Hi all, food for thought/consider the following:
While monitoring the LWIN system (scott, la) site with the usual cheap dongles, I noticed Unitrunker
periodically indicated that control channel was usually a solid decode (green), but periodically dipped
into the red, and sometimes, briefly dropped altogether. I began to wonder if this is the LSM distortion
that many talked about, but really wasn't sure the reason for the dropouts.
So, after a time, I fired up my airspy with SDRSHARP. This allowed me to have a graphic representation
of all the 700mhz repeater outputs on the LWIN system within range of my location. What I found was that when
I was experiencing strong dips or dropouts on the control channel using the dongles, it coincided with a repeater coming on the air very near by in frequency, usually within a few khz. Thus, the cause of my dropouts looks like adjacent channel interference. The front end of the dongle is too wide to deal with very close strong signals, and so decoding of the desired signal is harmed.
This situation leads me to wonder, how often (if at all) is what people my fellow scanists believe to be LSM distortion or the like, actually related to adjacent channel interference?
Please note, I am in no way suggesting simulcast problems are not real. Rather, I am proposing an additional, and potentially confounding variable, that I suspect consumer scanners may also suffer from.
regards
JB
While monitoring the LWIN system (scott, la) site with the usual cheap dongles, I noticed Unitrunker
periodically indicated that control channel was usually a solid decode (green), but periodically dipped
into the red, and sometimes, briefly dropped altogether. I began to wonder if this is the LSM distortion
that many talked about, but really wasn't sure the reason for the dropouts.
So, after a time, I fired up my airspy with SDRSHARP. This allowed me to have a graphic representation
of all the 700mhz repeater outputs on the LWIN system within range of my location. What I found was that when
I was experiencing strong dips or dropouts on the control channel using the dongles, it coincided with a repeater coming on the air very near by in frequency, usually within a few khz. Thus, the cause of my dropouts looks like adjacent channel interference. The front end of the dongle is too wide to deal with very close strong signals, and so decoding of the desired signal is harmed.
This situation leads me to wonder, how often (if at all) is what people my fellow scanists believe to be LSM distortion or the like, actually related to adjacent channel interference?
Please note, I am in no way suggesting simulcast problems are not real. Rather, I am proposing an additional, and potentially confounding variable, that I suspect consumer scanners may also suffer from.
regards
JB
