Cruisers Forum
 


Join CruisersForum Today

Reply
 
Thread Tools Rate Thread Display Modes
Old 24-02-2013, 06:06   #1
Registered User

Join Date: Apr 2011
Location: Cambridge MD
Boat: Carter offshore 35
Posts: 333
Ground Plane

Can anyone explain why the VHF comes out of the box gets plugged in and works? Yet the SSB needs an intricate grounding system that seems to have as many opinions as the best anchor.
__________________

__________________
DeborahLee is offline   Reply With Quote
Old 24-02-2013, 06:44   #2
Registered User
 
Artful Dodger's Avatar

Join Date: Apr 2008
Location: Toronto, Ontario
Boat: 42 Passage CC
Posts: 177
Images: 7
Send a message via Skype™ to Artful Dodger
Re: Ground Plane

In simple terms VHF is at most line of sight, and SSB needs a launching pad to project its signal so with the best launching pad SSB works better. There are more tech explanations but one must try to keep it simple in understanding.
__________________

__________________
The Artful Dodger
Passage 42 Centre Cockpit
Toronto, Canada
Artful Dodger is offline   Reply With Quote
Old 24-02-2013, 06:51   #3
Registered User
 
dockbumdan's Avatar

Join Date: Feb 2011
Location: Onboard Georgetown, MD.
Boat: Seidelmann, S37' 1985
Posts: 46
Send a message via Skype™ to dockbumdan
Re: Ground Plane

it all comes down to wavelength and antenna theory. vhf = very high frequency. SSB = high frequency. VHF are shorter HF are longer. most antennas are based on 1/4 wl (wavelength) construction which produces a lobe of radiation closer to the ground. which with vhf allows for line of sight communication. In order for SSB to produce the correct lobe for communications it needs very long antennas. so since you could not phyically construct an antenna long enough to be 1/4 wl you "fool" the radio using something called a counterpoise. (this electrically makes the radio think it has a full 1/4wl antenna but in fact is using the grounding system ie. counterpoise to create the missing part of the antenna.since a true 1/4wl antenna has an impedance of 50 ohms. you then add a "tuner" which matches the impedance of the antenna + counterpoise (grounding system) to the radio's 50 ohms. Now you should have enough information to becoume extremely dangerous.
Dan (KO2V). The above will surely cause a bunch of pureists to correct my description. But basically that's how it works.
__________________
SV\Trinity
www.sailingtrinity.com
Docbum@me.com
dan.sloopjb@gmail.com
If you never ran aground, Your Not Sailing!
dockbumdan is offline   Reply With Quote
Old 24-02-2013, 07:17   #4
Registered User
 
Teknav's Avatar

Join Date: Jul 2012
Location: Texas - USA
Boat: Twin Otter de Havilland Floatplane
Posts: 1,838
Re: Ground Plane

Hello DeborahLee! VHF transmission uses "line of sight" propagation; if a boat is within your "line of sight", it will detect your signal. But since earth is not flat, not everyone will detect your transmitted signal; hence the short 15 mile range for a very narrow band of VHF frequencies. That is why it easier to install a VHF antenna and broadcast away! SSB transmission has a longer range, because your straight-line transmitted signal bounces up and down several times between the ionosphere (upper atmosphere ionized layer) and the "ground". Every time your signal bounces, the signal loses strength but still can reach the other side of the world. In order for your SSB transmitter to effectively do that, you need a "very long antenna", but this is limited by the size of your boat. On a sail boat, your "backstay" needs to be electrically insulated prior to installing the antenna. The length of an antenna must be relative in size to the wavelength that you will be transmitting on. Now comes the ATU (Antenna Tuning Unit), which "adjusts the performance" of your antenna to suit the frequency your are using; remember your antenna's length limitations. Then comes the "Groundplane", which provides you with a stronger signal and with a better performance! For an efficient transmission, "ground area" must be bigger than the antenna; the ocean is your ground. To achieve a proper equipment grounding, a plate is attached to the outside of the hull, or bonded to large metal objects in your boat. In "bonding", a large copper wire is used; straight line bonding between all grounding metals is a must. If the hull is metallic, you'll have the optimum ground connection. In summary, when installing SSB you need to insulate the backstay and insure a ground plane connection to avoid interference with other on-board electronics. That is why, it is not as easy to install an SSB antenna like installing a VHF's. Mauritz
__________________
Teknav is offline   Reply With Quote
Old 24-02-2013, 10:25   #5
Moderator
 
Paul Elliott's Avatar

Cruisers Forum Supporter

Join Date: Sep 2006
Posts: 3,875
Images: 4
Re: Ground Plane

Because of the high frequencies (and thus short wavelengths) involved, and the very narrow range of frequencies, the VHF whip antenna can be designed to perform well without a groundplane.

