On 6/7/23 13:25, JOHN HARTZELL via time-nuts wrote:

I am using a DX Engineering RF-Pro loop for everything from 60kHz (WWVB)
to 20MHz. Works great.

https://www.dxengineering.com/parts/dxe-rf-pro-1b

--

*Brian Lloyd *
WB5BL - J79BL - NNA6BL
706 Flightline
Spring Branch, TX 78070
brian@heaviside-hf.com mailto://brian@heaviside-hf.com
+1.210.620.0011

JOHN HARTZELL via time-nuts writes:

I do:  I played a lot with VLF/SDR and LORAN-C, before people turned
all the transmitters off and installed lawn-mower robots in the
radio-spectrum.

The crucial trick is to /not/ make the loop resonant, ie: no parallel capacitor.

I made all my Loran-C/VLF experiments with this $20 home-brew antenna:

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

The mad ELF-VLF scientists at VLF.IT has plenty of other good
schematics, but this one worked a treat for me.

Today I would have built two loops, mounted at an right angle, and made my
ADC dual-channel as well.

First round of LORAN experiments:

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

Second round:

http://phk.freebsd.dk/AducLoran/

The two .gif animations are the only recordings I know of, showing "dance of the nightwave"

Enjoy:  It is an incredibly satisfying thing to play with.

Poul-Henning

--
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.

Hi

There are a number of sites around the web that go through the details
of doing large-ish loop antennas for various LF signals. Are you trying to
do something small (fit in your pocket) or something fairly large (10 foot
diameter) ?

Bob

For WWVB time signals, I use a resonant ferrite rod antenna, but depending
on the rod, the antenna bandwidth can be several hundred to several
thousand Hz. Resonant multi-turn loops are likely to be similar.

You will need a broad-band (non-resonant) loop for receiving Loran-C, due
to the much wider modulation bandwidth of the signal.
--- Graham

On Wed, Jun 7, 2023 at 3:46 PM Bob Camp via time-nuts <
time-nuts@lists.febo.com> wrote:

Hi

The next layer to this is that some (but not all) WWVB receiver designs appear to rely
upon the “bandpass filter” of the antenna to provide reasonable rejection of “crud”.

Having any sort of resonant circuit out in the back yard has implications. As the resonance
shifts with temperature, so does the phase shift. At VLF phase is indeed a big deal. Just
how big a deal …..

As with a lot of things, you can indeed measure outside temperature and model this or that.
Lots of fun can be had.

Bob

Need and need...

For stationary timekeeping purposes, with minute-or-longer
integration time, less than three kHz bandwidth can work OK.

Lower than three kHz, figuring out what is the correct
zero-crossing gets too ambiguous.

But you get really big gains in both S/N and time stability
with a "HiFi" antenna which is flat from 90 to 110 kHz.

Note, that it should be "flat" in both amplitude and phase,
Loran-C, being spread-spectrum, gets really funky if you have
significant delay-distortion (aka. group-delay) across your
pass-band - however wide you decide it should be.

One advantage of going broadband, for instance 20-200kHz, is that
you can receive a lot of other signals at the same time, with the
same SDR implementation, for instance 40, 60 and 66⅔kHz timesignals.

--
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.

Hi Bob,
that is my 60kHz remote receiver,
the remote tuning could be made relative simple, see the attached
circuit diagram; by changing the supply voltage -- right to corner --
between 15V and 20V the tuning voltage for the varicaps  -- D8 and D9 --
will change between +1V and +10,5V, which causes 800pF capacitance
changing the coil  L6 is approx 2,2mHy,
D6 an D7 prevent the damage Q25 gate, the op-amp circuit is matching the
high impedance of the C108 L7 tank circuit to 50 ohm cable impedance. At
the 20 long end of the cable -- with 50 termination -- I could see a p_p
voltage  between 60mV and 500mV here in the Bay Area, in California,
behind the wall, inside of the house, outside I could get at least 6dB more.
I am using that antenna for a frequency reference  --  a 10MHz PLL is
locked to that 60kHz -- only just to verify that the output of the GPS
is locked correct

73
KJ6UHN
Alex

On 6/7/2023 2:47 PM, Bob Camp via time-nuts wrote:

Hello to the group.
If the solution is for LORAN C then a wider band antenna is needed. Exactly
as Poul states.
Then for narrow band signals such as wwvb narrow band.
My solution is as follows.
WWVB 10' X 10' square loop resonant at 60 KHz about 1Khz wide or so. It has
worked well for 10 years. Then a preamp.
eLORAN 4' X 4' square loop resonant at 100 KHz and broad banded to tp +/-
15 KHz. Preamp at the antenna.
Square loops are easy to build with plumbing parts. The eLORAN antenna can
be turned 180 degrees. Because currently the tests can come from any
direction. Though right this second they are west of me by 1800 miles.
I also have available simply by changing a connection a classical LORAN C
whip antenna.
I did build the eLORAN antenna just for the fun of it.

Reality is it depends on how far away you are and many other antennas can
work. Simple wire, whips and preamps etc.

Regards
Paul
WB8TSL

On Wed, Jun 7, 2023 at 9:29 PM Alex Pummer via time-nuts <
time-nuts@lists.febo.com> wrote: