"Radio_Dick" wrote in message
...
On Oct 24, 5:14 am, 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

Denis,

I agree with some of your previous posts - the outside receiver is
likely being desensed by a strong signal, perhaps away from or a
harmonic of the frequency you're using. I suggest trying the test away
from town and at least 10km from strong transmitting towers. Let us
know what you find out - may help those of us who do UHF/VHF mobile/
portable hamming.

As a ham I have NOT PROBLEM with the commercial community asking
questions on a ham radio group - we can ALL learn from this.

Cheers,

Dick Post, N7EMW
www.repdesign.us

************************************************** *
I don't know why I don't get the on your response, but whatever.
He can get some feel for what is going on by taking *both* radios outside
near his office, and walking around. He should be able to find a particular
area that has poor reception. I don't buy the explanations for antenna gain
and multipath, they should affect both directions of transmission equally.

Tam