For SSB, the frequencies are much lower and thus the wavelengths are longer. And, the frequency range being covered (multiple bands, covering about a 10:1 frequency range) For the end-fed backstay type of antenna the easiest and most practical antenna system requires a groundplane and tuner. It is possible to have an SSB antenna without a groundplane, such as a dipole, but these are realistically single-band antennas, at least for a permanent boat installation.
__________________
Paul Elliott, S/V VALIS - Pacific Seacraft 44 #16 - Friday Harbor, WA
www.sailvalis.com
Paul Elliott is offline   Reply With Quote
Old 24-02-2013, 12:26   #6
Guy
Registered User

Join Date: Feb 2013
Location: So. Oregon, USA
Boat: Seafarer36c
Posts: 4,308
Re: Ground Plane

Can anyone explain the KISS ground plane. It looks like a length of large cable with a small lead to the antenna tuner. Something we could easily make ourselves out an old hunk of battery cable?
__________________
Guy is offline   Reply With Quote
Old 24-02-2013, 12:50   #7
Registered User
 
LeaseOnLife's Avatar

Join Date: Apr 2008
Location: out cruising again
Boat: Sailboat
Posts: 1,046
Re: Ground Plane

Quote:
Originally Posted by Guy View Post
Can anyone explain the KISS ground plane. It looks like a length of large cable with a small lead to the antenna tuner. Something we could easily make ourselves out an old hunk of battery cable?
plenty of explanations here:
The KISS SSB Counterpoise - Revealed ( with Pics )
__________________
LeaseOnLife is offline   Reply With Quote
Old 24-02-2013, 15:24   #8
Senior Cruiser
 
colemj's Avatar

Cruisers Forum Supporter

Join Date: Oct 2005
Location: Presently on US East Coast
Boat: Manta 40 "Reach"
Posts: 10,049
Images: 12
Re: Ground Plane

A VHF antenna is a single band dipole antenna - equivalent to a SSB dipole which also does not need a ground plane. The VHF counterpoise to the radiating part of the dipole is either the coax shield on 1/4 wave coil loaded antennas (these can also include the mast in the counterpoise through their mounting brackets), or is build into the multi 1/4 wave elements on a fiberglass whip antenna.

So a VHF DOES have a counterpoise (ground plane), but because it is a single band antenna, it can be produced as a compact dipole without need for any external connections. Because SSB's are mostly used as multi-band antennas, they require a counterpoise "system" that can handle multiple bands through a coupler.

Mark
__________________
www.svreach.com

You do not need a parachute to skydive. You only need a parachute to skydive twice.
colemj is offline   Reply With Quote
Old 24-02-2013, 15:37   #9
Senior Cruiser

Cruisers Forum Supporter

Join Date: Jul 2006
Location: Chesapeake Region and Maine
Boat: 42' Bob Perry sloop
Posts: 4,038
Images: 4
Re: Ground Plane

In current parlance, I'm ROTFL at some of the very creative explanations above :-)

A 1/4-wave antenna for marine VHF is 1.5' long (234/156mHz). One-and-a-half FEET long! Pretty easy to construct and deal with.

A 1/4-wave antenna for the 8mHz marine band, for example, would be 234/8mHz or about 29 feet long. Most backstay antennas are longer than that, some much longer. But, they're not meant to be single-band antennas. As was noted above, they're meant to be used on multiple bands, from about 2mHz thru 27mHz. To do that, they need a tuner to transform the input impedence of the antenna to the 50-ohm load the transceiver likes. To work efficiently, they also need an RF ground (loosly, "counterpoise").

Properly, these are end-fed random length wire antennas. They are not dipole antennas in the usual meaning of the word, nor are their RF ground systems "the other half of the dipole".

VHF antennas need some sort of RF ground also. Usually, it's in the form of an untuned hunk of metal attached to the shield on the coax, e.g., the mast, or even the coax shield itself.

NB: the KISS is a simple radial counterpoise system which is very easy to install, very robust, and works pretty well, but is far from the best RF ground which can be used aboard a boat.

FWIW,

Bill
WA6CCA
__________________
btrayfors is offline   Reply With Quote
Old 24-02-2013, 20:37   #10
Registered User
 
ka4wja's Avatar

Join Date: May 2007
Location: Florida
Boat: Catalina 470
Posts: 2,033
Re: Ground Plane

DeborahLee,
What Bill said.... +1!!!


