Local RDS and FM modulation Parameter Measurements

[WHJ]

I just completed the firmware upgrade of my TEF6686 and TEF 6687 radios. They are up to the v2.11.27 revision, see:
(5) Discord | #updates | [FMDX.org] OpenRadio Community

There are two new readings:

1. US - Ultra-Sonic Noise
2. MP - Multipath

Multipath is from the same station arriving via multiple propagation paths. With the propagation delay not being the same via the different paths they do not combine well and hurt reception. Ultra-Sonic noise comes from neighboring channels and is measured from 80 – 150 kHz off the desired signal’s center frequency. CN (carrier to noise) appears to reference noise on a clear frequency. It does not take into account any interference, so it is possible to not understand a signal with a 10 dB CN figure. An old 2008 journal article by Fujitsu does a good job of detailing RDS, see:
Fujitsu RDS

Below is what a TEF6686 looks like after it has been updated. It starts showing what a local signal 34 miles away from me looks like with my 10 element Yagi pointed at it. It is followed by the same station with the antenna rotated 90˚. Notice the change in dBuV, CN, US and MP. It gets a lot worse for weak signals. At the bottom is what similar measurements are on my SI4743 tuner.

[WHJ]

Anyone looking closely at the parameters might have noticed my comment about KUCV's SCA audio being overmodulated. I thought that I'd provide some examples of how that is both seen and heard. Attached are recordings of both KHNE's and KUCV's SCA audio. Both have the same speaker on Radio Talking Book's programming. Here is the visual difference in the audio:


And below is how their MPX looks different:


Both stations are owned by Nebraska Public Media.

[Jim Thomas]

Even though I really like tech stuff, this is almost over my head. I guess it takes a REAL engineer to appreciate it. But I appreciate it also even though I'm not an engineer.

[WHJ]

I decided to get a PIRA P275R FM modulation monitor to better evaluate the local FM stations. For more information on it see: FM Broadcast Analyzer

It measures the FM modulation level, RBDS and pilot injection levels and a variety of related parameters. It is not meant to be a DX receiver. It needs to be wide band tuner for it to make accurate modulation measurements. An adjacent channel station getting close to the strength of the desired station or stronger will prevent accurate readings and often even reception. HD sidebands will prevent some parameter readings. I was curious on how the RDS injection level and phase readings compared to the ease of their being decoding.

I spent the past week logging the parameters on as many stations as possible. The following screen was referred to most often:

The pilot data can be quickly seen and any SCA can be spotted. Particularly for weaker signals, getting the correct input level is important. Too little might not be enough to obtain readings. Too much and interference and/or overload from a stronger nearby signal could do the same. I used a step attenuator to get the best reception as shown on the MPX spectrum display. I logged the SCA data and used my HD receivers to log the number of HD channels being transmitted as well as if they were also transmitting Artist Experience screens. While not a large number, there were more SCA’s found than expected. A few used it to provide readings to the studio site. An example of a Radio Talking Book SCA ID is attached. The above screen shows the recommended pilot parameters. And while the monitor provided the deviation levels in kHz, I converted them to percentages in my report since that’s how the FCC limits are defined.

Given the equipment limitations mentioned, I felt good in getting data on 83 different stations. My highly directional antennas helped. Incomplete data was obtained on a fair number of stations due to HD and other interference and/or too weak signals. For some of the stations I highlighted the missing measurement in yellow along with the likely cause. The HD evaluation was done just before the modulation monitor was received. There was a bit of a tropo opening then which made an HD reception possible while the later analog measurements were impossible. Due to a strong local station, two HD stations blended into a different analog station with changing propagation.

Two of the other modulation monitor screens are shown below as well as two more at the end of the report.



Now the measurements: