Advertisement
5. Calibration
This section is REALLY IMPORTANT! It is very important to realise that by far the hardest part of any
successful QRSS beacon operation, is tuning the oscillator to the correct frequency. For example, most
30m QRSS stations monitor a narrow 100Hz-wide band from 10,140,000 to 10,140,100. If you are much
outside this, the chances are that nobody will see your signal. It is therefore essential either to adjust your
output frequency using an accurately calibrated frequency counter, or an accurately calibrated receiver.
If you are going to use a GPS receiver module to provide a 1pps signal to the kit, no calibration is required:
the kit will self-calibrate from the 1pps signal.
In the case that you will not be using a GPS signal, you need to calibrate the kit by entering the correct
value of the 27MHz reference oscillator frequency into the "Ref. Frq." configuration setting.
It is possible that you have an accurate means to measure the 27MHz reference oscillator frequency itself
by probing the correct point on the Si5351A module. However most kit builders will not have the necessary
equipment, and such a measurement is not easy to make without itself risking disturbing the frequency.
The easiest method is to set the output frequency to something convenient such as 13.500000 MHz, and
measure it. Measurement can either be by using an accurately calibrated frequency counter, or by setting
up an accurately calibrated receiver with Argo and monitoring the output signal frequency that way.
Once you have measured the actual output frequency, you can calculate the required correction to the
27MHz reference frequency and enter it in the "Ref. Frq." configuration setting. For example, suppose you
set the output frequency to 13.500000 MHz but you actually measure 13.500075. Your output frequency is
75 Hz too high. Since your output frequency setting is 2 times less than the 27MHz reference oscillator
frequency, this means that the actual reference oscillator value is 150Hz too high. So enter 27,000,150 in
the "Ref. Frq." setting.
6. PA bias set-up
Initially the bias trimmer potentiometer R5 should be set all the way anti-clockwise. When you have set up
the software to configure your U3S for some transmission, connect a 50-ohm dummy load (two 100-ohm
resistors in parallel is fine, or a 47-ohm resistor is fine too). Monitor the power output. As you turn R5
gradually clockwise, the power output will increase. At some point beyond half way, the power output will
peak, and as you continue to turn clockwise, power will decrease. This is too far! Now your BS170 will start
getting hot. Maybe very hot. So back-off a little. My recommendation is to set the power output a little
below the peak setting. A little ANTI-clockwise, from the peak power output setting.
7 Resources
Please see the kit page http://www.hanssummers.com/ultimate3 for any information on latest updates and
issues.
For troubleshooting please refer to http://www.hanssummers.com/ultimate3/u3trouble
Further references are listed in the Operation manual.
13
Advertisement
