Our company is cooperating with a factory in Taiwan to create a 2-way 429.400MHz hand-held pager and car-based receiver for a car security system that will be sold in Japan (and therefore must comply with ARIB T-67). We have used the CC1020 chip in our RF products since about 2004. In our past designs, we have used trimmer (variable) capacitors on the CC1020 crystal, which must be hand-tuned at the factory. Unfortunately, we've had problems with frequency shifts due to voltage and temperature fluctuations. As such, we are closely examining AN027:
AN027 says that a trimmer capacitor can be eliminated if using the calibration method described in that Application Note. AN027 even says that a TCXO is not needed. Figure 2 on page 5 of the AN027 PDF then shows a block diagram and talks about a computer running LabView. Our factory has never used this kind of setup before, and as such they need some hand-holding.
My first question is, is this setup really better than using a TCXO? And I suppose a trimmer capacitor would still be required even when using a TXCO, to set the initial frequency during production?
But the problem is that when trimming by hand, you're trimming at varying "room temperature." And in light of our past problems with frequency shifts due to temperature fluctuations, we want a solution that we eliminate our past headaches. And yet, the method described in AN027 certainly doesn't look very easy or inexpensive. It's rather odd too because AN027 says that using a trimmer or TCXO is expensive and time consuming, implying that the alternative method which AN027 describes is "inexpensive and quick." But is that really so?
Can you provide me with greater detail about how to use the AN027 setup during production? Our RF engineer in Taiwan cannot make complete sense of AN027 due to the lack of details (combined with the fact you don't seem to have a version in the Chinese language either). How exactly do we do it? We've never used LabView to control our temperature chamber before, which is what page 5 seems to be talking about (in the AN027 PDF). Again, our main goal is to put an end to frequency shifts related to varying temperature. I would appreciate some clear guidance on just how to accomplish that, using the CC1020 chip.
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