Parallel power supply of the rotary antenna motor

The best place to get parallel power to the motor is a DiSEqC switch, but since it is not capable of passing large currents, it needs to be finalized.

Using an awl and a scalpel, carefully remove the spring-loaded cover of the switch so that it can be reinstalled in its original place:


In the places indicated by the red arrows, we cut the printed conductors, and in the places indicated by the blue arrows, we solder additional elements:

Between the power point of the control circuit of the switch and the central output of the 4th port is the inductor L1, which passes the direct current of the motor supply and the pulses controlling it with a frequency of 22 kHz, but is an infinitely large resistance for the RF frequency;

In the break of the signal line from the switching diode to the 4th port - capacitor C1 with a capacitance < 1000 pF so that the motor power does not open the switching diode;

Between the printed inductance to the left of the 4th port and the signal line between the capacitor C1 and the switching diode - inductance L2, through which the opening voltage is supplied from the control circuit in the presence of the command “switching the 4th port to the DiSEqC output of the switch”

Elements 2 and 3 allow you to connect a fourth LNB through the second motor connector. I connected an LNB with a director to the 4th port to receive the MITRIS “terrestrial” DVB-S2 broadcast system:


As you can see in the photo, the drop cable goes to the output of the converted DiSEqC switch, the focus LNB Inverto Black Ultra is connected to the first (connected by default) port; a multi-feed LNB with a depolarization plate is connected to the second port to receive circular polarization signals; an LNB with a director is connected to the third port to increase the signal in the “far” multifeed, and the cable from the 4th port goes to the WinQuest motor and from the second connector to the LNB with a director, which is directed to the MITRIS transmitting antenna.

The following shows the frequency response of the second channel (without a motor in the RF circuit) - on the left and the fourth channel (with a motor in the RF circuit) - on the right:


Due to the poor matching of OMICOM S2 with the wave impedance of the cable, intense (up to 2.7 - 3.3dB at high frequencies) standing waves appear in it, which are a source of in-band interference. The uneven frequency response reaches 5 - 6dB. The inclusion of the motor in the RF circuit catastrophically distorts the frequency response ...

The difference in frequency response was obtained without and with a motor in the RF circuit:


For the 1.05m antenna, which is connected to the TBS-6983 card through a motor according to the standard scheme, the frequency response was obtained with a significantly lower level of standing waves, which is explained by the presence of broadband matching transformers in the card:








After registering the spectra and parameters of the transponders, the setup was converted to parallel power supply of the motor through the 4th port of the DiSEqC switch:


Look how favorably the frequency response has changed - the total unevenness has decreased from 13 to 9dB, the amplitude of standing waves has decreased from 3 to 0.7dB:


Now you can see how the parallel power supply of the motor affected the reception of real signals.

After alteration of the installation, the unevenness of the amplitude-frequency characteristic decreased by 1 dB for V and 2 dB for H polarizations. The signal level, on the contrary, increased by 2-3dB for V and 1-3dB for H polarizations:



The number of found transponders increased by 2, and the number of blocked ones - by 5 units

Average SNRav =14.9dB (0.5dB more) and LM headroom =8.2dB (0.4dB more) :


The average SNR level has grown to 13.8dB, the lock margin is up to 6.9dB, the number of locked transponders is up to 60:



The number of found transponders increased by 3, and the number of blocked ones - by 7 units 

 Average SNRav =13.8dB (0.7dB more) and LM headroom =6.9dB (0.7dB more) :


To evaluate what the addition of two wire spirals and one PCB capacitor to the DiSEqC switch gave, I note that increasing the sensitivity of the receiving installation by 0.7dB is equivalent to increasing the diameter of the antenna aperture from 105cm to 113cm

Comments 1

  • Hervorragend Erklärung , einfach super.

    Excellent explanation, simply great.

    Отличное объяснение, просто супер.