The first transmitter of our POCSAG network has been installed to a "real" location on top of a local water tower where we have VHF antennas already installed. The transmitter outputs 20 W power on 144.975 MHz to a half-wave dipole which is about 100 m ASL. The single site has quite significant coverage area, much wider than I expected. I did not expect the little pager to be able to receive error-free pages from over 10 km distance from the transmitter while driving in a car, with pager on my belt. Also a DX-spot was received at the
OH2K clubhouse 7km from the site, which is a concrete bunker, very RF tight!
The transmitter at the site is the
first proof-of-concept transmitter build for testing (Motorola GM340), with breadboard POCSAG encoder. Lately we have also gained more information about the Tecnomen Hi-Q transmitters (200 W output power) to use them for POCSAG when the network spreads out.
There has been quite good interrest about the project over here in Finland but also from the readers of this blog. We try to document all we do as best as possible to make the work for other paging enthusiasts easy!
The pilot network delivers currently personal messages and few group messages for the subscribers. Currently the group messages are for DX-cluster spots which are fetch automatically from the DX-Cluster network; HF spots regarding Finland, 6m/4m spots regarding Finland and 2m and up spots regarding Finland. SAR-people (Search and Rescue, VAPEPA in finnish) have also impressed their interrest for group messaging for alerting and information delivery for their purposes.
RATS has a
SAM magnetometer online, we have also discussed about possibility to alert developing aurora conditions using the data from it.
Individual subscriber messages can be currently sent via APRS network as APRS messages to destination callsigns with a specific SSID, who are registered to the POCSAG network. In future, there are maybe ways to send individual messages using SMS or web-based forms.
The infrastructure has been designed and coded by Hessu OH7LZB, and the design seems to be quite robust. The client code (which resides at the computer at the transmitter) includes also a transmitter beacon function, which sends a specific group message (RIC 0011111) stating the station callsign (for identification) and the network status to notify the status of connectivity to the server. This group transmission occurring every five minutes is also a good method of evaluating the coverage area.
Parallel work is starting to design and build the tools needed for network and subscriber management. Currently Hessu touches the database quite directly to do things. Thoughts for subscriber management have included web-base tool where subscribers can add their RIC codes to the system and manage subscriptions to individual services, and propably even group services, if we get information about the OTA features in the pagers. OTA stands for Over-The-Air reprogramming, with which it would be possible to add and remove group affiliations from the terminals (pagers) and manage other settings amongst too. We have requested information about OTA from the pager supplier, waiting eagerly for answers!
73 for now!
