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The overall configuration is similar to
TX-Neptune, but while MT-Pluto/TX-Neptune generated SSB 100% using the PSN
method, this unit basically generates SSB using a 128KHz mechanical
filter. The characteristics of NEC and Fujitsu are listed below, and the
signal is generated as a USB signal so that the center is at 128.0KHz,
dropping by about -40dB, and the upper side is within the passband. In
this case, modulated signals below about 200Hz are blocked by the filter
and will not be transmitted. To enable low-frequency transmission like the
PSN method, the carrier point must be moved from 128.0KHz to a point 200Hz
higher. However, in this case, the slope component below 128.2KHz leaks
out as a reverse side suppression characteristic. Therefore, in this unit,
in order to enable low-frequency transmission to increase fidelity, two to
three stages of AFPSN are inserted to perform PSN modulation so that the
reverse side characteristic does not become a problem even if the carrier
point is moved sufficiently high. Since the SSB signal is generated by
PSN+filter configuration, it is called a hybrid system. For details on
AFPSN, please refer to the AFPSN section on the TOP page. ● Since the filter bandwidth is 3.4KHz, which is 400Hz wider than 3.0KHz, an audio filter is used to allow the cutoff to be set in 0.1KHz steps. ● In the balanced modulator, since the USB signal is 128KHz, the LSB/USB mode switching is performed by converting the IF mixer's carrier wave to a higher or lower carrier wave compared to 10.7MHz. ● The filters are not limited to 128KHz, but you can use any filter you have on hand, such as 300KHz, 455KHz, 1.5M/5.5M, etc., as the unit format allows you to simply insert the desired filter and set the frequency. ● Other features such as meter drive and display method are the same as those of the TX-Neptune. |
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The carrier point, CP, can be set from -999Hz to +999Hz in 1Hz resolution. When the 128KHz carrier frequency is changed, this unit controls the IF mixer carrier frequency so that the IF frequency is always 10.7MHz, not the VFO frequency, so that the final output frequency does not change. |
| Front | Back |
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MAIN-Board |
128KHｚ Filter DDS Board  Final-Amp 3StagePSN   |
NEC
Mechafil Characteristics |
Fujitsu Mecha Filter Characteristics |
2T signal at 280mW output at the final stage |
Filter terminal diagram |
| Input side (source impedance) | Output side (shunt impedance) | |
| Fujitsu | 3.9KΩ | 4.7KΩ |
| NEC-AType | 470Ω | 6.8KΩ |
| NEC-BType | 6.8KΩ | 6.8KΩ |
| ACN Operation |
| Even if there is carrier leakage from the
balanced modulator, depending on the position of the carrier point, for
example, at CP=000 (128.0KHz), there is a drop of -40dB, and stable
carrier detection is not possible even if the filter output is used as a
carrier amplifier, and carrier detection is not possible at all on the
CP=- side. Therefore, ACN operation is performed only in the receiving
state, and in order to fix it to the optimal adjustment value during
transmission, the carrier point is forcibly fixed to CP=000+500Hz in the
receiving state. In this way, even if a filter with a poor shape factor is
used, the carrier point is within the passband, stable carrier detection
is possible, and ACN operation is stable. When switching to transmission,
it is moved to the set carrier point. If stable carrier detection is not
possible at all times during reception, ACN operation will run out of
control and carrier leakage will occur. |
| Panel image |
