On 12/17/2012 10:18 PM, garyr wrote:

"Understanding Digital Signal Processing" by Richard G. Lyons is a good
source of information.

If you plan to do the FPGA code yourself check out: www.myhdl.org

For the antenna consider: www.febo.com/time-freq/wwvb/antenna

At 60 KHz RG-58 would be as good as RG-6 for a loop antenna and much easier
to work with. PCV pipe is a good material for the frame. email me directly
and I'll send you a photo of a 1m VLF antenna I made.

Unless you are located in Boulder, CO you will probably need an analog
amplifier.


Hi Gary,

Thanks for the info. I am familiar with Richard's book. He seems like
a good guy and will provide errata for anyone who has bought his book.
I am familiar with DSP in general and digital receivers specifically. I
have most of that part of the design analyzed enough to begin coding.
It is the ADC that I have had some trouble analyzing. I have been
planning to construct a Sigma-Delta converter in the FPGA. Turns out
this might be a little power hungry and I won't be able to use the
special dithering that shapes the noise. My primary goal is to do this
entire project with very, very little power consumption. If I can get a
strong enough signal I can just use an LVDS input without the
integration of a Sigma-Delta converter, but I won't know until I get
some of this built and tested.

I am very experienced with HDL so I should be ok there.

I have found any number of sites that talk about loop antenna
construction, but most don't really explain how to analyze them. I have
finally cobbled together a good picture of the technical aspects from a
number of web sites and have an antenna plan. I am looking at using 50
feet of RG-6 with copper inner conductor to optimize the Q. My initial
pass is a compromise between optimizing the signal strength and making
the final unit easy to construct and support. It will be 8 turns on 2
foot diameter wooden spokes. I expect the stiffness of the RG-6 to help
support the cable. This would likely be a decent design up to four foot
diameter.

In the end I may find I can use a ferrite loop. But the signal
strengths I have seen from commercial ferrite antennas do not seem to be
good enough, around 8 uV for 100uV/m field strength which is about what
I expect to see here on the east coast.

As to the amp, we will see. I have an equation to predict signal
strength at the antenna output and I am expecting a decent signal level
if I have a good Q and transformer couple the output. Total gain (Q and
transformer) over an untuned antenna will approach 10,000.

But there is many a slip between cup and lip. I hope to make some
progress on this over the holidays and have some test results.

Can you explain why you think RG-58 will be as good as the RG-6? The
inner conductor of RG-6 has only a small impact from skin effect, I
think it is around 21%. At 32 mil the inner conductor of RG-58
(compared to 40 mil for RG-6) will have even less impact from skin
effect, but will have a higher resistance and so a lower Q. The
capacitance per foot is nearly twice that of RG-6 as well although I'm
still not clear on the specific details of this effect. I believe
higher capacitance will lower the self resonant frequency although I
don't expect this to be a problem in my application.

Rick