I am looking to build a LF antenna for a home built WWVB receiver and
have found a number of antenna designs. The ones that might be best
look like shielded loop antennas. Here is a pretty good page showing
construction of one.

http://w5jgv.com/rxloop/index.htm

I will be looking to get as large a signal out of the antenna as
possible without using a preamp. From what I can tell, I will want to
use as many turns as possible, limited by the upper frequency of the
antenna. I assume this is because as the cable gets longer the self
resonant frequency drops.

Am I headed down the right path? The only other antenna I have found
for LF work is a ferrite core coil antenna, but my impression is that
they don't pick up as large a signal. That is somewhat mitigated by the
fact that nearly every crystal radio that isn't connected to a long wire
is connected to a ferrite core. These are powered by the received
signal itself, so it must pick up some decent signal. Then again, I
think they mostly pick up local stations without a very optimal antenna,
no?

I'm interested in any sources of info that might help me in my planning.

Rick

On Sat, 03 Nov 2012 20:30:11 -0400, rickman wrote:

I am looking to build a LF antenna for a home built WWVB receiver and
have found a number of antenna designs.

Oh, so that's what you were asking in sci.electronics.design.

The ones that might be best
look like shielded loop antennas. Here is a pretty good page showing
construction of one.
http://w5jgv.com/rxloop/index.htm

Yep. Loops are good. However, there are smaller, cheaper, and
possibly more appropriate antennas available if you have a fairly good
signal. That's the real problem. At 60KHz, the atmospheric noise is
sufficiently high to bury even strong signals. Worse, the propagation
varies with the time of day.
http://tf.nist.gov/stations/wwvbcoverage.htm
http://tf.nist.gov/tf-cgi/wwvbmonitor_e.cgi
http://www.febo.com/time-freq/wwvb/sig-strength/index.html
Adding more antenna gain does nothing as it increases the received
noise and signal equally. The ratio (i.e. SNR) remains the same.

More on the subject of WWVB antennas at:
http://www.c-max-time.com/tech/antenna.php
http://www.febo.com/time-freq/wwvb/index.html
http://www.tinaja.com/glib/WWVBexps.pdf
http://www.ka7oei.com/wwvb_antenna.html
http://lakeweb.com/rf/wwvb/
http://www.prc68.com/I/Loop.shtml
http://www.febo.com/time-freq/wwvb/antenna/index.html
http://www.leapsecond.com/museum/10509a/

Probing around a WWVB receiver:
http://www.leapsecond.com/pages/sony-wwvb/

I will be looking to get as large a signal out of the antenna as
possible without using a preamp.

That's possible, but preamps solve lots of problems. The big one is
the impedance match between the loop and the receiver input.

From what I can tell, I will want to
use as many turns as possible, limited by the upper frequency of the
antenna. I assume this is because as the cable gets longer the self
resonant frequency drops.

Sorta. What really happens is that you can build an antenna for size,
bandwidth, or gain, pick any two. Building a larger antenna will
yield more gain or more bandwidth (but not both). The little tiny
ferrite loopsticks are the same, lacking in either gain or bandwidth.

Am I headed down the right path?

Dunno. I'm not sure what you're trying to accomplish and what
limitations on cost, size, weight, power, etc are involved.

The only other antenna I have found
for LF work is a ferrite core coil antenna, but my impression is that
they don't pick up as large a signal. That is somewhat mitigated by the
fact that nearly every crystal radio that isn't connected to a long wire
is connected to a ferrite core. These are powered by the received
signal itself, so it must pick up some decent signal. Then again, I
think they mostly pick up local stations without a very optimal antenna,
no?


I'm interested in any sources of info that might help me in my planning.

Rick
--
Jeff Liebermann
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558

On 11/3/2012 10:24 PM, Jeff Liebermann wrote:
On Sat, 03 Nov 2012 20:30:11 -0400, rickman wrote:

I am looking to build a LF antenna for a home built WWVB receiver and
have found a number of antenna designs.

Oh, so that's what you were asking in sci.electronics.design.

The ones that might be best
look like shielded loop antennas. Here is a pretty good page showing
construction of one.
http://w5jgv.com/rxloop/index.htm

Yep. Loops are good. However, there are smaller, cheaper, and
possibly more appropriate antennas available if you have a fairly good
signal. That's the real problem. At 60KHz, the atmospheric noise is
sufficiently high to bury even strong signals. Worse, the propagation
varies with the time of day.
http://tf.nist.gov/stations/wwvbcoverage.htm
http://tf.nist.gov/tf-cgi/wwvbmonitor_e.cgi
http://www.febo.com/time-freq/wwvb/sig-strength/index.html
Adding more antenna gain does nothing as it increases the received
noise and signal equally. The ratio (i.e. SNR) remains the same.

