So who here is using a loop antenna?

--

Rick

"rickman" wrote

So who here is using a loop antenna?

I just a couple days ago set up my MFJ Hi-Q Loop (30 - 10 m) to compare it
to my 140' somewhat-inverted V up 30'.

Are you taking a poll, or do you have a specific question or two?

On 2/12/2016 4:13 PM, Howard Lester wrote:
"rickman" wrote

So who here is using a loop antenna?

I just a couple days ago set up my MFJ Hi-Q Loop (30 - 10 m) to compare
it to my 140' somewhat-inverted V up 30'.

Are you taking a poll, or do you have a specific question or two?


I got into loop antenna design to construct a WWVB receiver with a
"large" loop (compared to a ferrite stick) to maximize the voltage
output. This is not typical because the SNR is the actual limitation in
that band so that you can use an amplifier with the weak signal from the
stick antenna and get a good signal. But I wanted to try doing it
without an amp and directly sample the signal with a 1 bit ADC at 240
kHz. Then use signal processing to pull the 1 bps signal out of the dirt.

Never got that project off the ground mostly because I got distracted by
the antenna design. While digging around with that I learned about the
complexities of transmitting loops and now I am thinking of getting a
license and setting up a loop antenna for ham use.

I've always been a gear-head liking the details of a design more than
the use. lol

So how does your loop compare to the other antenna? I understand the
loops often have a better SNR. I know I've seen the name MFJ, but what
does it stand for again?

--

Rick

In article , rickman wrote:

So how does your loop compare to the other antenna? I understand the
loops often have a better SNR. I know I've seen the name MFJ, but what
does it stand for again?

Are you referring to its real meaning or its nickname? :-)

I've never used any MFJ antennas, but I used one of their tuners to
get a decent SWR from an aluminum awning and was very impressed with
that product. (I got DXCC and then some from the awning.)


N6BIS

On Sat, 13 Feb 2016 11:02:07 EST, rickman wrote:

On 2/12/2016 4:13 PM, Howard Lester wrote:
"rickman" wrote

So who here is using a loop antenna?

I just a couple days ago set up my MFJ Hi-Q Loop (30 - 10 m) to compare
it to my 140' somewhat-inverted V up 30'.

Are you taking a poll, or do you have a specific question or two?


I got into loop antenna design to construct a WWVB receiver with a
"large" loop (compared to a ferrite stick) to maximize the voltage
output. This is not typical because the SNR is the actual limitation in
that band so that you can use an amplifier with the weak signal from the
stick antenna and get a good signal. But I wanted to try doing it
without an amp and directly sample the signal with a 1 bit ADC at 240
kHz. Then use signal processing to pull the 1 bps signal out of the dirt.

It would be easier and more interesting if you demodulated the
relatively new BPSK enhanced format instead of the older AM/PWM
format. However, don't get any ideas about selling a WWVB product
that uses BPSK as it's locked up in patents held by a company that
seems unwilling to manufacture the promised chips.

There was an article on a WWVB receiver that did BPSK a few months
ago. Googling...
"A Frequency Standard for Today’s WWVB"
http://www.arrl.org/files/file/QEX_Next_Issue/2015/Nov-Dec_2015/Magliacane.pdf

Never got that project off the ground mostly because I got distracted by
the antenna design. While digging around with that I learned about the
complexities of transmitting loops and now I am thinking of getting a
license and setting up a loop antenna for ham use.

Just do it. Getting a ham license is fairly painless.

I've always been a gear-head liking the details of a design more than
the use. lol

So how does your loop compare to the other antenna? I understand the
loops often have a better SNR.

I know I've seen the name MFJ, but what
does it stand for again?

Martin F. Jue.
http://www.mfjenterprises.com/about_mfj.php
https://en.wikipedia.org/wiki/MFJ_Enterprises
Like all companies, the product quality, engineering, service, and
politics vary depending on the specific product and situation. I'll
spare you my opinion.


--
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 2/13/2016 1:55 PM, Jeff Liebermann wrote:
On Sat, 13 Feb 2016 11:02:07 EST, rickman wrote:

On 2/12/2016 4:13 PM, Howard Lester wrote:
"rickman" wrote

So who here is using a loop antenna?

