What TX amplifier do you plan to use?

  • I don't think I am brave enough to try that module. Although it is multistage with a lot of gan, I don't think I am experienced enough to try to snowflake a multistage amplifier at this point- and the inbuilt doherty worries me as I hate not knowing what is going on in a chip - I can't adjust the internal lines!


    I decided to opt for the dual MRF7S21110HS board that he has on offer. Probably a little less power - and a lot less gain but hopefully easier to work on!

  • As far as i understand the circuit on this amp looks like the first BLD (both FETs) is always on and with the additional doherty circuit the second BLD (both FETs) is activated when the first goes in saturation. With my mod both BLDs (all 4 FETs) are active.


    Till now i don't think there is a "special" doherty circuit inside the BLD. Of course you can realize the doherty mode with one BLD if you use only one of the FETs as peak amplifier. On the actual circuit it is done with a second BLD.


    As the naming with "N" in the suffix says the IDq is measured via the additional current sense leads (only 1 branch of each BLF is used).


    For sure this BLD look like a special produced device for this amp and that there is no datasheet on the web also points in that direction.


    In a few days when i return from vacation i will further test this amp.


    73s DB8TF

  • I was looking at the BLD6G22L-50 datasheet


    which looked like the 90 degree shifts were built in to the BLD. I assumed the -150 was just a higher rated version.


    To be honest - I'm out of my depth here - this isn't my area of expertise so I'm just guessing - that's what I like about this hobby - always something new to find out about.

  • I took the pin numbers on the diagram to match up with the pins shown on the device


    This is just curiosity for me as I have bought a different board now!


    Also:

    The BLD6G22L-50 and BLD22LS-50 incorporate a fully integrated Doherty solution using Ampleon’s state of the art GEN6 LDMOS technology. This device is perfectly suited for CDMA base station applications at frequencies from 2110 MHz to 2170 MHz. The main and peak device, input splitter and output combiner are integrated in a single package. This package consists of one gate and drain lead and two extra leads of which one is used for biasing the peak amplifier and the other is not connected. It only requires the proper input/output match and bias setting as with a normal class-AB transistor.

  • Because this "doherty" issue haunts me i had to take a closer look at the BLD6G22L-150BN/2 connections to assure that i am not wrong with my statement that there is NO doherty circuit (at least in the actual circuit) besides the external components.


    I took some pictures to show that there is no separate "Peak amp bias pin" or so connected.


    The used small Pins on the sides are only for regulating the IDq.


    BTW, the Xinger is OK for 2,4GHz use:


    https://www.mouser.de/datashee…D%20Data%20Sheet-7429.pdf


    vy73 DB8TF

  • Thats a relief, I wish I'd bought one now!


    I'm sorry if I caused you concern - I just assumed the BLD6G22L-150 and BLD6G22L-50 would have been similar devices given the both have the D for doherty!


    The only information I could find for the -150 was as below - so the Idq you measured of 1340 looks to be in the right region. Apparently the module was rated at 60W (linear) in the sales literature.


  • First report on ongoing modification:


    With 500mW drive at 20V i get "only" 25W out at 4A rf current, so abt 25% effective.


    The final supply with 28V will deliver much more power out, have to find a better PSU here :)


    The most annoing problem is that you need to mount and unmount the upper case after every "snowflaking" you carry out, that takes a lot of time.


    vy73 DB8TF

  • DB8TF Florian, the Doherty concept makes that when the 'main' amp is above saturation, a second (or 'peak') amp 'helps'.


    Mostly the main amp part is in class AB and the peak amp in class C.


    So, the overall efficiency is better compared to a balanced ('push pull') amp.


    Say AB has 60% efficiency and C has 80% efficiency (modern LDMOS can have these efficiencies) means that (push pull) 0.4 + 0.4 = 0.8 / 2 = 40% is dissipated, whereas

    (ideally) in a Doherty setup 0.4 + 0.2 = 0.6 / 2 = 30% is dissipated (so 25% less).


    In contrast to a push pull, where the phase difference between the two halves is 180°, the phase difference in a Doherty amp is 90°.


    Assume the input splitter of your amp is of a 'rat race' type and that 90° ports are

    selected, the output combiner must also have this 90° phase shift (but then in the opposite direction).


    Looking at the output circuit, you marked a 90° delay line from which I strongly conclude it is a Doherty setup (!)

  • Hi Remco,


    it is right that it is a doherty amp with those 90 degree splitter & combiners but there is no special doherty circuit IN the BLDs.


    I have the suspection that one of those BLDs is defective, no output but IDq and RF on the gate exists…


    Will investigate further (and change the Xingers if necessary)..


    73s

  • Sure! In the picture you'll see my homemade "connectors" using dual row, 2mm spaced pin array. Covered with hot melt glue. Original SMP output was located on the right of the circulator, ugly replacement SMA soldered instead. :) Could not find a SMP mating connector so I let it go.

    Hi,


    have you some information about modification and power supply for this amp ?

    Thank you.


    73 Alex

  • ik4idy :


    as Oh3WE wrote

    "The pair of fets have very different biases. The other one warms up and draws a lot of current, about 50 watts of idle power warms up the shack.

    Nevertheless the system delivers 70 watts output (perhaps more)."


    I think this amp is also configured as a dohery type. The LDMOS in the middle of the PCB is the main amp an the one to the Corner is the Peak amp.


    If you supply the 28V and measure only abt 1,9A current and only the main amp gets warm then you are sure. The gate bias on the main is about 2V, on the peak amp bias about 1,8V.


    If properly "snowflaked" you can expect about 30% of the rated CW power on 2,4GHz with a relatively poor effectivity of abt 20-25%. If this LDMOS are the -130 types then expect not more than 85W from that amp.


    vy73 DB8TF

  • Tu, giving up on this amplifier...


    regards.


    73