Sponsor Message:
Aviation Technical / Operations Forum
My Starred Topics | Profile | New Topic | Forum Index | Help | Search 
B747 HF Radio  
User currently offlineDiego From Italy, joined Apr 2001, 135 posts, RR: 0
Posted (10 years 5 months 4 weeks 1 day 14 hours ago) and read 3799 times:

Hi folks I am trying to understand the functioning of the HF radio and scrolling through the B747 300 cockpit photos I bumped onto a picture of an overhead panel showing the HF radio. The radio has a knob with 6 different positions: OFF-USB-LSB-AM-DATA and CW. Although the OFF position is kind of self-explainatory the others raise a few doubts such as when do you select the USB or the LSB and what AM DATA and CW stand for. In my previous post airplay answered a few questions about the LSB and the USB even though no mentioned was made about the using of the radio equipment itself.
Thanks

5 replies: All unread, jump to last
 
User currently onlineKlaus From Germany, joined Jul 2001, 21406 posts, RR: 54
Reply 1, posted (10 years 5 months 4 weeks 1 day 11 hours ago) and read 3773 times:

They are different modulation settings:

USB: upper side band (AM with carrier and lower side band suppressed)
LSB: lower side band (AM with carrier and upper side band suppressed)
AM: amplitude modulation (the same kind used for civilian "AM radio": carrier plus upper and lower side bands)
DATA: probably used for data link; There are multiple possible modulations. I don´t know which one would be used there.
CW: "continuous wave" (morse telegraphy)

For speech transmissions, USB/LSB are the most efficient ones; AM is probably used for compatibility (and for listening to civilian radio stations  Wink/being sarcastic).
CW filters make it easier to discern morse signals over a noisy background.

Can´t give you operational info; This is just as much as a radio amateur can tell you.  Wink/being sarcastic


User currently offlineSkydrol From Canada, joined Oct 2003, 963 posts, RR: 10
Reply 2, posted (10 years 5 months 4 weeks 1 day 11 hours ago) and read 3771 times:

USB = Single Sideband reception mode UPPER SIDE BAND
LSB = Single Sideband reception mode LOWER SIDE BAND

USB/LSB are forms of 'SSB' communication. SSB provides extra-long range communication capabiliy, but sacrifices audio quality to do so. SSB also requires tuning a balanced modulator to re-insert the missing carrier to allow the audio information to be used. This is finicky and mis-tuning can result in reception of voice communication sounding like Donald Duck. Note: throughout North America, most HF SSB transmissions are USB only, and many newer aircraft HF radios only support USB.

AM = AMPLITUDE MODULATION (standard braodcast - both sidebands, carrier frequency not suppressed). AM basically provides acceptable audio quality without extra clarification processes, but doesn't provide the extra-long range communication power associated with SSB.

DATA = I'm not completely certain here, but this will likely invoke filters which help block noise from interfering with reception of digital tramissions like RTTY (Radio TeleType) or FAX (weather maps)

CW = CONTINUOUS WAVE mixes a BFO (beat frequency oscillator) tone with the received signal to make morse code transmissions easier to decode (especially if they are unmodulated)



LD4



∙ ---{--« ∙ ----{--« ∙ --{-« ∙ ---{--« ∙ --{--« ∙ --{-« ∙ ----{--« ∙
User currently offlineSkydrol From Canada, joined Oct 2003, 963 posts, RR: 10
Reply 3, posted (10 years 5 months 4 weeks 1 day 11 hours ago) and read 3767 times:

Klaus: Looks like we attended the same school!  Big thumbs up


∙ ---{--« ∙ ----{--« ∙ --{-« ∙ ---{--« ∙ --{--« ∙ --{-« ∙ ----{--« ∙
User currently onlineKlaus From Germany, joined Jul 2001, 21406 posts, RR: 54
Reply 4, posted (10 years 5 months 4 weeks 1 day 11 hours ago) and read 3764 times:

I´m getting a bit rusty on this stuff, though, since I´ve not been "radio-active" for quite some time.  Wink/being sarcastic
Good to air it once in a while!  Big thumbs up


User currently offlineIakobos From Belgium, joined Aug 2003, 3312 posts, RR: 35
Reply 5, posted (10 years 5 months 4 weeks 1 day ago) and read 3751 times:

Ground > air and vice-versa voice transmissions in the HF spectrum are using USB exclusively. Every a/c has also its own SELCAL (selective calling) identity (similar to a telephone subscriber number) so that it can be called individually.
Most a/c HF transmitters have a power output of 150W (pep SSB).
When in flight, the performance of the HF antenna is poor due to the lack of ground (which otherwise acts as a reflector).

Rgds fm another ham (w/practical experience of HF onboard a/c)


Top Of Page
Forum Index

Reply To This Topic B747 HF Radio
Username:
No username? Sign up now!
Password: 


Forgot Password? Be reminded.
Remember me on this computer (uses cookies)
  • Tech/Ops related posts only!
  • Not Tech/Ops related? Use the other forums
  • No adverts of any kind. This includes web pages.
  • No hostile language or criticizing of others.
  • Do not post copyright protected material.
  • Use relevant and describing topics.
  • Check if your post already been discussed.
  • Check your spelling!
  • DETAILED RULES
Add Images Add SmiliesPosting Help

Please check your spelling (press "Check Spelling" above)


Similar topics:More similar topics...
HF Radio posted Wed Jan 28 2004 02:12:16 by Diego
Status Of Adding XM Radio To B6 Airbus Fleet? posted Thu Dec 28 2006 19:33:05 by Kearnet
Why Is There Still Aircraft Radio Splutter? posted Wed Dec 27 2006 15:50:44 by Jamesbuk
Hypothetical B747-9 posted Tue Dec 26 2006 10:36:50 by Zvezda
Which A/c Burns Alot Of Fuel B747-400 Or A340-300? posted Sat Oct 28 2006 00:41:40 by AirCanada014
HF Vs VHF Vs UHF R/T Frequencies Useage posted Fri Oct 20 2006 08:28:34 by BOACVC10
HF Communications posted Wed Aug 23 2006 06:31:33 by LimaFoxTango
B747 Reference Point posted Wed Aug 23 2006 03:34:15 by Kaddyuk
Runway Length Requirements For B747-400 With Mtow posted Tue Aug 8 2006 12:09:07 by F+ Rouge
Canadian Radio Ranges posted Mon Jul 17 2006 02:58:39 by Firefly_cyhz

Sponsor Message:
Printer friendly format