Greetings!

I would like to build a 2 element inverted VEE yagi antenna. I
have seen this type of antenna in a SWL publication.

I would like the Yagi to be used on 7 mhz

I am seeking opinions as to the performance of such an antenna

The driven element will be a 7 Mhz half wave dipole ( 66 feet total)

The reflector element will be about 5 % longer

The spacing of the reflector will be about .20 wave length. about 26
feet from the driven element.

The angle of the vee will be about 55 degrees .

The feed line will be open wire 200 Ohm feed line to a true balanced
tuner.... no baluns truly isolated tuning network just like the
1940's you know, the tank coil type with an adjustable link in the
center of the tank then up to the driven element.

I know that the driven element impeadance will be low so I will use
3/8 inch aluminum power line (ACSR cable) for all of the feed lines
and elements.


The terrain under the antenna system is a 'cow' Pond that has water
in in most of the time, the terrain is low and is alway wet.

Please provide your thoughts on this antenna

Thanks !!!

Dave WA4SZE

wrote in message
oups.com...
Greetings!

I would like to build a 2 element inverted VEE yagi antenna. I
have seen this type of antenna in a SWL publication.

I would like the Yagi to be used on 7 mhz

I am seeking opinions as to the performance of such an antenna

The driven element will be a 7 Mhz half wave dipole ( 66 feet total)

The reflector element will be about 5 % longer

The spacing of the reflector will be about .20 wave length. about 26
feet from the driven element.

The angle of the vee will be about 55 degrees .

The feed line will be open wire 200 Ohm feed line to a true balanced
tuner.... no baluns truly isolated tuning network just like the
1940's you know, the tank coil type with an adjustable link in the
center of the tank then up to the driven element.

I know that the driven element impeadance will be low so I will use
3/8 inch aluminum power line (ACSR cable) for all of the feed lines
and elements.


The terrain under the antenna system is a 'cow' Pond that has water
in in most of the time, the terrain is low and is alway wet.

Please provide your thoughts on this antenna

Thanks !!!

Dave WA4SZE


wow, heavy stuff to build a beam like that with. how high will the apex be?
my first impression is that the angle is a bit small, can't you spread it
out some more to get 90 degrees or better?

An inverted vee with that small an included angle will be narrowband and
have a low feedpoint impedance. Coupling from the other element will
further lower the impedance and narrowband the antenna even more. The
wide spacing (for a Yagi) will mitigate the latter somewhat, but it'll
still occur. The wire size you've chosen might be adequate to keep loss
reasonable, but there's nothing you'll be able to do about the very
narrowband property. Not only will the impedance change rapidly with
frequency, but so will the pattern. Typically, front/back ratio
deteriorates much more rapidly with frequency than gain does, so you
might or might not get a usable bandwidth if gain is your only goal. I
highly recommend modeling it to see what it'll do before you expend the
effort to put it up.

Roy Lewallen, W7EL

wrote:
Greetings!

I would like to build a 2 element inverted VEE yagi antenna. I
have seen this type of antenna in a SWL publication.

I would like the Yagi to be used on 7 mhz

I am seeking opinions as to the performance of such an antenna

The driven element will be a 7 Mhz half wave dipole ( 66 feet total)

The reflector element will be about 5 % longer

The spacing of the reflector will be about .20 wave length. about 26
feet from the driven element.

The angle of the vee will be about 55 degrees .

The feed line will be open wire 200 Ohm feed line to a true balanced
tuner.... no baluns truly isolated tuning network just like the
1940's you know, the tank coil type with an adjustable link in the
center of the tank then up to the driven element.

I know that the driven element impeadance will be low so I will use
3/8 inch aluminum power line (ACSR cable) for all of the feed lines
and elements.


The terrain under the antenna system is a 'cow' Pond that has water
in in most of the time, the terrain is low and is alway wet.

Please provide your thoughts on this antenna

Thanks !!!

Dave WA4SZE

wrote:
Greetings!

I would like to build a 2 element inverted VEE yagi antenna. I
have seen this type of antenna in a SWL publication.

I would like the Yagi to be used on 7 mhz

I am seeking opinions as to the performance of such an antenna

The driven element will be a 7 Mhz half wave dipole ( 66 feet total)

The reflector element will be about 5 % longer

The spacing of the reflector will be about .20 wave length. about 26
feet from the driven element.

The angle of the vee will be about 55 degrees .

The feed line will be open wire 200 Ohm feed line to a true balanced
tuner.... no baluns truly isolated tuning network just like the
1940's you know, the tank coil type with an adjustable link in the
center of the tank then up to the driven element.

I know that the driven element impeadance will be low so I will use
3/8 inch aluminum power line (ACSR cable) for all of the feed lines
and elements.


The terrain under the antenna system is a 'cow' Pond that has water
in in most of the time, the terrain is low and is alway wet.

