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