It's because the paths are not the same. Think of a silvered mirror. It can
transmit light much easier in one direction than the other. Take both
outside and see if it has the same problem. (extremely doubtful because the
path's is virtually identical)

On Oct 24, 8:14*am, "Jon Slaughter" wrote:
It's because the paths are not the same. Think of a silvered mirror. It can
transmit light much easier in one direction than the other. Take both
outside and see if it has the same problem. (extremely doubtful because the
path's is virtually identical)

Did you design the receive software?
Or did buy the receiver "off the shelve"?

Perhaps there is a problem
with the receivers and how they are
receiving the data.

"EE123" wrote in message
...
On Oct 24, 8:14 am, "Jon Slaughter" wrote:
It's because the paths are not the same. Think of a silvered mirror. It
can
transmit light much easier in one direction than the other. Take both
outside and see if it has the same problem. (extremely doubtful because
the
path's is virtually identical)

Did you design the receive software?
Or did buy the receiver "off the shelve"?

Perhaps there is a problem
with the receivers and how they are
receiving the data.

um, did you read his message? He said that it was independent of the
receiver because they exchanged them and the same problem. i.e., it helps to
read the original post.

dgleeson422111 wrote:
Hello All

We have a propagation issue that is confusing us. We have two 868MHz
modules on test, each capable of 500mW transmission.

We are testing to find the range of communication. We are testing them
as follows. One remains in our office while the other is taken to the
street outside. we are communicating charecter strings such as "Im at
the lamp post number 1" etc. There is somebody at each end sending
text strings in a continuous conversation. There is no protocol, error
checking or error recovery.

Do you have a license?

Dave wrote:
dgleeson422111 wrote:
Hello All

We have a propagation issue that is confusing us. We have two 868MHz
modules on test, each capable of 500mW transmission.

We are testing to find the range of communication. We are testing them
as follows. One remains in our office while the other is taken to the
street outside. we are communicating charecter strings such as "Im at
the lamp post number 1" etc. There is somebody at each end sending
text strings in a continuous conversation. There is no protocol, error
checking or error recovery.

Do you have a license?

Not required in EU for 868 MHz

--
Joe Leikhim K4SAT
"The RFI-EMI-GUY"©

"Treason doth never prosper: what's the reason?
For if it prosper, none dare call it treason."

"Follow The Money" ;-P

What we have repetadly found is that the radio in the office can
receive long after the radio in the street has stopped receiving. (The
person with the radio in the street is moving away from the office.)

You don't say if you are using the same antenna on both ends, but the
environment is very different at each end. Consider that Transmitting is
about putting signal into an area, while receiving is about capturing the
signals in near field of the antenna, then discerning the intellegence. You
would have to analyze the output to be sure, but it may be localized
reflections, shading or noise at the street level. Because of this it is so
difficult to quantify range. There is equipment and software specifically
designed to do what you are trying to do but it is expensive. The result is
highly detailed signal strength graphic output overlaid on 3d mapping for
each fixed site at various frequencies. Most commercial antenna sites have
gone to great expense to generate those maps in order to show what their
tower does because it is very different for each location.

On Fri, 24 Oct 2008 02:14:24 -0700 (PDT), dgleeson422111
wrote:

What we have repetadly found is that the radio in the office can
receive long after the radio in the street has stopped receiving. (The
person with the radio in the street is moving away from the office.)

Is the moving station manually portable or is it mounted on a vehicle?

If the moving operator is bored and continuously talks on a GSM phone
or if the (vehicle) generates some other kind of interference, this
would reduce the SNR at the moving station.

The radios are the same and the power supplies to the radios are the
same. Indeed switching the radios gives the same effect.

The propagation paths between the two radios are the same in terms of
distance. However the radio signal transmitted from the office travels
through walls first before then traveling through open space. Its the
opposite for the radio in the street, firstly traveling through space
and then through the walls in the office.

Does the transmitter have some kind of SWR protection ?

If the Tx antenna is close to the wall, it might detune the antenna,
increasing the SWR and the SWR protection drops the transmitter power.

Paul OH3LWR

On Fri, 24 Oct 2008 02:14:24 -0700 (PDT), dgleeson422111
wrote:



What we have repetadly found is that the radio in the office can
receive long after the radio in the street has stopped receiving. (The
person with the radio in the street is moving away from the office.)


Polarization could be a factor.
Reflections change the polarization appr. 90 degrees.

Rotate the antennas left & right to find out.

(you did not mention your type of antennas)

w.

On Fri, 24 Oct 2008 02:14:24 -0700 (PDT), dgleeson422111
wrote:



What we have repetadly found is that the radio in the office can
receive long after the radio in the street has stopped receiving. (The
person with the radio in the street is moving away from the office.)



This is typical for groundplane antennas.
They radiate upwards.


Polarization could be a factor.
Reflections change the polarization appr. 90 degrees.

Rotate the antennas left & right to find out.

(you did not mention your type of antennas)

w.

dgleeson422111 wrote:

Hello All

We have a propagation issue that is confusing us. We have two 868MHz
modules on test, each capable of 500mW transmission.

We are testing to find the range of communication. We are testing them
as follows. One remains in our office while the other is taken to the
street outside. we are communicating charecter strings such as "Im at
the lamp post number 1" etc. There is somebody at each end sending
text strings in a continuous conversation. There is no protocol, error
checking or error recovery.

What we have repetadly found is that the radio in the office can
receive long after the radio in the street has stopped receiving. (The
person with the radio in the street is moving away from the office.)

The radios are the same and the power supplies to the radios are the
same. Indeed switching the radios gives the same effect.

The propagation paths between the two radios are the same in terms of
distance. However the radio signal transmitted from the office travels
through walls first before then traveling through open space. Its the
opposite for the radio in the street, firstly traveling through space
and then through the walls in the office.

We did think we had identified an interfeering source in one direction
(when moving away from the office) so we started moving in the
opposite direction. We found exactly the same effect.

Are we getting interfeerance from GSM, ISM or Paging?

As far as GSM bands go in Europe 890-915 MHz OR 1710-1785 MHz So these
shouldnt be our problem.

ISM is where we intend to operate and the greatest band occupancy
should be 10%. So we should get communication even though we would get
some interfeerance.

Paging - well this has very much gone out of fashion in Europe. But
even if it was the cause then wouldnt it be intermittant
communication. We have a constant problem.

Can anyone shed light on this phenomonon? Is it an issue of wireless
propagation that Im not familiar with or is it Interfeerance?

Best regards, and thanks for any input.

Denis
_____________________
http://www.CentronSolutions.com

Have you tried relocating the office transceiver? There might be
something about the office environment that is interfering with its
transmission.

--
Paul Hovnanian
------------------------------------------------------------------
A mathematician is a machine for converting coffee into theorems.