David
Any LORAN C boat antenna will work fine. I do know that if you have a
distribution system then to make the SRS happy you need to add a 420 ohm R
to ground to act as a antenna preamp current load. It checks.
Equally a fet/transistor VLF preamp will work well. Even a long length of
wire if the signals strong.
Regards
Paul
WB8TSL

On Wed, Jul 15, 2015 at 12:02 PM, Dr. David Kirkby - Kirkby Microwave Ltd <
drkirkby@kirkbymicrowave.co.uk> wrote:

Hi Dave:

I've used both an active short whip antennas and what may be better a long wire (100 feet) resonated with a series
inductor (Miller adjustable 3 mH).

http://www.prc68.com/I/LF-Ant.shtml

http://www.prc68.com/I/Spec_0002.shtml

Mail_Attachment --
Have Fun,

Brooke Clarke
http://www.PRC68.com
http://www.end2partygovernment.com/2012Issues.html
http://www.prc68.com/I/DietNutrition.html
Dr. David Kirkby - Kirkby Microwave Ltd wrote:

In message 55A68425.6020700@kirkbymicrowave.co.uk, "Dr. David Kirkby - Kirkby
Microwave Ltd " writes:

I use a $20 loop antenna I have rigged up myself, it lives in my attic:

http://phk.freebsd.dk/loran-c/Antenna/

--
Poul-Henning Kamp      | UNIX since Zilog Zeus 3.20
phk@FreeBSD.ORG        | TCP/IP since RFC 956
FreeBSD committer      | BSD since 4.3-tahoe
Never attribute to malice what can adequately be explained by incompetence.

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.
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.

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

Den 15-07-2015 kl. 18:02 skrev Dr. David Kirkby - Kirkby Microwave Ltd :

ZOn 15 Jul 2015 22:18, "Poul-Henning Kamp" phk@phk.freebsd.dk wrote:

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.

In message 55A757D3.9050709@mail.tele.dk, Ole Stender Nielsen writes:

A note about Loran-C and loop-antennas:

The loop-antennas are sensitive to magnetic fields and therefore
sensitive to direction.

Depending on side of the loop you point at the Loran-C transmitter
you will get a "true" or inverted signal.

If you get an inverted signal, a Loran-C receiver will lock onto
the wrong zero-crossing, which will increase your phase noise
because only the 3rd positive crossing is truly steered.

If you want to receive more than one Loran-C transmitter, the
directivity of the loop-antenna is a disadvantage and you are better
of with a monopole (electric) antenna.

I can recommend Chris Trasks designs:

http://www.home.earthlink.net/~christrask/

I built one from the "Complementary Push-Pull Active Antenna Amplifiers"
document and it drags in signals from 4kHz to well north of 150Mhz.

--
Poul-Henning Kamp      | UNIX since Zilog Zeus 3.20
phk@FreeBSD.ORG        | TCP/IP since RFC 956
FreeBSD committer      | BSD since 4.3-tahoe
Never attribute to malice what can adequately be explained by incompetence.

In message CANX10hBuaHDwaChb+wHLKen4wcwn5_R2UEn9aJZmnvL8AxZe4Q@mail.gmail.com
, "Dr. David Kirkby (Kirkby Microwave Ltd)" writes:

Probably too many, all things considered, but I have no idea.

It was based on/inspired by a schematic I found on vlf.it

Plug it into a spectrum analyzer or oscilloscope.

Use average mode.

Trigger with a pulse generator with a period of:

 6731 * 2 * 10µs) = 0.13462 Hz

and you should see the pulses.

If you have a good spectrum analyzer, you can probably do this with
a few meters of wire as antenna.

The result should look something like:

http://phk.freebsd.dk/misc/dscf0275.jpg

100 kHz is practically audio, impedances hardly matter: The reflections
have wavelengths measured in km.

--
Poul-Henning Kamp      | UNIX since Zilog Zeus 3.20
phk@FreeBSD.ORG        | TCP/IP since RFC 956
FreeBSD committer      | BSD since 4.3-tahoe
Never attribute to malice what can adequately be explained by incompetence.

Ole,

What is the value of the "2E21" resistor?
Looks like a typo. 2k?

Feel inspired to rig up something for my FS700.

Will wooden frame my TP-cable wired to form a 8 turns times the cable-turns.

Cheers,
Magnus

On 07/16/2015 09:05 AM, Ole Stender Nielsen wrote:

Hi Magnus,

The 2E21 is a 2.21 Ohms resistor.
The RC network was found useful to ensure loading at higher frequencies.
Best regards
Ole

Den 16-07-2015 kl. 18:27 skrev Magnus Danielson:

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

Hi Ole,

Many thanks, 2.21 Ohm sounds more reasonable than 2 ZettaOhm (or 2 ZO),
which is what 2E21 would translate into if it where 2*10^21, so I wanted
to make sure there wasn't a typo. :)

Then I know that my values may vary for that part of the design.

