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: How hard would this be?  (Read 916 times)
2ST123
Member

Posts: 56




Ignore
« on: February 13, 2007, 05:04:08 AM »

How hard would it be to build a joe gun beam or a moonraker for 2M and 70cm?
Logged
N3OX
Member

Posts: 8853


WWW

Ignore
« Reply #1 on: February 13, 2007, 12:48:14 PM »

Not hard but I wouldn't try to copy CB designs.

Lots of them are all show and no performance.

If you want to try it, you just scale ALL the dimensions by the ratio of the frequencies... all the element diameters, lengths, and so forth.

If you want a good 2m or 70cm beam, you should build a better design.

Try http://www.fredspinner.com/W0FMS/CheapYagi/vjbcy.html for some easy ones.

I don't know if the Joe Gunn and Moonraker engineering is reasonable or not.  The claims made for gain and front to back are just stupid.

73,
Dan
Logged

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

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

Posts: 13033




Ignore
« Reply #2 on: February 13, 2007, 03:12:52 PM »

An excellent source of antenna information is W4RNL's web page at
html://www.cebik.com/radio.html

Down in the VHF antenna section you will find his articles on quads and
the OWA yagi designs.  Both of these are excellent and are easy to build.
I've built the 2- through 4-element quads for various bands and they've
worked great with no adjustments or tuning required.  (And I can
compare several antennas against each other, so this isn't just a "seems
fine" sort of recommendation.)  The OWA yagis have a very clean pattern
and a direct 50 ohm feed impedance, though I prefer the "Cheap Yagis"
referenced above for homebrew wire designs because the driven element
is mechanically more stable.  I think W4RNL has a downloadable
spreadsheet for quads and 3-element yagis - look for his Antenna
Design spreadsheets in the Antenna Modelling section.  These require
just the entry of the desired frequency and element diameter to generate
a number of antenna designs.



Also check his Antenna Options series of articles down near the bottom.
This will give you some idea of choosing antennas and how you can
build your own.  I use PVC pipe and copper wire and I think I estimated
that it cost about $1 per element to build a quad, but that was before
the cost of copper went up.  But it still isn't very expensive.

And it isn't difficult to build antennas for 440 that will run rings around
any CB antenna in terms of true gain - for example, he analyzes some
antennas with 20+ dB of gain that are over 13 wavelengths long.  That
would be over 400 feet long if built for CB!  But on 440 MHz it is less
than 30 feet - much more practical to build.  However, I suggest you
start with something more simple - perhaps a 3-element yagi or
2-element quad.
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!