> The other thing.... All of the RF power being produced at
> the 200 watt
> level may not be on the operating frequency. Remember that a
> watt meter
> reads total power, not just the power on the repeater
> frequency. If the
> transmitter or PA or both are spurious or dirty to some
> degree, you may
> actually have less power (on your transmitter frequency) than
> you think,
> even though the power 'reads' higher. Since the duplexer provides
> filtering, the power leaving the duplexer may show less due to the
> removal of the spurious energy.
>
> Kevin Custer
And to add to that, bear in mind that if you only have one wattmeter and you
use it to first measure the input power to the duplexer, and then disconnect
it and move it to the output of the duplexer that you've changed the
electrical length of the cabling between the devices. Unless everything is
tuned and operating at exactly 50+j0, changing the effective length of any
of the cables is going to change the Z that the transmitter sees. To get
around this problem you have two options:
1. Make up a short patch cable with the same connectors as your wattmeter,
and substitute it in place of the wattmeter to maintain a constant
electrical length when moving the wattmeter between devices in the system.
The cable must be the same electrical length as the wattmeter's effective
electrical length. For something like a Bird 43, the length is known (and
published by Bird) making this easy. For other wattmeters, particularly
non-thruline types, this becomes more difficult.
2. Use two wattmeters, calibrating the differences in readings by first
connecting the two back-to-back (preferably without an jumper cable).
Transmit through the wattmeters into a dummy load and record the forward
power readings of both wattmeters. Determine the error between the two in
dB. Then put the wattmeters into the system at their appropirate locations,
determine the measured loss based on their readings, and then correct that
value by the difference you originally recorded.
--- Jeff
--------------------------------------------
Jeff DePolo WN3A - [EMAIL PROTECTED]
Broadcast and Communications Consultant
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