On Apr 26, 5:10*pm, Art Unwin wrote:
On Apr 11, 3:58*am, Helmut Wabnig hwabnig@ .- --- -. dotat wrote:



On Thu, 9 Apr 2009 20:05:20 -0700 (PDT), Art Unwin

wrote:
I made a helical end fed antenna that is inside a cone shaped
reflector
The reflector is made from 1/2" mesh steel with an aluminum foil liner
and connected to the braid of the feed coax. No baluns are used, just
direct connections.
I was surprised to hear signals from the rear!
I thought that a dish reflector prevented such signals getting to the
receiver. So what can be wrong with the reflector or can signals get
reflected back from the frontal area? Antenna is at a 40 foot height
Any ideas as to what the fault could be?
Regards
Art
I have no experience with dishes thus the question Note, the helical
antenna does not protrude beyond the dish envelope.
Art

How do you know?
The "rear" signals may come from the front side actually, having
been reflected by your neighbours house, or distant mountains,
or anything in between.

w.

Helmut
I do not know if the rear signals were as you suspected.,
It is extremely windy here in the midwest for the last few days
so I took off the new dish of it's ground stand and placed the dish in
a corner outside the house with a TOA that I assume is about 10-15
degrees. Again I got rear signals
but I noticed the coverage was very narrow and maybe more than one.
So next two *weeks or so I will repeat the test but also play around
with the elevation
to see if there are other observables to determine if you are correct.
I am playing with circular polarisation which is a new experience for
me and I believe that is capable of picking up reflections that one
does not normally see with planar designs
Best regards
Art

Helmut. Re original thread on dish

I found out what the problem was! The dish itself was in the antenna
circuit thus
the dish was part of the antenna and receiving omni.ie chassis and
ground was the same connection I have discarded the dish experiment
and have gone back to the original design roots.
I can hold it up on one hand stretched out without problems and not
only is it light but also small. Have placed a small cctv rotator and
tipper on a table outside and am now setting up the controls. I
suppose I will have to add a decoder to the motors at a later date so
I can determine positions to follow the band conditions as they
change I do not have a direction indicator so I will wait for a warm
day where I can operate it and seethe position at the same time. The
tipping action will give me control of the skip distance so that
should prove to be very interesting. Anyway, glad that I now have
direction ability back. Tks for your interest.
Regards
Art

"Art Unwin" wrote in message
...
I found out what the problem was! The dish itself was in the antenna
circuit thus the dish was part of the antenna and receiving omni.

DOH!

I have discarded the dish experiment

AWWW, i would have loved to have a rotatable dish for 160m!

On Apr 29, 6:10*pm, "Dave" wrote:
"Art Unwin" wrote in message

...

I found out what the problem was! The dish itself was in the antenna
circuit thus the dish was part of the antenna and receiving omni.

DOH!

I have discarded the dish experiment

AWWW, i would have loved to have a rotatable dish for 160m!

David I still have that rotatable form for top band! I just gave up on
large dish experiments! As I stated I like the idea of small and light
antennas so I am keeping to those root desires. I am getting older so
the idea of climbing towers has to be adressed. Thus as an engineer I
solved that problem, now antennas where the height is not a necessity
for low take off angles! I now have to find out what the greatest
distance can be by substituting one skip for the presently used two
skips ie min TOA.
Since there are not the usual sun spots one has to be inovative and
devise means around it. I can still add a dish ofcourse but I like the
idea of a pencil beam as it will add more gain to that single skip
action. You really should get off that couch and figure out how you
are going to handle a poor sun spot cycle. My cctv rotator will never
be able to handle such a design when tipping is required as the weight
would overcome the motor and it would point into the ground, they are
built for just a small camera not a tank. By the way the antenna is
good for 2 meg upto 170 meg which are the range limits of my MFJ 259
meter. My guess is that it is good for broadcast band upto a giga or
more. Did you fall down?
Best regards
Art
Regards
Art

On Wed, 29 Apr 2009 23:10:03 GMT, "Dave" wrote:

"Art Unwin" wrote in message
...
I found out what the problem was! The dish itself was in the antenna
circuit thus the dish was part of the antenna and receiving omni.

On Thu, 9 Apr 2009 20:05:20 -0700 (PDT), Art Unwin
wrote:
No baluns are used

That alone is at least one thing wrong with the design.