I just a couple days ago set up my MFJ Hi-Q Loop (30 - 10 m) to compare
it to my 140' somewhat-inverted V up 30'.

Are you taking a poll, or do you have a specific question or two?


I got into loop antenna design to construct a WWVB receiver with a
"large" loop (compared to a ferrite stick) to maximize the voltage
output. This is not typical because the SNR is the actual limitation in
that band so that you can use an amplifier with the weak signal from the
stick antenna and get a good signal. But I wanted to try doing it
without an amp and directly sample the signal with a 1 bit ADC at 240
kHz. Then use signal processing to pull the 1 bps signal out of the dirt.

It would be easier and more interesting if you demodulated the
relatively new BPSK enhanced format instead of the older AM/PWM
format. However, don't get any ideas about selling a WWVB product
that uses BPSK as it's locked up in patents held by a company that
seems unwilling to manufacture the promised chips.

I don't know about "easier", but I will definitely be doing both to
compare the relative capabilities. I am told the phase modulation
provides better sensitivity. We'll see, but likely not soon. I haven't
worked on this in some time.

Odd that they could patent the demodulation of a BPSK signal. I took at
look at the patent, but I'm not so good at understanding the legalize so
I don't know exactly what it is they patented. It may well be their
patent is not valid, but determining that would require someone to
challenge it in court, very expensive.


There was an article on a WWVB receiver that did BPSK a few months
ago. Googling...
"A Frequency Standard for Today’s WWVB"
http://www.arrl.org/files/file/QEX_Next_Issue/2015/Nov-Dec_2015/Magliacane.pdf

I'll take a look. My thing is to do it at an exceedingly low power
level. I'm looking at a very low power FPGA, but it may be that the
power used by an MCU is lower. The FPGA has a very low dynamic power,
but the quiescent power is around 100 uW.


Never got that project off the ground mostly because I got distracted by
the antenna design. While digging around with that I learned about the
complexities of transmitting loops and now I am thinking of getting a
license and setting up a loop antenna for ham use.

Just do it. Getting a ham license is fairly painless.

Yes, I looked at it a couple of years ago and it just takes a little
memorization I seem to recall. Not much harder to get the next level
either.

--

Rick

On Mon, 15 Feb 2016 16:28:17 EST, rickman wrote:

On 2/13/2016 1:55 PM, Jeff Liebermann wrote:
On Sat, 13 Feb 2016 11:02:07 EST, rickman wrote:

On 2/12/2016 4:13 PM, Howard Lester wrote:
"rickman" wrote

So who here is using a loop antenna?

I just a couple days ago set up my MFJ Hi-Q Loop (30 - 10 m) to compare
it to my 140' somewhat-inverted V up 30'.

Are you taking a poll, or do you have a specific question or two?


I got into loop antenna design to construct a WWVB receiver with a
"large" loop (compared to a ferrite stick) to maximize the voltage
output. This is not typical because the SNR is the actual limitation in
that band so that you can use an amplifier with the weak signal from the
stick antenna and get a good signal. But I wanted to try doing it
without an amp and directly sample the signal with a 1 bit ADC at 240
kHz. Then use signal processing to pull the 1 bps signal out of the dirt.

It would be easier and more interesting if you demodulated the
relatively new BPSK enhanced format instead of the older AM/PWM
format. However, don't get any ideas about selling a WWVB product
that uses BPSK as it's locked up in patents held by a company that
seems unwilling to manufacture the promised chips.

I don't know about "easier", but I will definitely be doing both to
compare the relative capabilities.

See the QEX article I referenced below and note that rather strange
circuitry that the author had to add in order to get AM/PWM modulation
to work in the presence of BPSK.

I am told the phase modulation
provides better sensitivity. We'll see, but likely not soon. I haven't
worked on this in some time.

According to what I've read, BPSK is more sensitive.

Odd that they could patent the demodulation of a BPSK signal. I took at
look at the patent, but I'm not so good at understanding the legalize so
I don't know exactly what it is they patented. It may well be their
patent is not valid, but determining that would require someone to
challenge it in court, very expensive.

