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Amateur HF Ocean Wave Communication Using Bragg Resonance

from Ken Beck, WI7B on November 8, 2010
View comments about this article!

Amateur HF Ocean Wave Communication Using Bragg Resonance
By Ken Beck, WI7B

In October, 1977 D. E. Barrick, M. W. Evans, and B. L. Weber, all scientists at NOAA, published a paper in the journal Science titled, “Ocean Surface Currents Mapped by Radar.” They reported that ocean surface currents could be recorded up to 70 km from shore with simple mobile costal units using HF frequencies. This was boon to oceanographers for a number of reasons. Surface currents carry zooplankton and phytoplankton, which are the dominant components at the bottom of the ocean’s food chain and produce most of the world's oxygen. Fish eggs are borne by surface currents, and of concern to the fisheries industry. Yet, their technique to my knowledge has never been proposed as a potential form of amateur radio communication. So, I make this short proposal to fellow hams that are fortunate enough to live near a coastal region to consider the idea.

The principle underlying their technique is that the motion of the waves is appears as a frequency shift of the received echo signal from that of the transmitted signal; an echo Doppler shift. The HF transceivers can thus resolve and measure the component of velocity along the line between the waves scattering the signal and the HF transceiver; the radial velocity. At first order the HF echo signal derives from ocean wave trains moving toward and away from the HF transceivers on shore, having spatial periods precisely one-half the HF transmitted wavelength.

For potential amateur communications the salient feature is that this represents a Bragg resonance scattering mechanism utilizes the ocean wave trains as a giant diffraction grating for the transmitted HF signal such that it is constructively reinforced and re-appears as a Doppler-shifted echo signal back on shore with attenuation rates of ~1dB/km @25MHz [1]. The spectrum of a CW transmitted signal is a narrow peak at the carrier frequency location. In the absence of surface current, the received first order sea echo appears as two symmetrically spaced peaks about the carrier, whose Doppler shifts are given by the lowest-order dispersion relation of the scattering gravity waves; that is, plus/minus frequency of Doppler shift = 2(gL/2pi)^1/2/lambda = (g/pi*lambda)^1/2 where lambda is the transmitted wavelength, L = lambda/2 is the length of the ocean waves responsible for the first-order Bragg scattering, and g is the standard gravitational constant = 9.807 m/s^2. This is shown in Figure 1:


Figure 1 (From [2] D. E. Barrick, M. W. Evans, B. L. Weber, Science, 198, 138-144 [1977]. Reprinted with permission from AAAS under license 2503701272587)

Typical near-shore ocean waves have wavelengths on the order of 6 meters, calling for HF frequencies in our 12m band. For data-only transmission this would correspond to transmit frequencies of 24.890 - 24.930 MHz. To get an idea of what this might look like as an amateur “Field Day” station, a diagram of that original 1977 HF antenna system is shown in Figure 2.


Figure 2 Sketch of the system as operated on the beach. Transmitting antennas are on the left and receiving antenna on the right. (From [2] D. E. Barrick, M. W. Evans, B. L. Weber, Science, 198, 138-144 [1977]. Reprinted with permission from AAAS under license 2503701272587)

Their system worked with a portable generator to radiate a peak power of 2.2 KW with 20 microsecond pulses as a radar. The average radiated power was only 50 watts. Their system operated primarily between 25 and 26 MHz. The transmitting antenna is a log-periodic vertical monopole array of three (or four) elements. It was designed to have an input impedance of 50 ohms; the three-element version has a half-power beam width of pulse/minus 90 degrees, while the four-element version has plus/minus 43 degrees. The individual receiving elements are fiberglass-encased Citizens-Band whips cut to a height of ~1.58 m and each fed against a quarter wavelength, four-element, radial ground screen.

Do the receiving and transmitting stations have to be in a line with each other for this effect to dominant? No. They demonstrated that a four antenna configuration (arranged in a square) could resolve two signals from 360 degrees that permitted operation on a peninsula or an island with ocean water extending more than 180 degrees around the HF station.

For a straight coastline, the question arises as to how far apart the sites could be. Because their interest was in optimizing the superimposed surface current signal, they limited the distance between receiving station to 55 km. But one should view this distance a minimum between coastal HF amateur stations. One could imagine PSK31 or CW modes as viable first-attempts at amateur ocean wave communication along a coast line or between island and a coast line. Receivers would be tuned to the Doppler-shift of the transmitted signal. On mountainous or high-cliff shores, this may prove to be a useful form of communication.



[1] R. S. Lyons, D. E. Barrick, Radio Science, 19, 319-324 [1984]
[2] D. E. Barrick, M. W. Evans, B. L. Weber, Science, 198, 138-144 [1977].

