| Author |
Message |
    
Bigbob
Senior Member
Username: Bigbob
Post Number: 1767
Registered: 12-2001
| | Posted on Wednesday, March 17, 2004 - 6:52 am: | 
|
I know that the ocean can be considered "ground",for purposes of rf but how did the navy overcome the nessesity to surface their subs to tx,now they tx/rx through seawater,what changed,just technology or their way of thinking on "freespace" or both,or lol am I all wet. |
Ozzie
Intermediate Member
Username: Ozzie
Post Number: 130
Registered: 11-2003
| | Posted on Wednesday, March 17, 2004 - 9:29 am: |
|
Well for a start they went to an extremely low frequency measured inKHz not MHz. Technology improved. |
Mr_rf
Intermediate Member
Username: Mr_rf
Post Number: 285
Registered: 12-2001
| | Posted on Wednesday, March 17, 2004 - 2:27 pm: |
|
The scoop... http://enterprise.spawar.navy.mil/UploadedFiles/fs_clam_lake_elf2003.pdf
How ELF Communications works:
ELF communications systems make use of a principle in
physics where the attenuation of radio signals
(electromagnetic waves) from seawater increases with
the frequency of the signal. This means that the lower the
frequency a radio transmission, the deeper into the ocean
a useable signal will travel. Radio waves in the Very Low
Frequency (VLF) band at frequencies of about 20,000
Hertz (Hz) penetrate seawater to depths of only tens of
feet. The Navy’s ELF system operates at about 76 Hz,
approximately two orders of magnitude lower than VLF.
The result is that ELF waves penetrate seawater to
depths of hundreds of feet, permitting communications
with submarines while maintaining stealth. |
Tech833
Moderator
Username: Tech833
Post Number: 598
Registered: 8-2002
| | Posted on Friday, March 19, 2004 - 1:21 am: |
|
What he said...
Usually, subs are rigged with lutz wire antennas that trail behind them. VLF does work to depths much greater than Mr. rf eludes. However, some of the new high power satcom gear will work even when several feet below the surface. The rest is classified. |
Bigbob
Senior Member
Username: Bigbob
Post Number: 1776
Registered: 12-2001
| | Posted on Friday, March 19, 2004 - 11:35 pm: |
|
Thank you so much all of you ,bigbob. |
