868MHz Propagation problem
 

"dgleeson422111" wrote in message
...
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

its interesting that a commercial company would bring a problem such as this
to a bunch of amateur radio operators... true some of the amateurs may be
professional engineers, but the remainder are not! I guess that in today's
market place we try to gain information on the dirt and cheap way.

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

What is the modulation type and data rate? Could be a delay spread
issue. Maybe the outside unit is receiving a reflected signal from the
surface of a nearby structure and is experiencing inter-symbol
interference that by chance the base unit is shielded from. This would
occur only if a high symbol rate was being used.

--
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

868MHz Propagation problem
 

W3CQH wrote:

[...]

its interesting that a commercial company would bring a problem such as this
to a bunch of amateur radio operators... true some of the amateurs may be
professional engineers, but the remainder are not! I guess that in today's
market place we try to gain information on the dirt and cheap way.


Nah, that's ok. Every one of us occasionally runs into an unusual
situation. Then one can either stew on it for days without getting to
the ground of it, or ask. IMHO it is a sign of maturity if somebody has
the guts to say "Hey, guys, this problem here really has us puzzled".

That is especially true for EMI cases and this sure looks like one.
Sometimes a brief hint by someone who has been in the trenches for
decades can get things going again. And most older ham radio operators
had that exposure, fixing the neighbor's electronics because their
manufacturers messed up.

--
Regards, Joerg

http://www.analogconsultants.com/

"gmail" domain blocked because of excessive spam.
Use another domain or send PM.

868MHz Propagation problem
 

Tio Pedro wrote:

I agree. But, one thing that should be proven is that both modules
are working as intended. The one being used for the remote
application *could* be defective. Swap modules and see if the
receiving problem also switches locations, or remains the
same.

The OP said that he did that, and the problem remained. It's certainly a
desensing problem due to local interference at one end. That's the only
possible cause.

868MHz Propagation problem
 

In article m,
RFI-EMI-GUY 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

What is the modulation type and data rate? Could be a delay spread
issue. Maybe the outside unit is receiving a reflected signal from the
surface of a nearby structure and is experiencing inter-symbol
interference that by chance the base unit is shielded from. This would
occur only if a high symbol rate was being used.

what type of amateur radio application is this for? Or is it a
commercial application posted in this amateur radio group? just
wondering

868MHz Propagation problem
 

what type of amateur radio application is this for? Or is it a
commercial application posted in this amateur radio group? just
wondering

What amateur band covers 868 MHz? Did we get a new one? I'll have to
order another transverter, I guess ;)

Well, to get this post be on topic, does anyone know of a good source
for some SPDT coaxial relays good at 902 MHz and good for 350 Watts at
902?

Scott
N0EDV

868MHz Propagation problem
 

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

868MHz Propagation problem
 

What is the modulation type and data rate? Could be a delay spread
issue. Maybe the outside unit is receiving a reflected signal from the
surface of a nearby structure and is experiencing inter-symbol
interference that by chance the base unit is shielded from. This would
occur only if a high symbol rate was being used.



i was thinking about that...but no....

all the multi-path paths are reciprocal as well,,, so whatever the
delay spread is one way should be the same the other way.

Mark

868MHz Propagation problem
 

"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

868MHz Propagation problem
 

dgleeson422111 wrote:

...
Best regards, and thanks for any input.

Denis
_____________________
http://www.CentronSolutions.com

Since most of the posts, in their "EXPERT OPINIONS", relate to your
receiver being "de-sensed", do you have a way of negating/affirming this?

Begin there, and we can get down to "real problems!" :-) i.e., a
wide-band field strength meter, freq counter, etc. will either make all
this "right" or "wrong."

Regards,
JS