Re: Had to realign today #alignment

Alan de G1FXB
 

Joe,
Assuming no construction errors, and age & version of your kit / assembly manual.

If the belief is the QCX lacks sensitivity perhaps the first place to try is the C1 adjustment. This is the only one that effects the RF sensitivity.
The preset resistor adjustments, all operate in the I/Q circuitry and provides the opposite sideband rejection, as this is not a traditional superhet design.


C1 is the BPF alignment, Hans notes there can be more than one peak in the filter response, and to tune the one which shows the highest level.
Recent manuals advise making adjustment while connected to a dummy load as this better reflects real world use when connected to an aerial,
previously it was with an unloaded circuit.


From now on, the alignment is also dependent on the user AF gain setting, you need a high enough level to display a clear range between? min / maximum but not too high it overloads the detector.
See second paragraph of page 70

R27 I/Q Balance is adjusted for a minimum unbalance between the I/Q paths

R24 Phase Lo, is adjusted for minimum unwanted sideband response

R17 Phase Hi,
is again adjusted for minimum unwanted sideband response

You describe R24 & R17 show best performance when adjusted to their extreme clockwise limit.
If applicable to your age of kit see http://qrp-labs.com/qcx/qcxfaq.html#203
Alternatively, but only describing lack of ANTI-clockwise adjustment range of R24 due to component tolerances
is a component revision applied to the latest builds and is noted? at the bottom of page 7 of the current manual.

If problems are encountered perhaps:-
http://qrp-labs.com/qcx/qcxtrouble.html#bpfpeak
http://qrp-labs.com/qcx/qcxtrouble.html#iq


regards Alan.

On 20/06/2019 17:52, Joseph B Cotton wrote:
Today I needed to re-align my unit. Because, in the NAQCC sprint last night, I was disappointed.? Turns out that the sensitivity was way down, and I could hear stations on my big rig that were silent on my QCX.? So this morning I went through the alignment process (page 63 in the manual) again.? Don't know why, but aligning R27 (I/Q) helped in aligning C1 for peak.? R24 and R17 (audio phase adjust) seems to like it best when I crank them down all the way - clockwise.? Is this expected?

Joe

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