高灵敏度外网介绍。


83 24-07-01 21:35


The Kenwood KT-6040 is potentially one of the most selective non-RDS FM tuners. This is mainly due to the KT-6040's series of eight filters. For example, here is the author's preferred filter combination for fringe DX work:

Wide: two SFE10.7MHY 110 KHz filters.
Normal: three SFE10.7MHY 110 KHz filters.
Narrow: four SFE10.7MT 80 KHz filters + two SFE10.7MHY 110 KHz filters.

Wide: CF1 (110) + CF2 (110).
Normal: CF1 (110) + CF3 (110) + CF4 (110).
Narrow: CF5 (80) + CF6 (80) + CF7 (80) + CF8 (80) + CF3 (110) + CF4 (110).

Installing Murata SFE10.7MF 50 KHz filters in the KT-6040 is not recommended. Several tests indicated that SFE10.7MF filters introduced excessive distortion, but with no apparent selectivity advantage.

As one progressively selects from wide to narrow IF bandwidth, more of the KT-6040's filters are switched in-line, so in the narrow position there are six filters in series, thus producing very steep skirt selectivity.

Preliminary tests indicate that unmodified KT-6040 (European version) and Onkyo T-9090 II tuners both have similar selectivity and RF image rejection. Once modified, the KT-6040's 80 KHz narrow selectivity is clearly superior to the T-9090 II's selectivity (four Murata 110 KHz filters).

When the 80 KHz filters are switched in, the KT-6040's weak signal sensitivity is high. The high sensitivity is probably mainly due to the KT-6040's 3SK121 GaAsFET first RF amplifier.

The KT-6040's selectivity is superior compared to all other tuners so far tested at my location. One example is how the KT-6040 is able to resolve weak daily aircraft scatter signals from 96.7 MHz 3ABC-FM Taralgon, VIC (407 miles / 655 km) - audio sample. The Onkyo T-9090 II (four 110 KHz filters) is unable to resolve 96.7 3ABC-FM. This is largely because of the adjacent 96.9 MHz 150 kw local (6km) Nova-FM signal.

Murata filters tend to have a slightly degraded selectivity curve on the high side of adjacent unwanted signals. This is also true for the KT-6040's 80 KHz filters. However, daily meteor scatter reception of 105.9 MHz 3ABC-FM Melbourne and 3ABC-RN Mildura next to local 150 kw 105.7 MHz 2JJJ-FM is not possible on any of my tuners, except the KT-6040 (80 KHz wide FM) and Icom R-8500 (15 KHz narrow FM).

One experienced UK DXer reports that the KT-6040 was more selective against adjacent channel QRM and thus allowing clear audio through from a weak signal that was only 100 kHz away from a 70+dB local station.

One potential problem with some KT-6040 tuners is a sluggish tuning dial response. This problem is thought to be caused by cheap encoders.

European, U.K., and Australian versions of the KT-6040 are indicated as having marginall higher usable (DIN) sensitivity (0.7 uV mono) compared to the general market Canadian and U.S.A. versions (0.95 uV mono).

For European FM DXers seeking very high 100 KHz adjacent selectivity, a KT-6040, modified with 80 and 110 KHz Murata ceramic filters, is probably the best option.

In 1991-92 the KT-6040 was officially released in Europe, Australia, and Canada. The KT-6040 isn't usually available second-hand in Australia. However, the KT-6040 appears fairly frequently on eBay Germany. Prices range from approximately 60-150 Euros.

RDS connection to a Conrad unit

The multiplex output (for the RDS signal) is available at TP4 (earth ground at TP5). TP4 is at the output of IC7-2/2.

Kenwood KT-6040 AM/FM tuner specifications (unmodified)

Rotary tuning dial.
25 kHz tuning steps
Eight IF filters
Tuning range: 87.50 - 108.00 MHz

FM SECTION
50 dB Quieting Sensitivity
Mono - 15.3 dBf
Stereo - 37.2 dBf
Usable Sensitivity (DIN at 75 Ohm)
Mono: 0.7µV
Stereo: 25 µV
Selectivity (unmodified)
(DIN +/-300 kHz 80 dB (NORMAL))
(DIN +/-200 kHz 80 dB (NARROW))
Image Rejection Ratio (at 98 MHz)
90 dB
IF Rejection Ratio (at 98 MHz)
110 dB
Spurious Response Ratio (at 98 MHz)
100 dB
AM Suppression Ratio
68 dB
Signal to Noise Ratio (DIN weighed at 1 kHz)
Mono - 83 dB (85.2 dBf input)
Stereo - 76 dB (85.2 dBf input)

举报
举报主题
相关跟贴

回复