ZS1VDV went to Piketberg on Saturday to resolve 3 issues.
- The power drops almost 1 second after transmission starts
- Add filter to link radio fan
- Correct emphasis settings on radios
This was suppose to be a quick 2 hour visit, but again turned out to be much more.
The morning started around 09:00 on site.
The first step was to investigate the circulator as it was suspected to be the reason for the power drop. After checking the circulator and 2nd harmonic filter with a mobile network analyzer they where found to be in order. (about 0.5db insertion loss on circulator and a 40db filter on the 2nd harmonic). It was then found that the duplexer was causing a 1.7 SWR on the TX path. This was very strange because the duplexer was tuned on last visit. The duplexer was removed from the rack and rechecked and found that the possible cause for the hi SWR is wrong length linking cables between the cans. They only onsite solution was to “play” with the tuning of the duplexer (the result was that about 10db isolation was lost). This is not optimal, but would still work. The SWR now was 1.1 between the duplexer and circulator. This however did not take the power reduction away. The last step was to test the repeater on its own with an SWR meter and dummyload. No SWR problem, but the cause for the power reduction was found. The internal filters of the repeater needs to be re tuned and this cannot be done on site.
The filter was added to the fan of the link radio.
Emphasis settings was changed on the link radio and link cable updated on the repeater. Audio was aligned. At this stage it was about 13:30 with no water or food, this became a very long day.
On Sunday ZS1VDV returned to site to recheck the audio alignment and a few small tweaks was made.
The repeater and duplexer needs to be swopped out. The repeaters filter re tuned and the proper length linking cables for the duplexer made.