Hi,
I'm playing around with some 433MHz transmitter and receiver pairs.
Ideally I would like the transmitter to transmit in a narrow
directional beam, but I'm new to the art of radio waves and antenna
design, so I was wondering if you guys would be able to help me with
my project. I've read about a Yagi design for the antenna, I know it
receives from one direction only, but does it transmit in just one
direction too?

I thought I'd be able to basically stick the transmitter antenna in a
tube, sealed at one end, line either the inside or outside of the tube
with tin foil (or both) and it would transmit in whatever direction
the open end was facing. So far my tests haven't been too conclusive
but could that be poor setup on my part or is the idea fundamentally
flawed?

Many thanks for your time,

Simon.

Hope you have a Licence for this kind of thing



"Simon" wrote in message
om...
Hi,
I'm playing around with some 433MHz transmitter and receiver pairs.
Ideally I would like the transmitter to transmit in a narrow
directional beam, but I'm new to the art of radio waves and antenna
design, so I was wondering if you guys would be able to help me with
my project. I've read about a Yagi design for the antenna, I know it
receives from one direction only, but does it transmit in just one
direction too?

I thought I'd be able to basically stick the transmitter antenna in a
tube, sealed at one end, line either the inside or outside of the tube
with tin foil (or both) and it would transmit in whatever direction
the open end was facing. So far my tests haven't been too conclusive
but could that be poor setup on my part or is the idea fundamentally
flawed?

Many thanks for your time,

Simon.

Simon wrote:

Hi,
I'm playing around with some 433MHz transmitter and receiver pairs.
Ideally I would like the transmitter to transmit in a narrow
directional beam, but I'm new to the art of radio waves and antenna
design, so I was wondering if you guys would be able to help me with
my project. I've read about a Yagi design for the antenna, I know it
receives from one direction only, but does it transmit in just one
direction too?

As a general rule, the recieve and transmit patters of an antenna will be
the same. You may see some difference in propagation patterns due to
frequency differences between TX and RX pairs, but those should be very
minimal. The amount of difference will depend on the selectivity of the
antenna.

Simon.

--
Donovan Hill
VA7LNX

Question[s]: In the UK, is 433 MHz allocated to Amateur Radio? Simon, in
other words, is a license required for operation on 433 MHz in the UK?

Observation[s]: A yagi receives from ALL directions but has a preferred
direction where it has gain.

Yagis may not meet your requirements for narrow beam. A high gain Yagi
may have a beamwidth of +/-10 degrees or more. A moderate gain Yagi will
have a beamwidth of 30-40 degrees.

DD, W1MCE

Simon wrote:

Hi,
I'm playing around with some 433MHz transmitter and receiver pairs.
Ideally I would like the transmitter to transmit in a narrow
directional beam, but I'm new to the art of radio waves and antenna
design, so I was wondering if you guys would be able to help me with
my project. I've read about a Yagi design for the antenna, I know it
receives from one direction only, but does it transmit in just one
direction too?

I thought I'd be able to basically stick the transmitter antenna in a
tube, sealed at one end, line either the inside or outside of the tube
with tin foil (or both) and it would transmit in whatever direction
the open end was facing. So far my tests haven't been too conclusive
but could that be poor setup on my part or is the idea fundamentally
flawed?

Many thanks for your time,

Simon.

(Simon) wrote in message . com...
Hi,
I'm playing around with some 433MHz transmitter and receiver pairs.
Ideally I would like the transmitter to transmit in a narrow
directional beam, but I'm new to the art of radio waves and antenna
design, so I was wondering if you guys would be able to help me with
my project. I've read about a Yagi design for the antenna, I know it
receives from one direction only, but does it transmit in just one
direction too?

Yes, antennas have the same directionality transmitting and receiving.

I thought I'd be able to basically stick the transmitter antenna in a
tube, sealed at one end, line either the inside or outside of the tube
with tin foil (or both) and it would transmit in whatever direction
the open end was facing. So far my tests haven't been too conclusive
but could that be poor setup on my part or

----is the idea fundamentally flawed?----

Yes. You could do it, but you'd probably want a horn-shaped tube, and
the diameter at the outer end would have to be large compared with the
wavelength to do much good. You'll probably find the Yagi a lot
easier to do, using common materials like some 3/4" PVC pipe with
holes drilled through it, and ordinary 12-gauge or 10-gauge solid
copper wire put through the holes. You can use bare wire or wire with
insulation. The elements (wires) are only about 13-14 inches long, so
wire like that will be stiff enough to hold its shape well when
supported in the middle by the PVC (or a wood dowel, or...use your
imagination for other ideas). You should be able to find construction
ideas for Yagis on the web. You can scale the size with frequency
(size1*freq1=size2*freq2), but be sure to scale the element diameters
at least approximately, and not just the lengths and spacings. (Don't
use an 0.1" diameter wire if the plans call for 0.5" at that
frequency.)

Cheers,
Tom

Thanks alot for your quick replies guys,

As far as I know 433.92MHz is license exempt throughout Europe, if you
know otherwise let me know, but I've seen it written on the suppliers
website, so I'm inclined to believe them, plus I'm sure I used
transmitters at that frequency for a university project, but that was
a few years back, so I could be mistaken.

I'll look up the Yagi design, and see what I can build, would placing
a yagi inside a horn shaped tube be worthwhile, to get the best of
both worlds? or would a setup like that not benefit directional
transmission, my thoughts here are if a horn shaped tube almost works
and a Yagi antenna almost work, then together, they might give the
results I'm looking for. In an ideal situation I'd like to get the
transmission beam down to 1 degree, 10 degrees might be acceptable I'm
not sure.

