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

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.

Ignoring the obvious, the design suffers from the basic disregard for
scale and wavelength.

There are probably other issues beyond these violations of first
principles.

73's
Richard Clark, KB7QHC

In message
, Art
Unwin writes
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?

Diffraction off the edge of the reflector. It causes backlobes. It's
not a fault.

Brian GM4DIJ
--
Brian Howie

On Apr 9, 11:59*pm, Richard Clark wrote:
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.

Ignoring the obvious, the design suffers from the basic disregard for
scale and wavelength.

There are probably other issues beyond these violations of first
principles.

73's
Richard Clark, KB7QHC

The radiator is totally within the reflector envelope !
It is possible that the transmission line is picking up
some signal but a brief scan of the books show that
dishes do some how obtain some signals from the rear..
"Ignoring the obvious" is a nonsense aproach,
as is scale and wavelength.
I was hoping for somebody who is familiar with dish design
and not from one who is a talking head bent on agitation
and slander

In message , Richard Clark
writes
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.

Do you use a balun with a helix and a dish reflector? Surely that bit at
least is right!





--
Ian

"Art Unwin" wrote in message
...
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

There is a lot of very important information missing here.
What frequency are we talking about and what is the dish diameter?
Do you have any idea as to what your edge taper is or sidelobes?


Dale W4OP

Brian Howie wrote:
In message
, Art
Unwin writes
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?

Diffraction off the edge of the reflector. It causes backlobes. It's
not a fault.

Brian GM4DIJ

Ask him the working frequency and dimensions of his "dish reflector".

Don't be drinking anything when you read his answer.


--
Jim Pennino

Remove .spam.sux to reply.

Dale Parfitt wrote:

"Art Unwin" wrote in message
...
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

There is a lot of very important information missing here.
What frequency are we talking about and what is the dish diameter?
Do you have any idea as to what your edge taper is or sidelobes?


Dale W4OP


The last time he talked about it, it was "designed" to operate on the
160 meter band and the "reflector" was 3 meters in diameter.

No, those numbers are not typos.


--
Jim Pennino

Remove .spam.sux to reply.

On Apr 10, 9:50*am, "Dale Parfitt" wrote:
"Art Unwin" wrote in message

...

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

There is a lot of very important information missing here.
What frequency are we talking about and what is the dish diameter?
Do you have any idea as to what your edge taper is or sidelobes?

Dale W4OP

Dale
I thought that if the radiator was in the reflector envelope, that is
the radiator is below the top of the cone then there should be no
radiation from the rear though possibly a little edge refraction. I
know little regarding dish reflectors thus the question. I am of the
opinion that radio is a matter of particles and not waves so I can
easily visualize impregnation of the shield at the center as per
Rutherford foil and particle experiments, but I am not ready to jump
because of edge taper and other things that I am not aware of
What is very clear from dish radiation patterns in the books that
there is a localised radiation congregation at the dish axis rear
which appears unexplainable.
at the rear at the dishes axis tho it is in the area of direct impact
I appreciate the comments and thoughts applied but not the nonsensicle
writings of Richard who is wired so differently from the rest of us.
These signals appear at all frequencies though I fail to see what the
impact of frequency is because of the reflector envelope or umbrella.

Art Unwin wrote:
On Apr 10, 9:50 am, "Dale Parfitt" wrote:
"Art Unwin" wrote in message

...

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
There is a lot of very important information missing here.
What frequency are we talking about and what is the dish diameter?
Do you have any idea as to what your edge taper is or sidelobes?

Dale W4OP

Dale
I thought that if the radiator was in the reflector envelope, that is
snip
These signals appear at all frequencies though I fail to see what the
impact of frequency is because of the reflector envelope or umbrella.

Dale

You will, of course, have noted that he hasn't given a couple of the
important items that you requested. Based upon some of his earlier
babblings, I suspect that this is a helical antenna of perhaps UHF
dimensions that he is attempting to use on 160 or 80.

tom
K0TAR