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.

On Fri, 10 Apr 2009 07:54:41 +0100, Brian Howie
wrote:

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

Hi Brian,

You have hit the nail on the head. More, you have pushed in the tack
with a 10# sledge. This design we are talking about suffers immensely
from the violation of observing what you comment upon.

It is very much a fault.

73's
Richard Clark, KB7QHC

"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 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, 10:15*am, wrote:
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.

That antenna was when I used an old parabolic satellite dish which was
unsuitable.
Scanning past antenna papers point to the use of a cone shape similar
to a horn of 2 metres diameter
produces better results. The antenna needs a longer mast so at the
moment I can't compare
F/R. Either way, with the radiator within the reflector envelope it is
difficult to understand what creates
a rearward lobe regardles of scale or frequency of use with respect to
receive. At the moment I see nothing that points away from the
Rutherford particle experiments with foil .ie penetration when at
right angles , deflection at other angles.

That antenna was when I used an old parabolic satellite dish which was
unsuitable.
Scanning past antenna papers point to the use of a cone shape similar
to a horn of 2 metres diameter
produces better results. The antenna needs a longer mast so at the
moment I can't compare
F/R. Either way, with the radiator within the reflector envelope it is
difficult to understand what creates
a rearward lobe regardles of scale or frequency of use with respect to
receive. At the moment I see nothing that points away from the
Rutherford particle experiments with foil .ie penetration when at
right angles , deflection at other angles.

As usual Art you are avoiding answering the questions and choose to confuse
the issues
with you own preconceived ideas and terminology. The fact that the feed is
totally within the "reflector envelope" tells you or us nothing about
sidelobes and edge taper.
I really don't think you want answers, but I'll try once mo
1. What frequency
2. What is the dish diameter
3. What is the dish focal length to diameter ratio (F/D)

Dale W4OP

On Apr 10, 6:00*pm, "Dale Parfitt" wrote:
*That antenna was when I used an old parabolic satellite dish which was
unsuitable.
Scanning past antenna papers point to the use of a cone shape similar
to a horn of 2 metres diameter
produces better results. The antenna needs a longer mast so at the
moment I can't compare
F/R. Either way, with the radiator within the reflector envelope it is
difficult to understand what creates
a rearward lobe regardles of scale or frequency of use with respect to
receive. At the moment I see nothing that points away from the
Rutherford particle experiments with foil .ie penetration when at
right angles , deflection at other angles.

As usual Art you are avoiding answering the questions and choose to confuse
the issues
with you own preconceived ideas and terminology. The fact that the feed is
totally within the "reflector envelope" tells you or us nothing about
sidelobes and edge taper.
I really don't think you want answers, but I'll try once mo
1. What frequency
2. What is the dish diameter
3. What is the dish focal length to diameter ratio (F/D)

Dale W4OP

I am not avoiding questions, just those that appear irrelevant, but
here goes Anything to make you happy, this should be interesting how
you use these answers with respect to the posted question

1 160 metres upto 2 metres, tunable

2 2 metres

3 Doesn't have a focal length, it is an end fed ( series connection)
helix antenna.

At least to the best of my knowledge which is why I posed the question
Hopefully we will all stay on subject and not get side tracked. I will
leave it to others to respond to Richard when they determine what he
is talking about.

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

Maybe the coax ground is insufficent and a seperate ground from mother earth
is required.....Maybe


"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