YO4HFU
FI CONVERTER/CONTROLLER FOR ALCATEL ODU


 

During experimental testing of ALCATEL XVRT modules for 5.7GHz and 10GHz was neccesary to design a new IF down converter to 144 or 432MHz, power supply and controller. The frequency conversion is required to reject the image frequency, 1st FI will be relative high 700...1600MHz. The idea was to be a universal solution for any ALCATEL XVRT 7GHz or 11GHz. Also other versions are supported but not suitable for ham radio. I'm planning small modifications for 23GHz Wavelab XVRT.

The design must to meet next requirements:
- Flexible power supply, selectable +6V or +10V for driver stage due to different PA driver.
- Negative 5 volts bias voltage interlocked with +10V, +6V and +5V in order to avoid failure of FET transistors by over current in case of lost bias.
- PLL controller for 1st Alcatel LO ADF4106 and 2nd LO MAX2871. Jumper configuration 5.7/10GHz, high/low injection, 144 or 432 2nd FI, FI shift to 145/433MHz in case of local QRM.
- Output power monitoring and internal temperature sensor.
- Coaxial relay sequencer.
- Fan controller according adjustable setpoint.
- Integrated RF VOX, PTT or DB6NT voltage over coaxial.
- Good quality PLL reference 10MHz OCXO.
- SAW filters use for best image rejection and no tuning.
- LCD 2x16 I2C
- And many other small details...

Note:

Several versions of FI Converter/PSU were tested (sequencer with transistors/uC integrated, LTC6946/MAX2871 2nd LO, LED bargraph/LCD power monitoring, HMC213/RMS-25MH mixer). In order to avoid any confusion between photos and text content, I will speak only about last design - version 3, but the PCB is updated to version 4 to fix some small mistakes observed.
PCB version 4 was not yet manufactured. Is 99% same with tested version 3 (shileding improvment of MAX2871, ADF4106 uC lock detection correction, internal/external power monitoring for PA use, silksreen correction).
The schematic diagrams are matched with PCBs vers. 4.



Description of PSU/Controller Board:

The power supply has been designed to provide the necessary voltages for the Alcatel XVRT unit. The required 10V voltage for PA FET is interlocked with the negative bias voltage to avoid failure of the transistor in case of -5V malfunction.

Power supply voltage for PA driver stage can be selected 6V or 10V according XVRT type. Check the datasheet of driver power MMIC!
In general 11GHz version needs 6V and 7GHz with 10V. During experiments of 7GHz conversion to 5.7GHz was found better matching if power supply is decreased to 6V. Final PA stage is supplied only with 10V,regardless of model. Please note that above photo of PSU/Controller board v.3 has wrong silkscreen of driver voltage selection versus frequency. The error is fixed on layout v.4. For more informations read 7GHz or 11GHz page.

The transverter is capable of operating even at 11V, suitable for portable use when the battery is discharged. OCXO supply has been stabilized at 10V...10.5V even if it is below of specifications. Frequency drift due to unstable battery voltage is avoided. Switching power supply provides 6V and although I tried to avoid it, it was not possible because the TX driver absorbs a current over 2A and the dissipated power is ~15W for a linear regulator.
Negative voltage is generated by MAX660, higher current DC/DC voltage converter. I didn't try to use ICL7660 due to ~25mA/-5V required by XVRT.
PA stage idle current can be checked across "TP Id" terminals. Remove the jumper and read the current by an ammeter. The current is adjusted according datasheet (class A). Bias adjustable resistor is located on "21 pin PCB adapter", which is soldered on top of XVRT connector.

The control part is made with two microcontrollers. I chose this solution for higher flexibility during the experimental phase. One of the microcontrollers deals with temperature monitoring, output power, antenna relay sequencing, fan control and VOX. The thresholds for the fan and RF VOX can be adjusted by means of adjustable resistors. The LCD 2x16 communicates on the I2C, so it is necessary to attach a PCF8574 interface on the rear side of LCD. Of course, the display may be missing without affecting the operation of the transverter.
2nd microcontroller is responsible for programming of two PLLs (ADF4106 LO1 and MAX2871 LO2). It supports various configurations depending on the type of transverter and the chosen intermediate frequency. Jumpers changes take effect only after restart. Tx is inhibited if LO1 & LO2 PLL are not locked. PLL status is indicated on LCD (Lk/Uk).

The software logic was designed with Visuino and Arduino IDE. Both uC are internaly clocked at 1MHz (PLL uC) & 8MHz (MAIN uC).

Peak power bargraph monitor is a relative reading of forward voltage provided by Alcatel XVRT or by external power amplifier (max. 5V). Full scale is adjusted using "MON" resistor. Temperature indication is according LM50 temperature sensor located inside of XVRT unit.
RF VOX signal is compared by uC. PTT input is also availabe. RF VOX detector is DC coupled with 144/432 input, it is able to detect TX voltage via coaxial cable (DB6NT).
Relay sequenced output has 30msec delay and is suitable to drive RX/TX antenna coaxial relay. FAN output is not very useful but can be used to control a small cooling fan according the setpoint. The cooler is not required if Alcatel XVRT is installed on heatsink or aluminium plate.

 

Description of FI Converter Board:


Page Under construction... 20.09.2021




PSU/CONTROLLER schematic vers. 3
FI CONVERTER schematic vers. 3
ADAPTER CONNECTOR schematic vers. 1


PSU/CONTROLLER PCB vers. 4
FI CONVERTER PCB vers. 4
ADAPTER CONNECTOR PCB



PSU CONTROLLER view Top and Bottom
FI CONVERTER view Top and Bottom, Bottom shielded
5.7GHz XVRT using Alcatel 7GHz and FI/Controller board
5.7GHz XVRT front panel
PA 35W 5.7GHz



Firmware Attiny84 PLL controller v.1
Firmware Atmega328 main controller v.1











 
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