Call Search
     

New to Ham Radio?
My Profile

Community
Articles
Forums
News
Reviews
Friends Remembered
Strays
Survey Question

Operating
Contesting
DX Cluster Spots
Propagation

Resources
Calendar
Classifieds
Ham Exams
Ham Links
List Archives
News Articles
Product Reviews
QSL Managers

Site Info
eHam Help (FAQ)
Support the site
The eHam Team
Advertising Info
Vision Statement
About eHam.net

   Home   Help Search  
Pages: [1]   Go Down
  Print  
Author Topic: Prototype kayak vertical  (Read 1357 times)
9V1VK
Member

Posts: 15




Ignore
« on: July 29, 2006, 12:31:26 PM »

This weekend i decided to make a prototype wire vertical.  Instead of building it for the kayak, I thought I'd start with one I can post on the beach.  

My fishing pole is about 8m long, so I cut 4 radials and an element for a quarter-wave vertical on 14.060mhz.  The calculator said this should be radials and verticals all 5.073m.  I cut them accurately and soldered them onto a coax connector.

I took everything out to the beach with an MFJ-269 analyser.  Results were a bit suprising:

14.060mhz   SWR=4.0  Rs=90 and Xs=87

where is SWR=1.0?
12.817mhz SWR=1.0 Rs=49 and Xs=0

oops, not what I had hoped for.

Here is a photo of my setup on the beach. The radials are spread out (although not taut straight) and one is half in the ocean.  http://flickr.com/photos/karavshin/201141879/

I came home and tried the antenna out in my yard.  I got different, but unwanted, results there too:

14.060 had a 7.7SWR, Rs=132 and Zs=177

Resonance was at 11.892mhz  SWR=1.0 Rs=48 and Xs=2


So my question is how to interpret this data into a conclusion on what to do to make it work best at 14.060.  

My first reaction was the vertical element is too short. it should be  14.060 * 5.073 / 12.817 m long to resonate at 14.060.  IE: should make the element 17inches (0.448m) longer.  

But maybe that's naive.  Maybe there is more to interpret from the results?  And what about the radials...does this mean they should also be extended?  by the same amount? etc.etc.  

ideas?
Logged
9V1VK
Member

Posts: 15




Ignore
« Reply #1 on: July 29, 2006, 12:45:24 PM »

I was brain-dead when i wrote this at 0346.  The antenna is resonant at too low a frequency, thus it seems that it needs shortened.  It's too long by  (14.06 - 12.817)/14.06 = 9% or 0.45m. [my original message implied it was too short...]

When you trim the vertical element, what should you do with the radials?
Logged
N3OX
Member

Posts: 8853


WWW

Ignore
« Reply #2 on: July 30, 2006, 03:05:48 PM »

Since, if I recall correctly, you're intending on floating the radials on saltwater, they don't have to be any particular length.  They certainly don't have to be resonant.  They could be quite short and still be effective, as the current will flow in the surface of the sea with very little loss.  

Just trim up the vertical element and you'll be fine.

73,
Dan
Logged

73,
Dan
http://www.n3ox.net

Monkey/silicon cyborg, beeping at rocks since 1995.
9V1VK
Member

Posts: 15




Ignore
« Reply #3 on: July 30, 2006, 06:00:36 PM »

But if I just use this one on the beach shore, should i be trimming the radials too?  and by what percentage?
Logged
N3OX
Member

Posts: 8853


WWW

Ignore
« Reply #4 on: July 30, 2006, 09:32:59 PM »

I very much doubt you have to trim the radials at all.  You've got saltwater saturating the sand underneath the beach to some extent.  The radials are coupled heavily to the saltwater even on the beach, though not as much as when you're surrounded by water.

You should be able to get a low SWR without adjusting the radials at all.  Things might change a bit when you actually use the kayak ground system, but the saltwater should give you a fairly good nonresonant ground and it should work OK even on the beach with a couple of radials in the water like you showed.

Dan
Logged

73,
Dan
http://www.n3ox.net

Monkey/silicon cyborg, beeping at rocks since 1995.
WB6BYU
Member

Posts: 13040




Ignore
« Reply #5 on: July 31, 2006, 01:27:55 PM »

My suggestion would be to shorten the radials by half of
your calculated correction factor and see how much this
changes the resonant frequency.  Then shorten the radiator
and see how much that changes it.  (At this point you
shouldn't have shortened it too much yet.)

My guess is that shortening the radiator will make much
more difference than shortening the radials.  But if
you put it on the kayak with the radials up above the
water it will be more ground-independent, and the radial
length will have more effect on the resonant frequency.
(In that case you can trim the radials to change the
resonant frequency rather than the vertical length.)  So
to use it either place, set the radiator height for best
SWR with the radials laying on the ground on the beach,
then use the same radiator in the kayak and adjust the
radial length as needed so the same radiator gives the
same resonant frequency in both places.
Logged
9V1VK
Member

Posts: 15




Ignore
« Reply #6 on: August 05, 2006, 06:48:18 AM »

Did another round of experimentation on my wire vertical today and the results were pretty ok.    Heard a JA-call but I guess he didn't hear me.  Need to figure why my KX-1 would only poop 2.5w instead of 4.

http://karavshin.org/blogs/black-coffee/archive/001690.html
Logged
Pages: [1]   Go Up
  Print  
 
Jump to:  

Powered by MySQL Powered by PHP Powered by SMF 1.1.11 | SMF © 2006-2009, Simple Machines LLC Valid XHTML 1.0! Valid CSS!