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Discussion in 'Amateur Radio Amplifiers' started by WA4SIX, Jul 3, 2017.

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  1. WA4SIX

    WA4SIX Ham Member QRZ Page

    Well, here I go buying junk on Ebay again. But, the price was too good to pass up, and they are my LDMOS of choice, BLF278s.
    I have 8 pallets coming. All LDMOS tested & guaranteed. I will use 4 pallets for a 1.2KW 2M amp.
    These pallets are rated 120-200 Mhz (I am sure I might have to tweak a bit) 300W.
    This may be my first water or freon cooled amp.
    Now, for splitters/combiners....
    I am looking at Wilkinson S/C & probably using 75 ohm TL transformers (Just 1/4 wave*VF) & the proper resistors for isolation. I would probably use RG302 or just Quad shield RG6. Both have the same voltage rating. I cannot find the wattage rating for the RG-6. Also, the RG6 quad shield does have a better Db loss rating at 1Ghz.
    Would I be better off using lumped components? Sure would be smaller. If so, I could use a bit of help here.

    THank you,
    Last edited: Jul 3, 2017
  2. WB2WIK

    WB2WIK Platinum Subscriber Platinum Subscriber QRZ Page

    I'd use the Teflon cable instead of any kind of RG-6 for this.

    For TL combiners why not follow what Jim W6PQL has already done?
  3. WA4SIX

    WA4SIX Ham Member QRZ Page

    Well. I nèd a 4 port combiner set
    I could do strip line but would rather use tl or lumped.
  4. WB2WIK

    WB2WIK Platinum Subscriber Platinum Subscriber QRZ Page

    For four ports I've used three 2-port combiners, works fine.
    AI3V likes this.
  5. WA4SIX

    WA4SIX Ham Member QRZ Page

    That is my intention. If I try lumped, should I just use the inductance & capacitance per foot, or a transformation calculator from 50 ohm to 100 ohm?

    Thank you,
  6. WA4SIX

    WA4SIX Ham Member QRZ Page

    OK, using an impedance transformation for 100 ohm to 50 ohm at 146 Mhz, I get 54.505 nh series inductance & 10.901 shunt capacitance.
    For the inductor, #16 AWG gets me .2"D .203"L & 3.99 turns.
    Do you think I can fudge it to a 10pf cap? 11pf is an odd number.
    If I try this, can I put an MFJ 259C on the single input & 2 matching 50 ohm dummy loads at the output & sweep it?
    I don't have access to a network analyzer.

    Thank you,
  7. WA4SIX

    WA4SIX Ham Member QRZ Page

    OK, now thinking about it, I may swap the capacitor to the series & the inductor to the shunt. If so, I can make a test unit in a PL259 with a 100 ohm terminating resistor, to see if it works properly. Then, wind the inductors to test/tune them on the Boonton 250. I am looking at 1.5KV capacitors.

  8. K7JEM

    K7JEM Ham Member QRZ Page

    According to my calculations, changing to a 10pf cap will change the output impedance to 53.9 ohms or so.

    You could build a HV coaxial capacitor out of a few inches of Teflon coax, trim it to anything you want.
  9. WA4SIX

    WA4SIX Ham Member QRZ Page

    Well, I did find some 11pf 1KV SMT caps. I will start experimenting soon.

    THank you,
  10. WB2WIK

    WB2WIK Platinum Subscriber Platinum Subscriber QRZ Page

    Yes, that's what W6PQL does (caps made from open-ended sections of PTFE coax).
    WA4SIX likes this.

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