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Frequently Asked Questions
Firmware update
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Frequently Asked Questions

Why to decide for the P275 measuring system?
There are several reasons:
  • The P275 was designed as an FM measuring system ab initio. The FM deviation and modulation power measurement is the main purpose of this device, it is not only an additional function.
  • The P275 provides not only the numeric values but also watches over necessary measuring conditions and measured values sense.
  • The P275 is not only a radio tuner, it includes DSP based computing unit, user interface and can work stand-alone.
  • The P275 uses a technique that does not require individual calibration of each device. This also ensures that influences like time, temperature or humidity have no effect on the output values. If precise FM deviation and modulation power measurement is what you really want, the P275 may save more than 80 % of costs.
  • The P275 includes serial RS-232 interface which can provide long distance connection and can be easily converted to any other industrial or consumer bus (such as RS422, Ethernet etc.).
  • The P275 communication protocol is public and simple to use, allowing writing own control application for the device.
Can I use the analyzer as a portable DX receiver? Can I use the analyzer as a rebroadcast receiver?

Sorry, you can't. The P275 is primarily a measuring instrument, not a DX nor rebroadcast receiver. We underline that the P275 is not intended for hobby purposes. For full clearness the following table is provided:

The P275 is: The P275 is not:
Stand-alone measuring instrument,
FM modulation analyzer,
Radio Data System analyzer.
DX receiver, Rebroadcast receiver,
Streaming receiver, Radio scanner,
RF power meter, Coverage analyzer.
Can I buy the P275 from my local distributor?

The P275 is available only via our direct shipping service. We do not support resellers for this product. The device is not available within any distribution network.

Is there a possibility to output a composite (MPX) signal?
No, this is unfortunately not possible as demodulated MPX signal is not available anywhere on the device's board. Unlike standard receiver there's no analogue FM demodulator present. Characteristics of the MPX signal are accessible through the software.
Is it possible to show MPX voltage directly in kHz?

In MPX input mode, the P275 measures input voltage in volts peak-to-peak and in dBu as rms value (averaged over last 1 minute). The device also shows peak-to-peak voltage for pilot tone component and RDS subcarrier.

There's however no approachable technical solution how to calculate FM deviation in kHz from the MPX voltage. The kHz unit describes the signal behind the FM modulation but the MPX is taken prior to the FM modulation.

Unlike conventional ideas there's not a direct proportion between the MPX voltage and resulting FM deviation and this proportion has never been standardized. An approximation can be theoretically made if knowing all characteristics of particular FM transmitter (voltage sensitivity, input frequency characteristics, step response, sub-acoustic characteristics etc.) but applying such a method loses meaning for its difficulty and limited portability. It is much easier to connect the MPX to the FM transmitter and read the real FM characteristics from the RF output signal.

A simple estimation can be made if knowing particular transmitter's FM modulator sensitivity and multiplying the MPX voltage by such a constant. The CEPT/ERC REC 54-01 E however requires Ī2 kHz accuracy for FM deviation. Accuracy of the method proposed is 10 times worse, depending on what STL or transmitter you'll finally use. What can work well for a single sine tone may fail for the real MPX signal. For example older transmitters generate much higher deviation for the same input MPX and the same input adjustment, due to unstable PLL loop at sub-acoustic frequencies. Thus, that method is not applicable for the measuring purposes.

The FM deviation is a characteristic of particular FM transmitter rather than MPX voltage.

Would the P275 be suitable for our purposes?
Follow our Technical Forum or email and consult your application with us before buy!
How is the FM deviation measurement internally implemented?

Entire measurement is made inside the DSP. There's no analogue demodulator, the signal characteristics are measured directly in frequency domain, without conversion to voltage. There's also no AC coupling so square wave modulation signal keeps its shape. Accuracy of the FM deviation measurement is comparable to the top products from the branch.

The P275 measures the deviation in 50 ms intervals (without gaps) strictly using the formula:

ΔF = Max (Fcar-Fmin, Fmax-Fcar)


Fmin and Fmax is reciprocal of the maximum and minimum period detected in the IF signal corrected by inverse sinc low-pass filter,
Fcar is carrier frequency (average frequency) counted per last 2 seconds.

