Mod. High in RX
ENABLE
This parameter controls whether the PA amplitude modulator is set to High during Receive. If set
to “ENABLE” the PA voltage is high during Receive. This means the PA voltage is around +12V
(assuming +12V supply) during Receive.
The BS170 transistors are all off (zero gate voltage) and therefore there is no current flow through
the PA transistors. However the Drain-Source junction of the BS170 MOSFETs have a
capacitance which is dependent on applied voltage and it is best to MINIMIZE this capacitance,
and therefore the effect of the inactive PA on the receiver, during Receive. Furthermore the BS170
MOSFETs have an intrinsic “body diode” which will, at some level, act to clip the incoming Receive
signal; by applying a +12V reverse bias to this body diode, we can ensure that this never happens.
Leaving this setting at “ENABLE” is recommended to maximize theoretical dynamic range and IP3
performance of your QMX receiver, though the actual improvement has not been determined
experimentally by measurement. I am grateful to John Dzbrozek KJ4A for suggestion this feature
as a result of his PA simulations and subsequent theoretical analysis.
If you select “DISABLE” for this feature it will not damage your QMX but it may not optimize
Receiver performance.
Normal 5ms shape
ENABLE
When enabled, the normal 5ms (or similar, depending on configuration) Blackmann Harris
envelope shaping is applied on CW and Digi mode rise/fall times. When set to “DISABLE” the
Blackmann Harris envelope shaping is sped up by a factor of 33.33 times, which has the effect of
shortening the rise/fall time to approximately 0.15 milliseconds. This is used for testing the
response of the PA envelope shaping and Transmit/Receive switch and corresponding BPF switch
stability under fast rise/fall times, which are approximately equivalent to a full amplitude 3.2kHz
sinewave component of an SSB waveform and are therefore harsher than the worst case
conditions which will be expected during SSB transmissions. This feature is designed for
experimental and development purposes. In practical use it should be left at ENABLE.
20/80m BPF TXswap
ENABLE
Enabling this feature is part of a protective measure against instability which destroyed BPF the
multiplixer on Rev 2 PCBs. It is described in this forum post:
https://groups.io/g/QRPLabs/message/113662 and you are recommended to read this if
interested. Disabling this feature, particularly on an 80-20m Rev 2 (and above) QMX PCB, is
REALLY NOT RECOMMENDED.
QMX operang manual; rmware 1_00_012 45
To Next Page
Loading...
Need help?
General
