Sony XDR-F1HD
The XDR-F1HD is Sony's first home HD Radio tuner. It receives all AM and FM HD Radio modes, including multicasts, as well as analog AM and FM. It does not receive C-QUAM AM stereo.
At 7" x 6.25" x 2.375", the tuner is much smaller than standard stereo components. It weighs just 2.4 lbs. The FM antenna input is a 75Ω F-connector, while the AM input accepts wires. The tuner comes with an AM loop and an FM dipole with F-connector. RCA jacks provide audio output. The captive two-wire line cord has a polarized plug.
The front panel has an LCD and a small power button. On top of the cabinet near the front are ten control buttons. The rear panel has an indented reset button activated with a pointed object. The tuner includes an infrared remote control. It requires two AAA batteries, not supplied.
The cabinet is made of rigid plastic. Perforated vents cover much of the bottom and span the top part of the rear panel. Louvered vents span the top surface at the rear. The tuner gets quite warm while operating, and it remains slightly warm in standby. Rated power consumption is 13 watts.
This compares the size of the XDR-F1HD with that of the Sangean HDT-1X.
Under the Hood
Five screws retain the top cover, which easily comes off. Inside is a power supply board, main motherboard, display board, and pushbutton board. All rectifiers in the power supply are bypassed. The board delivers 10.5 V and 5.2 V, both unregulated. A number of surface-mount components on the underside of the motherboard are visible through the bottom vents. All boards are well marked, with signals and test points identified. There are no adjustments. The power transformer was still too hot to touch ten minutes after removing the cover. The silkscreen identifies both pins of the transformer's internal fusible link. Should the link ever fail, it may be possible to substitute an external fuse. Puzzle: how are ten pushbuttons encoded onto just three wires?
Mounted vertically on the motherboard is a voltage regulator IC on a large heatsink and two shielded modules with no identifying marks. One module is the tuner and the other is the HD Radio module. The snap-on shields are soldered together in one or two spots. Derek Kumar cut the shields off his tuner module. Inside he found the Philips (now NXP) TEF6730/SAF7730 chipset.
Features
The XDR-F1HD tunes in 100-kHz steps on FM and 10-kHz steps on AM with the TUNE + and TUNE – buttons. Press SCAN to scan the band (up only) in 200-kHz steps on FM and 10-kHz steps on AM. The tuner pauses for three seconds at each signal found. Press ENTER to stop the scan. Press HD SCAN to exclude analog signals.
The TUNE buttons, also labeled SELECT, select a multicast channel. A thoughtful feature is the little LCD arrow that tells whether another channel exists. You don't need to risk blowing HD lock checking for HD-3.
The tuner provides 20 presets on FM and 20 on AM. Select one with the PRESET + and PRESET – buttons, which increment and decrement the preset number. There is no random preset access (except by remote control), nor is there direct frequency entry.
The tuner has a clock and a sleep timer. The clock retained its time when I moved the tuner from one room to another, but lost it when I left it unplugged for five minutes. The presets behaved the same way.
A menu lets you set LCD brightness to one of three levels, change LCD contrast, and set the clock. A display button switches between a screen that shows frequency and another that shows time. For RDS or HD Radio you can select a third screen that fills with transmit text, which only scrolls across a small window in the other screens. The tuner does not display music-genre or callsign RDS fields. The latter is a serious liability for DXing.
A signal-strength indicator shows zero to three bars. Successive bars appear at RF signal levels of 19, 29, and 38 dBf.
The XDR-F1HD does not display carrier-to-noise ratio, HD Radio station ID, HD Radio transmission mode, or firmware version. It does not have a stereo indicator. It does not provide forced mono, forced analog, split-audio mode, or digital output.
The control buttons respond quickly with no sluggishness.
The dimmest LCD setting is still too bright in a bedroom.
Analog FM
The XDR-F1HD uses adaptive noise reduction. This feature dramatically improves reception of stereo signals corrupted by noise and interference. The processor forms a filter that fits the spectrum of the detected audio, adapting the filter as the spectrum changes. The filter suppresses noise between and beyond spectral peaks without noticeably affecting signal quality or restricting signal bandwidth.
Unlike the HDT-1X, the XDR-F1HD does not unconditionally blend stereo to mono at low RF signal levels. The Sony can provide high stereo separation at signal levels below 20 dBf. The adaptive noise reduction may result in the blending of some lower-level sounds on certain noisy signals, but the effect is conditional, not fixed. The tuner can deliver a clean stereo signal with wide separation at far weaker signal levels than can any other tuner. The only thing remotely comparable is a Carver tuner with Asymmetrical Charge Coupled Detector.
