Cruisers Forum
 


Join CruisersForum Today

Reply
 
Thread Tools Rate Thread Display Modes
Old 05-12-2013, 19:00   #46
Registered User

Join Date: Jul 2013
Posts: 126
Re: Hand held VHF range

I was reading an article on the ham radio site eham.net and thought it might be useful for some on here and pertinent to this discussion. The author describes some mods he made to improve the performance of a handheld vhf radio. He shows how to connect a simple wire to act as a counterpoise for the whip antenna and a method to make a 1/4ƛ antenna from a brass welding rod. I thought some of you might like the suggestions. Just remember to use the formula 234/f MHz to get the proper length at VHF marine freq's.
__________________

__________________
El Rubio is offline   Reply With Quote
Old 05-12-2013, 19:42   #47
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
Re: Hand held VHF range

Quote:
Originally Posted by El Rubio View Post
I was reading an article on the ham radio site eham.net and thought it might be useful for some on here and pertinent to this discussion. The author describes some mods he made to improve the performance of a handheld vhf radio. He shows how to connect a simple wire to act as a counterpoise for the whip antenna and a method to make a 1/4ƛ antenna from a brass welding rod. I thought some of you might like the suggestions. Just remember to use the formula 234/f MHz to get the proper length at VHF marine freq's.
Presumably imperial; for the rest of us, use 75/f MHz to get 1/4 wavelength in metres.
__________________

__________________
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
Old 07-12-2013, 06:59   #48
Registered User

Join Date: Dec 2011
Posts: 41
Re: Hand held VHF range

Thats exactly the formula with speed of light 300 000 000m/sec.
But take 5% more length due to a "reduction effect" and you mitht want to trim.
Greetings, Wilhelm
__________________
_ _ /) _
Seefunk
funk-an-bord.de is offline   Reply With Quote
Old 07-12-2013, 07:19   #49
֍֎֍֎֍֎֍֎֍֎

Cruisers Forum Supporter

Join Date: Apr 2006
Posts: 13,033
Re: Hand held VHF range

To clarify: The speed of light is not a constant. It varies depending on what the "light" is traveling through. So in a vacuum, one number. In air, water, treacle, copper wire, other numbers. Slower in the denser medium, so a "correction factor" is applied, which is available for specific materials and wire types. In a plain copper wire, 95-97% of vacuum speed, so you make the wire a tad long, and trim it to best performance, unless you want to gamble on finding exact numbers.

"en.wikipedia.org/wiki/Speed_of_electricity "

And then there's the odd new physics, apparently they can make light travel dog slow or even in reverse in a Bose-Einstein condensate.
__________________
hellosailor is offline   Reply With Quote
Old 07-12-2013, 11:26   #50
Registered User

Join Date: Jul 2013
Posts: 126
Re: Hand held VHF range

It's not that critical, just make a little longer and trim to best match. All this hair splitting clarification may discourage the average cruiser without a doctorate in physics. In other words, it's fun. Don't make it complicated.
__________________
El Rubio is offline   Reply With Quote
Old 07-12-2013, 11:56   #51
Marine Service Provider

Join Date: May 2011
Location: PDX
Boat: Gulfstar 50
Posts: 895
Re: Hand held VHF range

Quote:
Originally Posted by hellosailor View Post
To clarify: The speed of light is not a constant. It varies depending on what the "light" is traveling through. So in a vacuum, one number. In air, water, treacle, copper wire, other numbers. Slower in the denser medium, so a "correction factor" is applied, which is available for specific materials and wire types. In a plain copper wire, 95-97% of vacuum speed, so you make the wire a tad long, and trim it to best performance, unless you want to gamble on finding exact numbers.

"en.wikipedia.org/wiki/Speed_of_electricity "

And then there's the odd new physics, apparently they can make light travel dog slow or even in reverse in a Bose-Einstein condensate.

Actually it is a constant. The speed of light does not change only the observed speed of light.

Imagine tossing a ball back and forth across a room between 2 people. This represents the speed of light. Now add in a bunch of other people in a line and toss the ball to the first who tosses it to the next till it gets to you. It takes much longer to cross the room but the speed when being tossed between any two people is constant. The ball is not traveling when inthe hands of one of the people (thus is not "light").

From Wikipedia:

In exotic materials like Bose–Einstein condensates near absolute zero, the effective speed of light may be only a few metres per second. However, this represents absorption and re-radiation delay between atoms, as do all slower-than-c speeds in material substances.
SNIP
However, the popular description of light being "stopped" in these experiments refers only to light being stored in the excited states of atoms, then re-emitted at an arbitrarily later time, as stimulated by a second laser pulse. During the time it had "stopped," it had ceased to be light. This type of behaviour is generally microscopically true of all transparent media which "slow" the speed of light.[60]
__________________
evm1024 is offline   Reply With Quote
Old 07-12-2013, 15:22   #52
Registered User

Join Date: Jul 2013
Posts: 126
Re: Hand held VHF range

Quote:
Originally Posted by evm1024 View Post
Actually it is a constant. The speed of light does not change only the observed speed of light.

Imagine tossing a ball back and forth across a room between 2 people. This represents the speed of light. Now add in a bunch of other people in a line and toss the ball to the first who tosses it to the next till it gets to you. It takes much longer to cross the room but the speed when being tossed between any two people is constant. The ball is not traveling when inthe hands of one of the people (thus is not "light").

From Wikipedia:

In exotic materials like Bose–Einstein condensates near absolute zero, the effective speed of light may be only a few metres per second. However, this represents absorption and re-radiation delay between atoms, as do all slower-than-c speeds in material substances.
SNIP
However, the popular description of light being "stopped" in these experiments refers only to light being stored in the excited states of atoms, then re-emitted at an arbitrarily later time, as stimulated by a second laser pulse. During the time it had "stopped," it had ceased to be light. This type of behaviour is generally microscopically true of all transparent media which "slow" the speed of light.[60]

Thank you Dr Sheldon Cooper.
__________________
El Rubio is offline   Reply With Quote
Old 07-12-2013, 15:29   #53
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
Re: Hand held VHF range

Quote:
Originally Posted by hellosailor View Post
...........

And then there's the odd new physics, apparently they can make light travel dog slow or even in reverse in a Bose-Einstein condensate.
Quote:
Originally Posted by El Rubio View Post
It's not that critical, just make a little longer and trim to best match. All this hair splitting clarification may discourage the average cruiser without a doctorate in physics. In other words, it's fun. Don't make it complicated.
OK, the OP's question has been answered it seems a little thread can't hurt.

I plan to call by the local chandlery tomorrow and get a small packet of Bose-Einstein condensate (presumably in the HiFi audio rack).

With my new found knowledge from CF, I figure if I put it on the front of my torch, the light will reverse and then charge up my torch batteries.

Not sure what will happen when I put it on my solar panel but I am hoping they will turn into a huge light source - I will report back and let you all know. Maybe these experiments will go some way towards me getting my doctorate in physics
__________________
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
Old 07-12-2013, 16:24   #54
Marine Service Provider

Join Date: May 2011
Location: PDX
Boat: Gulfstar 50
Posts: 895
Re: Hand held VHF range

Quote:
Originally Posted by El Rubio View Post
Thank you Dr Sheldon Cooper.

More like A. J. Libby Long
__________________

__________________
evm1024 is offline   Reply With Quote
Reply

Tags
vhf

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




Copyright 2002- Social Knowledge, LLC All Rights Reserved.

All times are GMT -7. The time now is 10:24.


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.