Signal reception quality is monitored simultaneously. Depending on many criteria an additional correction may be applied on the values or some values may be discarded.

Can I connect test RF output from my transmitter directly to the analyzer?

Such output is primarily not intended for modulation characteristics measurement using an analyzer based on a receiver as the P275 is. In most cases it can be used for this purpose but this usually does not carry any advantage. Special care is required before connecting the analyzer to this output. Make sure the output signal power does not exceed 20 mW (13 dBm) for the P275 or 5 mW (7 dBm) for the P75/P175. In some cases the test RF output gives 30 dBm (1 W) or more. This signal must be attenuated before connecting to the analyzer.

Sometimes it is better not to use the test output and get the signal "from air". The modulation characteristics are not affected in near field. Another recommended way is to connect only the transmitter's and analyzer's ground (shielding).

On the transmitter sites where many transmitters are operating the user may be forced to find one of the methods mentioned that gives full quality result. Itís due to intermodulations caused by many strong signals and their harmonics that are present in this environment.

What is the best antenna for the analyzer?

There is no generally valid choice for the antenna. The device comes with no antenna enclosed. The requirements for the antenna differ with local conditions and kind of use. The essential condition for the measurement is enough signal level of the desired station on the antenna input. Not all signals that you can listen on any radio receiver can be also measured. Itís possible to say that optimal signal strength range for full measurement coincides with the range which is required for high quality stereo reception. From this observation it's clear that simple telescopic or whip antennas are not enough for some applications. On the other hand special calibrated antennas for EMI and RF field applications have no reason for FM modulation measurements.

In the transmitter's near field (up to 1 km distance from the transmitter) any piece of wire connected to the antenna input should be always sufficient. When measuring other than only local stations or where number of stations reaches a couple of tens, a single dipole or 3-element Yagi antenna will give considerably better results than simple telescopic or whip antenna. In many cases this kind of antenna must allow positioning in horizontal plane.

Always make sure there is no pulse interference source near the antenna. These sources especially include computers, cars, electric motors, PWM regulators, high voltage lines etc. Assure stable antenna position during the measurement. Especially the frequency deviation should not be measured in motion like in ridden car.

What is a recommended portable telescopic BNC antena for the P275?
We offer a suitable basic telescopic antenna in limited quantity as an optional accessories. From commercially available products search your favourite locations for "Comet CH-99" or "DIAMOND RH-795" or "BNC Antenna Q9 765mm". In general, the antenna shall be at least 75 cm long for appropriate sensitivity of entire equipment.
What are the differences between the P275 and P175 analyzers?

P275 vs. P175: The P275 is backward compatible at the software level. The differences are due to slightly redesigned RF section and using a new generation of the DSP.

  • Frequency range extended down to 76 MHz (64 MHz with reduced sensitivity)
  • Accepts RF input power up to 20 mW
  • Accepts also baseband MPX signal on the input
  • Lower operating current
  • 2-channel audio output
  • Only one operating mode that includes all the measurements, RDS decoding and stereo decoding
  • Much more CPU power and memory space for future upgrades
  • No adjusting element on the board, all parts have fixed value incl. RF coils
How to access the USB port in the P275?
Follow the simple steps from the Software section. After installing USB drivers the device will appear as a new serial COM port in the system so can be easily accessed by any application.
Can I connect the P275 to internet?
The P275E product variant supports the Ethernet connection directly. The control software supports remote control as well. For other product variants the connection can be realized via remote PC or using any commercially available Ethernet-to-RS232 converter. The software also integrates a simple web server and its scripting engine includes MySQL client, FTP upload etc.
Does the P275 work properly on stations that include SCA channels or HD Radio carriers?

The P275 works correctly in presence of 67 kHz SCA channel. The device however does not indicate any characteristics of that channel.

The HD Radio (IBOC FM) spectrums partially overlap with the original FM channel. That overlap is almost inaudible but makes impossible to measure the FM parameters in the required (full bandwidth) quality. The P275 detects increased noise floor and hides the values which are potentially affected. For adjusting or measuring the FM parameters, the HD Radio channels must be temporarily switched off.

