25. Measuring the performance between the "Tx"- and the "Rx"-port.

 25.1 Connect the signal generator directly to "Tx", or via 50 ohms cable, a 1/2 wave long (68 cm), or 1/1 wave wave long (136 cm).

25.2 Connect a 50 ohms terminator to "Ant".

25.3 Connect the signal detector to "Rx" via a 50 ohms cable, 1/2 wave long (68 cm) or 1/1 wave wave long (136 cm).

25.4 Tune the generator and the detector to the exact downlink (repeater-transmitter) frequency.

25.5 Turn up generator-output until a good readable value is indicated at the detector.

25.6 NOTICE the signal-level at the detector, and the amount of attennuation at the generator. Do not change the output of the generator at this moment.

25.7 Check that the signal you see is the signal coming from the filter.

25.8 If OK, directly connect the generator-cable to the detector-cable.

25.9 Turn up the signal until the same signal level is obtianed at the detector then before measuring trough the filter.

25.10 NOTICE the amount of attennuation on the generator.

25.11 The difference in attennuation with / without the filter is equal to the separation between "Tx"-connector and the "Rx"-connector. It must be 90 dB or more.

25.12 Repeat this process for the uplink frequency (lower-sideband of Tx at -600 kHz).
It gives an idea how much the unwanted transmitter sidebandnoise at the uplink frequency is suppressed.

25.13 Repeat for the other (upper-) sideband at +600 kHz distance.
This part of the noise-sideband can mix with the 2nd harmonic of the transmitter. It then can mix to a noise-signal on the receiver-input-frequency.
This filter adds extra wideband selectivity to the repeater-receiver, becouse of the included banspass-cavities.

25.14 You also can measure, over a range of 125 to 165 Mhz and on the 2nd and 3rd harmonic of the transmitter, the wide-band frequency characteristics of the filter from "Ant" to "Rx" with "Tx" terminated.
This should be done with the measuringcables correctly terminated at the filter-side, to avoid measuring-faults due to "transformer-working" of the cables at surtain frequencies (odd 1/4 wave lengths). So, connect 12 dB attennuators directly at "Rx" and "Ant" of the duplexfilter.


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