On 11/30/2012 4:00 PM, Michael Black wrote:
On Thu, 29 Nov 2012, Arid ace wrote:


With a one turn loop coupled to the one turn primary of an RF
transformer, there's no need for a shield. It's fairly easy to provide
the piece of wire used for the primary with a center tap that will be
grounded so the loop is symmetrical. That also obviates the need for a
differential amplifier. A 50 feet loop is huge. I once (in Europe)
designed a frequency standard synchronized to DCF77 and reception was
OK at distances over 2,000 Km with just a ferrite rod of 12 cm length
and 1 cm diameter. In order to keep it easy for constructors, the coil
had just 140 turns with 2n2 to resonate the LC. I don't think the
approach for WWVB at 60 KHz could be much different (apart from the
modulation format). I had designed the ferrite antenna amp as a small
device that could be fed via coax, so one could install it in a place
with the lowest noise.

Some of the issue may be habit. Over the decades, various WWVB receivers
were described, and I remember them all as using some sort of larger
loop.
It may have nothing to do with design so much as habit, once an idea is
planted, others continue it.

Hi Michael,

I certainly don't have a habit in this area. I am a total newbie in
antenna and even radio design. What I know somewhat is DSP and my goal
is to design a 100% digital RCC (Radio Controlled Clock). I am also
trying to make it as low power as possible so that it can be powered
from scavenged energy sources... no batteries, no wall plug. Just set
it on the wall and it runs.


In the early days of "amateur radio", everything was so low in
frequency, big loops and 60KHz probably weren't that foreign. So the
collective memory may retain that, a long time after hams were relegated
to those "uselss" shortwave frequencies.

The fact that all those WWVB clocks have relatively small loops is an
indicator that not much is needed. I don't know how complicated the
receivers have become, if at all. I can get WWVB here in Montreal on my
Casio Waveceptor watch, and whatever that uses has to be way smaller
than the loops in the small WWVB clocks.

Yes, they aren't terribly high power either. As I've said elsewhere, I
am starting with a loop antenna because it can give me the largest
output voltage without an amp and I can save that amount of power. If
it turns out that I can find an amp that will provide adequate gain and
not use much power I can go that route. For now I want to try the large
loop antenna.


The better the loop, of course, the more selectivity it provides. I
don't have any of those WWVB receiver articles handy, but again I
remember them as being relatively simple amplifiers, fairly depending on
the loop for selectivity. The larger the loop, the more directional it
can be, which presumably helps with all the local junk generated that
can cause issues.

I've seen a number of these designs, none are optimized for low power
using load resistance in the 10 kohm or lower range.


Don Lancaster did an article about WWVB, more an introduction, and he
has it on his webpage at www.tinaja.com, titled something like
"Experiments in WWVB Reception".

Yes, I have this article.


Ralph Burhan, who was a ham, wrote a lot about low frequencies. Using
Loran as a frequency standard (or was it time?), all kinds of articles
in various hobby magazines about low frequency antennas (sometimes
loops, but often short whips, directly coupled to a very high impedance
buffer). I'm not sure any of that is online, but it might be worth a
search.

I've found tons of self-construction web pages on loop antennas, but no
so many cover the theory a lot. I've found a small number that are
better than most and have useful info. It was Randy Yates in the
comp.dsp forum who gave me the formula for received signal strength from
a loop antenna from the ARRL handbook. That helped tremendously and
allowed me to understand a similar formula I had found for antenna
equivalent height.


The interest may be picking up, talk of a low frequency ham band (or is
it already in place? I forget). And of coruse, there is the 160-190KHz
"license free band" that some have put a lot of effort into, "lowfers",
searching for that sort of thing might turn up useful information,
albeit needind scaling down to 60KHz.

One of the antenna pages I read was about using a low frequency band
with "special" permission. He wanted a loop receiving antenna so he
could steer the null to his transmitting antenna. This was 2 turns, 10
foot in diameter, a big one! He is the one that used a ferrite doughnut
to transformer couple the output with 10 turns IIRC.

Rick