Does anybody have data on the CEX “Local Oscillator Frequency Extension” band ranges for the NS73M? I can’t seem to find anything in the data sheet —but then I have been known to miss stuff like that before.
I have the chip running at 97.3 with Register 8 set to band 2 per the example(s) and it works fine around that frequency, but when I stray to far things stop working.
My assumption is that the bands are divided over the FM range and that I could probably just make some arbitrary bounds to get things working, but it would be nice to have the actual numbers.
The example flow chart in the application note (Set CEX Routine, page 22) shows how to set up the registers, but does not give the band ranges.
As a matter of interest; I have an eight pin 12F683 PIC driving the NS73M with frequency entry done by a simple sequence of button presses. This gives a very low component count. The PIC EEPROM stores last frequency for use when the system is turned on.
I have partly answered my question about the ranges of the CEX register bands.
I did some measurements of ‘lockup’ range for the four bands. The bands overlap quite a bit, but none cover the whole US FM spectrum.
Here’s what I got:
Band 0: 96.1 - 106.1 (didn’t test above 106.1)
Band 1: 93.1 - 100.1
Band 2: 89.1 - 99.1
Band 3: 87.9 - 94.1 (didn’t test below 87.9)
Beyond these ranges, the unit doesn’t put out any carrier. Disregard the tenths, it’s just the way my system is set up.
I suspect the actual spec’d bands are smaller than I measured, but, in any case, a set of conservative band limits can be developed from the above. A few lines of code can accomodate this situation.
Hopefully somebody can supply the actual spec for these ranges.
I spent some time today studying the datasheet and trying to find the information on the net. The information doesn’t seem to be posted anywhere. The flowchart references testing f against low and high ranges to select the proper value for register 8. As there was no mention of the ranges, I was thinking that the bands were split evenly to cover the range of 87.5 MHz and 108.0 MHz(a difference of 2502 between the lowest and highest frequency units divided by 4). That appears to be entirely incorrect based on your experiments.