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Circuit Diagram Block
Diagram Bill
of Materials Operation
check/adjustment method operation manual |
● A 10dB ON/OFF attenuator circuit has been added to the ANT circuit. ● The bandpass filter is a 4-element configuration with 7 bands: FULL/MW/3.5/7/14/21/28. FULL = Create your own BPF and insert it in unit form. MW = Receives AM medium wave broadcasts. ● The RF amplifier is what is commonly referred to as a Norton amplifier (approximately 12 dB) using 2SC1747s. ● The detector circuit is a bus switch (FST3253), and each output (I/Q output) is output in differential format, which is then converted to single by an instrument amplifier (INA163). ● The all-pass filter consists of 8 stages, and the LSB signal/USB signal is demodulated by addition and subtraction. ● There is no AGC for RF, and AGC processing is performed on the demodulated audio signal. In the block diagram, AGC detection is performed commonly for LSB/USB, but in order to ultimately demodulate ISB mode as well, the AGC detection circuit is set up independently for LSB/USB. ● As an aside, LSB stands for Lower-Side-Band, USB stands for Upper-Side-Band, and ISB stands for Independence-Side-Band. ISB stands for Independent Sideband, and the lower and upper signals are separate. For example, the LSB side transmits SSTV signals, and the USB side transmits normal audio. AM signals transmit the same information on both the lower and upper sides, but the bandwidth is 3KHz for the lower side and 3KHz for the upper side, occupying ±3KHz. ISB signals transmit as LSB = L-CH signals and USB = R-CH signals, and are often used for sound play. When transmitting with ISB radio waves, you may hear complaints that the band is too wide or that the other side is leaking, but just like AM signals, ISB radio waves have proper mode qualifications, so it's not a problem. In any case, you should refrain from transmitting during prime time or other times when the band is crowded, and you should never cause trouble to other stations. ● The Head-Phone-VR and Speaker-VR are independent, and if they are connected to the transmitter and the system, the Head-Phone is always active. However, since the SP may also be used as an air monitor, the Speaker line is muted during transmission. ● It also has an ON/OFF function for the transceiver function, and when it is ON, the band information (frequency, mode) is synchronized with the transmitter by operating the receiver. ● The downside of direct is that in order to obtain sufficient sensitivity, the AGC is an audio AGC, so this unit sets the AGC operating point to about S9+5dB, so signals below S9 will increase or decrease in magnitude in proportion to their strength. If you set an AGC on the RF, it will be controlled by unintended (unwanted) signals, which will create a strange feeling. When ragchewing with an S9+ signal, you can receive a very good S/N ratio and comfortable sound quality. ● The S meter of this unit is adjusted to S9=-67dBm, but many commercially available radios are adjusted to S9=-73dBm, so the reading is one S lower than these, so S9+40dB=-27dBm. |
Finished
Product power supply  |
Interior photo |
MAIN Detector Amplifier  |
DDS LPF  AFPSN  |
4-element RF bandpass
filter |
DET
(detection) amplifier circuit diagram The audio signal demodulated by ST3253 is output as an I/Q signal for PSN demodulation. The I/Q differential signals are fed into the DET amplifier circuit to create a balanced I/Q signal. In the case of a direct receiver, it is necessary to set the gain distribution properly in order to obtain sufficient sensitivity and receive many unwanted interference signals, especially strong continental radio waves. There is some know-how to eliminate such interference. The DET amplifier is composed of an instrument amplifier + low pass + amplifier. ● Anywhere within the receiving F coverage range, unwanted strong radio waves may be demodulated at the output of the low pass, but they must never be saturated to the power supply voltage; if they are saturated, the harmonics cannot be completely removed even if they pass through the low pass. ● If the low-pass cutoff frequency is narrowed, the phase difference between the I/Q signals will occur within the passband, and the reverse side characteristics will deteriorate when the LSB/USB signal is generated in the later stage. Conversely, if the cutoff setting is set too wide, the removal characteristics of unnecessary strong radio waves will decrease. This setting is difficult, but also interesting. The cutoff of this unit is set to around 10KHz, which means that unnecessary radio waves with frequencies more than 10KHz away from the carrier point of the receiving frequency are removed by this low-pass filter. ● The gain of the final amplifier sets the maximum allowable input of the receiver. Before the audio AGC is applied, the power supply voltage is ±15V, and the linear region is about 23Vpp. The AGC operating point, ANT maximum allowable input, and sensitivity are all taken into consideration. This unit is set to maximum allowable input = S9+40dB, and AGC operating point = S9+5dB, which results in a practical sensitivity = -110dBm, meaning that with ANT = -110dBm, the S/N ratio at the audio line output is 30dB. The gain is set so that with an ANT = S9+40dB signal, TP1/TP2 will be 20Vpp. |
| Detection circuit modification | Opposite side suppression adjustment method |
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| Strong input characteristics from antenna and actual sensitivity characteristics | |
| Line output
with S9+40dB (-27dBm) input (3rd order IMD=-66dB)  |
Line output at
-110dBm input (usable sensitivity)  |
| I/Q carrier to direct detector |
| DDS
Circuit Diagram In order to demodulate the PSN, an I/Q carrier is required, and the frequency must be directly output under IQ conditions from 500KHz to 28MHz. In addition, when the frequency (band) changes in the detector, the carrier phase difference for I/Q detection must be finely adjusted. This unit uses two AD9854s from Analog Devices to generate the I/Q carrier. This DDS has a configuration of D/A = 12bit, frequency resolution = 48bit, and phase resolution = 14bit, allowing very fine frequency setting and phase = 20 millidegree resolution adjustment. However, this IC is powered by 3.3V, but consumes a lot of electricity. Depending on how it is used/mode, it is about 350mA. The reverse side adjustment adjusts the I/Q 90 degree carrier for each band and the I/Q amplitude balance of the demodulated audio signal, and the adjustment value for each band is stored. This receiver does not require measuring equipment such as a SG when adjusting, as it has an internal SG for adjustment. By pressing the 'SG' button, the AD9851 oscillates to supply a S9+40dBm signal to the ANT terminal, allowing you to freely set the frequency above or below the receiving carrier point. |
DDS I/Q
output |
| Low-pass filter |
| LPF
circuit diagram It is an 8th order low pass filter, and can be switched between 4 types (2.4KHz/3.2KHz/3.8KHz/4.7KHz) by switching the resistor element box. Since there are 4 boxes, you can freely set the cutoff by changing only the resistance value. Initially, it was a low pass filter configuration using a switched capacitor, and there was no problem if it could be placed after the AGC circuit, but it needs to be placed before the AGC (AGC must not operate with signals outside the passband), and in that case, a dynamic range that can pass signals of 20Vpp or more linearly is required, so it was redone as an active filter. |
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