the attic, I added additional
> amplification, not due to a low signal level, but because I wanted to use
> the loop antenna for other longwave services too, and that required that I
> had to split out the signal.
>
> Best regards
> Ole
>

Thank you Ole. That at least gives me something to start from. I guess the
op-amp design Poul-Henning Kamp used offers more flexibility for gain
adjustment. I might look at that too. If the amplifier is in a box with a
couple of banana jacks and a BNC socket, it is fairly easy to change one
amp for another. I assume from what you say that the FS700 will report the

Dave