Cheers,
Magnus

On 07/16/2015 09:21 PM, Ole Stender Nielsen wrote:

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

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

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.

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

On 16 July 2015 at 23:23, Bob Camp kb8tq@n1k.org wrote:

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

On Fri, 17 Jul 2015 10:03:00 +0200
Magnus Danielson magnus@rubidium.dyndns.org wrote:

xEy is some kind of semi-standard notation for resistor values
in the first three decades, when people do not want to write R
(as it might be confused with the part number) or a dot (which
might get lost when printing). But I don't know where this notation
came from, or what the E stands for. I can only say I have seen it
quite a few times already.

		Attila Kinali

--
It is upon moral qualities that a society is ultimately founded. All
the prosperity and technological sophistication in the world is of no
use without that foundation.
-- Miss Matheson, The Diamond Age, Neil Stephenson

Hi

The power into the loop is a function of the area.

simply the standard thermal noise equation for a resistor

but the load resistance (and thus the thermal noose in that load) goes up at the same time. If you
have a very low impedance buffer (common base stage etc) the number of turns will be very different
than if you have the input gate of a MOSFET.

Bob

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@kirkbymicrowave.co.uk> wrote:

On Fri, 17 Jul 2015 12:55:07 +0100
"Dr. David Kirkby (Kirkby Microwave Ltd)" drkirkby@kirkbymicrowave.co.uk wrote:

I would probably replace the AD797 with it's younger cusin the AD8099.
The noise performance is very similar, but it has a GBW-product of

gain in the first stage. And best is: you can run it from a +5V supply
and don't need to bother with a +/-5V supply (keeping in mind that the
AD797 specs are for +/-15V, so they are likely to be worse at +/-5V).

Please note that neither of those opamps are rail-to-rail. You need
to stay 1.3V clear of the rails for the AD8099 (both, input and output)
and 2.5V and 3V for input and output respectively for the AD797.
The datasheet does not specify what happens when you cross the input
rails limit, but I would expect nasty stuff like gain reversal and such.

Also, the absolute maximum ratings have a maximum differential input
voltage of 1.8V and 0.7V respectively. Do not cross that line, lest
you want to smell magic smoke (ok, not really, but it might at least
detoriate the input protection diodes, if not fry them)

		Attila Kinali

--
I must not become metastable.
Metastability is the mind-killer.
Metastability is the little-death that brings total obliteration.
I will face my metastability.
I will permit it to pass over me and through me.
And when it has gone past I will turn the inner eye to see its path.
Where the metastability has gone there will be nothing. Only I will remain.

In message 36E5F870-B2DD-42BB-A1D5-24D241ACAE88@n1k.org, Bob Camp writes:

I think they're barking up another tree:  The number of turns you
can make is inversely proportional to cross-section of the wire,
so given a fixed mass of conductor, you can trade current for voltage
by the number of turns.

--
Poul-Henning Kamp      | UNIX since Zilog Zeus 3.20
phk@FreeBSD.ORG        | TCP/IP since RFC 956
FreeBSD committer      | BSD since 4.3-tahoe
Never attribute to malice what can adequately be explained by incompetence.

In message CAD2JfAhdfe1ZQccukXFyEZnnPa35QwP1cQPbgKptfmhS9fCkPQ@mail.gmail.com
, paul swed writes:

You cannot use a tuned/resonance loop for LORAN-C the way you can for CW
stations like WWVB.

Loran-C needs +/- 15kHz flat bandwidth (85-115 kHz) otherwise you
loose the pulse-shape which allows you to find the right zero-crossing.

--
Poul-Henning Kamp      | UNIX since Zilog Zeus 3.20
phk@FreeBSD.ORG        | TCP/IP since RFC 956
FreeBSD committer      | BSD since 4.3-tahoe
Never attribute to malice what can adequately be explained by incompetence.

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

A couple of questions

1. Do you have any suggestions for a replacement for the LM394CN, which is
   obsolete and unobtainable from any reputable source? There are plenty on
   eBay for a few $'s from China, but the probability of them being fakes is
   greater than 0.99. The MAT12 seems to be one possible candidate for a
   replacement and while not cheap, is available from reputable sources like
   Farnell.

2. What is the "Ca. 3 Ohm" to the left of your circuit? Is that what you
   estimate the input impedance is? I've got 95 m of 2.5 mm^2 wire. The
   resistance of that is about 7.41 mOhm/m so my 95 m would have a DC
   resistance of around  7 Ohms if I used it all.

I have built the loop 1.0 x 1.2 m. Hopefully that will be ok to receive at
least one or both of

• Lessay, France, power = 250 kW, distance = 321 km, bearing = 211 degrees.
• Anthorn, England, power =- 250 kW, distance = 419 km, bearing 331 degrees.

