I’m testing 4 HL7800 modules in a security product consisting of 2 base stations and 2 pagers. During normal operation, each unit will contact the remote server host once a minute with a short UDP message. If there is no acknowledgement the module will continually resend the message. Network problems result in a lot of resend requests.
Suddenly yesterday most of these messages do not make it through the network to my server. On a terminal I watch the server host send replies but they do not make it to the modules. I watch the modules send messages but they do not make it to the server. I have tried restarting the devices, and then it may take several minutes to a half hour for them to connect to the network. Then lots of the URC +CREG: 3 which means network registration denied. After eventually connecting, often the first message succeeds but then it is back to being deaf-mute.
Today I re-positioned one unit to the other side of my residence, and took 3 other units for a drive away from the area. The re-positioned unit worked better and the newly remote units seemed back to normal. When I brought everything back to home location it was back to network mayhem again. Now I am convinced this is radio interference. The HL7800 does not have provision to detect jamming. Also my VOIP cell phone works normally during this time. The modules are on PCBs with a short trace to a U.FL connector. A 50 ohm LTE cell antenna with good advertised gain (5 - 6dB) is used. This is the first time I have been testing this over a year and this is the first time I’ve seen this problem. Is there a better module for rejecting interference?