Cruisers Forum
 


Join CruisersForum Today

Reply
 
Thread Tools Rate Thread Display Modes
Old 04-10-2009, 17:22   #16
Registered User
 
bill good's Avatar

Join Date: Oct 2006
Location: Brisbane Australia
Boat: sold
Posts: 721
If you wont short range daytime comms yes. i.e. AM broadcast radio Vertical using ground wave radiation for approx 50miles. At night sky wave will give the same hundreds+ miles. Horizontal is selected where distances greater than the 50 miles are required & the direction of the transmission other than omnidirectional. Further the angle of radiation effected by the height of the wire much as optical light rays. & more the frequency, solar activity with the list going on. In simply terms divide the freq by 10 & this is approx the daytime distance covered & will give the first choice of which frequency to select. 2000kz =200mls 6000kz = 600mls where stations are not set up for ground wave coverage.i.e. coastal stations,weather transmissions, air/ground, national broadcasters.
Enjoy the HF services while you can because it will fade into history & someone will gain your paid services for what has been free.

Bill
__________________

__________________
bill good is offline   Reply With Quote
Old 04-10-2009, 19:22   #17
֍֎֍֎֍֎֍֎֍֎

Cruisers Forum Supporter

Join Date: Apr 2006
Posts: 13,051
Wotname-
With SSB you are probably talking about HF ("high frequency") and long distance communications. This is fundamentally different from the needs for VHF antennas.

The main difference is that an SSB signal may be bouncing off atmospheric layers, rather than "beaming" on a line of sight from one antenna to the other. When the signal bounces off anything (atmospheric layers, skycrapers, terrain effects, etc.) the polarization of the signal changes. And that's the gotcha:

If two antennas are set up, one horizontal and the other vertical, you can lose a fast 20db of signal strength (3/4 of your power) simply from the change in polarization. That's not my opinion, that's the physics of antenna systems. So, for two VHF radios where it IS possible to have both antennas very close to vertical, that's a good way to do things.

But for HF systems including marine SSB, where thesignal will be rotated as it bounces off things anyway, the polarization is not as critical and you'll often find that taking the antenna OFF vertical can improve results. This is a situation where the environment is outside of your control, and "what works best" is literally going to need experimentation to suit your environment and purposes, i.e. whether you are intentionally using atmospheric bounces for long range, or trying to send a signal straight up and down for NVIS (Near Vertical Incidence Signal) transmission, which shoots an HF signal "straight" up in order to bring it back down to stations within a couple of hiundred miles of you. And that's what the military does for HF radios when they want to communication inside the local dead zone that they would otherwise have--the run the antenna parallel to the ground, not vertical at all!

Vertical? Sometimes yes, sometimes no. Best to run the antenna so it is physically robust, and then it is most likely to be there and be working--at all--when you need it. Every boat is different, every rig is different, there's no one yet who has been able to just "run the numbers" and come up with a "best" installation compared to experimenting on it.
__________________

__________________
hellosailor is offline   Reply With Quote
Old 04-10-2009, 20:15   #18
Certifiable Refitter/Senior Wannbe
 
Wotname's Avatar

Cruisers Forum Supporter

Join Date: Jan 2008
Location: South of 43 S, Australia
Boat: Van DeStat Super Dogger 31'
Posts: 7,331
Quote:
Originally Posted by s/v Jedi View Post
Wotname,

So, how do you communicate with a fellow cruiser who is nearby but just out of VHF range? And how about 2182 kHz?
Again I see we are using the HF for different purposes (assuming you do communicate with such cruisers and use 2182) whereas I don't.

As for 2182, Most of the time I think one would be hard pressed to raise anyone (shore or ship) in the waters around Aust. It certainly was that way 10 years back and HF services have only reduced in that time.

How often is 2182 used in other parts of the world these days?

However your point is valid .


Quote:
Originally Posted by bill good View Post
...........
Enjoy the HF services while you can because it will fade into history & someone will gain your paid services for what has been free.

Bill
Aint this the truth and one reason I plan to work whatever HF services I can once I am back afloat just so there is a tiny bit more traffic to justify their existence. I am sure the operators don't want to shut down their services, rather they have to justify their existence to the accounting gods (lower case g intentional).
Quote:
Originally Posted by hellosailor View Post
Wotname-
With SSB you are probably talking about HF ("high frequency") and long distance communications. This is fundamentally different from the needs for VHF antennas.

The main difference is that an SSB signal may be bouncing off atmospheric layers, rather than "beaming" on a line of sight from one antenna to the other. When the signal bounces off anything (atmospheric layers, skycrapers, terrain effects, etc.) the polarization of the signal changes. And that's the gotcha:

If two antennas are set up, one horizontal and the other vertical, you can lose a fast 20db of signal strength (3/4 of your power) simply from the change in polarization. That's not my opinion, that's the physics of antenna systems. So, for two VHF radios where it IS possible to have both antennas very close to vertical, that's a good way to do things.

But for HF systems including marine SSB, where thesignal will be rotated as it bounces off things anyway, the polarization is not as critical and you'll often find that taking the antenna OFF vertical can improve results. This is a situation where the environment is outside of your control, and "what works best" is literally going to need experimentation to suit your environment and purposes, i.e. whether you are intentionally using atmospheric bounces for long range, or trying to send a signal straight up and down for NVIS (Near Vertical Incidence Signal) transmission, which shoots an HF signal "straight" up in order to bring it back down to stations within a couple of hiundred miles of you. And that's what the military does for HF radios when they want to communication inside the local dead zone that they would otherwise have--the run the antenna parallel to the ground, not vertical at all!

Vertical? Sometimes yes, sometimes no. Best to run the antenna so it is physically robust, and then it is most likely to be there and be working--at all--when you need it. Every boat is different, every rig is different, there's no one yet who has been able to just "run the numbers" and come up with a "best" installation compared to experimenting on it.
Sounds like we are batting for the same team Hellosailor. For awhile I felt like Robinson Crusoe.
__________________

__________________
All men dream: but not equally. Those who dream by night in the dusty recesses of their minds wake in the day to find it was vanity: but the dreamers of the day are dangereous men, for they may act their dreams with open eyes, to make it possible. T.E. Lawrence
Wotname is offline   Reply With Quote
Reply

Thread Tools
Display Modes Rate This Thread
Rate This Thread:

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
Vertical Take Off Monohull ireaney Monohull Sailboats 7 27-05-2009 01:13
vertical shaft play sailormark45 Monohull Sailboats 1 09-04-2009 09:35
Vertical Axis Wind Generator DeepFrz Electrical: Batteries, Generators & Solar 0 14-03-2009 20:45
Vertical Ice trays phorvati Plumbing Systems and Fixtures 0 08-07-2007 16:19
Vertical learning curve! Borden Meets & Greets 3 18-10-2005 18:28



Copyright 2002- Social Knowledge, LLC All Rights Reserved.

All times are GMT -7. The time now is 13:08.


Google+
Powered by vBulletin® Version 3.8.8 Beta 1
Copyright ©2000 - 2017, vBulletin Solutions, Inc.
Social Knowledge Networks
Powered by vBulletin® Version 3.8.8 Beta 1
Copyright ©2000 - 2017, vBulletin Solutions, Inc.

ShowCase vBulletin Plugins by Drive Thru Online, Inc.