I now need to work out how many turns to put on it.

Dave

The value of 2.21 Ohms was picked from the drawer, and you may need/want
to use another value.
In fact, the values of the input RC network should not be critical, but
the values in the schematic are those I ended with while doing some
experiments with different loops.
Best regards
Ole

Den 17-07-2015 kl. 10:03 skrev Magnus Danielson:

On Fri, 17 Jul 2015 21:49:01 +0100
"Dr. David Kirkby (Kirkby Microwave Ltd)" drkirkby@kirkbymicrowave.co.uk wrote:

The SSM2212 seems to be a quite compatible replamcement, with most
parameters being in the same range. Cost ~6USD/pcs

But i guess, for this application, the noise performance of the
transistors is not that critical and something like a BCM847 should
do the job as well. (cost <0.5USD/pcs)

ca. = circa = approximately. Probably an abrevation that is only
common around europe.

Hmm.. I think the impedance matters more than the resistance.
But the schematics does not make any reference to that.
Consider me confused.

		Attila Kinali

--
I must not become metastable.
Metastability is the mind-killer.
Metastability is the little-death that brings total obliteration.
I will face my metastability.
I will permit it to pass over me and through me.
And when it has gone past I will turn the inner eye to see its path.
Where the metastability has gone there will be nothing. Only I will remain.

MAT12 of ADI is good replacement and it is available at Mouser

http://www.mouser.com/Search/Refine.aspx?Keyword=MAT12

On 7/17/2015 1:49 PM, Dr. David Kirkby (Kirkby Microwave Ltd) wrote:

I had a few LM394CN left and used one for the pre-amp.
I would try to use another low-noise transistor. Furthermore, you do not
necessarily need a matched pair. The transistor on the right in the
schematic is merely used for biasing the amplifying transistor on the
left. The prices for matched pairs can get ridiculously high, so I too
would try to look for alternatives. If you still want a matched pair,
there's the SSM2212 from Analog Devices, which is priced lower than the
MAT12. You may also be able to find the earlier SSM2210, which now is
obsolete. Another alternative is the THAT300 from THAT Corporation,
which has 4 low-noise NPNs in a 14-pin DIP (great for experiments...)
Useful single NPN transistors I can think of would likely be the BC337
or perhaps the 2SC3324 which both have low Rbb, and they are quite cheap.

The "Ca. 3 Ohm" was indeed the estimated input resistance, including the
series resistance of the input capacitor as I recall.

Best regards
Ole

Den 17-07-2015 kl. 22:49 skrev Dr. David Kirkby (Kirkby Microwave Ltd):

On 18 July 2015 at 09:45, Ole Stender Nielsen olstni@mail.tele.dk wrote:

Hi,
I ordered the parts for this, including a MAT12. I do consider some
arguments put by others - the first on the mailing list, the second
privately.

1. There are cheaper low noise devices - that in itself has generated into
   another thread.

2. The atmospheric noise at 100 kHz is high

But given

• A MAT12 is not a fortune from reputable semiconductor suppliers like
  Farnell (I would not consider eBay, due to fakes)
• I am only building one, so cost is not a huge issue.
• The MAT12 is specified for low noise, without me wasting time selecting
  devices.
• MAYBE the argument about atmospheric noise is valid - I tend to agree
  with it, but again due to the one-off nature of this, I am going to ignore
  that argument.

So I bought a MAT12. I'm not going to change that - it is bought, paid
for and here.

If the input resistance of that common-base amplifier is 3 Ohms, does it
make sense to have the loop resistance 3 Ohms too? For maximum power
transfer one wants the source and load to be the complex conjugate, but I
know for microwave devices, you do not design the input match for maximum
power transfer, but generally minimum noise.

I just checked my HP 4284A precision LCR meter, which covers from 20 Hz to
1 MHz in 8000 and something discrete steps including 100 kHz. I can set the
voltage as low as 5 mV, so I could measure the input impedance (R + j X) of
the amplifier at 5 mV RMS. So while Ole's estimate is no doubt good, I can
actually measure it with the MAT12 in place.

I have 95 m of 2.5 mm^2 mains cable, with a PVC (?) jacket. The copper
conductor which should have a DC resistance of about 0.7 Ohms. I'm
wondering if I would be better

• Having a longer piece (more resistance, higher cost, a larger thermal
  noise voltage, but better impedance matching)
• Use thinner wire, which would be less costly, but again aim for a DC
  resistance of 3 Ohms - or whatever my LCR meter says in the input Z at 100
  kHz.

In the short term I am just going to put on the 95 m, as I have that here,
but longer term I wonder if I would be better increasing the number of
turns, to put the DC resistance closer to the input resistance of the
amplifier.

Any comments?

Dave