Re: Low Power fix on QCX 80 and a suggestion for a possible addition to QCX test gear to measure inductance.
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Hi Des, Keith
Yes, adding an inductance meter would be a nice feature... or some way of measuring/checking the toroids. I am thinking about how that could be done.?
Note that yes, it is true, the quadrature LO will only work down to 3.2MHz - this does not affect transmit. The quadrature LO is used only on Receive.?
73 Hans G0UPL
On Wed, Nov 29, 2017 at 10:30 PM, QRP_nut <raspiham1973@...> wrote: Hi Keith,
Interesting idea regarding the swept source, it would also be a useful additional feature for the QCX test equipment.
While my QCX was delivering lower than expected output I did try winding the frequency up/down to get an idea of what was happening in the filter section of the PA but unfortunately the QCX VFO (while in quadrature mode) drops out below 3.2 MHz but it was clear the power was increasing as the frequency was reduced which in turn helped me identify the problem with the number of turns on the cores.
Good luck with the build Keith and a couple of tips regarding the toroids when you come to them. Solder the PA and filter toroids in "lightly" or semi permanently until your sure the turns are correct. I was "silly" and trusted to luck Hi. I followed the manul to the letter but on re-checking the toroids inductance I found they all needed two or three turns removing in order to bring them to the correct value. Wish now I had checked them prior to fitting to the PCB. I also made the mistake of soldering them in "fully" which made removal/replacement harder than it needed to be but with care and patience they came out OK and the PCB was none the worse for the hacking about.
If you have good eyesight then winding and fitting T1 will probably not be an issue for you but if you have to work under a magnifier as I do then this sometimes reduces the depth-of-field and makes identification of the 8 connections hard. I found the job becomes a "breeze" if you wind secondary-1 and secondary-2 with different colour coil/ magnet wire if you have it. This means each alternate winding is a different colour on the core and makes identification of the windings and connections much easier.
Anyway, have fun building the QCX.
73,
Des (M0AYF)
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