Sutherland Repeater maintenance 2019-06-11

Posted on by

Transmitter:

Output power:                  21.6W
Frequency error:              -315Hz
Deviation:                          1.49kHz

Receiver:

Sensitivity:                          0.683uV for 12.2dB SINAD (NOT CCITT weighted)
                                             @1.5 kHz deviation AT 1kHz
Squelch                              Could not be measured. Comms test set only goes down to 0.350uV

TX Filter unit:

RF power before filter:   42.63dBm (18.3W)
Return loss:                       3.4dB  !!!!!!(VSWR 1:5.23)
RF Power after filter:      34.3dBm (2.7W)
Antenna Return loss:      15.7dB (VSWR 1:1.39)

After tuning the filter unit, I got the following results:

RF power before filter:   42.85dBm (20.1W)
Return loss:                       23.2dB (VSWR 1:15)
RF Power after filter:      40.34dBm (10.3W)
Antenna Return loss:      15.7dB (VSWR 1:1.39)

RX Filter unit:

Measured loss at intended frequency:     20.6dB
Isolation at plus 600kHz                               Around 50dB

After tuning the filter unit, I got the following results:

Measured loss at intended frequency:     2.4dB
Isolation at plus 600kHz                               Around 50dB

Repeater without filters at high input RF level; 20uV 88.5Hz CTCSS @400Hz and 1.5kHz deviation @1kHz tone

Repeater without filters at low RF level; 0.683uV 88.5Hz CTCSS @400Hz and 1.5kHz deviation @1kHz tone

RF power going into the filters. Note poor return loss.

After tuning the filter. Note marker on 145.000MHz. Reference at the -10dB mark.

Results after tuning the TX filters.

Receiver filters before tuning: Reference is at the -10dB mark (-22.6dBm) indicating filter loss at 20dB.and off frequency.

Receiver filter after tuning. 2.4dB loss and on frequency. +600kHz isolation of around 51dBm

Repeater performance through both TX and RX filters after tuning filters.

The Site: Gentle reminder not to tamper……..

Conclusion:
I could probably get better results tuning the filters if I had the directional coupler with me. Maybe next time. I would have also preferred to have the manufacturers specifications to test against but did not have at the time. In my experience the repeater performs well according to what I measured. I tested the repeater from the town using a 5W hand held radio and got full quieting from the repeater with good quality audio. I there is someone who can test from the N1, some feedback would be great.

Report compiled by Neville Gleeson (ZS1NEV)

Site tested by: Neville Gleeson (ZS1NEV) and Deon Lamprecht (ZS1AFU)