Three weeks and 300 messages ignored to discover first principles were
violated.

Is this discovery in time for this year's NoBell prize?

73's
Richard Clark, KB7QHC

Roy Lewallen wrote:
There's no such thing as "standing wave current". You'll find no
references to this fictitious entity in any electromagnetics text.

On the contrary,

"Traveling Wave Engineering", R.K.Moore, page 134:

Fig. 5-12. Voltage and Current Standing Waves on
open-circuited line.

i = Re(V+/Z0)[e^j(wt+bd)+e^j(wt-bd)

This is the same equation for standing wave current
that appears in "Fields and Waves ...", Ramo and
Whinnery.
--
73, Cecil, IEEE, OOTC, http://www.w5dxp.com

Cecil Moore wrote:
Roy Lewallen wrote:
There's no such thing as "standing wave current". You'll find no
references to this fictitious entity in any electromagnetics text.

On the contrary,

"Traveling Wave Engineering", R.K.Moore, page 134:

Fig. 5-12. Voltage and Current Standing Waves on
open-circuited line.

i = Re(V+/Z0)[e^j(wt+bd)+e^j(wt-bd)

This is the same equation for standing wave current
that appears in "Fields and Waves ...", Ramo and
Whinnery.

So I guess that ups the total now to at least two that we know of. Just
exactly how many different kinds of alternating current do you reckon
there are, Cecil? :-)

ac6xg

Jim Kelley wrote:
So I guess that ups the total now to at least two that we know of.
Just exactly how many different kinds of alternating current do you
reckon there are, Cecil? :-)

The point is that the current in a pure standing wave has
a different equation from the current in a pure traveling
wave. Any fields and waves reference book will have those
equations. The current in a pure standing wave cannot be
used to measure any kind of phase shift between points
because the phase doesn't shift between points on a wire
or on a coil. The current in a standing-wave antenna, like
a loaded mobile antenna, is primarily standing wave current.
Why do you think they are called standing wave antennas?
--
73, Cecil, IEEE, OOTC, http://www.w5dxp.com

Cecil Moore wrote:
Jim Kelley wrote:
So I guess that ups the total now to at least two that we know of.
Just exactly how many different kinds of alternating current do you
reckon there are, Cecil? :-)

The point is that the current in a pure standing wave has
a different equation from the current in a pure traveling
wave.

No, actually the point was the name.

Any fields and waves reference book will have those
equations.

And what they don't have is different and assorted pet names for current.

The current in a pure standing wave cannot be
used to measure any kind of phase shift between points
because the phase doesn't shift between points on a wire
or on a coil.

If there is no difference in the relative phase of the forward and
reflected waves, then there is no change in the amplitude of the
standing wave in x. But when there is a change in the amplitude of the
standing wave in x, and I max is known, then determining the shift in
phase from the equation is a no brainer, Cecil. Other than Imax (and
you claim that assuming it's unity is good enough), there's virtually
nothing else that determines the amplitude of the standing wave envelope
along x. Helloooo.

The current in a standing-wave antenna, like
a loaded mobile antenna, is primarily standing wave current.

And you keep saying that as if it had some special significance.

ac6xg

"Art Unwin" wrote in message
...
On Apr 29, 6:10 pm, "Dave" wrote:
David I still have that rotatable form for top band! I just gave up on
large dish experiments! As I stated I like the idea of small and light
antennas so I am keeping to those root desires.
I can still add a dish ofcourse but I like the
idea of a pencil beam as it will add more gain to that single skip
action.

good, when you get that rotatable pencil beam antenna for 160m let me know.

On Apr 30, 6:09*pm, "Dave" wrote:
"Art Unwin" wrote in message

...
On Apr 29, 6:10 pm, "Dave" wrote:

David I still have that rotatable form for top band! I just gave up on
large dish experiments! As I stated I like the idea of small and light
antennas so I am keeping to those root desires.
I can still add a dish ofcourse but I like the
idea of a pencil beam as it will add more gain to that single skip
action.

good, when you get that rotatable pencil beam antenna for 160m let me know.

I believe I have it now but I have yet to demonstrate and thus
prove. But for you tomorrow is another day and tomorrow never comes.
Regards
Art