More on the subject of WWVB antennas at:
http://www.c-max-time.com/tech/antenna.php
http://www.febo.com/time-freq/wwvb/index.html
http://www.tinaja.com/glib/WWVBexps.pdf
http://www.ka7oei.com/wwvb_antenna.html
http://lakeweb.com/rf/wwvb/
http://www.prc68.com/I/Loop.shtml
http://www.febo.com/time-freq/wwvb/antenna/index.html
http://www.leapsecond.com/museum/10509a/

Probing around a WWVB receiver:
http://www.leapsecond.com/pages/sony-wwvb/

I will be looking to get as large a signal out of the antenna as
possible without using a preamp.

That's possible, but preamps solve lots of problems. The big one is
the impedance match between the loop and the receiver input.

From what I can tell, I will want to
use as many turns as possible, limited by the upper frequency of the
antenna. I assume this is because as the cable gets longer the self
resonant frequency drops.

Sorta. What really happens is that you can build an antenna for size,
bandwidth, or gain, pick any two. Building a larger antenna will
yield more gain or more bandwidth (but not both). The little tiny
ferrite loopsticks are the same, lacking in either gain or bandwidth.

Am I headed down the right path?

Dunno. I'm not sure what you're trying to accomplish and what
limitations on cost, size, weight, power, etc are involved.

The only other antenna I have found
for LF work is a ferrite core coil antenna, but my impression is that
they don't pick up as large a signal. That is somewhat mitigated by the
fact that nearly every crystal radio that isn't connected to a long wire
is connected to a ferrite core. These are powered by the received
signal itself, so it must pick up some decent signal. Then again, I
think they mostly pick up local stations without a very optimal antenna,
no?


I'm interested in any sources of info that might help me in my planning.

Rick

Hey Jeff,
I did some searching for info for him but didn't find a lot on just a
loop resonant at 60 Khz. I was looking for turns and capacitance but
found no designs.
So I think he needs to pick a size that he is comfortable with and
calculate turns somewhere between 100uh and 200 uh and find some
polystyrene 10,000 pf caps put 4,5, or 6 in parallel and then find a
large air variable to fine tune it with. (135uh and 5000pf is resonant
at 60khz) Then he needs a matching pickup coil, I've seen a small coil
about 1/5 dia. of the larger coil used. There are other methods.
Should he use coax? Wrap it with foil when complete? (with gap)
You're thoughts? (maybe more uh's?

kb8viv, you need to give use some idea on the physical size you can
tolerate. also, are you sure you don't want a preamp?
Mikek

rickman wrote:
I am looking to build a LF antenna for a home built WWVB receiver and
have found a number of antenna designs. The ones that might be best
look like shielded loop antennas. Here is a pretty good page showing
construction of one.

http://w5jgv.com/rxloop/index.htm

I will be looking to get as large a signal out of the antenna as
possible without using a preamp. From what I can tell, I will want to
use as many turns as possible, limited by the upper frequency of the
antenna. I assume this is because as the cable gets longer the self
resonant frequency drops.

Am I headed down the right path? The only other antenna I have found
for LF work is a ferrite core coil antenna, but my impression is that
they don't pick up as large a signal. That is somewhat mitigated by the
fact that nearly every crystal radio that isn't connected to a long wire
is connected to a ferrite core. These are powered by the received
signal itself, so it must pick up some decent signal. Then again, I
think they mostly pick up local stations without a very optimal antenna,
no?

I'm interested in any sources of info that might help me in my planning.

Rick

You would likely get better results if you did a specific Google search,
i.e. WWVB antenna.


There are lots of articles out there specifically for WWVB antennas
and receivers.


Here's some:

http://www.febo.com/time-freq/wwvb/antenna/index.html

http://www.ka7oei.com/wwvb_antenna.html

http://www.moorepage.net/Loop.html

http://www.creative-science.org.uk/MSF3.html

On Sun, 04 Nov 2012 08:55:50 -0600, amdx
wrote:

I did some searching for info for him but didn't find a lot on just a
loop resonant at 60 Khz. I was looking for turns and capacitance but
found no designs.
So I think he needs to pick a size that he is comfortable with and
calculate turns somewhere between 100uh and 200 uh and find some
polystyrene 10,000 pf caps put 4,5, or 6 in parallel and then find a
large air variable to fine tune it with. (135uh and 5000pf is resonant
at 60khz) Then he needs a matching pickup coil, I've seen a small coil
about 1/5 dia. of the larger coil used. There are other methods.
Should he use coax? Wrap it with foil when complete? (with gap)
You're thoughts? (maybe more uh's?

