QRP Labs QCX 5W CW, Руководство по сборке, Страница: 127 / 138

QCX assembly Rev 1.08
127
If you do NOT see any power output on key-down, then you probably have a fault in the Power
Amplifier. A common mistake, as I mentioned previously during the assembly steps, is failure to
remove or burn off the enamel insulation on the enamelled copper wire wound onto the toroids.
Check the RF power wire touched to the BS170
drains first (see diagram). You can still touch the
wire to these BS170 drains from the top side of
the board. Key-down and check the wattage
reading. At this point the indicated power will be
even less reliable than across the dummy load.
But at least see if it reads e watts.
If you see power output at the BS170 drains, but
not at the overall transceiver RF output, then this means that the fault lies in the Low Pass Filter.
Check the soldering and the enamel situation, on those toroids.
If you do not even see power output at the BS170 drains, then perhaps the L4 drain inductor in the
PA has incorrectly soldered wires, that have not made an electrical connection
– so check the L4
wires first and make sure the enamel is properly scraped or burnt off, to make a proper
connection.
To probe other parts of the Power Amplifier circuit is less easy, because the LCD module prevents
easy access. You will need to prop the PCB up vertically, and reach behind with the wire, while
trying to still be able to watch the LCD screen from the front.
6.6 Audible continuous clicking noise during receive
This is not a fault of the radio, it is a consequence or limitation of the simple design. When the
LCD is updated by the microcontroller, the activity on the signal lines to the LCD and in the
microcontroller, causes digital noise which propagates into the sensitive radio receiver. In most
cases when the display is updated, for example, when you change the frequency, this weak click
is completely inaudible. In any case altering the frequency results in an inevitable audio
discontinuity as the received spectrum suddenly shifts to the new LO frequency, and this more
than masks any weak click from updating the display.
The continuous clicking noise during receive, sounding like the motor of a boat (perhaps), is due to
the display update for the S-meter. You are likely to only notice this noise when the antenna is
disconnected, or you have a dummy load connected. Ordinary band noise normally massively
exceeds the weak clicking.
In some cases (depending on your power supply, antenna, grounding etc) the interference may be
worse than normal. If this is the case, you can just switch off the S-meter. Remember that the S-
meter indication is anyway only a rough indication, and with a little experience your own ears will
do a much better job of estimating Signal level of the received station. The S-meter can be
switched
off in the “Show S-meter” configuration parameter in the “Other” menu.
7. Measurements
The measurements in this section were performed on assembled kits. There will always be
differences from one kit to the next, due to component tolerances, adjustment differences, how
you wound toroids, etc. In addition, it is often difficult to make good RF measurements. Therefore,