On Fri, 30 Nov 2012 16:00:38 -0500, 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.

It could be a habit indeed because calculation would show that unless outside
the intended range, a fairly small loop is required. Another topic where habit
shows well regards PLL: even for AM reception, design resembles that for FM
reception (limiter).


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.

Low in frequency and power, big loops might be useful. Here in Panama with many
months of thunderstorm activity, a broadband loop with S/N comparable to a long
wire but without the QRN would be rather useful. It's a work in progress but if
it would be easy, it would already exist.


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.

With DCF77 it's the same. Good enough reception with a ferrite antenna as used
in small MW portables. After a source-follower eventually an amp with more
selectivity, when (back then) interference from TV sets would be a problem
(harmonics of line output transformer).


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.

When the major issue was a reference frequency, I used a 10 MHz VCXO,
and with the proper dividers that resulted in a mixer as the first or second
stage, with an IF so low that simple RC audio filters could be used. The
selectivity was phenomenal.

The analog part (or what most people were interested in until recent
times), wsa the antenna and selectivity and a good amplifier. Simple and
complicated at the same time. And it's a spectrum area often "unkonwn",
not many receivers to tune down there, so one wonders if the signal is
there, or it's the equipment, until the equipment becomes right enough for
the signal to appear. if I'm building a WWV receiver, it's easy to check
for the signal since I have a few receivers that cover the frequency
range.

Several of my receivers can be tuned down to a few KHz as well, and on the 85
meter long wire, despite complete mismatch to 50 ohm, WWVB can be received
though not more than ~10 dB above noise - on a rare day without thunderstorm.
Panama is clearly outside the intended service area.


It's not a new field. There was one guy, I can't remember his name, who
wrote a number of articles in QST about WWVB and WWVL reception, and high
stability frequency standards, I can picture on in the summer of 1971.

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".

Nice site, the article including a WWVB receiver leaves no questions.
The web has quite a few photos of WWVB receivers, also indicating how simple the
loop can be. One: http://www.nixiemagic.com/

Ken Cornell spent a lot of time writing about low frequency work, he had a
"cookbook" out at one point, initially self-published but a later edition
published by Ham Radio Magazine. But he died, and access to the book
other than used died with him.

I started reading Ham Radio in 1975 so probably missed that. The importance of
LF is without doubt, just count the number of (military) FSK transmitters below
~400 KHz. With an online SDR in the Netherlands they can even be heard below 10
KHz.

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.

If I remember well, Loran (navigation system) was about time (difference).

There have been quite a few WWVB receiver articles in the ham magazines,
though I have no dates. I think one wsa in September 1971 "73". The ones
I saw all predate WWVB's more recent visibility as a feed to all those
"atomic clocks". Most were interested in the station as a frequency
standard, though as early as that seventies Don Lancaster article, people
were thinking about decoders to get the time.

The use as frequency standard was very popular in Europe too, hence I had to
design one for DCF77 (77.5 KHz) and later for DLF, a LW transmitter at 153 KHz.
The output had to be a synchronized 10 MHz clock and an error indicator, when
the signal was temporarily interrupted.


I think there are groups and pages devoted to this sort of thing, but I
don't follow it so anyone's search is as good as mine would be.

Since the timing info also was sent as phase modulation, I lost interest.
Although the average frequency remains the same, the modulation is transferred
to the VCXO which makes short time measurements inaccurate. In Europe, LW
transmitters were phase modulated with program info to facilitate automatic
receiver tuning so DLF no longer was useful either.

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.

Michael VE2BVW

In Panama, ham radio regulation follows that of the US, with exception of CB
which is prohibited. The new ham band (136 KHz) might be a good idea here too,
plenty of room for a balloon antenna like the one described he
http://www.alg.myzen.co.uk/radio/136/experi_vert.htm

Jan