rak313
Member
In various places, (even in the FAQs here) I have seen reference to interference in simulcast P25 systems caused by interference from multiple transmitters on the same frequency.
The reference below states that the multiple transmitters (on the same frequency) are a feature not a liability - that they are synchronized - and that the combined transmiter's signal allows for fewer transmitter sites (see slides 18-19).
Why would one purposely design a system for 1st responders - that transmits the same signal (on the same frequency) on several physically separated transmitters where mobile receivers will hear the multiple transmitters - unless the system was designed such that the resulting time skew from the multiple signals is small enough to allow proper decoding.
Even if interference from the other transmitters occurs and causes poor eye patterns - would be relatively easy to implement an equalization filter to remove it (as is used in digital cell phones - which have a similar issue - except it's from multipath - not multiple transmitters).
With more and more Police/Fire going to P25, and vendors pushing simulcast systems as more frequency efficient than multicast - it would seem that if scanner vendors don't find a way to receive P25 simulcast reliably - there will be little value in having a scanner.
So I don't get it.
Can someone lighten me?
The reference below states that the multiple transmitters (on the same frequency) are a feature not a liability - that they are synchronized - and that the combined transmiter's signal allows for fewer transmitter sites (see slides 18-19).
Why would one purposely design a system for 1st responders - that transmits the same signal (on the same frequency) on several physically separated transmitters where mobile receivers will hear the multiple transmitters - unless the system was designed such that the resulting time skew from the multiple signals is small enough to allow proper decoding.
Even if interference from the other transmitters occurs and causes poor eye patterns - would be relatively easy to implement an equalization filter to remove it (as is used in digital cell phones - which have a similar issue - except it's from multipath - not multiple transmitters).
With more and more Police/Fire going to P25, and vendors pushing simulcast systems as more frequency efficient than multicast - it would seem that if scanner vendors don't find a way to receive P25 simulcast reliably - there will be little value in having a scanner.
So I don't get it.
Can someone lighten me?