【2019/3/25】
This is a revised version of the MR-Neptune (direct receiver) that I made previously. I solved some issues and aimed to create a receiver that can be paired with a direct transmitter (TX-Saturn) in terms of design. There is no problem when receiving a strong signal, but the AGC range was narrow, so it was difficult to use when there were differences in strength, especially when it came to round QSOs with multiple stations, although it would be fine if all the stations had strong signals. I am currently testing it with a prototype, and I think the AGC is a success.

①　The AGC is divided into RF and AF, and the operating point of the RF-AGC is set to S=9+20dB or 30dB, while the AF-AGC operates from S=5.
②　Overall, a range of 70 to 80 dB is ensured, but the wider the range, the higher the noise level becomes, so an AGC Gain-VR is attached to the panel, allowing manual adjustment of the gain depending on the strength of the received signal.
③　In the case of direct, the carrier leaks into the antenna terminal because it is demodulated at the top of the RF, but I assume that this is buffered by providing an RF-AGC. This will not be clear until it is built and installed in the cabinet, but even if some leaks, this can be resolved with an antenna distributor (active).
④　The filters are the same as Neputune, with four types available: 2.4KHz, 3.2KHz, 3.8KHz, and 4.5KHz.
⑤　The receiver has an SG function, so adjustments can be completed with just one oscilloscope.
⑥　When adjusting the opposite side, a new automatic SG scan function has been added, allowing you to check instantly with a 3KHz bandwidth.
⑦　In addition, the link with the transmitter will continue to include transceiver and monitor functions as before.
Basically, we decided to continue with the blocks that we had designed so far that had no particular problems, and after completing the design and PWB artwork design, we ordered the PWB. It is expected to arrive in about a week, and we will proceed with the production and measurement in due course. In the end, three unused areas were generated during the PWB design, but these three areas were used to insert a 4-way distributor, an OPA2677, and a high-level mixer, and these are also included in the circuit diagram file.

System Block Diagram Circuit Diagram 　　Bill of Materials PWB
       

　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　Silk PDF file for each unit
The final specifications for the front and back panels were as follows:


　

　



The optical encoder is mounted independently on the panel, so you can choose and install the one you like, and you can set it to 100 pulses per rotation, or you can use the software to set it to 50 pulses or 25 pulses.

　　　　





I have put together the production.　　　　　　　　　　　　　　　　　　RX-Saturn Production


Finished compiling the motion test section.　　　　　　　　　　　　　　　　　　　RX-Saturn Dynamics



Wire connections for connecting boards.　　　　　　　　　　　　　　コネワイヤー Wiring Diagram



Only the modifications and changes have been listed.　　　　　　　　　　RX-Saturn Renovations and changes

This completes the whole process and the adjustments are complete, so starting tomorrow I will try running the actual machine and using it.
Next I will create the adjustments section, actual measurement data, and operation manual.


We have summarized the adjustment and confirmation sections.　　　　　　　　　　　　　　　RX-Saturn Adjustment Check



We have put together the operation manual.　　　　　　　　　　　　　RX-Saturn Operation Manual



I tried recording the received sound. I would be heavily criticized if I recorded the actual voices of each station, so I tried recording the L-CH/R-CH signals going to the AF-AMP input in each mode for music recording. In both cases, the ANT terminal signal level was about S9+20dB, and the AGC-VR was slightly lowered.

【1】Music source: Adamo's "Snow is Falling"
　　①　Transmission mode: ISB, Bandwidth: 3.5KHz　 Receiver mode = ISB, LPF = 3.6KHz
                                                　　　　ISB reception recording = 1 minute
　　②　Transmit mode = LSB, Bandwidth = 3.5KHz   Receiver mode = LSB, LPF = 3.6KHz
                                                　　　　LSB reception recording = 1 minute
　　③　Transmission mode = LSB, Bandwidth = 4.0KHz
　　 　　　Receiver mode = LSB, LPF = switched sequentially at approximately 10 second intervals from 4.3KHz to 3.6KHz to 3.0KHz to 2.4KHz to 3.0KHz
            to 3.6KHz to 4.3KHz.　LSB Bandwidth Test Recording
【2】Music source: Yoshio Tabata "Futami Love Story"
　　①　Transmit mode = ISB, Bandwidth = 3.5KHz   Receiver mode = ISB, LPF = 3.6KHz
                                                  　　　　ISB reception recording = 1 minute
　　②　Transmit mode = LSB, Bandwidth = 3.5KHz   Receiver mode = LSB, LPF = 3.6KHz　
                                                      　　LSB reception recording = 1 minute
　　③　Transmission mode = LSB, Bandwidth = 4.0KHz
　　 　　　Receiver mode = LSB, LPF = switched sequentially at approximately 10 second intervals from 4.3KHz to 3.6KHz to 3.0KHz to 2.4KHz to 3.0KHz
            to 3.6KHz to 4.3KHz.　LSB Bandwidth Test Recording

LSB = mono sound, ISB = stereo sound. Were you able to distinguish the sounds in the bandwidth test? If you can't tell the difference, your ears are bad.



I printed out the S meter sticker and stuck it on the meter, and asked a designer if they could make the font size look a little bigger, but I wonder what will happen? I'm using this sparsely populated receiver every day.

　


AF-AGC's C62/C65 have had 1uF added to the backing or changed to 2.2uF, respectively.
　　　　　　　　I have revised the circuit diagram, including the previous constants.　　　Circuit Diagram 0501


 It's been a while since I last wrote about this, but the RX-Saturn I made broke. To check, I removed the connector wire, connected it in a different place, and turned on the power, but there was no sound. After investigating, I found that the RF was normal up to the detection circuit, and the I/Q carrier was also normal, but nothing was coming out of the detection output. Eventually, U19 (op-amp) in the final stage of AF (where the signal is supplied to the AF-AMP) was broken. So I turned the power off and checked, and found that the connector supplied from the power supply to MAIN was connected to CNP4 (5P) instead of CNP8 (5P), and this was a big problem.
　　　　　　　　　

