What TX amplifier do you plan to use?

  • ... problem solved.

    Its not the SMA plug, its the cable who is heating.

    I have now exchanged the thin coaxial cable for an RG-142. The heat development is now much lower. The 40cm piece still has a loss of about 4 watts at 60 watts of power. With a longer transmission passage, the heat development of the cable is well visible on the thermal scan ....

    So, be careful with high power on 2,4 GHz and thin cables ... :-)

    73s de Robert

  • Hello together, can someone help me to interpret the specifications in a technical data sheet?

    The FET´s data sheet specifies two performances. In the case of the MRF6S21140HS it shows:

    Typical 2 - carrier W - CDMA Performance: VDD = 28 volts, IDQ = 1200 mA,

    1.: Pout = 30 Watts Avg., F = 2112.5 MHz, Channel Bandwidth = 3.84 MHz,

    2.: Capable of handling 10: 1 VSWR, @ 28 Vdc, 2140 MHz, 140 Watts CW Output power

    Does this mean now that you can load at a bandwidth of 3.84 MHz only with 30 watts (may), in narrowband operation like CW probably 140 watts.

    How is it with DATV? Is it possible to load more than 30 watts with a correspondingly lower bandwidth (for example 500 kb/s)?

    Is the maximum load between narrowband and 3.84 MHz bandwidth linear, from 140 watts down to 30 watts?

    What can I accept?

    73´s de Robert

  • 140W CW is single tone performance.. call it P1dB. 30W is W-CDMA performance with a specified ACPR (adjacent channel power ratio) of -41dBc (according to datasheet). So the 30W is more likely the usable DVB-S2 power in our situation.. which incidentally is about -6dB of the CW output power. Seems to be a good rule of thumb according to the BATC experts.

  • DD4YR It has all to do with linearity, so that 'in channel intermodulation' (free translation from Dutch) doesn't smear out (to other channels).

    Just like the old analogue CATV systems, which used e.g. BFW16's or other 'power' transistors in their distribution amplifiers. In my (illegal) FM transmitters at that time (80's) these BFW16's were able to produce almost 1 Watt, but for linear purposes there needs to be an OPBO (Output Power BackOff) of ... say .. 10 dB (or more depending on the application).

  • PA3FYM

    thanks for the explanation.
    Are the IDQ = 1200 mA given in the data sheet sufficient for the 30 Watt and DATV linear operation? I always thought, "Mode A" amplifiers need significantly higher IDQ?

  • Yes, like Achim said , that delivers the most spectral pure impact. With these multi carrier signals it's not anymore 'adjust bias for max output' (like with single carriers in the old days ; -)

  • Quote

    For mrf21045, my bias voltage is 2.7-3.0, 0.55-0.9a at 24v, and 42DB is output when 30DB is input

    So you have 12dB gain? 42dBm out for 30dBm input.

    I wonder if 50W output is possible, perhaps the internal matching is not so good at 2400. (28V and 14.7dB gain at 2200MHz on datasheet)