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FM Reference 25th Anniversary

Read the latest Stereophile Magazine review.

Overview. The Signature Upgrade is designed to breathe new life into every DaySequerra FM Reference by addressing head-on the two major challenges facing the 25 year-old high performance analog design:

  • Limited life expectancy of its cathode-ray tube (CRT) display used for tuning and

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  • Reduced signal-to-noise performance caused by HD RadioTM  OFDM sideband interference, commonly called HD Radio “self-noise”.

Other electronic components typically affected by old age, such as power supply electrolytic capacitors and incandescent bulbs, are also replaced with more modern solutions to extend the FM Reference’s useful life.

Click here for Owners' Comments on the FMR 25 Upgrade.

TFT to the Rescue. To replace the decades-old CRT display, DaySequerra engineers developed a synthesized VHDL file to configure a Xilinx Spartan 6TM Field Programmable Gate Array (FPGA). The analog IF and audio signals are digitized using a 64X oversampling TI Burr-Brown 24-bit, 96 KHz A-D converter; the FPGA then processes each respectively to provide the Tuning and Audio Vector displays. The user-selected display is output to high contrast 480 by 272 pixel ruggedized TFT display with a fast 20 mS response time.

The resultant front panel display has more contrast than the original CRT and its blue trace compliments the DaySequerra timeless industrial design.

Another benefit to eliminating the CRT is a substantial reduction in internal heat and electrical noise on the ground plane caused by the original high-voltage CRT drive circuitry.

HD Radio – Analog Radio Interference. HD Radio was approved by the Federal Communications Commission in October, 2002, as the only system for digital AM and FM broadcasting in the United States. HD Radio In-Band On-Channel (IBOC) technology is developed and licensed by iBiquity Digital Corporation, and HD Radio broadcasts are available subscription free but require specially designed HD Radio enabled receivers.

One negative side-effect of HD Radio IBOC broadcasting is an increase in the analog FM stereo noise floor caused by IBOC Orthogonal Frequency Division Multiplex (OFDM) sidebands; this is known in the industry as HD Radio “self-noise.” HD Radio self-noise negatively affects the performance of almost all analog radios in the U.S.

Stop. Here’s a message from our Legal Department.

1]. The term “HD” in HD Radio does not stand for “high definition” rather it relates to “hybrid digital” technology used in HD Radio.

2]. DaySequerra is the leading provider of modulation monitors and confidence monitors to AM and FM HD Radio broadcasters in the U.S.

3]. DaySequerra’s founder, David Day, speaking most recently at the National Association of Broadcasters Show in April, 2013, said, “Taken as a whole, HD Radio delivers incredible dynamic range with a vanishingly-low noise floor. The HD Radio lossy-codec is quite good; and while not as transparent as the best closed-circuit analog FM broadcasts, its real-world performance and feature-rich user experience outweighs its shortcomings, and moves broadcast radio into the internet age.”

HD Radio… continued. HD Radio IBOC “hybrid digital” technology used today provides the analog FM stream on the same center frequency as before but with IBOC OFDM digital sidebands on either side of the analog broadcast.


Here is screen capture of a real-world HD Radio FM broadcast:

HD Radio unique features include: Additional digital-only local FM multicast channels e.g. HD2/HD3 Channels; PSD - Program Service Data, which displays song title and artist name on the radio screen; iTunes Tagging which allows listeners to store song information with the touch of a button for later purchase and download through iTunes; Artist Experience which enables images that match the audio content to be displayed on the radio screen; and subscription-free traffic and data information sent directly to your car’s display radio or navigation system. 

As of April 2013, there were over 2,200 AM and FM stations broadcasting HD Radio in the U.S, meaning there are HD Radio stations on-the-air in every major U.S. market.

HD Radio Self-noise. As stated earlier, HD Radio self-noise and increased IBOC power provide for a lively dialog in the industry; read more here and here. Simply put, HD Radio self-noise substantially increases the FM analog stereo noise floor; this is caused primarily by the linear sum and intermodulation of the FM analog FM L+R (sum) L-R (difference) signals and IBOC OFDM sidebands. In most high-quality FM receivers, this means more than a 40 dB increase in stereo noise floor.

In the DaySequerra FM Reference in Wide IF Bandwidth mode this means a substantially decreased SNR: from -75 dB to -25 dB, meaning continuous hiss and white noise on every HD Radio FM station and on most analog FM stations adjacent to an FM HD Radio station.

Back to Basics. Luckily for DaySequerra, the solution to HD Radio self-noise in the 25-year old FM Reference design was fairly straightforward and has almost no side effects: a post-FM demodulation filter designed to remove noise energy starting at 53 KHz and above.

As illustrated below, if the post demodulation filter removes most noise energy above 99 KHz, there will not be any noise energy to translate into the audio band by the FM Reference’s stereo decoder. The challenge here, however, was to preserve the L-R response so that stereo separation was not negatively affected while eliminating the noise above 99 KHz. DaySequerra’s engineers employed a 7th order elliptical filter to maximize the attenuation of noise outside the pass band while minimizing group delay variation.


Recently upgraded FM Reference units have measured SNR of better than -78 dB (3 dB improvement over 25 years ago) and stereo separation of better than 50 dB – equal to pre-upgrade performance.

Other Improvements. The FM Reference Signature Upgrade includes a few other improvements as well: new hand-matched JFETs are installed in the IF filter amplifiers and in the input buffer for the Class-A biased audio outputs. Also, key electronic components typically affected by old age such as power supply electrolytic capacitors, are replaced. All incandescent bulbs are replaced with LED indicators.

Call 856-719-9900 or email sales@daysequerra.com to schedule your FM Reference for the FMR 25 Signature Upgrade.  Older FM Studio units can be updated to FMR 25 Signature Upgrade.


Unfortunately, FM Reference Panalyzer and original Sequerra Model One units cannot be upgraded.


There is a one year limited warranty on each FMR 25 Signature Upgrade unit, even covering the parts that are 25-years old. 

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