Moving a Point-to-Point Microwave Link

At one station I volunteer for, we use a 1.5GHz microwave link to connect between the studio and the transmitter site on top of a hill nearby. Now I should stress that microwave link doesn’t mean digital. It’s a one-way FM link where, with the multiplexed baseband signal for transmission generated at the studios. The up shot is that while the link itself is expensive, the remote equipment is simple – receive on 1.5GHz, demodulate and re-transmit on the broadcast FM frequency.

The down side is that we get little telemetry from the unit. We can see SWR, signal and other transmission metrics on the units but there’s no reporting back from the remote end. That said, once it’s operational, there should be very little maintenance required.

Due to the building we hang the studio end antenna on being renovated, and at the council’s request, we were tasked with moving the link with as little outage as possible. Not much of an issue with it being a short distance move but we did learn a few lessons.

First of which is that these analogue microwave links are rather robust. We were allowed a fair bit of movement as we unbolted the “mast” from the rusting brackets. Though it did result in us holding the pole in place for a number of minutes while an ad break played out!

Another lesson was that there’s not much to these – get the right co-ax (50 ohm, RG-213 or better) and terminate it properly – there’s little to go wrong. Remember to weather seal it properly and it should be good for years with little active work.

Rough line-up was simple, keep twisting the pole until we got something on air. Final line-up involved a visit to the remote end and keeping an eye on the signal strength meter built into the receiver. That visit also allowed us to look into coverage problems that had been reported by some volunteers. We were able to confirm the correct operation of the transmitter and even give the antenna system a clean bill of health.

The one thing that did catch us out on this job was the simplest part – moving a minidish used to pick up IRN. We had real problems trying to line it up and even started coming to the conclusion that the LNB had been damaged in the move. Turned out to be a short length of co-ax used to connect the signal meter had shorted.

Oh well, it’s always the “simple” and “easy” bits that catch you out!

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