[50mhz] antenna

[jeremy-ca]

I disagree that "most" builders insulate the elements from the boom. In fact 
I believe that the opposite is true.

With available software the boom correction factor requires a few key 
strokes.

As well as being at DC ground an all grounded antenna has less precipitation 
static. My own VHF/UHF yagis use an all metal T match as does the Cushcraft 
Boomer and others.

With a Yagi program and access to some aluminum tubing the Cushcraft 6 el 
can be upgraded to an outstanding performer. With 8 elements the gain is 
within a tenth dB of theory for the boom length and the full F/R is in 
excess of 25dB over 500 KHz and approaches 40 dB at 50.2.  The stock Boomer 
suffers severely in both gain and F/R as it is a pre computer 60's design.

Ive used those mods on single and stacked Boomers for about 15 years. The 
F/R alone makes the change worthwhile as it eliminates most local noise 
sources.

Carl
KM1H

----- Original Message ----- 
From: "LANCE COLLISTER" <w7gj at q.com>
To: <na4d at vvdsi.com>
Cc: <50mhz at mailman.qth.net>
Sent: Monday, February 04, 2008 10:26 AM
Subject: Re: [50mhz] antenna



Lloyd C. Curry wrote:
> I am planning to replace my old Cushcraft 6 el yagi with a newer
> antenna. I am leaning toward either the M2 6M7 or 6M7jhv. I like the
> idea of the 6M7 because it is heavier but there is not much difference
> in gain. Anyone have any other comments? Thanks Lloyd, NA4D
>
> Moderator: Ray Brown, KB0STN
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Hello Lloyd,

Most 6m operators only seem to get on during strong Es, F2 or TEP openings, 
when
just about anything connected to the end of a piece of coax will do the job.
However, since you are interested in upgrading your old antenna, you 
obviously are
concerned with real performance under weak signal conditions :-)  In such
situations, there is a HUGE difference between the old types of antennas and 
the
newer, computer-optimized designs.

The M2 6M7JHV is a very well proven antenna, is lightweight, has very low 
wind
loading and can be broken down to be a UPS-shippable and airline 
transportable
package.  On 6m EME - where every dB counts - the 6M7JHV has earned the 
reputation
as the antenna of choice for success on DXpeditions.

If you prefer to homebrew your own high-performance 6m yagi, I suggest you
seriously consider duplicating one of the 7 or 8 element antennas designed 
by YU7EF:

http://www.yu7ef.com/

These antennas are no doubt heavier and less well suited to airline
transportation, but are very well proven in the field to perform up to the 
very
high performance shown on the website.  I have completed 6m EME contacts 
with a
number of stations using these great designs.  In addition to the design
information on his web page, there are dozens of construction photographs
available that show how different people attached the elements to the booms,
constructed the driven elements, etc.  Note that all the YU7EF antennas are
designed to provide 50 ohm driven elements, so it is not necessary to build 
T
matches, hairpin matches or folded dipoles...just connect the split dipole 
to 50
ohm cable and provide a ferrite RF choke over the coax next to the driven 
element
connection!  Simple and effective.

Most builders follow Pop's suggestion and insulate all the elements from the 
boom.
  In case you don't have a handy plastics supply house just down the street,
success has been had by simply cutting up a 1/2" thick HDPE cutting board to 
serve
as element mounting blocks...such cutting boards are available in many 
hardware
and grocery stores all over the world.  You simply can't go wrong with one 
of the
YU7EF designs, and if you have any questions, Pop is always ready to help 
provide
additional information for your particular situation.

And if one of your primary reasons for upgrading your antenna is to build a 
more
rugged antenna, you certainly have that option with the YU7EF designs!  Note 
that
Pop provides options for element diameters, so you can make the thing as 
heavy
duty as is necessary...if you need the thing to be hurricane or ice-proof, 
he
shows the dimensions for 3/4" diameter elements!

I hope to see you on Es with your new antenna in a few months!  GL and VY 
73, Lance

-- 
Lance Collister, W7GJ (ex: WN3GPL, WA3GPL, WA1JXN, WA1JXN/C6A, ZF2OC/ZF8)
P.O. Box 73
Frenchtown, MT  59834  USA
QTH: DN27UB
TEL: (406) 626-5728   URL: http://www.bigskyspaces.com/w7gj
2m DXCC #11, 6m DXCC #815

Moderator: Ray Brown, KB0STN
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