Posts by IZ4RYB

  • IZ4RYB Ampleon 500w ready for Dattv tests

    Project doc completed.


    See

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  • IZ4RYB Ampleon 500w ready for Dattv tests

    Hi,


    first 500w Ampleon Pa tests, first changed PA to 105cm cable to 1/2inches Cellflex to stand up to 700w at 2,4Ghz as in attacched 105cm-ofset.jpg.

    First dattv tx trial at 1Msymbol immediately stopped due to over power.

    Second tests 2Msymbol see pictures 2Msymb.jpg.

    Last but not least new upstation see Upstation.jpg.


    Power around 130w shoulders 50db.


    Bye!

  • Ampleon 250w pallet

    Hi,


    this kind of thermal bias NTC compensation is suitable only for CW operation with a bias current around 20ma, using water cooling.

    When the LDMOS is used around its maximum power the NTC reduce the bias current and the output power decreases leaving the
    LDMOS temperature under 60 degrees. We are using the LDMOS at half of the maximum power with around 800ma bias current.

    If we leave any kind of NTC thermal compensation we are not getting any power decrease with bias we will only reduce the bias
    current and the linearity creating DVBS distortions.

    The best DVBS thermal compensation suitable for DVBS operation, should be a microprocessor measuring with internal ADC the NTC
    resistance and regulating the input power with a digital step attenuator.

    We are not a SAT broadcasting TV so we do not need to have continuous operation, so I've just placed one ohmmeter connected to
    the internal pallet NTC sensor and I just check the resistance stays around 400 ohm during Tx.


    Bye!

  • IZ4RYB QO100 experience

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  • Ampleon 250w pallet

    Hereunder movies


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  • IZ4RYB Ampleon 500w ready for Dattv tests

    Hi,


    not at all I prefer seafood. It rained a lot in Italy during this month but not to have

    flying seafood :).


    In reality the dual ldmos is 500w CW, I'll use it at around 200w DVB-S2 to get better shoulders.


    I've also modified the pcb taking out the output Duroid section and placed RG142 cannot stand more than 300w at 2,4GHZ.


    I've forgot to tell the Fausto Coletti call sign is IK4NMF, he manufactured the 500w PA for me.


    Bye!

  • Siemens UMTS-PA for WB ?

    Hi,


    I'm sorry to tell you that siemens amplifier is not working on 2,4ghz, I've spent a lot of time on it, at the end I've discovered the driver drops dramatically after 2380Mhz. I've than tried input rf directly two the final stage getting not more than 30w but with 28vx14amper.

    I've than used the case with the ampleon pallet. That siemes amplifier is only suitable for 2320mhx datv.


    Sorry for that but it is my experience even with suggested modification.


    Bye!

  • Ampleon 250w pallet

    Hi,


    the Ampleon 250w pallet has been a good challenge I had to fight a lot with bias circuit before understanding
    the real problem root cause.


    I had really to read carefully the data sheet and application note.


    First of all we have to think what is the pallet designed for. Not at all for DVB-S2 but for CW or CSW pulsed.

    We do not have to forget it is for ISM energy professional usage, continuous operations.


    If you have look on the Ampleon application
    note, the water cooling system is recommended, you know when an American designer is writing recommended it means
    we mast follow the recommendation. Not only the pallet requires water cooling but cold water cooling, yes 5 degree

    centigrade water cooling.


    The pallet data sheet says there is an internal bias compensation but I've not been able to find any circuit details.

    I'm in a good relationships with Ampleon people, I've opened several support tickets getting fast and detailed answers,

    but no way to get the bias details. I've then done pcb pallet reverse engineering finding the internal bias compensation

    it is just one 1500ohm ntc feeding the bias input current to ground. I had a look on the BPC2425M7X60 and I think
    it has also same ntc as 250w pallet, so using this 60w pallet you will run same problem I had.


    Here attached the ntc resistance/temperature table I've got from ampleon. Reading that table you see the ntc has
    around 1500ohm at 25 degree centigrade and the resistance drops dramatically to 600ohm at only 40 degree centigrade.


    I've chosen a really simple external bias circuit done by a regulator from 28v to 12, than a couple of resistors and a

    potentiometer generating a bias voltage from zero to 8V. The 250w pallet has 1,6v threshold.


    I've than applied the 28V and adjusted the bias to 500ma as suggested from ampleon tiket regarding DVB-S2 usage.


    I've than applied rf input and seen the output power was initially getting well and after a couple of second dropping

    dramatically.


    I've than measured the operating bias directly to the LDMOS gate discovering it was drooping from initial 1.7V to 0.5 volt.


    I've than thought the bias current was not enough.


    Even I know the LDMOS bias current is around one microampere, I've decided to add on transitory to my bias circuit to

    increase the current. I've than adjusted the bias current to 500ma and applied the rf in. Nothing changed same behavior

    as before good initial power and than dropped again.


    Luckily the pallet has another ntc, same as the bias compensation one called temperature sensor, measuring it resistance
    I've discovered just applying rf in it drops from 1500ohm to 600ohm in a couple of second.


    I do not want to bore you with all the tests I've done, but at the and I came to the conclusion I had two options, the first
    add cold water cooling to the pallet, the second take out internal pallet bias compensations.


    Due to the fact I do not have continuous operations needs for amateur DVB-S2 operation, I've taken out the ntc from
    the pallet and added an ohmmeter to the ntc temperature sense. Looking to the ampleon ntc table I check the ohmmeter

    not drooping less to 200 ohm corresponding to 60 degree centigrade. That is the maximum pallet temperature suggested
    by ampleon.


    Since than I'm using the pallet for DVB-S2 operation with 140w power and I've never seen the internal sense dropping

    less than 550ohm.


    The best would bee to add an alarm circuit to switch off the pa when the internal sense drop to 200 ohm.


    I'm now working in an ampleon 500w LDMOS pa I think I'll do the alarm for it.


    I hope I've my experience will help someone else working with ampleon pallet.


    Bye, ... have fun with bias and ntc.


    DE IZ4RYB

  • Vmix streaming portsdown pi ampleon 250w 1 megasymbol

    Hi,


    I'm sorry I've forgot to comment the video in English, anyway I think you have understood the setup anyway.


    About the power to have a shoulder around 30 db I'm getting 140w, I've not tried to drive more because the BU500 DATV limit
    is around 125mw. As soon as I'll have time I'll prepare a better presentation with all technical details.


    Bye!

  • Ampleon 250w pallet

    Hi,


    I've preferred to by the complete module, I had a lot of problem with temperature and bias but now look working well. Let me know how your pcb works when you finished it.


    Bye!