My final point is that I've also seen 868Mhz transmitters, assuming no
license is required for these, could this frequency be used to create
a directional transmission more easily than the 433MHz?

Thanks again and sorry for my ignorance,

Simon.

(Tom Bruhns) wrote in message om...
(Simon) wrote in message . com...
Hi,
I'm playing around with some 433MHz transmitter and receiver pairs.
Ideally I would like the transmitter to transmit in a narrow
directional beam, but I'm new to the art of radio waves and antenna
design, so I was wondering if you guys would be able to help me with
my project. I've read about a Yagi design for the antenna, I know it
receives from one direction only, but does it transmit in just one
direction too?

Yes, antennas have the same directionality transmitting and receiving.

I thought I'd be able to basically stick the transmitter antenna in a
tube, sealed at one end, line either the inside or outside of the tube
with tin foil (or both) and it would transmit in whatever direction
the open end was facing. So far my tests haven't been too conclusive
but could that be poor setup on my part or

----is the idea fundamentally flawed?----

Yes. You could do it, but you'd probably want a horn-shaped tube, and
the diameter at the outer end would have to be large compared with the
wavelength to do much good. You'll probably find the Yagi a lot
easier to do, using common materials like some 3/4" PVC pipe with
holes drilled through it, and ordinary 12-gauge or 10-gauge solid
copper wire put through the holes. You can use bare wire or wire with
insulation. The elements (wires) are only about 13-14 inches long, so
wire like that will be stiff enough to hold its shape well when
supported in the middle by the PVC (or a wood dowel, or...use your
imagination for other ideas). You should be able to find construction
ideas for Yagis on the web. You can scale the size with frequency
(size1*freq1=size2*freq2), but be sure to scale the element diameters
at least approximately, and not just the lengths and spacings. (Don't
use an 0.1" diameter wire if the plans call for 0.5" at that
frequency.)

Cheers,
Tom

"Simon" wrote in message
om...
Thanks alot for your quick replies guys,

As far as I know 433.92MHz is license exempt throughout Europe, if you
know otherwise let me know, but I've seen it written on the suppliers
website, so I'm inclined to believe them, plus I'm sure I used
transmitters at that frequency for a university project, but that was
a few years back, so I could be mistaken.

I'll look up the Yagi design, and see what I can build, would placing
a yagi inside a horn shaped tube be worthwhile, to get the best of
both worlds? or would a setup like that not benefit directional
transmission, my thoughts here are if a horn shaped tube almost works
and a Yagi antenna almost work, then together, they might give the
results I'm looking for. In an ideal situation I'd like to get the
transmission beam down to 1 degree, 10 degrees might be acceptable I'm
not sure.

My final point is that I've also seen 868Mhz transmitters, assuming no
license is required for these, could this frequency be used to create
a directional transmission more easily than the 433MHz?


the higher the frequency the smaller the antenna is for the same effect.
yagi designs are nice but can be complex and interact with their
surroundings, so putting a yagi in a can is not a good idea without some
very careful and complex modelling. the simplest way to get a reasonable
beam pattern at uhf and above is probably a horn, though they must be built
reasonably well and fed with a proper feed system. if fed at the wrong
location or with the wrong type of element they can be as bad as just using
a random hunk of wire. another simple one is a corner reflector. the exact
design you need will depend on many factors including:
1. path length, obstructions, frequency(determine losses between tx and rx)
2. transmitter power and receiver sensitivity(how much signal can you get to
rx)
3. required s/n ratio(how much signal do you need to detect the data you
want to get)
4. rejecting interference sources(preventing received interference)
5. allowable sidelobes on transmit (preventing interference to others when
you transmit)

all these factor interact and can offset each other. i.e. if you can double
your transmitter power you can probably go with 3db lower gain in the tx
antenna, but not always, one tree in your path can almost totally block
signals at certain frequencies and be negligable on others, ect... go
through your college library for books on rf communications system design,
but don't expect it to be a simple formula to plug in, there are lots of
variables and choices to make. it may also be that you are overdesigning,
if the path is short with no obstructions and you have reasonable tx power
many of the other factors can be ignored... but if you are pushing for
distance or have a tough path then you may have to include more.

I'll look up the Yagi design, and see what I can build, would placing
a yagi inside a horn shaped tube be worthwhile, to get the best of
both worlds? or would a setup like that not benefit directional
transmission, my thoughts here are if a horn shaped tube almost works
and a Yagi antenna almost work, then together, they might give the
results I'm looking for. In an ideal situation I'd like to get the
transmission beam down to 1 degree, 10 degrees might be acceptable I'm
not sure.
-----------------------------------------------------------------------
1 deg? That will be one long antenna!
Greg Z
to thine own sound be true

"Simon" wrote in message
om...
In an ideal situation I'd like to get the
transmission beam down to 1 degree, 10 degrees might be acceptable

Simon,

I suspect you are at least an order of magnitude too low in frequency to do
this, and have an antenna that you can easily handle. I have a 430 MHz
antenna with a 27 degree beam width, and it is 12 feet long. If this is line
of sight, use infrared.

Tam/WB2TT

Simon wrote:
Thanks alot for your quick replies guys,

SNIP

In an ideal situation I'd like to get the
transmission beam down to 1 degree, 10 degrees might be acceptable I'm
not sure.


Simon, About 10 years ago I worked on a 1 degree beamwidth antenna [gain
equals something around 45 dB] for a satellite ground station. It was 12
feet in diameter and the frequency range was 24 GHz!!

A simple scaling of that dimension yields 12*(24,000/433)= 665 feet
diameter!!

Are you sure you really want/need that narrow a beamwidth or an antenna
with more than 40 dB gain?

DD, W1MCE