 There is a 5P connector nearby, so be sure not to make a mistake. I replaced U2/U3 and got a detection output. I haven't checked it since. U2/U3 will break, and replacing it is a difficult part because it is a modification, so please be careful if you are making it. There is no mistake with the other power supply connectors, so this is the only one.
In the end, I destroyed U2/U3, U23/U27 (NJU7043D), and U19, a total of five. Other than that, I restored it without any problems. When I made the second machine, I thought I would change the level distribution, but it turned out to be for a different reason. There is no problem with the current situation.


I broke another precious IC. It's 2018. There is a GND pin right next to TP2. It's better not to install this, I want a GND near here, but there is a GND in the output terminal arrangement of the LPF unit, so I put the GND pin here. The GND pin next to TP2 is likely to hit ⑩ of 2018 when you pinch the oscilloscope's alligator clip, which is the -15V line. When I touched it, a spark came out and destroyed 2018, but only one was destroyed.
　

①　Headphone amplifier gain is too high (reduce it)
　　　R28／R29＝822→392
②　AF-AGC time constant
　　　I think there was initially information that the values ​​of C62 and C65 were changed from 1uF to 2.2uF, and although I prefer this value, I suspect that stations would prefer it to remain at 1uF.
③　Adjust and check the opposite side
　　　The RX-Sturn adjustment confirmation section has been updated. Correction and confirmation method for reverse side adjustment. A video has been uploaded.

During scanning, the reverse side AGC will be at full gain, so you will hear the sound from the speaker, but if there is no fluctuation in the S meter between 100Hz and 3KHz, it's OK. The operation method is listed in the adjustment and confirmation section.

　　　　　　　　　　　　　　　　　　Reverse side automatic scan video
　　　　　　　　　　　　　　　　　　　　　　　　


 【Changing RF-GAIN-VR】
Currently, the AF-AGC gain is adjusted using a dual VR, and although the gain adjustment is linear, it feels strange when you actually try to operate it. Therefore, since RF and AF cannot be performed simultaneously, I stopped AF-AGC control and tried to control the gain only with RF-AGC. This is a method that does not require much modification or readjustment. However, it does not feel like the RX-Uranus, and it is a little difficult to adjust because it has a time constant when variable, but I judged it to be better than the current situation. It would be a hassle to redesign only this part, so you can think of it as an extra feature. However, since the gain is controlled even with the current situation, you can compare and choose the one you like.

　

The case arrived on June 7, 2019. I immediately started assembling the panel.

　

　


 5/7/2019: I drilled the necessary holes in the back panel and completed the back panel unit.
I tried to do the next step, but I didn't know how to assemble the case (I don't remember even though I've assembled it many times). I'll have to think about it carefully.
　

2019/6/112019/6/11
Assembly completed today, and everything works perfectly fine.

　



I couldn't measure the sensitivity accurately in the shack, but I measured it after it was boxed up. I was able to measure it perfectly and stably. The sensitivity may have been a little too good, but the sensitivity measurement is determined by the ANT terminal input level at the point where the S/N ratio is 30 dB at the audio output. S/N ratio of 30 dB is defined as practical sensitivity, and S/N ratio of 10 dB is defined as maximum sensitivity. The results for RX-Saturn are
　　　　　　　　　　　　　　　　　　　　　Practical Sensitivity　　　　Maximum Sensitivity
　　　　　　　　　　　3.550MHｚ　　　　    　-124ｄBm　　　　　　-138ｄBm
　　　　　　　　　　　7.135MHｚ　　　　    　-121ｄBm　　　　　　-136ｄBm
　　　　　　　　　　14.135MHｚ　　　    　　-121ｄBm　　　　　　-136ｄBm

By the way, the practical sensitivity of the New Japan Radio JRD-535 receiver is -117dBm (1.6M to 30MHz)

RX-Uranus
　　　　　　　　　　　　　　　　　　　　Practical Sensitivity　　　　Maximum Sensitivity
　　　　　　　　　　　3.550MHｚ　　　　　-112ｄBm　　　     　　　-126ｄBm
　　　　　　　　　　　7.135MHｚ　　　　　-109ｄBm　　　     　　　-127ｄBm
　　　　　　　　　　14.135MHｚ　　　　　-106ｄBm　　     　　　　-126ｄBm

RX-Saturn's practical sensitivity
　
Maximum Sensitivity
　

BPFの挿入損失がそのまま感度差に出ている、私の場合、3.5M＝-1.4ｄB、7M／14M=-4.4ｄB
This is the last change. The AGC gets excited by the pulse noise from the antenna and is suppressed. To solve this, we made the following changes.

　　

 Modified constants. R23 = 683 is OK, R91 and R113 = 102.
I did a lot of testing on the actual machine in relation to attack distortion, but this is the final version.
RF-OUT audio detection characteristics
Here, the characteristics are those of RF-AGG (AD603).



2TONE detection characteristics at ANT terminal input strength
S＝５　　S＝９　　S＝９+２０ｄB　　S＝９+３０ｄB　　S＝９+４０ｄB　　S＝９+５０ｄB　　S＝９+６０ｄB
The RF-AGC operating point starts working from S=9+20dB, but with this alone the audio output is too small for a signal equivalent to S=9, so the overall AGC characteristics are determined by where you set the operating point of the subsequent audio AGC. For example, if you secure an operating width of about 25dB for the audio AGC, the AGC starts working from about S=9. If you try to widen the AGC operating range, noise will increase, and if you narrow it too much you will want to adjust the audio VR.