(cropped from a full sphere photo)
Daniel 9V1ZV, Harish 9V1HP, and I installed the new duplexer (a Sinclair Q2330E) on Wednesday, however its TX insertion loss and VSWR seemed a little on the high side, so during installation we dropped power to 5W to avoid transmitter overheating problems. Today I visited again and with Harish reverted the antenna configuration to the two separate antennas that we’ve been using since the move:
- the collinear Diamond V2000 on the lower balcony for receiving; and
- a ground-plane quarter-wave antenna on the upper balcony for transmitting.
Prior to making the change, I conducted a simple blind test of four different configurations to establish an empirical basis upon which to choose. I made test transmissions in each configuration and requested signal reports be provided privately. The reported results are as follows:
| Configuration | 9V1KT | 9V1AW (Woodlands) | 9V1ZV (pre-amp) | 9V1ZV (no pre-amp) |
|---|---|---|---|---|
| 1 | S9+40 R5 - Audio quality almost full quieting. Minimal hiss. | R2 | S9+15dB | S9+1 or 2 segments |
| 2 | S9+40 R5 - Audio quality no apparent difference from (1). | R6 | S9+21dB | S9+5 segments |
| 3 | S9+40 R5 - Audio quality is better than (1) and (2). Full quieting. No any hissing. | R4 | S9+20dB | S9+5 segments |
| 4 | S9+40 R5 - Audio quality no apparent difference from (1) and (2). | noise only. No copy | S9+9dB (5segs) | S8+2 segments |
2 and 3 are clearly ahead of 1 and 2, with small differences between 2 and 3 depending upon who was reporting.
The tested configurations were:
- Two antennas, 5W into the upstairs antenna in its original position close to one end of the balcony.
- Two antennas, 25W into the upstairs antenna in its original position close to one end of the balcony.
- Two antennas, 25W into the upstairs antenna, moved near to the centre of the balcony.
- Downstairs antenna only, 5W through the duplexer.
Observations:
- As you’d expect, power clearly matters. 25/5W ~= 7dB or slightly more than 2 S-Units, as the reports for 1 and 2 show.
- The downstairs location is looking like a poor choice, but note that for this particular test the duplexer was in use which makes the situation look worse than it is.
- The choice for today was simply which of those four configurations to leave the repeater in. 2 and 3 were the clear leaders and — as we’d already moved the antenna to the centre of the balcony — we left it at 3.
The data invite some additional inferences and suggest additional measurements to perform, but today’s visit was very limited in duration (90 minutes) and the intention was only to make the best improvement that we could make quickly so we didn’t test further.