Firmware update

Select the product:  

Download here: (version 2.2c, released on 25.04.2024)

To finish the update, follow the text included and the pdf manual instructions.


  • Version 2.2c
    MPX spectrum FFT added
    ?D command now returns also RT+
    Improved RDS reception (reduced BER by ~10 %)
    Added support for another P275 device variant
  • Version 2.2b r6
    Added support for analogue output setup via serial line (requires FM Scope 1.6.1 or later)
  • Version 2.2b r5
    RDS PI on page 6 blinks if no RDS is being received
    RDS RT+ class names added to Page Context - More RDS Data
  • Version 2.2b r3
    RDS output to LCD: characters 128-254 converted to basic character set for correct reading on all types of LCD
    RDS static PS filter improved
    Bug fixes: Max Hold, MPX mode signal clipping, MPX mode RDS level
    Support for silicon revision A4 added
  • Version 2.2b
    Improved S/N and channel separation of audio output, configurable deemphasis added.
    Improved RDS reception and RDS level measurement.
    10 MHz REF input added (J3 pin 3) for precise RF carrier frequency measurement (not applicable for boxed version).
    Active power supply ripple suppressor added.
    115200 bps communication speed with autobaud support added.
    Support for high resolution MPX FFT added.
    New ASCII commands added: ?s, ?c, ?f, *B, *b
    RDS TA can drive any alarm pin.
    Many small improvements made.
  • Version 2.1a
    Enhanced menu system implemented.
    Pos/Neg indication added (Page 1 - Main Menu - Page Context - Show Peaks).
    "DIP Switches" added to the menu.
    Configurable source/load impedance for MPX input voltage calculation.
  • Version 2.1
    First public release.

Download here: (version 1.5 r2, released on 10.01.2015)

To finish the update, follow the text included and the pdf manual instructions.


  • Version 1.5
    Added support for showing fast peak deviation bar indicator in the control software.
    Pm rounding error suppressed.
    Bug fixes: ?h, -0.0 and some more.
    Added support for SSD1803-based LCD.
  • Version 1.4
    Alarm outputs may be used as independent general purpose outputs (P175).
    Modulation power estimation is now showed immediately after tuning to a new station and becomes exact after elapsing the 1 minute period.
    Modulation power low quality signal correction added. Value is now exact up to Noise of 50.
    Deviation histogram now shows also percentual values.
    Audio output: optional noise cancellation (squelch) added for measuring mode.
  • Version 1.3c
    Deviation MAX: interference filtering added.
    LED bargraph support added.
    Alarm outputs user configurable (P175).
    A lot of small improvements made.
  • Version 1.3b
    Support for the new P175 hardware added.
    RDS/RBDS decoder: RT+ decoding added.
  • Version 1.3a
    RDS/RBDS decoder: Optimized RDS reception.
    RDS/RBDS decoder: ODA AID decoding added.
    Low battery indicator added.
    10 sec. MAX hold function added.
    Small improvements made.
  • Version 1.3
    Raw MPX data readable via RS232, allowing oscilloscope and FFT functions in the control software.
    RDS decoder: Group order and Group content viewers added.
    Menu: Scan and Set as Normal items added
    Control buttons: Up/Down directions inverted in some situations.
    DIP switches function added.
    A lot of small improvements made.
  • Version 1.2b
    Baseband frequency response flatness specified and guaranteed.
    A lot of small improvements made.
  • Version 1.2a
    RDS/RBDS decoder: Some features added.
    Some small improvements made.
  • Version 1.2
    RDS/RBDS decoder added.
    Deviation histogram range expanded to 0-121 kHz.
    Many small improvements made.
  • Version 1.1a
    Expanded dynamic range of bandscan feature.
    Some small improvements made.
  • Version 1.1
    Stereo decoder added.
    Volume control added to menu.
    Deviation histogram range expanded.
    Many small improvements made.
  • Version 1.0c
    First public release.
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