The adaptive noise reduction very effectively suppresses weak-signal noise, co-channel interference, and multipath distortion. An unidentified process suppresses hiss from adjacent-channel HD Radio signals. The sound quality for slightly marginal to deeply compromised signals is strikingly better than that from other tuners. The performance of the Sony XDR-F1HD on stereo FM is spectacular and unprecedented.
This shows the right-channel response for a single-channel, 1-kHz tone at an RF level of 22 dBf. The horizontal scale is 200 Hz/div and the vertical scale is 10 dB/div. The shape of the adaptive filter that forms around the tone is evident from the noise hump, which is not quite centered on the tone.
This is the left-channel response. The noise has a pronounced narrowband sound quality. The hump follows the tone as its frequency changes. Above 1.2 kHz, the hump centers on the tone. Multiple tones cause multiple humps, and a complex signal spectrum acquires a filter adapted to its specific shape.
The adaptive noise reduction processes only the L-R stereo subchannel. A 1-kHz L-R test signal yields an audio level down about 17 dB from that for L, R, or L+R. Conventional tuners decode all four signals at the same level. Although antiphase L = -R signals do not naturally occur, I think the XDR-F1HD suppresses pure L-R simply as a consequence of the way it works, not as a special case. In fact, I suspect it attenuates L-R whenever |p| >> 1 or |p| << 1, where p = (L-R)/(L+R) is amplitude-induced sound position. p = 0 is centered sound, p = 1 is at the left speaker, while p = -1 is at the right. |p| > 1 implies a sound image beyond the speakers, which can occur for some program material. So far, I've noticed no loss of ambience or reverberation, which may have higher values of |p|.
The adaptive noise reduction seems remarkably well behaved. The only artifact I've noticed is for centered sound on very noisy stereo signals, signals that would otherwise be unlistenable. For some of these signals, low-level L-R noise may emerge from time to time from a quiet background. Summing the channels to mono inhibits the noise, although the XDR-F1HD provides no way to do this. The only image displacement I've noticed is for some lower-level sounds in certain noisy signals. The noise reduction algorithm seems to know when to stay out of the way. For strong, quiet, local signals I cannot distinguish the sound of the XDR-F1HD from that of a conventional tuner, except that the Sony occasionally suppresses a slight sibilant splash due to a touch of multipath.
In addition to the adaptive noise reduction on L-R, the XDR-F1HD begins to invoke a simple lowpass noise filter on L+R when the RF level drops below 25 dBf. The filter corner frequency drops with signal level. This filter is similar to the one in the HDT-1X, which begins at 29 dBf and whose corner levels off at 2.9 kHz. The Sony corner continues to drop past this point, the entire curve eventually falling with signal level. This seems intended to provide a continuous soft mute. With the antenna disconnected, output noise is 30 dB below the level of a 100%-modulated 1-kHz tone.
This shows the lowpass filter response in mono at 73 dBf and 16 dBf. The modulation is 15 preemphasized tones from 1 to 15 kHz. The level at 1 kHz has dropped 2 dB, and at 15 kHz it is down about 13 dB.
This is the response for left-channel stereo, which consists of equal parts L+R and L-R. 1 kHz has dropped 6 dB and the response is flatter. In fact, above 20 dBf the curve is almost completely flat, dropping mostly uniformly with signal level from 25 dBf to 20 dBf. The stereo response may be a combination of the lowpass filter operating on L+R and the adaptive noise reduction operating on L-R.
The lowpass filter is active only for signals with zero or one bar.
The tuner's ability to suppress hiss due to an adjacent-channel HD Radio signal is a mystery. It can do this even for monophonic audio (no adaptive noise reduction). The unwanted digital sideband overlaps the desired analog signal to within 2 kHz of channel center on one side. It can't be filtered away without taking half of the desired signal with it. A sufficiently complex algorithm might reconstruct the signal from the remaining sideband, which is in the clear. But I doubt the tuner attempts anything so daunting. Yet there is a night and day difference between the XDR-F1HD and other tuners in suppressing this interference. I don't have a good explanation.
For the following measurements I used IEEE 185-1975, modified as described here. I used the test equipment listed here.
