What TX amplifier do you plan to use?

  • Do you have any photo of the final result?

  • That won't help you much, just try and increase the PCB tracks until you get max power. Start on the input path an then modify the output till you are satisfied.


    If you get 15W out of that little PA then be happy.


    And of course after modification measure with spectrum analyzer for unwanted signals from the PA or use a good bandpass filter after it.

  • Hallo,
    I use this amplifier. It works well together with a LimeSDR Mini. I would like to know, if there is any solution for a standby mode.
    The idle current generates some dissipation. It would be nice to avoid this.
    Thanks
    73
    Andreas, DL5CN

  • Hi Achim,
    thanks for the hint. SDR-Console supports an USB-Relay meanwhile, so switching the supply is simple but not very elegant. The LimeSDR Mini gives approx. 0 dBm, the total current to the amp. is about 2 Amps.
    At present, I use all the equipment in a portable way, the dissipation is limited. But for longer standby a switch off of the idle current is useful. The picture shows the "Radio" below the laptop.

    73s
    Andreas, DL5CN

  • Hi OMs,


    because nearly every day a couple of emails arrive here about the modification of the small Andrew MRF21045 amplifier i digged mine out of the pile of "old" amplifiers and took some pictures.


    vy73 DB8TF

    What is the purpose of adding copper sheet?How does the dimension of copper sheet work out?I am curious and want to learn this reason.The pa design work I used is between 1900 and 2100. I also need such modification.

  • Hi Achim,
    thanks for the hint. SDR-Console supports an USB-Relay meanwhile, so switching the supply is simple but not very elegant. The LimeSDR Mini gives approx. 0 dBm, the total current to the amp. is about 2 Amps.
    At present, I use all the equipment in a portable way, the dissipation is limited. But for longer standby a switch off of the idle current is useful. The picture shows the "Radio" below the laptop.

    73s
    Andreas, DL5CN

    Beautiful design.Does the limesdr mini work properly on the usb hub?

  • Hi, yes it does.
    It must be an USB3.0 Hub. The hub is feeded with a 5V switching regulator. It is connected with a small sound card and the relay also. The Lime board is mounted upside down with some thermal pads. The actual version of SDR Console works in duplex mode. I use a dual feed with a 1,3 m offset dish. Beside the LNB no further components are needed. The "Radio" operates with 12V.
    73s
    Andreas, DL5CN

  • @BG0AUB


    those Little copper pieces act as additional capacitors on the input and output pcb tracks and help to optimize the matching of the normally for (2,17GHz) UMTS freq designed circuits and internally matched LDMOS.


    You could calculate the needed capacitances and the position where to install them but i used the "try&fail" method till i achieved a (for me) satisfying output level from the PA.


    I got max. 16W out with 500mW drive from this MRF21045 (IDq 300mA) and that is not bad. ;)


    Vy73 DB8TF

  • Surely adding capacitance "lowers" the frequency ? Where as we want to go "higher" from 2.1/2.2 to 2.4 ?


    Dave

    Dave Cawley | Ex G8EAO & G6ANG/T |
    (when you had to have a separate TV license !)

  • Surely adding capacitance "lowers" the frequency ? Where as we want to go "higher" from 2.1/2.2 to 2.4 ?


    Dave

    I clearly tried first to decrease (smaller PCB tracks) the capacitance, but the results were not good.

    Google for UMTS PA Mods and you will see only Pictures with Increased capacitances.


    vy73 DB8TF

  • Do you know why that is ? And why it flies in the face of logic ?


    BTW I just Googled "UMTS PA Mods" and came up with nothing ?

    Dave Cawley | Ex G8EAO & G6ANG/T |
    (when you had to have a separate TV license !)

  • Do you know why that is ? And why it flies in the face of logic ?


    BTW I just Googled "UMTS PA Mods" and came up with nothing ?

    I dont' know why but with added capacity it works far better.


    On my Ericcson UMTS PA no modification on the input or output works best.


    So it seems that this rule of adding capacity works not on all UMTS PAs.


    Maybe with this MRF21045 adding capacity helps and with other LDMOS not.


    Try it for yourself and see. If you find a better way then let us know.


    In this Pic: What TX amplifier do you plan to use? it also looks like he added some caps to the preamp?


    vy73 DB8TF

  • 实践是检验真理的唯一标准

    The copper looks like a capacitor, maybe showing more inductance...For lack of standard measuring equipment and more theoretical knowledge support, practice is the best method.I like that, maybe one day there will be an opportunity to have a measure or a theoretical analysis of the results.You will say.Oh, I see.

  • The transmission line - copper track - transforms the capacitive impeadance of the tuning flap. A quater wavelength away and the impeadance is inductive.


    So if you want inductive impeadance, you place a capacitance one quater wavelength away.


    73 Ole