Category Archives: Design
When your ISP blocks incoming SMTP Connections
Things keep changing in Qatar. Just before Christmas the local ISP (QTEL) decided to start blocking inbound port 25 connections to the DSL line I use for work. This posed a problem for me as I run a mail server … Continue reading
RF line of sight propagation
Introduction For communications systems to operate reliably a good signal needs to be received. Too weak a signal will cause loss of data and too strong a signal can result in overloading of the receiver or interference to other communications … Continue reading
Driving antennas from two sources.
I came across an interesting design problem recently in an indoor PMR distribution system. The system comprised both radiating feeder and antennas all driven from two RF over fibre amplifiers in different locations. The two amplifiers are used for resilience … Continue reading