Member Comments:
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Amateur HF Ocean Wave Communication Using Bragg Resonance Reply
by K1CJS on November 8, 2010 Mail this to a friend!
This seems to be a nice idea--for experimentation, just like meteor scattered or moon bounced signals. Other than that, there is no practical application of such a method of communications.
 
RE: Amateur HF Ocean Wave Communication Using Bragg Resonanc Reply
by AB2RC on November 8, 2010 Mail this to a friend!
I will agree that it is not practical for communications, but it is for ocean studies.

http://marine.rutgers.edu/cool/codar.html

and

http://rucool.marine.rutgers.edu/index.php/COOL-Data/what-is-codar-and-how-it-works.html





 
RE: Amateur HF Ocean Wave Communication Using Bragg Resonanc Reply
by K0BG on November 8, 2010 Mail this to a friend!
Well, it's sort of like back scatter along mountain ranges. Not reliable perhaps, but certainly fun when it works.

Alan, KØBG
www.k0bg.com
 
RE: Amateur HF Ocean Wave Communication Using Bragg Resonanc Reply
by W9PMZ on November 8, 2010 Mail this to a friend!
people have been bouncing signals over the ocean for a long time...

73,

carl - w9pmz
 
RE: Amateur HF Ocean Wave Communication Using Bragg Resonanc Reply
by W9PMZ on November 8, 2010 Mail this to a friend!
people have been bouncing signals off the ocean for a long time...

this is what i wanted to say...

73,

carl - w9pmz
 
RE: Amateur HF Ocean Wave Communication Using Bragg Resonanc Reply
by KF5AHV on November 8, 2010 Mail this to a friend!
There is a place near here named "The Texas City Dike". It is billed as the worlds longest pier and you can drive 5 miles directly out over water on a 2 lane road with water on both sides. Local CB'ers here are able to drive out and work/hear stations extremely far inland that nearby base stations with high antennas cant hear. Its normal to talk into Beaumont, North West Houston, Huntsville, Livingston, and alot of other places that are not even along the waters edge. I could understand why you would be able to drive out there and talk to other stations on or near water but nobody has been able to figure out how it does so well inland. Driving out there with a 4 watt cb and a 1/4 wave vertical is like having a 1,000 foot high base antenna with a big amp.

 
Knowledge is one thing, communication another. Reply
by AI2IA on November 8, 2010 Mail this to a friend!
A summary at the beginning introducing the concepts and stating some practical use for hams would help the reader decide if it is worth his time to wade through all the details.
 
RE: Knowledge is one thing, communication another. Reply
by W5DQ on November 8, 2010 Mail this to a friend!
Nice idea but methinks I'll need lots of power and some good antennas to get to the ocean from here in the upper Mojave Desert. There are 2 mountain ranges and the vast San Joaquin Valley between us :)

 
Amateur HF Ocean Wave Communication Using Bragg Resonance Reply
by VE2ITZ on November 8, 2010 Mail this to a friend!

Quite interesting indeed!
 
RE: Knowledge is one thing, communication another. Reply
by N3OX on November 8, 2010 Mail this to a friend!
"Knowledge is one thing, communication another. "

Ham radio isn't only about communication.

There don't have to be practical applications to things like this. This is interesting in its own right and might be more interesting for some hams than talking to people using 12m skywave!

 
Amateur HF Ocean Wave Communication Using Bragg Resonance Reply
by K5END on November 8, 2010 Mail this to a friend!
This is one of the best articles I have seen on eham.

Well worth the time to read.

Thanks to the author.
 
RE: Amateur HF Ocean Wave Communication Using Bragg Resonanc Reply
by KJ6BSO on November 8, 2010 Mail this to a friend!
>This seems to be a nice idea--for experimentation, just like meteor
>scattered or moon bounced signals. Other than that, there is no
>practical application of such a method of communications.

The same could be said about at least half of what we do in amateur radio. Who cares if it's practical? It's FUN, and that's the point. This is a hobby, after all.
 
Amateur HF Ocean Wave Communication Using Bragg Resonance Reply
by W7KNA on November 8, 2010 Mail this to a friend!
Fascinating!! Really thinking outside of the box.
 
RE: Amateur HF Ocean Wave Communication Using Bragg Resonanc Reply
by BHARDIMON on November 8, 2010 Mail this to a friend!
It's so sad to see hams living in the past, Modern technology kind of left you guys in the dust, right? Granted, I'll be old some day (2040) and will probably still be hanging on to my little outdated cell phone and sending txt messages thinking I'm the coolest Popsicle around, meanwhile the rest of the culture realizes I'm just an old kook living in the past.
 
RE: Amateur HF Ocean Wave Communication Using Bragg Resonanc Reply
by ZENKI on November 9, 2010 Mail this to a friend!
What would be of more interest too hams is the modern adaptation of these methods using DSP.