Mono 50-dB quieting sensitivity 13.5 dBf Stereo 50-dB quieting sensitivity 13.5 dBf Mono THD, 1 kHz 0.07% Stereo THD, 1 kHz 0.055% Stereo separation, 1 kHz 54 dB Mono S/N, 65 dBf 70 dB Stereo S/N, 65 dBf 68 dB Capture ratio, 30 dB 1.1 dB Capture ratio, 50 dB 8.4 dB Capture ratio, stereo 30 dB 1.3 dB Capture ratio, stereo 50 dB 13.5 dB AM suppression ratio 80 dB Adjacent-channel selectivity 82 dB (noise limited) RF intermod 89 dBf (97.7 + 98.5 -> 96.9) RF spur 96 dBf (96.24 -> 96.9) Image rejection 74 dB (118.3 -> 96.9) Modulation acceptance 200% Stereo pilot injection for lock 3.5% Deemphasis error, mono +0.0/-2.2 dB Deemphasis error, stereo +0.0/-1.3 dB Bass response, -3 dB 19 Hz Output level 0.7 V Output impedance 2.2kΩ Latency 27 ms
The XDR-F1HD is the most sensitive tuner I've ever measured. This is partly due to the noise reduction provided by the lowpass filter. Also contributing may be threshold extension, an advanced technique used in high-performance satellite and terrestrial FM systems that mitigates the impulse noise caused by detection-vector phase reversal for weak signals.
The stereo sensitivity figure is not a typo. Noise is 50 dB down for an unmodulated 13.5-dBf stereo signal. Channel separation is still 26 dB. Background noise near the tone frequency does rise with modulation, as shown in the previous images, and a single tone does not entirely mask it. A conventional stereo sensitivity test really isn't appropriate for a tuner with adaptive noise reduction. Nevertheless, stereo reception of actual broadcast signals is an order of magnitude better with the XDR-F1HD than for the most sensitive conventional tuner.
The stereo THD figure is 13 dB lower than that for the Sangean HDT-1X.
The S/N figures are 5-6 dB worse than those of the HDT-1X. Neither tuner comes close to the best conventional designs, which exhibit S/N in the high 80s or low 90s. The low figures suggest that background noise might be audible on very quiet signals. So far, I have been unable to hear it.
Capture ratio (simplified IEEE definition) is how far below a 65-dBf unmodulated monophonic signal a 100%-modulated monophonic signal must be to obtain the specified quieting. Stereo capture ratio (no IEEE definition) is the same, with both signals in stereo. At 50 dB down, in stereo the XDR-F1HD can suppress a co-channel signal 19 dB stronger than one the HDT-1X can suppress. At my location this has a profound effect on reception quality for many signals.
The astronomical selectivity figure seems real. The XDR-F1HD is noticeably narrower than the superb Sangean HDT-1X, often retrieving listenable signals that are buried beneath adjacent-channel splatter or completely inaudible in the Sangean. The Sony's selectivity is more than 30 dB better than that of the best conventional tuner I've ever measured, one which cascaded one 150-kHz and two 110-kHz Murata ceramic filters.
RF intermod is the 50-dB quieting level for a third-order intermodulation product. This figure is 5 dB better than that for the HDT-1X. RF spur is the 50-dB quieting level for an untuned signal. It is 9 dB better than for the HDT-1X. Image rejection is 15 dB better than for the HDT-1X. These measurements were made in a way that sidesteps the phase-noise sidebands of the tuner and signal generators.
Modulation acceptance is the modulation level of a 1-kHz tone for 1% THD. The XDR-F1HD figure may seem like overkill since FCC rules limit stations to 100% modulation (110% with SCA). But one local PBS station with no SCA regularly deviates 140%. Another station just across the border in Mexico hits at least 170% on some peaks. These signals are impossible to receive cleanly on tuners with narrow ceramic filters. The XDR-F1HD has no problem with either signal.
Deemphasis error is for an IEEE load (100kΩ || 1000 pF). Sony recommends a load impedance greater than 10kΩ.
This is the left-channel deemphasis error. I don't know why the curves differ or why they are wavy.
This is the low-frequency response for preemphasized modulation.
