MWRS hosted a test for the Sydney ATV group, as they have lost their Lawson repeater and are trying to find another site. The initial test used a 9dBd 6-element Yagi, pointed SSW, and 20W FM. FM was used for convenience (equipment is easy to access). The Yagi was located on our tower, below the rotator, but not quite at the top as we had to avoid a guy wire. Iain Schwilk VK2DAB graciously volunteered to put the Yagi up for us. 25m of FSJ4-50B had insertion loss of 2.18dB at 438MHz giving about 12W of radiated power.

Most of the initial path plots (via heywhatsthat) looked generally OK:

VK2MB – VK2CRJ Ryde
VK2MB – VK2ATU Revesby
VK2MB – VK2EK South Windsor

Simon VK2YU assisted the preparation with some drone shots showing the correct pointing direction. This is approximately what the antenna will see, the path is in the direction of the BoM radar:

Reception reports were mixed. Generally the signals were weak but readable on FM
(N/A in the table below means not available for the test):

Alan VK2ALA was well off to the side of MWRS’s antenna pattern, but his altitude in Springwood provided a very favourable path and we still had a good report. Height is might!

Gary VK2CRJ also used his SDR to take C/N readings, and reported that the received signal fluctuated about 6dB so with a noise floor of about -82dB, the C/N varied from 24dB to 30dB:

Gary’s signal at MWRS was also fluctuating by an S-point or so, it sounded a lot like mobile station flutter and we suspect interference from traffic on Mona Vale Road. Other signals were much more stable.

As an approximation, if the bandwidth of an FM signal is about 7kHz and a DVB-T signal is 7MHz,
there is a 30dB bandwidth penalty. Then if a DVB-T signal requires a minimum C/N of 6dB to
decode plus a margin of 4dB, the FM signal needs to have a C/N of 40dB so the same average
power DVB-T signal will be decodable. So there is a further 10dB to 16dB increase in signal
strength required to receive a TV picture.