1.6W image transmission

Updated
2022-11-03 Initial version content
2022-12-19 Updated V1.2 hardware version
  1. Maximum power increased to 1.6W
  2. Optimized RF circuit matching and RF line design to improve overall RF efficiency, 1.6W output overall power 5.5W in A4 band
  3. Fixed LED power display error
  4. The firmware of v1.2 hardware is incompatible with the firmware of v1.1 hardware, and the v1.2 version needs to recompile the firmware
  5. Output 1.6W requires adding a new top heat sink
1. Hardware design
The amplification factor of SE5004L is basically constant. The MCU reads the current output power from the VDP pin of SE5004L, and then adjusts the amplitude of the 6705 output signal through RTCBIAS to control the size of the 5004 input signal to achieve output power control. The
crystal oscillator uses a DSX321G with an operating range of 40℃-125℃ to ensure the stability of the crystal oscillator frequency when the image transmission is at a high temperature. Do not use ordinary crystal oscillators. The unstable frequency of ordinary crystal oscillators during high-power transmission may cause image tearing and other problems.
The DC-DC part uses MP9943, which is designed to have an output capacity of 5V/1.5A and can output 5V to power the camera.
When selecting components, please note that the withstand voltage of C31, C32, and C33 needs to be greater than 25V.
2. The laminated structure of the board
is 1.6mm thick + JLC04161H-7628,
and the lamination order is GTL-G1-G2-GBL
! ! ! !
The picture in the article is the v1.0 version used for testing, and the attachment is the v1.1 version. Some 0201 packaged originals were changed to 0402 for easier welding, and the wrong silk screen
board in v1.0 was changed. AD design is used. It is recommended to use Gerber files to place orders. The original pictures and PCB imported by LiChuang EDA are for reference only.
3. Welding
The image transmitter is a single-sided design. You can use a heating table or hot air to weld the front and back of
the finished product. 4. Heat dissipation Due to the large output power of the design, an external heat sink is required to ensure the stability of the image transmitter. Heat sink Taobao search keyword "fan board heat sink" , specification 25*25*4, you can use a heat sink of the same specification with a higher height to get better heat dissipation. Using a 25*25*4 heat sink, under a wind speed of 3m/s in the test environment, the maximum power of 800mW works for 10min. The temperature of the heat sink and IC is stable at around 50℃. The heat sink needs to be processed, and three teeth width and two teeth depth grooves need to be opened for the SH1.0 interface. I also expanded the mounting hole to 3mm. Use thermal grease on the open pad, and use silicone thermal adhesive in other positions to fix the heat sink and the image transmission together. v1.2 version update: After actual testing, the output of 1.6W requires an additional top heat sink to ensure the stability of PA operation. There is a back heat sink + fan cooling under the condition of maximum power operation The temperature heat sink is made of 1mm aluminum plate with a size of 28*28mm. It is slotted for the mmcx port and has holes with a spacing of 20*20mm and a diameter of 2.5mm. You can use the closed PCB as a template to punch holes. After pasting the back heat sink, use copper pillars with specifications of M2*4*3.2 to directly fix them to the four holes. Apply silicone thermal adhesive on the four copper pillars of the inductor, and paste 2mm thick silicone pads on RTC6705 and SE5004L to fix them until the thermal adhesive dries. 5. Firmware burning 5.1 BootLoader burning The firmware burning of OPENVTX requires VSCode+PlatformIO environment, and the bootloader needs to be flashed in through SWD first. Bootloader.bin is in the attachment. The Bootloader version in the attachment also supports the latest Openvtx v0.2.0 version. For environment construction, please refer to https://blog.csdn.net/chenyuanlidejiyi/article/details/120217832. Bootloader needs to be downloaded using an ARM downloader, such as STLINK, JLINK, and various LINKs. Use the matching download software to load bootloader.bin and download it. After the bootloader is successfully flashed in the attachment , the red light of the flight control will flash slowly when it is powered on. The connection is shown in the figure. The SH1.0 interface on the back has the same pin order, and power can also be supplied through the SH1.0 interface. 5.2 Firmware Burning At present, this DIY hardware has not been merged into the mainline firmware. You need to compile and download it yourself. The attachment contains the v0.2.0 version code. It is best to get the latest code from github https://github.com/avanx/OpenVTx After the bootloader is successfully flashed in the previous step, connect the flight control and the image transmission to the flight control ground station, set the corresponding UART connected to the Smart Audio protocol, save and close the ground station to confirm the connection of the flight control, and then find the DIY_VTX820 project in PlatformIO, click Upload and wait for the progress bar to finish. 6. Configuration and Test The JSON file for configuring the image transmission is in the attachment, betaflight-configurator Select Import from File in the vtx tab, select vtx_table_smart_audio_1_0_VTX820.jsonTest environment, fan speed 3m/s, connect the power meter through a 30DB attenuator, use the frequency band BOSCAM_A, 4 channels, frequency 5805MHzSet 100mW reading -10.6dBm, actual power -10.6+30 = 19.4dBm = 87.1mWSet 200mW reading -7.1dBm, actual power -7.1+30 ​​= 22.9dBm = 194.9mWSet 400mW reading -4.1dBm, actual power -4.1+30 ​​= 25.9dBm = 389.0mWSet 600mW reading -5.5dBm, actual power -2.0+30 = 28dBm = 630.9mW set to 800mW reading -5.5dBm, actual power -1.1+30 ​​= 28.9dBm = 776.2mW v1.2 version: 100mW 400mW 800mW 1.2W 1.6W 7. Suggestions for use

























 







 








1. In actual testing, it was found that SE5004L has the highest efficiency at around 5800MHz. When the output is 800mW, the overall power is 1W lower than that near 6000MHz or 5600MHz. It is recommended to use the frequency band near 5800MHz to obtain the maximum endurance and minimum heat generation.
2. When the transmission power is 800mW near 6000MHz or 5600MHz, the overall power consumption of the image transmission will reach about 6W. It is not recommended to carry an external camera load at this time.
3. I hope that model friends with more professional instruments can more accurately adjust the VDP parameters to obtain more accurate power output values.
8. Actual flight
to be updated