Ok, let's do the math (for the 2nd time as my PC crashed in the middle
of the first attempt).

The loop antenna is basically an impedance transformer. To feed with
50 ohm coax and no preamp in the antenna, the require turns ratio is:
( main-loop-turns / 1-turn-coupling )^2 = Xl-main-loop / 50 ohms
Using your 0.01uF tuning capacitor, which has a reactance of:
Xc = 1 / (2 * Pi * Freq * 0.01uF) = 265 ohms
At resonance, the inductive and capacitive reactances are equal.
Plugging in, I get a turns ratio of:
sqrt ( 265 / 50 ) = 2.3
which isn't very practical for a loop antenna. To get a higher turns
ratio, a smaller cap will be needed. For example, with 1000pF, the
reactances are 2600 ohms for a turns ratio of 7.2, which is somewhat
better. The main loop and the coupling loop would need to be rather
close together. No problem with a ferrite core, but not very
practical with an air core shielded loop. You could use your 1/5th
size coupling loop (as is used in a magnetic loop HF antenna), but at
60KHz, efficient coupling will not happen. The loops need to be
physically close (or wrapped around a ferrite rod). However, a tapped
loop would work if you insist on not using a preamp.

The more common way is to use a preamp at the antenna. It's purpose
is to amplify the received signal, but also to deal with the loop to
coax impedance conversion. See the schematic at:
http://www.ka7oei.com/wwvb_ant_1_1.gif
Note that the amp if connected directly across the main loop. The
0.4uF tuning cap yields a reactance of 6.6 ohms, so the 1K amplifier
input resistor will have no effect on Q. I would have used a smaller
capacitance, but since the author elected to use a bipolar xsistor
instead of a FET, the lower reactance will result in a smaller voltage
swing and will help prevent clipping.

Then, there's bandwidth or Q. The main loop will probably require
about 15ft of #26awg wire according to some of the construction
articles. At 0.041 ohms/ft, 15ft = 0.6 ohms.
Unloaded Q = Xl / R = 265 / 0.6 = 440
So, the -3dB bandwidth of the loop will be:
60Khz / 440 = 135 Hz
Since the bandwidth of WWVB is about 700Hz, that should work. It will
never really have a Q of 440 due to loading and losses, but that
should give a clue on how critical the tuning might become with a
huge, single turn loop. Incidentally, I was aiming for a Q of about 5
on the LORAN antennas which was required because the 100KHz LORAN
signal is 20KHz wide. Loops were possible, but amplified whip
antennas were much easier to deal with.


--
Jeff Liebermann
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558

On 11/4/2012 12:00 PM, Jeff Liebermann wrote:
On Sun, 04 Nov 2012 08:55:50 -0600,
wrote:

I did some searching for info for him but didn't find a lot on just a
loop resonant at 60 Khz. I was looking for turns and capacitance but
found no designs.
So I think he needs to pick a size that he is comfortable with and
calculate turns somewhere between 100uh and 200 uh and find some
polystyrene 10,000 pf caps put 4,5, or 6 in parallel and then find a
large air variable to fine tune it with. (135uh and 5000pf is resonant
at 60khz) Then he needs a matching pickup coil, I've seen a small coil
about 1/5 dia. of the larger coil used. There are other methods.
Should he use coax? Wrap it with foil when complete? (with gap)
You're thoughts? (maybe more uh's?

Ok, let's do the math (for the 2nd time as my PC crashed in the middle
of the first attempt).

The loop antenna is basically an impedance transformer. To feed with
50 ohm coax and no preamp in the antenna, the require turns ratio is:

This may be a wrong assumption. This antenna will be very close to the
receiver and this is a home brew receiver, not a commercial one. I can
make the input impedance anything I want really. I am looking at
directly driving a high impedance input on the ADC. Is there some
reason to work with a lower impedance for a very short run?