This one?
http://www.google.com/patents/US8774317
It appears to be specific to a receiver that does both AM and BPSK. It
would seem that a BPSK only receiver could be sold. I've written some
things about the problem in the distant past. I'll see if I can find
my rants. The basic problem is that Xtendwave promised to sell or
sub-license a suitable chip, but hasn't. Vaporwa
http://finance.yahoo.com/news/xtendwave-announces-first-shipment-sample-171151210.html
http://www.xtendwave.com (broken web site?)
https://www.febo.com/pipermail/time-nuts/2014-July/085445.html

There was an article on a WWVB receiver that did BPSK a few months
ago. Googling...
"A Frequency Standard for Today’s WWVB"
http://www.arrl.org/files/file/QEX_Next_Issue/2015/Nov-Dec_2015/Magliacane.pdf

I'll take a look. My thing is to do it at an exceedingly low power
level. I'm looking at a very low power FPGA, but it may be that the
power used by an MCU is lower. The FPGA has a very low dynamic power,
but the quiescent power is around 100 uW.

Nice. E-paper display clock? Just paste it on the wall?

Never got that project off the ground mostly because I got distracted by
the antenna design. While digging around with that I learned about the
complexities of transmitting loops and now I am thinking of getting a
license and setting up a loop antenna for ham use.

Just do it. Getting a ham license is fairly painless.

Yes, I looked at it a couple of years ago and it just takes a little
memorization I seem to recall. Not much harder to get the next level
either.

You will probably be more successful just memorizing the answers, or
repeatedly taking the online practice tests, than by actually trying
to understand the material. Some of the test questions are rather
vague and some of the answers ambiguous. There are also questions
where some previous operating experience is helpful. At your
experience level, you should have no problems with the technical
questions and just study the rules-n-regs and operating questions.

--
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 2/16/2016 6:44 PM, Jeff Liebermann wrote:
On Mon, 15 Feb 2016 16:28:17 EST, rickman wrote:

On 2/13/2016 1:55 PM, Jeff Liebermann wrote:
On Sat, 13 Feb 2016 11:02:07 EST, rickman wrote:

On 2/12/2016 4:13 PM, Howard Lester wrote:
"rickman" wrote

So who here is using a loop antenna?

I just a couple days ago set up my MFJ Hi-Q Loop (30 - 10 m) to compare
it to my 140' somewhat-inverted V up 30'.

Are you taking a poll, or do you have a specific question or two?


I got into loop antenna design to construct a WWVB receiver with a
"large" loop (compared to a ferrite stick) to maximize the voltage
output. This is not typical because the SNR is the actual limitation in
that band so that you can use an amplifier with the weak signal from the
stick antenna and get a good signal. But I wanted to try doing it
without an amp and directly sample the signal with a 1 bit ADC at 240
kHz. Then use signal processing to pull the 1 bps signal out of the dirt.

It would be easier and more interesting if you demodulated the
relatively new BPSK enhanced format instead of the older AM/PWM
format. However, don't get any ideas about selling a WWVB product
that uses BPSK as it's locked up in patents held by a company that
seems unwilling to manufacture the promised chips.

I don't know about "easier", but I will definitely be doing both to
compare the relative capabilities.

See the QEX article I referenced below and note that rather strange
circuitry that the author had to add in order to get AM/PWM modulation
to work in the presence of BPSK.

I'm not sure which circuitry you are referring to. His design seems to
have some legacy circuitry in it and with the diagrams sideways from the
text it was too much work to try to follow what much of the design does.
I believe the complications were so he could extract the 60 kHz as a
reference rather than just decoding the bits.

As I indicated above, I am working *all* digitally. I would prefer not
to have a preamp but I'm not sure if that is practical. It depends on
how much processing gain I can get vs. how much noise/distortion is
introduced by the comparator.


I am told the phase modulation
provides better sensitivity. We'll see, but likely not soon. I haven't
worked on this in some time.

According to what I've read, BPSK is more sensitive.

Odd that they could patent the demodulation of a BPSK signal. I took at
look at the patent, but I'm not so good at understanding the legalize so
I don't know exactly what it is they patented. It may well be their
patent is not valid, but determining that would require someone to
challenge it in court, very expensive.

This one?
http://www.google.com/patents/US8774317

Yes


It appears to be specific to a receiver that does both AM and BPSK.

That's not what I read. It is for receiving a signal that is modulated
in both AM and BPSK, but they are only demodulating BPSK. In rereading
this I think claim 5 is invalid since it is obvious. Claim 4 is
decoding the phase only during the time the AM modulation is high.
Claim 5 is demoding *all* the time. Duh!