Please provide your thoughts on this antenna


Dave, You might want to consider an alternative: an inverted vee phased
array with .125 wave spacing, having equal lengths of coaxial cable to
the shack. You can build a small enclosure with a switch and enough
coaxial cable to produce 135 degree phase shift. The switch can be set
up to reverse the array and a center position (maintaining equal lengths
of feedline) will allow both antennas to be fed in phase, resulting in a
nearly omnidirectional pattern. You'll get about 3 db of gain with a
nice null directly off the back.

I used this scheme to advantage when I lived on a city lot in Cincinnati
for a number of years.

Dave K8MN

I am seeking opinions as to the performance of such an antenna

The opinion is it will be a great antenna.

The modeling facts a
It will give you approx. 11 dbi gain, and 13 db f/b. It will have a feedpoint
Z at resonance (7.025 MHz) of 33.3+j0.

The gain will vary from 11.24 dbi at 7 MHz to10.2 at 7.2
The f/b will vary from 12 db at 7 MHz to 9 at 7.2 (peaking at 13.6 db at 7.05
MHz)
The feedpoint Z will vary from 30-j6 at 7 MHz to 50+j33 at 7.2

The parameters of this particular antenna a
ht above ground 23 meters
Length of one side of driven ele = 10.3 meters
Length of reflector = 10.66 m
spacing = 6.7 m
angle between legs=120 degrees

There are of course hundreds (no, thousands) of different combinations of
these parameters that will give different performance characteristics. This
one is not necessarily optimized for any particular objective.but it is close
to what you said you want to build. Naturally I highly recommend that you
model your own antenna and see what changes affect what !! I'd be happy to
give you my 4NEC2 file that I used to determine the above. It and the program
are free. It would be a great starting point for you.

Interesting observation - I have made similar trial runs for others who have
inquired on this newsgrouop, and the tower reflector, and always offer to send
my file and offer to help get them started in modeling (10-20 minutes on the
phone with both of us looking at the same data in the program). To date no
one has either acknowledged my postings or accepted my offer!! Is modeling
that intimidating? I learned what little I know by hacking around for hours.
I could teach someone what I know in 10 minues if they were interested and
computer literate, short circuiting many hours off the learning curve.
Modeling is fascinating. All the tradeoffs that Roy just aluded to can be
studied easily on your own PC without taking the word of others. You can
change the angle, the height, the ground under, the dimensions,the size of
wire, the spacing. You can examine the gain, f/b, pattern, imedances, takeoff
angle, bandwidth.
And I will GIVE you the simple little file that you load into your own free
copy of the modeling program that allows you to do all of this.

Rick K2XT

Rick wrote:
I am seeking opinions as to the performance of such an antenna

The opinion is it will be a great antenna.

The modeling facts a
It will give you approx. 11 dbi gain, and 13 db f/b. It will have a feedpoint
Z at resonance (7.025 MHz) of 33.3+j0.

The gain will vary from 11.24 dbi at 7 MHz to10.2 at 7.2
. . .

Try deleting the parasitic element and see what the gain of just the
driven element is. The difference between this and the Yagi gain is the
gain relative to a single element at the same height. This is a more
meaningful measure of gain than dBi for this application.

Roy Lewallen, W7EL

On Mon, 12 Nov 2007 18:54:14 -0800, Roy Lewallen wrote:


Try deleting the parasitic element and see what the gain of just the
driven element is.

Ok, I did. The gain at 7 MHz went from 11.2 to 7.22 dbi, at 30 degrees
elevation angle.

Rick K2XT

On Nov 13, 8:05 am, (Rick) wrote:
On Mon, 12 Nov 2007 18:54:14 -0800, Roy Lewallen wrote:
Try deleting the parasitic element and see what the gain of just the
driven element is.

Ok, I did. The gain at 7 MHz went from 11.2 to 7.22 dbi, at 30 degrees
elevation angle.

Rick K2XT

That seems more reasonable... Heck, a NBS yagi with 3 elements
only gives about 9.4 dbi plus or minus.
MK

wrote:
Heck, a NBS yagi with 3 elements
only gives about 9.4 dbi plus or minus.

Free space?
--
73, Cecil http://www.w5dxp.com

wrote:
On Nov 13, 8:05 am, (Rick) wrote:
On Mon, 12 Nov 2007 18:54:14 -0800, Roy Lewallen wrote:
Try deleting the parasitic element and see what the gain of just the
driven element is.
Ok, I did. The gain at 7 MHz went from 11.2 to 7.22 dbi, at 30 degrees
elevation angle.

Rick K2XT

That seems more reasonable... Heck, a NBS yagi with 3 elements
only gives about 9.4 dbi plus or minus.
MK

That's the gain of an NBS Yagi in free space. It's more like 13 or so
over ground, depending on height and ground characteristics. Comparing
the gain of one antenna over ground to another (for example a dipole) in
free space is a trick often used by antenna manufacturers to fool naive
people. Both must be in the same environment for a comparison to be
meaningful.

Roy Lewallen, W7EL