A small group of members ventured to our West Gap repeater site to investigate the poor performance of the repeaters since the installation of the new 2m repeater a few weeks ago. In short, since the new repeater was installed the range of the 2m repeater had been drastically reduced, with noisy audio, which had also been noticed on 70cm.
Kaz VK8ZKZ, Geoff VK8LDR, Geoff VK8GG and Glen VK8FORD made the trip, with Phil VK8FHIL also attending for a short time. The first task was to identify where the problem was - the repeater or antenna? Geoff (8GG) and Kaz disconnected the antenna feed from the diplexer in the hut and connected the club's MFJ antenna analyser. Tuned to 146.950, the analyser was showing an SWR of well over 3:1 - not a good sign.
However given that the analyser had not been used for some time, a second opinion was needed. Geoff connected his SWR meter inline, and when manually keyed the 2m repeater indeed had an SWR of about 10:1, with output power reduced to 10W - so the repeater's SWR protection works well! The same tests were performed on the 70cm repeater, which also showed an extremely high SWR and output power reduced to only 7W.
So the problem was definitely at the antenna end.
Glen produced a ladder and climbed up to lower the antenna to the ground. The new Heliax feed was disconnected, and the problem was immediately apparent - the fingers inside the antenna's N connector had been severely splayed.
A theory as to the cause of this problem was quickly agreed on - the Heliax feed had been directly connected to the antenna base. When the wind started to blow a few hours after the original installation, the movement of the antenna against the rigid heliax caused the fingers to be pushed apart by the center pin of the connector. Lesson learnt - ALWAYS install a flexible tail between the feed and antenna. Phil very carefully straightened the fingers inside the antenna's N connector whilst Geoff (8LDR) made up a new tail, which was duly installed.
Whilst the antenna was on the ground, a dummy load was connected to the antenna end of the feed line, and both 2m and 70cm repeaters were tested for SWR and output power - both were well under 1.5:1 SWR and delivering full power, ruling out any other issues with the feed line itself. The tests were repeated with the antenna re-connected and standing upright before being mounted on the pole, and again the results were perfect.
Glen then re-installed the antenna on the pole and a final set of SWR/power checks were performed, and recorded for future reference:
2m SWR (1.3:1) and Power output (50W)
70m SWR (1.2:1) and Power output (25W)
The "Repair" performed to the antenna's N connector is only temporary - the inner pin of the connector has been considerably weakened due to the bending, and it is quite possible that it will fail completely in the future, so a replacement antenna is going to be arranged for a swap-out during a future site visit.
Also during the visit the 70cm repeater was reprogrammed to align with the 2m configuration, with the tail length and subtone operation being set up for future IRLP integration. The CW ident was also tweaked so that it is a slightly higher pitch than the 2m ident, so they can be readily identified when monitoring both repeaters together.
Thanks to all involved in assisting with this repair operation to restore the repeaters to full service.