BTW, I have seen loop coupled antenna described but one of the pages I
found talked about the complexity of correctly coupling the antenna to
cables, not just impedance, but the balanced/unbalanced issue. This web
page seems to talk about it pretty well.

http://www.w8ji.com/magnetic_receiving_loops.htm

The page I refer to in my original post uses a toroid transformer to
couple the output to the antenna rather than a loop. I like the idea,
but I have no idea how to calculate the number of turns on the toroid.
His app was for 50 ohm cable and a higher frequency than mine.

http://w5jgv.com/rxloop/index.htm

I think this guy did a lot of research in designing his antenna and was
very skilled in building it.


( main-loop-turns / 1-turn-coupling )^2 = Xl-main-loop / 50 ohms
Using your 0.01uF tuning capacitor, which has a reactance of:
Xc = 1 / (2 * Pi * Freq * 0.01uF) = 265 ohms
At resonance, the inductive and capacitive reactances are equal.
Plugging in, I get a turns ratio of:
sqrt ( 265 / 50 ) = 2.3
which isn't very practical for a loop antenna.

I'm a bit unclear on this. Is the 2.3 the number of turns in the
primary loop to one turn on the pickup loop? What is unpractical about
that? Or is this the other way around with 2.3 turns in the pick up to
one turn on the antenna primary?

In case you haven't figured it out, this is my weak suit. I didn't have
a lot of the core courses in various EE disciplines while focusing on
digital. I've picked up a lot over the years in the analog domain and
signal processing, but am still rather weak in E&M. On the other hand,
I got an 'A' in P-chem! In terms of flunking undergrads, that is the
chemistry equivalent of E&M theory in EE.


To get a higher turns
ratio, a smaller cap will be needed. For example, with 1000pF, the
reactances are 2600 ohms for a turns ratio of 7.2, which is somewhat
better. The main loop and the coupling loop would need to be rather
close together. No problem with a ferrite core, but not very
practical with an air core shielded loop. You could use your 1/5th
size coupling loop (as is used in a magnetic loop HF antenna), but at
60KHz, efficient coupling will not happen. The loops need to be
physically close (or wrapped around a ferrite rod). However, a tapped
loop would work if you insist on not using a preamp.

The spacing seems to be a critical factor for optimizing transfer of
energy. One web page talked about spacing the pick up loop, not too far
and not too close.

What exactly is a tapped loop? I'm not picturing this.

I'm thinking of maximizing the voltage out of the antenna into a high
impedance load. Is that not a good thing to do? With the direct RF
sampling by the ADC I need as high an input as I can get.


The more common way is to use a preamp at the antenna. It's purpose
is to amplify the received signal, but also to deal with the loop to
coax impedance conversion. See the schematic at:
http://www.ka7oei.com/wwvb_ant_1_1.gif

Yes, I've seen this page. I noticed that he used steel conduit for the
shield and another page says to avoid magnetic materials for the shield,
although I expect the magnetic shielding of thin wall conduit is minimal.


Note that the amp if connected directly across the main loop. The
0.4uF tuning cap yields a reactance of 6.6 ohms, so the 1K amplifier
input resistor will have no effect on Q. I would have used a smaller
capacitance, but since the author elected to use a bipolar xsistor
instead of a FET, the lower reactance will result in a smaller voltage
swing and will help prevent clipping.

Really? Clipping is a concern? These antennas are typically very
highly peaked at the frequency of interest and I don't expect much
interference from strong sources like AM radio stations. Would the
clipping just be from noise? My understanding is that here, on the east
coast, it is hard to receive WWVB but then that is likely with ferrite
antennas. Will a large loop, say 3 foot diameter, pick up a
significantly larger signal?


Then, there's bandwidth or Q. The main loop will probably require
about 15ft of #26awg wire according to some of the construction
articles. At 0.041 ohms/ft, 15ft = 0.6 ohms.
Unloaded Q = Xl / R = 265 / 0.6 = 440
So, the -3dB bandwidth of the loop will be:
60Khz / 440 = 135 Hz
Since the bandwidth of WWVB is about 700Hz, that should work.

Is the bandwidth that wide? The signal is AM and BPSK modulated at 1 Hz
rate with minimum modulation periods of 0.2 and 0.1 seconds
respectively. I'm surprised the BW is that wide. I understand that the
sharp edge of the modulation requires some bandwidth beyond the bit
rate. But a document I found on a government page says the antennas
only have bandwidths around 260-310 Hz. But they also say the "system
bandwidth" is 5 Hz based on the AM pulse width minimum of 200 ms. I'm
not sure this is a good way to figure it.


It will
never really have a Q of 440 due to loading and losses, but that
should give a clue on how critical the tuning might become with a
huge, single turn loop. Incidentally, I was aiming for a Q of about 5
on the LORAN antennas which was required because the 100KHz LORAN
signal is 20KHz wide. Loops were possible, but amplified whip
antennas were much easier to deal with.

