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