The 1st local oscillator is MS5351 PLL managed by PIC18F1320. There is a rotary encoder to tune the frequency. We can select 100kHz or 10kHz step frequency by pushing the RE knob. The frequency is displayed on the front 7 segments 4 columns LEDs as 1215 at the case of 100kHz selected. At the case of 10kHz, 1 is omitted and displays as [215.0]MHz.
They say that 1215 displaying means 1215*100kHz=121.5MHz at 100kHz mode and 215.0 means 1215.0*100kHz=121.5MHz at 10kHz mode.
I shall later refer to how to operate the setting for frequency, volume, squelch level, and 25MHz adjusting.
MS5351 is based on a 25MHz crystal oscillator and can be adjusted by RE to compensate for the error. Below is PLL-BOB. There may be a low pass filter for clock output.
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I bought the kit and investigated the circuit to draw the diagram as below.
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The mixer is NE602. The output signal of NE602 is going into a ceramic filter of FM radio use.
a. The front end filter and LNA The front stage filter is a stager style with two LC resonating circuits. L is D5x5 size, 4.5 turn(Estimated inductance is 68nH by WEB service "http://gate.ruru.ne.jp/rfdn/Tools/ScoilForm.asp#p1"). And C is 15pF. Between LC circuits there is 2.7pF connecting capacitor. I had simulated filter design by using ELSIE. "http://tonnesoftware.com/elsie.html" To keep the bandwidth for the airband we shall tune the front filter coil size. 60/68nH is somehow well for bandwidth and accordingly pass-through gain is declined. We should use the VNA or the spectrum analyzer to tune more precisely.
LNA is NE5204 which is DC-200MHz wide and 20dB gain.
I'm wondering to buy R80 kit or not. I have been interested in various functions on R80.
1. They are saying that the LO is PLL. And I had come to know that the chip was MS5351 as was Si5351a clone. If so, their providing frequency setting function is a little bit poor. The major style of receiver usage is waiting for a signal on several determined frequencies.
2. Airband communication frequency plan is 25kHz separation and near London and New York that is 8.33kHz especially. The step frequency of R80 is 100kHz or 10kHz.
Prior to buying R80, I studied its circuit. And I will introduce it below.
I sent a request mail for Mr.ken to report what chip is used as PLL LO. He had opened the case and investigate the name on the IC chip and he taught me the name being MS5351. Alibaba is selling MS5351 as a compatible od Si5351a for amateur radio usage.
As I bought Si4732 receiver kit, I made up a crystal converter to receive air band communication. I utilized the MPU 20MHz crystal for the 5th overtone oscillating as 100MHz. The correct frequency is 100.06MHz. I composed the stagger coupled 2 10K-8t coils as a front-end filter and used 2SK439 FET for LNA.
To connect the crystal converter for the Si4732 receiver I tuned Osaka international airport ATIS. As Osaka international airport ATIS's frequency is 128.6MHz, I should tune 28.54MHz derived 128.6 - 100.06 = 28.54MHz. The result of filter is -15dB between 115 - 135MHz and -25dB @ 100MHz.
The sensitivity is less than the Chinese receiver kit. I can receive a 118.1MHz signal from airplanes because of being very strong. Speaking of received sound feeling, it is special for SDR. SDR is naturally tuning modulated signal and it takes some time to generate sound after capturing modulated signal. No signal: very noisy, On capturing signal being calm at first, after then coming up demodulated sound.
To boost the signal I connected 0.1-2000MHz Wideband AMP bought from Amazone, and it brought well result. As a result, the sensitivity became as same as the Chinese airband receiver kit.
The project of the 5th overtone crystal converter brought enough achievement.
Worse sensitive. 1stis machine is composed of an enamel wire coil filter but 2nd machine is composed of PCB pattern coil one. I added the resistor for impedance matching so this causes much loss.
I bought the Si4732 receiver kit and assembled it. This is the same as ATS-20 with the case. The original PCB is based on Turkish HAM, TB5CVN copied and is selling it on PCB WAYs as USD5.
There is 10.7MHz IF output on the Chinese remodeled receiver. Si4732 is set 10.7MHz AM and fed the above signal. I could hear airband radio communication on this combination. It is special as DSP receiving feeling. When signal comes, once calm and after then the demodulated sound is coming up.