The MUSIC and ESPRIT algorithms used by modern ocean radar systems can be used for direction finding applications in ham radio. Better still is beam steering using DSP methods.

The SDR receivers that can do this at an affordable price are fast becoming available. All we need is a creative ham that can write the DF application for the PC.

Just imagine having the capability of finding a station anywhere on the planet within in a 1 mile radius!

Single site location methods can be accomplished with 2 or 3 loop antennas and 2 or maybe 3 receivers. More is better, however if hams networked their resources we could have the worlds biggest HF operational DF system.

This link has a excellent summary of what can be achieved.

www.g4axx.com/HF_Radio_Direction_Finding.pdf

If a lot of hams had this capability jamming would truly be a thing of the past!

I own a old Watkins Johnson system and its performance is spectacular on ham signals on 40 and 75 meters. If I had access to more accurate radiosonde ionosphere information the system would be even more reliable and accurate.

Direction finding using DSP direct sampling receivers might be a standard feature on ham transceivers of the future.
 
RE: Amateur HF Ocean Wave Communication Using Bragg Resonanc Reply
by W9PMZ on November 9, 2010 Mail this to a friend!
"Modern technology kind of left you guys in the dust"

Did you read the article? 1978?? Technology now as compared then??? All tube radios were still on the market. Even radar systems during this period have become more advanced than in 1978.

It is an interesting read, but I hardly think that this is a form of communication; measuring the doppler shift of waves. Electromagnetic waves bounce off most everything (unless it is designed to be stelth). Why not publish a article on communication using the doppler shift of cars moving up and down any interstate?

73,

Carl - W9PMZ
 
RE: Amateur HF Ocean Wave Communication Using Bragg Resonanc Reply
by K8QV on November 9, 2010 Mail this to a friend!

"Modern technology kind of left you guys in the dust, right?"


This kind of remark amuses me. They don't get it. It's like chiding someone who makes oil paintings for living in the past since photography has been invented. It's a HOBBY that isn't all about "cutting edge."

I know who you can go tell they're living in the past - classic car enthusiasts, people who ride horses, cane pole fishermen, bicyclists and home gardeners.

 
Amateur HF Ocean Wave Communication Using Bragg Resonance Reply
by VE2ITZ on November 9, 2010 Mail this to a friend!
"Modern technology kind of left you guys in the dust, right?"


This kind of remark amuses me. They don't get it. It's like chiding someone who makes oil paintings for living in the past since photography has been invented. It's a HOBBY that isn't all about "cutting edge."

I know who you can go tell they're living in the past - classic car enthusiasts, people who ride horses, cane pole fishermen, bicyclists and home gardeners.



Precisely! You nailed it right on the spot!


Many people often ask me why not use a cell phone to communicate. As if though i was interested in the means to communicate.

The issue with a lot of people nowadays is that they have become comfortably numb. They expect instant gratification.

I am not into ham radio as a means to communicate. I am an enthusiast of experimentation and building and understanding how things work.

It is the same as why should i play in a musical instrument and sing a song if i can listen to a recorded song!


 
Amateur HF Ocean Wave Communication Using Bragg Resonance Reply
by K1CJS on November 9, 2010 Mail this to a friend!
Not trying to change the subject, but it looks like a few of the posts between yesterday and today either got lost--or deleted.
 
Amateur HF Ocean Wave Communication Using Bragg Resonance Reply
by K4LVR on November 9, 2010 Mail this to a friend!
I was at Point Reyes National Seashore, north of Marin in 2001. AFter visiting the KPH antenna farm, I went down to the beach to the north of the Point Reyes lighthouse and saw several antennas that looked to be sized for 150MHz. There was a sign posted on them I recall, that it was an experimental sea state determining experiment. It had a very similar drawing to the one posted in this article. Interesting to see this posted here.

-lu-
 
Amateur HF Ocean Wave Communication Using Bragg Resonance Reply
by KC5CQW on November 9, 2010 Mail this to a friend!
This reminds me of the HF radar method for tracking aircraft.
You need a remotely transmitted carrier and a RX with the audio fed into a sound card waterfall program.

http://www.qsl.net/g3cwi/doppler.htm

73, Damon
 
Amateur HF Ocean Wave Communication Using Bragg Resonance Reply
by KL7AJ on November 9, 2010 Mail this to a friend!
A somewhat similar principle is used for incoherent scatter radar, where you can get a lot of information by looking at the frequency spread of the return signals. As things move around faster you have more different Doppler frequencies, which creates a broadbanded signal. You can actually determine electron temperature by the return signal bandwidth.

This is actually the sort of experiment where hams can contribute to the science.

