Over the years I have intentionally sought out some of the top performing FM tuners for DX work. With this context in mind, I was able to empirically determine if the bold claims regarding the Sony XDR-F1HDI FM DX performance were true. The ideal setup for testing tuner sensitivity/selectivity is to have a stable weak signal (signal generator, or low powered local). I choose to use a weak local Indian language pirate TX on 90.0 MHz. There are strong local adjacent FM signals on 89.9 and 90.1 MHz, hence this is an ideal situation for selectivity testing.

A standard Onkyo T-9090 II (5 x 150s) is completely swamped by 89.9 and 90.1 adjacent channels. Even the T-9090 II (with 4 x 110s) is unable to detect any trace of 90.0 MHz. I suggest that a modified Yamaha T-85 (with 5 x 110s) would not detect the 90.0 signal.

The modified R-8500 wide FM mode (using 2 x 110s) as expected is swamped by 89.9 and 90.1. It should be noted that the T-9090 II selectivity is miles ahead of the R-8500 (with 2 x 110s).

The Icom R-8500 (15 KHz nFM) is able to detect 90.0 MHz without any splash from 89.9 and 90.1. However, intelligibility is abysmal. I can only hear on/off modulation. I can't even tell if the modulation is mx or talk. In other words, I can only hear very weak slush. This of course precludes any form of identification.

The Onkyo T-4970 (with DYNAS) can't lock on to the 90.0 signal. The signal breaks up, hence there is no intelligibility.

The KT-6040 (with stock filters) is swamped by 89.9 and 90.1.

The KT-6040 (with 4 x 110s) is able to resolve the 90.0 signal with moderate levels of splash.

The KT-6040 (with 2 x 110s + 4 x 80s) is able to resolve the 90.0 signal with no adjacent channel splash from 89.9 and 90.1. Although moderately distorted, the intelligibility is just adequate, especially when the signal strength increases.

The Sony XDR-F1HD (stock DSP filter) is able to resolve the 90.0 signal with no adjacent channel splash from 89.9 and 90.1. Out of all the above tuners, the intelligibility is best on the XDR-F1HD.

With regards to selectivity / fidelity performance, the clear winners are the KT-6040 (80 KHz filter) and XDR-F1HD (stock DSP filter).

The KT-6040 (with 2 x 110s + 4 x 80s) is the ideal tuner for extremely weak scatter modes, (e.g. MS, AS, TS). The 110 KHz bandwidth is adequate for the stronger Es and tropo signals, but don't expect XDR-F1HD level selectivity.

The Sony XDR-F1HD (stock DSP filter) is the best tuner available for Es and tropo DX in congested areas (e.g. Europe, North America). The XDR-F1HD selectivity is equal to a modified KT-6040 (80 KHz bandwidth), but with much higher levels of intelligibility.

IMD Performance

In terms of filter ultimate rejection and general IMD performance, I rank the above tuners in the following order from worst to best:

Onkyo T-4970 (DYNAS DSP filter activated)
Onkyo T-9090 II (4 x 110 KHz filters)
Onkyo T-9090 II (stock 5 x 150 KHz filters)
Pioneer Supertuner IIID
Kenwood KT-6040 (4 x 80 KHz + 2 x 110 KHz filters)
Sony XDR-F1HD (stock DSP filter)

Potential Applications

Onkyo T-9090 II: good overall performer for general Es and tropo DX for DXers not exposed to excessively strong local transmitters. Best ergonomics and overall functionality. Two RF inputs automatically select the strongest signal by using the APR function, 25 KHz tuning steps, 3 IF bandwidths, switchable mute.

Pioneer Supertuner IIID: highest selectivity, sensitivity, and IMD performance of any car FM tuner. AM sensitivity/selectivity also above average compared to other car tuners.

Kenwood KT-6040 (modified with 4 x 80 KHz + 2 x 110 KHz filters): when used with MosFET or GaAsFET RF preamp, best tuner for extremely weak signal modes (aircraft scatter, meteor scatter). Low noise RF preamp + 80 KHz bandwidth equates to the highest sensitivity performance obtained on any tuner. Without preamp inline, RF sensitivity slightly down compared to the Onkyo T-9090 II / T-4970. The KT-6040 110 KHz wide FM selectivity somewhat better than T-9090 II 110 KHz selectivity. Relatively poor construction quality - more likely to develop technical fault compared to all tuners listed above. 80 KHz IF bandwidth audio quality relatively distorted - especially on pop/rock stations featuring wide deviation.

Onkyo T-4970 (DYNAS DSP filter activated): high sensitivity and selectivity combination performance for DXers who desire high fidelity audio response on DX signals. When listening 200 KHz below a local signal, selectivity performance is equal to the Sony XDR- F1HD. However, the DYNAS DSP asymmetrical filter response often means the T-4970 will have difficulty locking on to a DX signal above or in between the local signal(s). The T-4970 features two RF inputs, 25 KHz tuning steps, switchable mute. Applications include 100 KHz adjacent channel DX.

Sony XDR-F1HD (stock DSP filter): highest selectivity and IMD performance for any tuner available. Especially suitable for DXers who desire high fidelity audio response on DX signals, but with 82dB adjacent channel rejection. Applications include 100 KHz adjacent channel DX, and superior IMD immunity in very high RF areas. Without a preamp, the soft mute can sometimes mask extremely weak signals. However, having said that, the XDR-F1HD 50 dB quieting RF sensitivity is so low that most meteor scatter signals are readily received despite the soft mute. Threshold extension and adaptive noise reduction technology means that noise is 50 dB down for an unmodulated 13.5-dBf stereo signal. With low noise RF preamp added, the 50 dB quieting level is only ~ 1 uV. This means that weak signals rapidly increase to full quieting.

Low Noise Preamplifiers and the XDR-F1HD

At a quiet rural listening location, some sensitivity tests were conducted using three 88-108 MHz preamplifiers with the Sony XDR-F1HD. The results were as follows:

The ULNA 3013 88-108 MHz 0.3 dB NF 20 dB gain preamp was the best overall preamp in terms of noise performance. We all agreed the S/N improvement was significant when the ULNA 3013 was inserted inline with the Sony XDR-F1HD. Without a doubt this is the most sensitive tuner/preamplifier FM DX combination we have ever seen.

The Jim Dietrich UA-701 GaAsFET 40-230 MHz wideband preamp was the second overall performer which produced useful improvement on most signals.

My BF981 MosFET tunable 88-108 MHz home-constructed preamp was the third overall performer in terms of S/N improvement. The relatively low sensitivity improvement obtained with this preamp could be due to impedance mismatching on the input stage. IMD performance was best due to the high Q narrowband tuning. The BF981 preamp is not recommended for rural locations, but essential (for most) in metro/city locations.

So the ULNA 3013 is the overall best performer provided the preamp is operating in rural or semi-rural areas that feature minimal high power transmitters.

Sony XDR-S3HD

Performance wise, the Sony XDR-S3HD exactly matches the XDR-F1HD. However, in addition to a remote control unit, the XDR-S3HD also includes a rotary tuning dial and inbuilt speaker.

One Australian FM DXer reports that the XDR-S3HD features marginally higher sensitivity/selectivity performance compared to a modified Kenwood KT-6040 (4 x 80 KHz + 2 x 110 KHz filters).

Conclusion

With the introduction of the new Sony XDR-F1HD and XDR-S3HD DSP FM tuners, why bother with portable radios, ceramic IF filter mods, and most other tuners out there? There's no point trying to re-invent the wheel, just seek out the best DXers, take note of what they use, analyse why it works, and then model what they do.