On Friday 13th Jan 2017 team of seven people (Rory ZL3HB, Rob ZL3RX, Rod ZL3ROD, Mike Zl3TMB, Morrie ZL3RP, Steve ZL2UCX and myself ZL4FZ) spent a day at Herbert. We met at Diamond Harbour at 0830 and finished around 1630. We have replaced the mounts with a 48mmOD water pipe, reinstated the original whip antenna after refurbishment, checked the duplexer tuning, tested the repeater with Comms Test set, checked all cables and feeder with VNA. Tidied old feeders and rubbish from the pole etc.
Net result is 725 is back on air, performance appears by reports so far (Geraldine/Timaru) to be going well, and measurements from my QTH support the improvement. Good day, not much wind, good weather, lots achieved.
Repeater opening power from ZL4FZ QTH
| Repeater | Today | Last measured | Comment |
| 705 (with CTCSS) | -7 dBm | -6 dBm | No change * |
| 705 (no CTCSS) | +3 dBm | +1 dBm | Nochange |
| 725 | -10 dBm | +1 dBm | 9 dB improvement |
| 675 | +5 dBm | +5 dBm | Consistent with results Oct 2015 |
| 6975 | N/A | N/A | At upper limits of Sig Gen |
| 5625 | +10 dBm | +5 dBm | 5 dB worse than last (Jan 16) |
Received Signals at ZL4FZ QTH
| Measured | Today | Last measured | Comment |
| 705 | -54dBm | -55dBm | no change since Jan 2016 |
| 725 | -67dBm | -79dBm | 12 dB improvement |
| 675 | -77dBm | -75 dBm | last measured Oct 2015 – no change |
| 6975 | -89 dBm | -88 dBm | last measured Oct 2015 – no change |
| 5625 | -71 dBm | -72 dBm | last measured Oct 2015 – no change |
Summary
With off air measurements, variation of 1- 3 dB is not unusual (worse for longer paths). Given that if a result is within 2 dB I have considered it as “no change”. Despite this the results are on the whole rather consistent.
705 – No change in performance – but this also includes the problem with this repeater of poor de-sense performance. This shows up with a base sensitivity of -11 dBm but needing -7 dBm to stop the repeater pulsing – a 5 dB degradation. This would suggest that at least 11 dB more isolation is required in the duplexer, OR we drop the Tx power back to 25W, (6dB drop in Tx power) which should stop the pulsing.
725 – A marked improvement since last time (11 dB Rx performance, and 12 dB Tx performance) compared with January 2016. Even comparing with the best results I have (Mar/Apr 2015) the Rx is 6 to 8 dB better, and Tx is 9 dB better.
5625 – Appears to be less sensitive on RX by 5dB. This could be as simple as Rx gate setting as Tx signal is no change
All others appear to be “no change”
Rob (ZL3RX) – we may be able to check the pulsing/isolation issue with remote access to 705
This makes 725 currently the best ‘local’ repeater for hand-held use as the 5dB extra receive signal needed to overcome the pulsing outweighs the stronger Tx signal from 705. Obviously coverage of 725 is more constrained because of shadows across the Port Hills. The difference in gating levels also does not adequately measure additional S/N degradation on low level receive signals, but in my opinion would this about a further 6dB of additional S/N degradation. This is because the measurements are based on gate opening levels rather than SINAD.
Author Richard ZL4FZ
