868MHz Propagation problem
 

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

868MHz Propagation problem
 

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

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

Nope a question of height

868MHz Propagation problem
 

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

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

Nope a question of height

Shouldn't the path be reciprical?

868MHz Propagation problem
 

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

You may experience receiver desensitization from a strong out-of-band
interferer which is not penetrating well into your office and hence not
interferring there.

Pere

868MHz Propagation problem
 

Hi Guys

Thanks for your input on this.

The idea of height being a problem is interesting. The radio in the
office is on the 1st floor (i.e above the ground by one floor).

If the antenna were at the same height would the problem go away?

We will test and see


On Oct 24, 11:57*am, oopere 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.

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

You may experience receiver desensitization from a strong out-of-band
interferer which is not penetrating well into your office and hence not
interferring there.

Pere- Hide quoted text -

- Show quoted text -

868MHz Propagation problem
 

higher antennas = longer range. Thats your issue.
Also lack of error correction, poor antenna pattern to meet the low
power regulations, and a less then robust protocol, ie your probably
using some form of on/off modulation where the receiver does not have
a continious wave signal to locl on and track. Try sending a preamble
character that is 10101010 a few times, assuming your receiver is
sophisticated enough to use AGC. This sets the DC level in the
discriminator more accurately and reduces errors.

your using a radio with intentionally designed in limited range to
allow reuse of the frquency.

Steve

868MHz Propagation problem
 

"dgleeson422111" wrote in message
...

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.

Is your office in a concrete building? Or one with any steel reinforcement
or steel or aluminum studs? If so, it could well be that there is a
standing wave issue, so that a portion of your transmitted signal is being
reflected back, and so not making it to the receiver. This would not
necessarily affect the reception on the radio in the office from the outside
radio.

868MHz Propagation problem
 

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.)

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

The radio outside is likely being desensitized by some other signal.

868MHz Propagation problem
 

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.)


I see you have other responses. One test that would establish that is
environmental (adjacent signal, receiver desense, etc), if BOTH units
could be moved to a relative RF free environment such as a rural setting
and then test the range.

If this eliminates the problem, then its probably time to break out a
spectrum analyzer and take a look at what is around your operating
frequency.

Andy

868MHz Propagation problem
 

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)