The curious case of the missing signal
A recent activity in the amateur radio hobby is deploying an always-on radio frequency network that is essentially a replacement for the internet. This is part of our emergency preparedness plan to enable ongoing communications in the event of a disaster and failure of the internet, which has become more and more integrated into our hobby.
As an experiment to get started, we established a 5.7GHz link between my house and my friend Jerry, another ham who lives about 2 km away. We used the Radio Mobile software by Roger Coudee, VE2DBE, to determine if we had a path between us, and it showed that we had a good one, which should have at least a 30 dB signal to noise ratio without line of site. To determine how to point the antennas, we used Google Maps in the earth mode to draw a line between our houses, which gave a reasonable indication of where to point the antennas.
We installed mine first on a tripod on the roof, mounted on the side of a pole which was topped by a discone antenna, that would be used for my VHF and UHF radios, and also a 900 MHz repeater system. At the other end we mounted the radio atop Jerry’s tower and when all was turned on, it performed well and the measured signal to noise ratio (an indication of signal quality) was very close to what we expected from the software model. Yahoo! It worked!
Of course, a good thing cannot last too long, and soon I found out that the discone antenna seemed have a problem. Water had encroached into a ceramic insulator and frozen, causing it to shatter. The antenna was pretty much useless, any radio connected to it could be heard across the street on a clear day. I found some alternate antennas and built a new pole that I could swap with the current one, this time with two antennas, one for VHF and UHF, and a second one for 900 MHz, mounted to the side. The plan was to take down the old antenna system, move the link radios (now there were two) to the new pole, and mount the new pole in the tripod on the roof. Pretty straightforward.
We started by taking down the old pole, marking exactly where it was in the tripod, and before the radios were removed their position on the pole was transferred to the new one, so they would occupy the same height and be pointed in the same direction as before. Everything was carried up to the roof, the radios were connected, and the big moment arrived…it was disastrous. The strong signal had now been reduced to about 9 dB above the noise, the connection was not even good enough to send a text message. The project was abandoned for a while until I could get my roofer to come back and remount it for me, as we were about to leave on a lengthy road trip.
By the time we returned there had been several hailstorms throughout the summer and one of the radios failed. I suspected that it had been damaged, but the 5.7GHz radio was still working. My roofer arrived, and we spent a considerable time moving the radio up, down and side to side, with little or no improvement in the signal. As the day went on and the sun had gone down, by then he could see the LED’s on the radios, and that one radio appeared to be working and the other not, which confirmed what we already knew. He asked me which direction the dead one should be pointing towards and also the live one. After that, a discussion ensued about which radio was which, (they were even labelled), and we determined that they had been swapped around! The low signal over the link was caused by an incorrectly aimed radio from day 1, and re-aiming it back to where it was supposed to be restored the link, with even a small improvement!
The moral of this story is that if you are transferring antennas or radios from one mount to another, ensure that you have them in the correct position! A lesson I learned the hard way.