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TS-590S RX Auxiliary Circuits | Radioaficion Ham Radio

TS-590S RX Auxiliary Circuits

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Typical built-in RX auxiliary circuits include the variable pass bandwidth circuit, notch filter and noise blanker (NB). In modern HF transceivers, most of these auxiliary circuits (=auxiliary functions) are made possible by an arithmetic process of the DSP. As well as the TS-590S, only two auxiliary circuits operate genuinely at the IF stage: NB and AGC (ATT circuit that functions by receiving the control signal provided by the DSP).

On the TS-590S, there are two methods available to achieve noise blanking: NB1 and NB2. NB1 is realized by analog processing and NB2 by digital processing of the IF DSP. Still retaining an analog noise blanker, TS-590S may seem out of step with the times. But it is critical to have an analog noise blanker for a receiving system design using narrow roofing filters.

Noise is typically pulse-shaped and when the noise passes a narrow filter, the pulse waveform is changed to have a wider (longer) pulse width.

Within the DSP, the processing block of the noise blanker is placed in a stage earlier than the filter block that determines the final pass bandwidth. Thus, even if the final pass bandwidth is narrowed, the blanking operation can work properly, free of the influence of the narrowed bandwidth.

However, roofing filters are located far earlier than the DSP, in the later stage of the first mixer. As a result, in the event the bandwidth of the roofing filter becomes as narrow as 500 Hz, the pulse width becomes wider and a conventional digital noise blanker would not deliver a sufficient blanking effect.

This is the exact case while down conversion is active on the TS-590S and a digital noise blanker alone may not produce a great enough effect. That is the reason we have placed a filter of pass bandwidth 6 kHz right after the first mixer. The filter deters the transformation of the pulse shape and prevents false operation of the noise blanker due to adjacent signals while sending the noise signals to the analog noise blanker.

During the up conversion, the noise signal is derived from the second IF stage and delivered to the noise blanker circuit as in previous models.

Hints and Tips "What are NB1 and NB2?"

NB1and NB2 are the name of the functions that have been used in TS-930S and all subsequent products. NB2 was especially designed to have a blanking effect against noise with a long pulse width and a long period that has been known as the "Woodpecker." After the woodpecker noise disappeared, the NB2 function was not employed, but in recent years a new breed of noise called the "China Dragon" has appeared. So, there may be cases when NB1 alone may not have a great enough effect on the China Dragon, NB2 has been spotlighted again. Note, however, NB2 on the TS-590S is realized with digital processing and, thereafter, totally different from NB2 in the TS-930S era.

As explained above, while the narrow bandwidth of the roofing filter is employed, the noise blanker of the DSP cannot have a sufficient effect. However, the NB2 realized with the DSP on the TS-590S turns out to be unexpectedly effective in many occasions, even while the bandwidth is less than 500 Hz in CW mode. This is because the new NB2 can fully adjust the blanking time to the length of the pulse.

NB2 of the TS-590S is most effective when you want to pick up a weak signal that is almost buried in the noise with a long pulse width that cannot be eliminated by NB1. Try NB2 in such occasions and be surprised.

Hints and Tips "Improvement of sensitivity in the BC band and alteration in ATT attenuation"

On the TS-590S, by changing the circuitry configuration inside the transceiver, you can change the sensitivity in the bC band and the attenuation amount of the [ATT] key on the front panel.

Following is a figure that represents the TX-RX UNIT that has the circuitry configuration in question. By detaching the lower case, you can access the jumper connectors CN101 through CN103.

TS-590S Hints and Tips "Improvement of sensitivity in the BC band and alteration in ATT attenuation"

1) Raising sensitivity in the BC band:

Remove the jumper for CN103 and insert the jumper into CN102. This will increase the sensitivity in the BC band for 20 dB. (Assuming that there is the high output power in local broadcasting stations in the BC band, the sensitivity is lowered by 20 dB as the is factory default.)

2) Changing the attenuation amount of ATT:

Remove the jumper of CN101. This changes the attenuation of ATT from 12 dB to 20 dB. (Store the removed jumper in a secure place for future use.)

Hints and Tips "The output level of the headphone jack is too high?"

The headphone jack of the TS-590S is designed to have, as on the previous HF transceivers, an impedance of 8 Ohm (standard). Therefore, if you use a headphone with impedance higher than 8 Ohm, you will experience the symptoms as below.

  • The volume level is too high overall.
  • Even if AF Volume is turned down, a hissing residual noise is audible.
  • Even if the beep sound level is set to minimum, the beep sound is loud.

If you experience these symptoms, use a set of headphones with impedance close to 8 Ohm.

The tradition of high quality audio technology that users rely on Kenwood to deliver is produced by combining analog and digital technologies that Kenwood has nurtured thus far. The DSP controls modulation and determines the sound quality and analog circuits convey and amplify the signal cleanly.

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