Thursday, August 30, 2012

Using Arbitron To Determine Station Format

When DXing, it's often helpful to know the broadcast format of stations on frequency for identification purposes. I recently had the case where I was DXing at a remote site on 1470 KHz up along the Canadian border. Two stations were down at the noise level, one slightly above the other. The stronger one was broadcasting in country music format, the other undetermined. I couldn't quite catch a call sign.

When I got home it was a simple matter to check the Arbitron data on the two possibilities and determine which one I heard. It turned out it was WPDM-1470, out of Potsdam, NY. The weaker station was WNYY-1470 out of Ithaca, NY. The Potsdam catch was the better of the two, and at lower power too. I would not have been able to determine this without the ability to check station formats.

I've covered the availability of station lists for mediumwave DXers in two previous articles on RADIO-TIMETRAVELLER, Mediumwave Station Reference Lists and Mediumwave DX Meets The Tablet Computer. Many of these lists don't document station formats. Those that do may be out of date, or incomplete. And that's just for US data - information for Canada is even more suspect. This is not surprising considering the frequency at which stations change formats.

Those lists that do document station formats are Lee Freshwater's AM Logbook (perhaps the most complete), Topaz Designs, and presumedly the National Radio Club's AM Radio Log (though at a steep price - currently $28.95 for non-members and out of print). radio-locator - technically not a list site, but you can generate a list from this link using search parameters - will also provide a nice custom list of stations which includes format information. It seems fairly complete.

Virtually all US and Canadian stations subscribe to Arbitron. Arbitron, of Columbia, MD, is an international media and marketing research firm serving all types of media — radio, television, cable, etc. It is Arbitron's business to measure network and local market radio audiences across the United States, survey the retail, media and product patterns of U.S. consumers, and provide measurement and analytics. This includes, of course, what formats stations are using. It is probably the most up-to-date format reference of all.

The Arbitron Radio Station Information Profiles (SIPs) contain information about all radio stations in the United States: current addresses, station names (including call letters), frequencies and formats. Many if not virtually all Canadian stations are also represented in the profiles.

So how do we use Arbitron to identify station formats? Though the Station Information Profile used to be made directly available on their web site, lately the link has been moved to a members only site, My Arbitron. However, still buried deep within the Arbitron's main web site are a couple of links which can get us our needed information.

Stations are asked to update their Arbitron reference data four times per year. This goes into a seasonal "survey". We must take an educated guess of the current season on file that we wish to extract information from. Survey codes are:

  • WI (winter)
  • SP (spring)
  • SU (summer), noted as SU12 in the example (12 = current year, 2012)
  • FA (fall)

Using the call letters of the station, compose a link for the AM broadcast service as such:

Note the use of the surveyID=SU12 (summer of 2012), and callLetter=WHAM fields. You can also check FM stations by substituting the band=fm field.

A station search page is accessible as well, if you know the current survey season and date:

Old surveys do not seem to be accessible. Use the current season and year, or sometimes the season just past if the current season is not yet up for inspection.

Keep trying with your link until you have success. I have found the Arbitron site to be quite busy at times. During busy periods, it also may return a "survey not found" message. Persistence is good.

Thursday, August 2, 2012

The Silicon Labs 477x Chip - A New DSP DX Champ?

Silicon Labs recently released a new "high performance" consumer electronics broadcast radio receiver DSP chip, the Si4770/77 A20 (477x) series. What makes this chip special or any better than the familiar Si4734 chip used in the Tecsun PL-380, PL-310, and other consumer DSP-based receivers? I recently downloaded the spec and programming sheets on the new Si477x series and had a look. This chip set has some interesting new features.

A Sensitivity Boost

One thing was immediately apparent: the new chip has received a sensitivity boost. Where the old Si4734 chip's AM sensitivity was pegged at 25µV (27.9dBµV), the Si477x's comes in at 14µV (22.9dBµV). AM adjacent channel (±9 KHz) rejection for the new chip is 62dB, alternate channel (±18 KHz) is 62dB. AM image rejection is 72dB. Impressive figures for a chip radio.

FM sensitivity has also improved from 1.1µV (Si4734) to 0.66µV (-3.5 dBµV, Si477x). Selectivity is pegged at 65dB at ±100 KHz and 72dB at ±200 KHz frequency offset.

