K7HIO.NET

Now that all the pagers are behaving and we've got the transmitter hardware mostly set, we had two questions to answer:

1. What is our coverage footprint?
2. Which baud rate should we choose?

The first one is mostly out of our control, we just need to see if having the transmitter at a low-level site is good enough to cover the people we're interested in notifying.

The second, however, seemed like a no-brainer.  The pager service manual clearly states that each paging baudrate affects the sensitivity of the receiver.  The pagers support 512, 1200, and 2400 baud so it seems obvious that paging at 512 baud would be ideal.  We don't need to worry about a heavily multiplexed channel, so why not go for the slowest rate for the best chance of the signal getting through, considering our less-than-ideal conditions?

What we found with some unscientific testing was that 2400 baud seemed to perform the best of the speed options.  We really didn't understand why this would be, and figured that a more scientific study was in order.  So, we set out to determine the answer to both.

With an operator at the station and one in a vehicle, we tested all three speeds at various places around Hillsboro.  This didn't cover all of our responding members but did give us a pretty good idea.  We went southwest from the station which should be the worst propagation path because of the buildings and other development.

View Paging in a larger map

What we found was mostly in line with our initial testing: 2400 baud seems to behave the best.  At the very least, it performs no worse than either of the other options.  We're really not sure what to make of this, as it seems counterintuitve.  Perhaps we're dealing entirely with multipath and not signal strength and the 2400 baud signal is somehow more resistant to that.

We may need to reevaluate this decision if we move the transmitter to a high-level site with different propagation characteristics.  However, as you can see, we're able to get pretty reasonable coverage with 150W and a modest antenna about 25' off the ground.