RadioBanter - 868MHz Propagation problem

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868MHz Propagation problem

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.

868MHz Propagation problem

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

868MHz Propagation problem

"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

868MHz Propagation problem

On Oct 24, 2:00*pm, "Paul Hovnanian P.E." 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

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.- Hide quoted text -

- Show quoted text -

wow so many of these replies are wrong..

in almost all cases, RF path losses are RECIPROCAL.

(even a 1/2 silvered mirror is reciprocal to light)

As some have said, the cause of your issue is probably interference to
the outside receiver.

Or maybe something about the indoor setup is causing the indoor Tx to
operate at lower power.

It is very unusual for RF path loss to be non-reciprocal.

Mark

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

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.

868MHz Propagation problem

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.

868MHz Propagation problem

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