Author Topic: P275 measurements  (Read 948 times)

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P275 measurements
« on: November 03, 2023, 05:08:09 am »
I have had the chance to compare the performance of my P275 to several FM Signal analyzers which cost a LOT more.. and I can tell you without a doubt the P275 delivers repeatable and reliable measurements based on YOUR ability to use it right.

Now, I would like to know if I can write a script, or such, that allows me to measure the pilot FREQUENCY (and if I can, also measure on the RDS or other subcarriers) in addition to seeing the pilot display in the MPX screen.  I can see it at about 19k, or 38, or 57.. the P257 does the math and I can convert it to percent.. but how to get the pilot FREQUENCY out of the mix?

  I've tried rolling the mouse through, I see X and Y values change, but I'd like to know if there is a way to get those frequencies reasonably measured by pointing and clicking, or running a script.

The values I get right now for modulation, RDS level, Pilot level are close (within a few fractions of a percent) of what I see on devices costing many times what the P275 costs.. which is fine because it is REPEATABLE and reliable. 


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Re: P275 measurements
« Reply #1 on: November 03, 2023, 09:43:36 pm »
Here's a simple script you can use:

Code: [Select]
send(MEM 1B0C?v)
if (%pltfreq=0)
if (%pltfreq<7367)
if (%pltfreq>7368)

textwindow.addline(No pilot or poor signal)

textwindow.addline(Pilot frequency failed)

textwindow.addline(Pilot frequency OK)


The script reads internal undocumented register and works with firmware version 2.2 r6, operation with previous or future firmware is not guaranteed.
Value of 7367 covers a range from 18.997,5 to 19.000,0
Value of 7368 covers a range from 19.000,0 to 19.002,5
Unlike a frequency counter, the P275 does not contain TCXO so any frequency measurements are limited to accuracy of about +/- 0.005% (that is +/- 1 Hz for the pilot)
The P275 contains 19kHz NCO for the pilot recovery. Internally the pilot frequency is held with 32-bit precision. Higher word is at address 0x1B0C, lower word at address 0x1942. These addresses may differ accross the firmware versions.
We will consider adding a special command for getting the pilot frequency directly.