This compares monophonic S/N curves for the XDR-F1HD and HDT-1X. S/N is the ratio of audio output levels for 100% 1-kHz modulation and no modulation. The sudden change in HDT-1X slope at 17 dBf marks its FM threshold. Here additive noise is large enough to begin to cause phase reversal, which the FM detector renders as high-amplitude spikes. Spike occurrence greatly increases as the signal level drops. The XDR-F1HD S/N curve shows a gradual change in slope with no threshold. (The XDR-F1HD data is for a second tuner that is slightly less sensitive than the one used for the test results reported above.)
This shows the S/N components and compares the audio presentation strategies at low signal levels. The HDT-1X signal level is nearly constant while the XDR-F1HD maintains a nearly constant noise level. The XDR-F1HD soft muting suppresses noise bursts during signal fades. But it makes DXing awkward when steady signals are weak enough to incur significant audio attenuation. 0 dB is the HDT-1X signal level at 23 dBf. The XDR-F1HD signal level there is 0.1 dB lower.
This is the distortion spectrum for 1-kHz, left-channel, stereo modulation deviated 75 kHz (9% pilot).
For a strong unmodulated test signal, I could hear a slight whine in the background noise with the volume turned way up. This image shows the audio output spectrum to 20 kHz using a 30-Hz analysis-filter bandwidth and postdetection smoothing. (The plot took 500 seconds to generate!) I think I was hearing the spike just above 3 kHz. Close examination reveals it to be at 3125 Hz and 78 dB below 100% modulation. I have yet to hear it in a broadcast signal. (If you look closely at the thicket between 13 and 14 kHz, you'll see that the curve traces out S O N Y in katakana. This must have been very difficult to accomplish even with DSP.)
At 63", the FM dipole supplied with the XDR-F1HD is rather long. Mounted in the clear about 6' above the floor, resonance occurred below the FM band at 85 MHz. Reducing the effective length with a piece of string as shown optimizes the response for 88-92 MHz. Slide the string until the horizontal wires are 3" above the mounting hole. This configuration reduces mismatch loss 0.3 dB at 88 MHz, 1.4 dB at 90 MHz, and 2.0 dB at 92 MHz.
Analog AM
The AM antenna is a 4" x 5" rotatable loop with eight single-layer turns. Its inductance is 21.3 µH and its Q is 83 at 1000 kHz. The loop exhibits two nulls in opposite directions at all frequencies, handling the loop does not increase signal strength, neither AM antenna terminal is marked as ground, and each terminal has a resistance of 1Ω to ground. All this suggests that the tuner provides a balanced AM antenna input, which can reduce local noise pickup. The usual unbalanced input causes a loop and its feedline to respond to the electric-field component of the electromagnetic wave as well as to the magnetic-field component it is designed for. The electric component is much stronger than the magnetic for nearby noise sources.
The wires from the loop are thin, stranded, untinned conductors. They seemed rather fragile when inserted into the pushdown antenna terminal clamps, which bent and separated the strands. I tinned the wires to make them more robust.
The operating instructions warn not to place the loop near the tuner as it may pick up noise. I noticed some low-level interference at the low end of the band, but it was easy to minimize by repositioning and reorienting the loop.
For AM measurements I connected a signal generator terminated in 50Ω between one antenna terminal and the shell of an RCA audio jack. Either terminal yielded the same sensitivity, confirming the input balance.
At 1500 kHz, the signal required for noise down 30 dB from a 90%-modulated 1-kHz tone was -93 dBm.
400-Hz THD at 30% modulation was 0.08%. It reached 0.14% only at -10 dBm, and the audio stayed clean all the way to 0 dBm. This is a much higher RF level than the Sangean HDT-1X tolerated without noticeable audio distortion.
This compares the frequency response of the XDR-F1HD and HDT-1X with the NRSC-1-A AM deemphasis standard. Ideally the red and blue curves should coincide with the green curve.
This is the output spectrum for a test signal consisting of 40 preemphasized tones from 250 Hz to 8 kHz. The horizontal scale is 1 kHz/div and the vertical scale is 10 dB/div. This plot confirms my listening impression that the XDR-F1HD severely rolls off the AM high-end.
Unlike the HDT-1X, the XDR-F1HD does not seem to dynamically vary its IF bandwidth on AM. It also does not seem to use a synchronous detector. I heard distortion on some skywave signals during selective fades.
AM latency is 3 ms.
HD Radio
The XDR-F1HD sounded and operated just like the HDT-1X on HD Radio signals. Except for one occasion when the Sony locked to an FM HD signal and the Sangean would not, their performance seemed exactly the same in all respects.
More is here.
Updated May 12, 2008
