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

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 -

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

dgleeson422111 wrote:

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

If I remember my antenna/propagation theory correctly, such a change
should affect both the transmit and receive gains equally. That is to
say, if moving the office antenna lower will reduce its transmit range,
it will also reduce its receive range.

What you are looking for is something that is reducing the office end
transmit power while leaving its receive sensitivity intact. Someone
else suggested an SWR problem due to near field interference with the
antenna.


--
Paul Hovnanian
------------------------------------------------------------------
Don't anthropomorphize computers. They hate that.

"oopere" wrote in message
...


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


Such as traffic light electronics.

Without error correction protocols being employed, you are also at the mercy
of multipath interference. You're QRMing your own signal. 8)

Ed, NM2K