It
would seem that a BPSK only receiver could be sold. I've written some
things about the problem in the distant past. I'll see if I can find
my rants. The basic problem is that Xtendwave promised to sell or
sub-license a suitable chip, but hasn't. Vaporwa
http://finance.yahoo.com/news/xtendwave-announces-first-shipment-sample-171151210.html
http://www.xtendwave.com (broken web site?)
https://www.febo.com/pipermail/time-nuts/2014-July/085445.html

I think much of the patent is invalid as it is simply a general
description for a receiver of phase modulated data *required* by the
WWVB data format. In that sense it is *obvious*.

I'm not an expert, but much of this patent seems repetitious. They
claim a receiver method (1 through 5), then the same claims are repeated
as a "receiver" (6 through 10). The rest are these repeated again with
the addition of "accumulating received energy over multiple broadcast
signal data frames thereby providing a corresponding gain in reception;"

I guess the very last claim (21) is about also demoding the AM as well.
Again, obvious.

I see in their illustrations they do not properly align the phase shifts
with the AM. I wonder if that is sufficient to invalidate the patent in
the context of the WWVB signal? My understanding is only the claims
matter.


There was an article on a WWVB receiver that did BPSK a few months
ago. Googling...
"A Frequency Standard for Today’s WWVB"
http://www.arrl.org/files/file/QEX_Next_Issue/2015/Nov-Dec_2015/Magliacane.pdf

I'll take a look. My thing is to do it at an exceedingly low power
level. I'm looking at a very low power FPGA, but it may be that the
power used by an MCU is lower. The FPGA has a very low dynamic power,
but the quiescent power is around 100 uW.

Nice. E-paper display clock? Just paste it on the wall?

E-paper is *not* low power. It retains the image with the power off,
but updating the display even just once per second draws a lot more
power than an LCD. The image quality can be very good though.


Never got that project off the ground mostly because I got distracted by
the antenna design. While digging around with that I learned about the
complexities of transmitting loops and now I am thinking of getting a
license and setting up a loop antenna for ham use.

Just do it. Getting a ham license is fairly painless.

Yes, I looked at it a couple of years ago and it just takes a little
memorization I seem to recall. Not much harder to get the next level
either.

You will probably be more successful just memorizing the answers, or
repeatedly taking the online practice tests, than by actually trying
to understand the material. Some of the test questions are rather
vague and some of the answers ambiguous. There are also questions
where some previous operating experience is helpful. At your
experience level, you should have no problems with the technical
questions and just study the rules-n-regs and operating questions.

The main hassle is just getting to the test site.

--

Rick

On 2/16/2016 6:44 PM, Jeff Liebermann wrote:

This one?
http://www.google.com/patents/US8774317
It appears to be specific to a receiver that does both AM and BPSK. It
would seem that a BPSK only receiver could be sold. I've written some
things about the problem in the distant past. I'll see if I can find
my rants. The basic problem is that Xtendwave promised to sell or
sub-license a suitable chip, but hasn't. Vaporwa
http://finance.yahoo.com/news/xtendwave-announces-first-shipment-sample-171151210.html
http://www.xtendwave.com (broken web site?)
https://www.febo.com/pipermail/time-nuts/2014-July/085445.html

I read it a bit more closely and I think demodulating the phase carrier
will not infringe this patent. The patent refers to demodulation of the
phase aligned to the PWM/ASK modulation scheme. The NIST spec says the
phase inverts 100 ms after the ASK bit starts and so is not "aligned" in
that way. If you simply demod the BPSK without regard to the ASK bits I
can't see how it would be infringing the patent.

My thought was always to sample the signal at a high rate and analyze
the data in 100 ms blocks or smaller. My main concern is to get a good
resolution of the transitions traded off against processing gain. LCDs
are happy with a 30 Hz backplane rate so that would be a convenient value.

I just realized that the actual second change will need to be offset
from the transition of the phase change by 100 ms... in the wrong
direction. "Hey, the second updated 100 ms ago!"

Durn Google patents lets you download a PDF, but you can't copy text,
just images of the text. Otherwise I would quote and comment on a bit
more.

--

Rick