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Thread: TBS crossfire relay station (with 1,2GHz video)

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    Aug 2014

    TBS crossfire relay station (with 1,2GHz video)

    Hello guys,

    As I use the Crossfire about 3 years, could be helpful for CX users my setup and experience.
    I do use the Crossfire in combination with 1,2GHz video. Due to nearness of SRD band frequency (868MHz) to sensitivity area of known video receivers with Comtech modules, is this combination known as a bit problematic – see: https://fpvlab.com/forums/showthread...h-1-2GHz-Video.
    Further I am not friend of any cables when I do fly and therefore the setup I had made is simple wireless relay. I am transmitting the control signal from Jeti DS14 to Jeti Sat2 receiver in relay. Signal from Sat2 receiver is as PPM routed to RC Input socket. Parallel is connected the power from battery to DC Input – just for case of need for 500mW transmitting power - even I do not use such power levels. The relay had been in first version powered from 2S Li-Pol with capacity 3,6 Ah. Crossfire is equipped with tuned dipole from TBS. The electronics is placed in case made of square U-shaped aluminum profile with thickness 10 mm and two 5 mm covers – lower with aluminum bracket for tripod quick mount. Size of relay case is ca 90x90x150mm. On side is power switch and XT60 charge connector. On backside is placed 50 mm 12V fan and balance plug. Front side is covered with polycarbonate with few cooling holes by the heat sinks of Crossfire and conical hole for access to joystick. Case is powder coated to white color, to avoid heating on direct sun.

    Click image for larger version. 

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    First version of Jeti/Crossfire relay

    I had been using the first version for approx. year. After gaining some experience with the system I had found 3 major problems:

    Interference with 1.2GHz video receiver with Comtech module
    Insufficient stability of 2,4GHz signal
    Insufficient battery life.

    All problems are more less connected. With dynamic power on Crossfire is the Tx jumping very early on 500mW power level, what had caused the interference with VTx and relatively quick drained battery.
    There was some solution developed from TBS with notch filter on VTx, nevertheless there was not full success for solving the interference. Notch filter had shorted the range of video and the noise was not fully neglected.
    First what I had tested was how much power I need for reasonable range. We had set up the power on 10mW and moved with Fascination to few places in different distance but with direct visibility. Furthest we were about 13 km away and the link has flawlessly working. Then we had started to remove elements from custom made dipoles mounted to diversity Rx, and the link stopped working first when one antenna was only coax with terminals and the second antenna was without active element – just coax with “ground”. Therefore we had set up the dynamic power level to 10-100mW. 10 times higher power as by test to 13km should be sufficient for target flight range about 30km.

    To further reduce the interfering signal, I had to increase the distance between Crossfire and VRx, in demand to increase the free space loss. First version of relay has the ordinary “monopole” antennas – just cut shielding from active element. Both antennas had been placed inside of relay station, under the polycarbonate front cover. By testing when I was standing between relay and Jeti there was beeps announcing lower signal level on Jeti receiver already at distance of 50 meters. Theoretically fine nevertheless I wanted a bit perfection there. Had agreed with Jeti direct that they will solder to the PCB of receiver not direct the coax cables but uf.l connectors. On new receiver and no warranty anymore but it was not no go for me. Therewith I could connect two pigtails with standard SMA connectors that had been placed on front panel of relay. That had allowed me to place the standard Wi-Fi dipoles outside of case. Testing had shown more as 300 meters range even I had been standing between transmitter and relay.

    Click image for larger version. 

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    Sat2 receiver with ufl/SMA pigtails

    Click image for larger version. 

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    Antenna placement outside

    For thermal flying for relatively short time was the 3,6 Ah Li-Pol ok, but during practicing of thermaling I had been increasing the flight times more and more. Each time had bothered me that I had to take care of relay – mostly depleted. After experience with high capacity 18650 Li-Ions I had used for increase of “life” of DS14 to more as 13 hours, have made similar solution to relay. Samsung INR18650-35E cells are connected to 2S2P pack. Therewith is the capacity on low power (10-100mW dynamically) sufficient for more as 10 hours.

    Click image for larger version. 

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    2S2P battery pack inside of case

    With final setup (new battery, and antennas outside) I had made several duration flights without any significant problems. For short range I do use Fatshark FSV2443 module direct in Dominator V1 goggles and the tripod is placed approx. 10-15 meters from goggles.
    Had not tested for long range direct in flight, nevertheless on 8 km where the setup with SPW 1.2 from Circular-Wireless as omni is on edge of range, I had no interference with Crossfire on my goggles, but there were moments with visible Crossfire interference on friends ground station with VRx with Comtech module. The Fatshark module for Dominators seems to be less sensitive to interference on SRD band frequencies.
    Lowest RSSI I had seen was only when I flew direct overhead, RSSI had shown about 13%, and LQ had been falling to 56%. Further test was in short distance of about 7km but inside of cloud where the moisture should drastically reduce the signal penetration and LQ was never lower as 98%. By that circumstances had already video giving up. Therefore I hope there will be no problems with interference with Crossfire in future – the time and long range will show :-).


    Last edited by zlutyslamak; 15th August 2018 at 09:35 AM.

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