Bandwidth Options Galore

The old Si4734 chip had 7 programmable bandwidth options, the ability to set AM IF bandwidth at various widths from 1 - 6 KHz. Five AM bandwidths were implemented in the Tecsun PL-380: 1, 2, 3, 4, and 6 KHz. The Si477x chip enters with what Silicon Labs is calling "Dynamic AM/FM channel bandwidth control". The AM and FM IF channel bandwidths are dynamically optimized according to the on-channel RSSI (signal strength), and with the ability to further refine bandwidth by detection of the adjacent and alternate channel RSSI. Channel filter bandwidth is programmatically settable from 0 Hz to 15 KHz in 100 Hz steps for both AM and FM. Further, automatic bandwidth selection can be triggered not only by RSSI, but by signal to noise ratio. It can also be hard set to a fixed width by software. This could present some interesting possibilities if full user control is ever implemented in a consumer device.

Uh-oh, Soft Mute Again

Once again, programmable audio soft mute is implemented in the new chip. Soft-mute, a further lowering of the audio level of the received signal when it drops below a prescribed strength, is undoubtedly meant to provide a more comfortable listening experience for the casual listener and not the DXer. The idea is to relieve the listener from all that nasty low level "static" and "interference", or as Silicon Labs states: " attenuate the audio outputs and minimize audible noise in compromised signal conditions." Soft mute attenuation in the Si477x is available in 0-31dB steps (default is 12dB of attenuation, unfortunately twice the amount of the Si4734), and can be triggered at a pre-programmed S/N ratio (default is 8dB, the Si4734 was 3dB).

New Audio Bandpass Filters

Silicon Labs has deemed these "Hi-cut" and "Lo-cut" filters. The AM hi-cut control is employed on AM audio outputs having degradation of signal quality. Signal strength and signal-to-noise ratio thresholds can be programmatically set to activate the filters. The Hi-cut filter can be disabled by setting the Hi-cut filter  margin to the default audio bandwidth for AM. AM Lo-cut is employed on audio outputs for rejection of power-supply 50/60 Hz interference. AM Lo-cut is a high pass filter, and is enabled by default and can be disabled by programming. Note that the Lo-cut filter is not available for FM.

HD Radio

For HD Radio (IBOC) buffs, the Si4777 model of this chip series has AM/FM HD Radio capabilities. Additionally, an interesting innovation has been added called "IBOC Blend". This feature supports the ability to blend between analog and digital audio. When the bit error rate of the HD Radio digital signal falls below a predefined threshold and the digital audio fades out, the analog audio is blended in. This prevents the received audio from muting when the digital signal is lost. The audio will "blend to digital" upon reacquisition of the digital signal.

It will be interesting to see if the HD version of the Si477x chip is incorporated in any new, portable consumer electronics device. Car radio seems to be the only outlet anymore for HD Radio, which may die on the vine in the end anyway.

Improved Inductance Handling

Usable antenna inductance has expanded somewhat from 180-450µH to 180-540µH, though the documentation does show the chip capable of maintaining tuning up to a 688µH inductor. Again, like the Si4734, the chip is adaptable to an external air loop antenna if a ferrite rod is not used. An air loop antenna is supported by using a transformer to increase the effective inductance of the air loop. Using a 1:5 turn ratio inductor, the inductance is increased by 25 times and easily supports all typical AM air loop antennas which generally vary between 10 and 20µH.

Frequency Coverage Suffers

Unfortunately, shortwave and longwave band coverage are not available, unlike the Si4734. FM range is 64 MHz - 108 MHz. AM range is 520 KHz - 1710 KHz, at 9 or 10 KHz channel spacing.


The Si477x is Silicon Labs' cutting edge consumer electronics broadcast AM/FM receiver radio chip. It brings us higher sensitivity for both AM and FM. IF Bandwidth is now dynamically set dependent on signal conditions, using primary, adjacent, and alternate channel signal information. Soft mute is still in force, and is even more heavy handed when left to its default settings. New high and low audio bandpass filters shape the audio signal and are dynamically set by signal conditions. HD Radio for both AM and FM is made available in one version of the chip series. Finally, ferrite loopstick inductance range is expanded.

It is likely that consumer grade AM/FM radios using this chip will stick with default settings for bandwidth and soft mute, basically rendering the increased sensitivity and enhanced DX capability of this radio chip nearly moot. Opening up the myriad bandwidth options to manual selection, allowing soft mute to be manually controlled, and further, allowing the audio bandpass filters to be manually controlled would render this a nice DX machine for both AM and FM.

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