And, Guy, for more info than you'd ever imagine on the KISS, have a look at the SSCA thread...
SSCA Forum • View topic - KISS-SSB Counterpoise


Fair winds..

John
s/v Annie Laurie
__________________
ka4wja is offline   Reply With Quote
Old 26-02-2013, 06:02   #11
Registered User
 
Bill_E's Avatar

Join Date: Aug 2008
Location: New Mexico and Puerto Rico
Boat: Sunbeam, 37, Ziamar
Posts: 300
Re: Ground Plane

This is an interesting discussion but brings up a few questions of my own. First, is there a technical difference between the terms counterpoise and ground plane? Maybe I should look them up in more detail.

On a practical note. My SSB is fairly old. I purchased it used over 5 years ago. When we installed it we put the tuner in the starboard Lazarette, close to the insulated backstay. Then we epoxied about 6-8 sq ft of copper foil to the hull under the lazarette. This is connected to the tuner with 3-4 ft of heavy copper wire. (I'm not sure of the gauge.) We also kludged a connection to the rudder post with about 8 ft of the copper foil. That rudder post connection has eroded but I don't see a significant difference in performance. I will want to improve the ground before I upgrade my SSB. I am sure that I'd do better with something like 1 inch braid connecting the copper sheet (ground) to the tuner. Should I use braid and redo the connection to the rudder post? Also, a couple of years ago when I hauled the boat, I realized that I have a pair of dynaplates on the top of the keel. As far as I can tell nothing is connected to them, though there may be some indirect connections through keel bolts that I don't know about. Should I use the dynaplates as part of the SSB ground? It would mean running about 10-12 ft of copper braid through the engine compartment to the bilge connection to the dynaplates. Or are they best used as a DC ground and should I work on that?

It may be relevant that my zincs seem to last for a very long time, like 2-3 years so I assume that the AC and DC grounding is pretty good.

This may have raised some questions that are answered elsewhere in the forum so I'll have to do some more checking in the next day or so.

Bill
__________________
Don't believe everything you think
Bill_E is offline   Reply With Quote
Old 26-02-2013, 06:34   #12
Registered User

Join Date: Dec 2009
Posts: 3,016
Images: 4
Counterpoise is a fancy word used by loose-talking pontificators - mostly rag chewers - to keep the uneducated in awe of their magic. It is improperly cast about on CF. Maybe because of its fancy french roots.

When you hear the word in the context of marine SSB just replace it with ground ... And discount the opinion of the writer.
__________________
daddle is offline   Reply With Quote
Old 26-02-2013, 09:09   #13
Registered User

Join Date: Sep 2008
Location: Camden, ME
Boat: A Thistle and a Hallberg-Rassy 36
Posts: 664
I think counterpoise is often used to make a clear distinction from a DC ground.

Chip
__________________
SoonerSailor is offline   Reply With Quote
Old 28-02-2013, 12:06   #14
Registered User
 
ka4wja's Avatar

Join Date: May 2007
Location: Florida
Boat: Catalina 470
Posts: 2,033
Re: Ground Plane

Bill,
Hopefully I can briefly clarify a few things....
1) Counterpoise vs. ground plane???
Quote:
Originally Posted by Bill_E View Post
This is an interesting discussion but brings up a few questions of my own. First, is there a technical difference between the terms counterpoise and ground plane? Maybe I should look them up in more detail.
Contrary to what some think, they are not buzz words used by pretentious a**holes....
But, rather are words which have meaning...
Most "professionals" do not like the word "counterpoise".....but this is how I learned ~ 40 years ago....so while it might make some PhD's cringe, I know that when I use it, I mean the generic ground / artificial ground of an antenna system...whether the dirt/soil, the sea water, copper wire radials, lead keels and metal tanks, etc....

And, when I use the term ground plane, I'm almost always referring to tuned/resonant radials....

Please note that these are NOT the engineering-accepted definitions, but when dealing with the real-world of antenna construction, it helps to use definitions that are easily delineated...

Regardless of what you call things, follow some simple rules and things will work fine!!!!





