Optimizing a WIFI Grid Antenna for Maximum Efficiency by António Pereira

Wifi grid dishes, come in a variety of center frequencies, yet they are all basically the same wifi grid, made by the same manufacturer and sold under different names. The big difference is the feed and the dipole box. António Pereira in Portugal decided to try and see if he could increase the performance of the dipole by modifying it. This increase in performance is beneficial for receiving HRPT transmissions such as Meteor M2-3, NOAA 19, NOAA 18, MetOp-C, and other L-band satellites. This would also work very well for tuning in a dish and dipole feed for LRIT, HRIT transmissions using GOES, GK2A, and other geo sats in L band as well.

Tools and Materials Needed:

  • Heat gun
  • Pry tool
  • Soldering iron
  • 1/4 copper tube
  • Hammer
  • Wire stripper

Instructions:

  1. Remove the dipole box from the aluminum arm. Use a heat gun to soften the glue and slide the box off the arm.

2. Open the dipole box. Unscrew the screw and use a pry tool to open the box.

3. Modify the dipole. The original dipole will be too short. Use the measurements in the picture to create new dipoles from copper strips. António made the copper strips by cutting a 1/4 copper tube lengthwise and flattening the copper with a hammer and cutting to length.

4. Remove the original dipole from the cable. Strip the cable to solder it to the new dipole.

Pocket sized torch might be needed for soldering copper strips

5. Tune the dipole. Use a VNA (vector network analyzer) to tune the dipole to 1.70 GHz. This is the frequency that worked best for the António, but you may need to adjust it depending on your specific antenna.

6. Close the dipole box and put it back in the arm.

7. Place the reflector in its original position without any spacers.

8. Adjust the focal point. Pull the arm forward 3.5 cm from its original position for maximum signal. Note: António’s clever adjustment fix using longer blots to allow the feed to be adjusted from what was a fixed position.

Congratulations! You have now optimized your WIFI grid antenna for maximum efficiency.

António noticed that there was a signal loss at peak elevation, or, a signal glitch, the constellations showed a brief glitch and SNR dropped to zero for a brief moment resulting in those lines on the imagery directly above the location of the dish.

With a suggestion from Jamie Vital https://github.com/JVital2013 The center signal dropout is caused by the center carrier of the HRPT signal crossing the center of the SDR’s tuned frequency. It’s an interaction with the SDRs DC spike. Trying IQ correction won’t help much.

To rectify the issue, your best bet is to tune the frequency off by 100 kHz or so, then set SatDump to use a 100 kHz frequency shift the other way to “re-center it in SatDump’s mind”. This makes it so the center carrier of the HRPT signal never crosses the actual middle of the SDR.

From what I’ve seen, METOP isn’t affected since it has no center carrier.


Build Your Own Rotator with a Meridian Flip Fix

António also designed a very slick rotator and is sharing the build instructions here:
This software package provides everything you need to build your own rotator with Meridian Flip Fix. This means that when a satellite is crossing north, there will be no interruptions to make a full turn back to 360°. The rotator will keep going until the end of the pass.

ZIP Rotator Files for this Build

Software

The software package includes:

  • An Arduino script
  • An ESP32 script to act as a Wi-Fi to serial bridge
  • Hamlib files
  • USR-VCOM
  • A circuit diagram
  • A pre-made rotctld.bat file set to COM10

Hardware

The hardware you will need includes:

  • A 12V power supply
  • A 12 to 5V DC buck converter
  • An Arduino Nano (I recommend the Arduino Nano Every)
  • An Arduino Nano I/O shield (optional but makes connections much easier)
  • An ESP32 to allow wireless control of the rotator
  • 2 stepper motor controllers (I recommend TMC2160, it’s super quiet and smooth)
  • 2 Nema 23 stepper motors
  • 2 optical home switches

Mechanical Hardware

You can use whatever mechanical hardware suits you. In António’s case, He used 50:1 worm gears, and the Arduino script is preset to a 50-gear ratio. However, you can use whichever ratio you want and change the script accordingly. The script is also preset for 1/8 micro-stepping (1600 steps per rotation), and that’s the minimum setting for the TMC2160.

Additional Notes

  • The circuit diagram shows how to connect the hardware components.
  • The Arduino script controls the rotation of the rotator.
  • The ESP32 script allows wireless control of the rotator.
  • The hamlib files are needed for the ESP32 script to communicate with the rotator.
  • The USR-VCOM is a virtual COM port that allows the Arduino script to communicate with the ESP32 script.
  • The pre-made rotctld.bat file is used to start the rotator software.

I hope this information is helpful.