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Topic Summary

Posted by: Jan
« on: Yesterday at 07:33:23 am »

This peak is not present in your previous image.

It is likely to be a fault in the PC power supply unit. These older devices were relatively sensitive to the quality of the power supply. In the devices we manufacture today, the power supply is handled differently, and a dedicated voltage regulator is always used.

You do not mention the origin of the device. We do not have your email in our database. It is also possible that the previous owner handed it over to you in a damaged condition. The only way to determine this is to test it on another PC.
Posted by: rafaelhol
« on: Yesterday at 04:05:34 am »

Another question: I’ve noticed a signal appearing on the FFT at 27 kHz on virtually every station I tune into. It seems the equipment is picking up this information and displaying it incorrectly—it’s impossible for every station on the dial to have the exact same issue.
I am using the device connected to a computer, with an external antenna attached.
I’ve taken care to ensure there are no noise sources near the equipment; is there any way to resolve this? How should I proceed?
Posted by: Jan
« on: November 10, 2026, 06:18:53 pm »

You can find the relevant setting for the margin in the menu Options - Preferences - General.

Regarding your other question: Yes, the FCC once introduced the parameter "percentage modulation," which is still in use today. The FCC's concept of "percentage modulation" provides a convenient way to define and evaluate regulatory modulation limits. It does not establish a physical unit of frequency deviation, nor does it require measuring instruments to display frequency deviation in percentages instead of kHz.

Frequency deviation remains a physical quantity expressed in kHz, while percentage modulation is simply a derived, dimensionless value referenced to a specified frequency deviation (75 kHz in USA).

Since the P275 also provides advanced frequency deviation analysis, including deviation histograms, it is important to retain kHz as the fundamental unit of measurement throughout the instrument and the software. Replacing kHz with percentages would, for example, result in histograms x-axis expressed in percentages. While mathematically valid, this would be unnecessarily confusing and counterintuitive.

The FM Scope supports % in the FM deviation bar, you may toggle the unit by clicking on its scale.
Posted by: rafaelhol
« on: November 10, 2026, 05:46:29 pm »

That puts my mind at ease!

Regarding other observations, is it possible to display the measurements as a percentage rather than as a deviation value?

Another detail: would it be possible to extend the deviation error margin—currently at 5 kHz—to 7.5 kHz or 10 kHz? In my country, an error margin of up to 7.5 kHz is permitted (within a total of 82.5 kHz at 110%) for stations that use RDS.
Posted by: Jan
« on: November 10, 2026, 05:17:14 pm »

I have carefully examined the image you attached, but I do not see any problem. Although your device is an older model, that is not a factor in this case. The device includes a simple indicator for detecting unwanted AM modulation; however, this indicator only functions within a specific input voltage range (roughly 40 to 80 dBuV). It operated in the same way in the old firmware version. Therefore, your concern that the firmware update caused an issue is unfounded.

The official recommendation issued by the authorities for the minimum input voltage when measuring frequency deviation is 60 dBuV. In your case, you are nearly 30 dB below this recommendation.
Posted by: rafaelhol
« on: November 10, 2026, 05:02:06 pm »

Pira P275 FM Analyzer Firmware: 2.2F R3 (Issue with AM noise analysis and measurement)

After updating to the latest firmware (2.2F R3), the device no longer displays the AM noise level in the FM SCOPE V 1.7.8 software.

The system worked perfectly with the previous firmware version (2.1a R3).

What steps should I take to resolve this?

The signal level when acquiring data is 5/5.

Additionally, in my country, local regulations require modulation measurements to be expressed as a percentage—covering the pilot signal, RDS, and total modulation—rather than in frequency deviation (kHz). Could this conversion feature be added in a future firmware update? Furthermore, could support for the extended FM bands used in the Americas be included—specifically the 76–108 MHz range (used in South America), in addition to the standard 87–108 MHz range (used in North America)?

I look forward to a resolution!