2) RF Grounds, Counterpoises, Ground Planes, Radials, etc.....only things more controversial on-board are anchors!!!
Seriously though, there is some GOOD news here for you!!!
Quote:
Originally Posted by Bill_E View Post
On a practical note. My SSB is fairly old. I purchased it used over 5 years ago. When we installed it we put the tuner in the starboard Lazarette, close to the insulated backstay. Then we epoxied about 6-8 sq ft of copper foil to the hull under the lazarette. This is connected to the tuner with 3-4 ft of heavy copper wire. (I'm not sure of the gauge.) We also kludged a connection to the rudder post with about 8 ft of the copper foil. That rudder post connection has eroded but I don't see a significant difference in performance. I will want to improve the ground before I upgrade my SSB. I am sure that I'd do better with something like 1 inch braid connecting the copper sheet (ground) to the tuner. Should I use braid and redo the connection to the rudder post? Also, a couple of years ago when I hauled the boat, I realized that I have a pair of dynaplates on the top of the keel. As far as I can tell nothing is connected to them, though there may be some indirect connections through keel bolts that I don't know about. Should I use the dynaplates as part of the SSB ground? It would mean running about 10-12 ft of copper braid through the engine compartment to the bilge connection to the dynaplates. Or are they best used as a DC ground and should I work on that?

It may be relevant that my zincs seem to last for a very long time, like 2-3 years so I assume that the AC and DC grounding is pretty good.

This may have raised some questions that are answered elsewhere in the forum so I'll have to do some more checking in the next day or so.
a) Your set-up sounds pretty good....(see details below)

b) Do NOT use "braid", as this will deteriorate very quickly...even tinned-copper braid is a poor choice for RF grounding....
Copper strap is what is recommended, or even a heavy gauge copper wire (if the run is short), but do NOT use braiding!!!

Also, the thin "copper foil" that is sold by many marine chandleries, is crap!!!
It is thin and weak....and won't last....
Use copper strapping....and paint it this some clear lacquer (or any good paint/epoxy), before installing it and it will last a LONG time....(remove the paint/epoxy from the connection points, using sandpaper or Scotchbrite or wire brush, etc....)
Use Pentrox-A as a "conductive grease" to seal/weather-proof the connections as well as provide an excellent "dis-similar-metal-to-metal-connection"....(I've been using this stuff for 30+ years!!)


c) If you have two Dynaplates already installed, use 'em!!!
No question that having them closer to your tuner would be better, but a 10' - 12' run of 3" wide copper strapping (at least 0.012" thick) will cost you about $25 - $35, and will work well...
{I', assuming these are large Dynaplates for your RF grounding, and not the smaller 3" x 6" "ground shoes" for your lightning ground???}

d) Attaching a short and wide copper strap, from your tuner's grd connection, to an underwater metal (Dynaplate, bronze thru-hulls, etc.) is almost always going to provide you with an excellent wide-band "counterpoise" (the sea water), that will outperform almost anything else you can install on-board...

But, I do not know if your rudder post provides this direct sea water connection or not....nor how this connection to the rudder post was done (as the rudder post does need to move/turn), so I cannot know if this would be an effective way to gain access to the sea water....


e) It appears that your AC and DC grounds are fine...don't mess with them...


f) If your existing Dynaplates are the larger ones, it's doubtful they're tied into your DC ground system.....but if they are OR if the are the smaller "ground shoes", you can still use them as part of your HF antenna system ground/counterpoise....you may wish to add some DC-blocking caps (three or four .1uf or even .01uf caps across a small gap of strap, allows good RF grounding, but blocks DC...)



3) Sorry to be so brief....but I've wriiten so much about RF grounds and counterpoises lately, I'm a bit burned-out!!!

Have a look at the SSCA Disc Boards for a LOT more info/details!!!
http://www.ssca.org/forum/viewforum.php?f=5&sid=2abd6ce02807c9b0a6fa8641aae1 4940
Especially here....
http://www.ssca.org/forum/viewtopic.php?f=5&t=13490&start=75
http://www.ssca.org/forum/viewtopic.php?f=5&t=13490



Fair winds...

John
s/v Annie Laurie
__________________
ka4wja is offline   Reply With Quote
Old 28-02-2013, 17:32   #15
Registered User

Join Date: Dec 2009
Posts: 3,016
Images: 4
Quote:
Originally Posted by ka4wja View Post
Hopefully I can briefly clarify a few things ... Counterpoise vs. ground plane ...
You have it mixed up. See your ARRL handbook. Or Google counterpoise for papers on the very subject (by professionals and PhD's perhaps).

Several radio hobbyists told me that I must change my grounding conductors to copper foil "because HF currents will not go thru a wire..." Seriously? They were a bit stumped when I pointed out that the entire tuner, feed, and antenna are constructed of simple, and relatively small, plain wire. I know there can be some advantages to using foils, but in the typical case plain old wire will work well enough.
__________________

__________________
daddle 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




Copyright 2002- Social Knowledge, LLC All Rights Reserved.

All times are GMT -7. The time now is 13:14.


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.