I would be doing simulations on the digital design, but I found my FPGA
software license is out of date. Good thing I didn't get pulled over!
:^) But I'll have to wait until tomorrow to get a new license so I can
work on that.

Rick

On 11/4/2012 6:38 PM, rickman wrote:

BTW, I have seen loop coupled antenna described but one of the pages I
found talked about the complexity of correctly coupling the antenna to
cables, not just impedance, but the balanced/unbalanced issue. This web
page seems to talk about it pretty well.

http://www.w8ji.com/magnetic_receiving_loops.htm

So many pages, so little time. I realize that the issues of coupling
are *solved* by using the loop coupling just like the ferrite core
coupling. Opps.

A fair number of LF loop antenna I have found don't bother with this,
but many do.

What will be the impact of not having an actual ground connection
anywhere? Will it be important for the shield to be grounded to a
"proper" ground to be effective? There will be no power line connection
for this device.

Rick

On 11/4/2012 11:32 AM, wrote:
wrote:
I am looking to build a LF antenna for a home built WWVB receiver and
have found a number of antenna designs. The ones that might be best
look like shielded loop antennas. Here is a pretty good page showing
construction of one.

http://w5jgv.com/rxloop/index.htm

I will be looking to get as large a signal out of the antenna as
possible without using a preamp. From what I can tell, I will want to
use as many turns as possible, limited by the upper frequency of the
antenna. I assume this is because as the cable gets longer the self
resonant frequency drops.

Am I headed down the right path? The only other antenna I have found
for LF work is a ferrite core coil antenna, but my impression is that
they don't pick up as large a signal. That is somewhat mitigated by the
fact that nearly every crystal radio that isn't connected to a long wire
is connected to a ferrite core. These are powered by the received
signal itself, so it must pick up some decent signal. Then again, I
think they mostly pick up local stations without a very optimal antenna,
no?

I'm interested in any sources of info that might help me in my planning.

Rick

You would likely get better results if you did a specific Google search,
i.e. WWVB antenna.


There are lots of articles out there specifically for WWVB antennas
and receivers.


Here's some:

http://www.febo.com/time-freq/wwvb/antenna/index.html

http://www.ka7oei.com/wwvb_antenna.html

http://www.moorepage.net/Loop.html

http://www.creative-science.org.uk/MSF3.html

Thanks for the suggestions. I have looked at dozens of pages so far.
Many of them are very good, but they only talk about what they did and
don't actually teach so much.

Rick

In article , rickman
wrote:

I'm interested in any sources of info that might help me in my planning.

Rick-

Jeff and others have probably answered your questions with regard to
antenna design. I was wondering what your WWVB receiver was to be used
for?

I considered such a receiver, as well as amplifying WWV at other
frequencies. My goal was to derive an accurate frequency to be used for
calibration of counter timebases.

What I settled on was a Rubidium Controlled Oscillator. I found an
Efratom (Ball) unit on E-Bay, that generates an accurate 10 MHz. I had
to build a 24 Volt power supply for it. It is probably accurate within
a few parts per billion, and is not affected by propagation or
interference.

Fred
K4DII

On 11/7/2012 7:47 PM, Fred McKenzie wrote:
In ,
wrote:

I'm interested in any sources of info that might help me in my planning.

Rick-

Jeff and others have probably answered your questions with regard to
antenna design. I was wondering what your WWVB receiver was to be used
for?

I considered such a receiver, as well as amplifying WWV at other
frequencies. My goal was to derive an accurate frequency to be used for
calibration of counter timebases.

What I settled on was a Rubidium Controlled Oscillator. I found an
Efratom (Ball) unit on E-Bay, that generates an accurate 10 MHz. I had
to build a 24 Volt power supply for it. It is probably accurate within
a few parts per billion, and is not affected by propagation or
interference.

Fred
K4DII

Hi Fred,

I am building the antenna as part of a radio controlled clock whose
purpose is to construct it to use as little power as possible. This
will be powered from scavenged sources such as thermal differences,
pressure variations, vibration, light, etc. So the receiver will be
done in a very low power FPGA using minimal circuitry and as little
analog circuitry as possible.

I may create a PLL to track the phase of the signal. This would use a
tunable crystal oscillator which would be "conditioned" against the WWVB
signal over long periods of time.

I'm not specifically looking for a reference source, but this would be
capable of providing one.

Rick