On Wed, 29 Oct 2008 14:46:49 +0900, "Brenda Ann"
wrote:


"John Smith" wrote in message
...

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?

Desense caused by out of band signals if of course possible when we
talk about such toy receivers as most wireless LAN or wireless
headphones are.

However, since the 868 MHz band is a non-licenced band, it is quite
likely that there might be other transmitters (e.g. wireless
headphones) in the area of the moving transmitter, but not near the
office transmitter.

Give a spectrum analyzer to the moving station operator to monitor the
interference level in that frequency band, when the moving transmitter
is off. A scanner receiver with a decent signal strength indicator
might even suffice.

Desense is definately a possibility, but I still believe that it's at least
AS good a chance that it's a standing wave issue on the office end.

This is out of the question for any single frequency half duplex
connection, since the path would be reciprocal. In a full duplex dual
frequency point to point system between two _fixed_ station, this
would be definitively possible. Even in this case, moving the other
station by 10-30 cm, you would find a spot, in which there is a good
connections both ways.

Based on my experience at 1297 MHz with a narrow band (16 kHz) signal
in urban environment, you definitively have a lot of multipath nulls
(several nulls every meter), For speech communication, this is not
much of an issue, the faster you move, you have hundreds of nulls
every second and it does not much affect the readability of the
speech. The only problem is that if you stop at a traffic light, you
usually will end up in a multipath null and the communication is
broken, unless you can slide the car a few centimeters.

Others
have said to take the 'office' radio outdoors and test the setup that way.
That's a good (and simple) test.

The OP did swap the radios, but he did not tell if the power supply
was also swapped. If the office power supply was faulty and the office
transmitter could not deliver the nominal power, this could explain
the situation.

Paul