Eric
 
RE: Amateur HF Ocean Wave Communication Using Bragg Resonanc Reply
by N3OX on November 9, 2010 Mail this to a friend!
"This reminds me of the HF radar method for tracking aircraft.
You need a remotely transmitted carrier and a RX with the audio fed into a sound card waterfall program. "

Yeah, I was thinking about that too. I've done it on VHF. Here's a trace of the WA1ZMS beacon on 144.285 and Doppler shifted aircraft traces (receiver's a little drifty).

http://n3ox.net/files/WA1ZMS_0042Z_082309.jpg

I've actually made contacts assisted by passing aircraft in VHF/UHF contests. WA1ZMS/B is great. It's running big power and just the right distance from me to be audible all the time but get really loud with extra enhancement. Excellent resource for "radar" applications here. Spent about an hour one night this summer listening to it scatter off the ionization trails of lightning strikes (I think):

http://n3ox.net/files/wa1zms_052810_lightning_scatter_nulled.mp3
 
Amateur HF Ocean Wave Communication Using Bragg Resonance Reply
by NZ4O on November 11, 2010 Mail this to a friend!
In the late 1970's I was involved in the early ocean current detection HF radar experiments while in the U.S. Coast Guard and stationed at the USCG Oceanographic Unit in Washington, DC.

The CODAR units are now deployed around the world and QRM whole SW broadcast bands, a real shame. Check out 60 meters (4.6-5.1 mc) at night and you will hear them.

http://www.bcdx.org/?p=9

http://www.codar.com

73 & GUD DX,
Thomas F. Giella, NZ4O
Lakeland, FL, USA
http://www/solarcycle24.org
 
18MHz-24MHz HFpack S.F. Bay Sea Wave Effects Seen Reply
by KQ6XA on November 12, 2010 Mail this to a friend!
About 5 years ago I did a lot of HFpacking on an island beach in the middle of San Francisco Bay and noticed this unusual form of sea water propagation. My backpack radio was a 25W SSB transciever (Vertex VX-1210) with a whip antenna and dragging wire counterpoise.

Walking around on the beach, I found what we have called the SWA (SaltWater Amplifier) to be good for about +20dB signal boost on receive and transmit. The SWA effect happens when the antenna is about 1 wavelength or less from the water's edge. But, another effect happens with propagation locally that cannot be explained by a simple increase in signal strength or lower angle of radiation.

We often work on the HFpack calling frequency 18157.5kHz USB, with a large group of operators around North America. We have several other "QSY frequencies" programmed into memory, so we all can instantly try out different bands without losing track of each other http://hfpack.com/air/
14342.5 kHz USB
18157.5 kHz USB
21437.5 kHz USB
24977.5 kHz USB
28327.5 kHz USB

My friend Budd W3FF, is located in Redding, California, 200 miles from my base station QTH near San Francisco. We usually can not work each other, base-to-base even with our good antennas and kilowatts on 18MHz because we are beyond groundwave/line-of-sight range over several mountain ranges.

However, when I go HFpacking with just 25 watts SSB on the San Francisco Bay island beaches, I can easily work 200 miles away to W3FF on 18MHz or 21MHz, night or day with somewhat variable signal strength. We have also observed this effect peaking on 24MHz. This effect is not present (or very diminished) on other HF bands.

Hams and maritime mobiles have known about the SWA (Salt Water Amplifier) and Sea-Wave propagation for a long time, but it seems that there is also something special about scattering salt water propagation, and it it may be somewhat similar to the effects used in HF ocean wave radar.

73 Bonnie Crystal KQ6XA, VR2/KQ6XA
HFpack http://hfpack.com
HFLINK http://hflink.com
Global ALE High Frequency Network http://hflink.net



 
RE: Amateur HF Ocean Wave Communication Using Bragg Resonanc Reply
by WA2JJH on November 13, 2010 Mail this to a friend!
K8QV made a goodpoint. The Bragg effect may be fun to see what you can do for something fun.
IMHO, the average ham to avid contester will see it as too much trouble to emulate.
Then again stupid me thought ESSB(HI-FI SSB) would also be too much trouble. It was a micro-fad on 20M. Years ago. Yet retired broadcasters to CB like liddy hams buy rigs for ESSB ability. Sounds great, but at what cost on crowded bands.

Of course with multiband HF military radio's with the added
auto link(ALE), turns HF transceivers into a Trunk like operation used one UHF radio's.

THE BRAGG effect is far more usefull at EHF,SHF, Quasi-optical infrared and visable light. The ultra short wavelengths allow Bragg devices to work with millimeter waves...100GHZ.

I once had a 35 mile hop-QSO using FRS H-T's. Of course it was over water and high elevation. 35 miles on UHF with 500mw was very cool. Dead full quieting copy for hours.


Actually huge leaps in Laser diode's benefit from a Bragg effect bragg resonator. Yes a fine micro machined ripple is added to VSEL laser diodes.

Result is almost 50% laser out per DC watts in.
The Bragg effect has been known since Einstein.
 
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