Discussion in 'Amateur Radio Amplifiers' started by AA7QQ, Jul 3, 2017.

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  1. AA7QQ

    AA7QQ Ham Member QRZ Page

    Yes, it surely did. Now, while I wait on parts, I am figuring the bias. There is part of a bias circuit on the board that I will strip off & replace. By what is there, it had a temp sensor in the heat sink that went to an off board circuit.
    I will be copying this one: http://www.vklogger.com/forum/downl...id=cb5aecd57f3dfe09fba1bb89b8671c62&mode=view
    I might just be able to fit it on the existing lands already on the board.
    I have a 600W 50VDC power supply for each BLF278. The power supplies did not work out at my job, so I am "Recycling them. Luckily, each has a 1.5A 5VDC line to provide for the bias circuit. The power supplies can also be monitored & controlled through the I2C line, which will be running to an arduino, or Pi.

    AF6LJ likes this.
  2. KD2ACO

    KD2ACO Platinum Subscriber Platinum Subscriber Life Member QRZ Page

    Last edited: Jul 28, 2017
  3. AA7QQ

    AA7QQ Ham Member QRZ Page

    With my Larcan, there is an amp of bias per LDMOS. The instructions on the VKLogger amp uses the same. But, it's an amp at about 2-3 VDC. My amplifier pallets are already ready to go for 130-200 Mhz. Just split, bias, combine, filter & measure.
    The cooling system is ever evolving.
    I am planning a 5 gallon tank. The amp will have a pump & valves (To even the flow out) in & out of the tank.
    There will be another coolant circuit that will go to a car radiator outside. I am thinking about using a 5 gallon jug type water cooler for a bit of freon cooling at the output of the radiator & back into the amplifier, if needed in the high heat. They can be had rather cheap on Craigslist. I have a friend that can supply me with food service grade propylene glycol for the coolant.
    I have a general plan for the manifolds of each pallet & have to work on it some more.

    AF6LJ and KD2ACO like this.
  4. AA7QQ

    AA7QQ Ham Member QRZ Page

    So, to 90* Wilkinson or standard? http://www.vklogger.com/forum/downl...id=cb5aecd57f3dfe09fba1bb89b8671c62&mode=view
    This is just as an example. It seems that 90* is better.
    It would add about 7' of RG142. That would be .3db loss, or 92.8% efficiency by the Times Microwave calculator.
    The RG302 at about 14' (Already calculated standard splitter & combiner) gives .6db loss.
    Would it be worth the .3db loss for the gain in efficiency? That would be a loss of 21.45 watts added to the total splitter/combiner set (Input & output).

    Oh yeah, back to splitters & combiners...

    AF6LJ likes this.
  5. K7JEM

    K7JEM Ham Member QRZ Page

    I'm not sure the losses would be what you are calculating. Each module will have to pass through 2 Wilkinsons on the output. That is about 26" of cable in each leg, from output of module to antenna connector. Neglecting loss in the divider itself, all you really have is loss in the coax. That loss would be approx .1dB, which is pretty small.

    If each module is outputting 300 watts, that means that 293 watts are getting to the antenna per module, or 1172 watts out for 1200 in.

    The input side would be the same loss, and is of less concern, since you just adjust input power to compensate for any losses.
    AF6LJ and AA7QQ like this.
  6. AA7QQ

    AA7QQ Ham Member QRZ Page

    Well, alrighty, then.... That sounds much better now. I was looking at it all wrong. I was thinking loss would be the same as in series & should have known better.

    THank you,
    AF6LJ likes this.
  7. AA7QQ

    AA7QQ Ham Member QRZ Page

    So, I guess I will do the input splitters with the RG-179, as some attenuation there might be a good thing. I also have them tuned & cut.
    About the 90* 50 ohm phasing lines, I think that I will add them right at the out put of 1 amp per pallet & to an RPSMA bulkhead (Bought in bulk)Mount the 100 ohm of resistor right there at the end of the phasing line to the output of the paired amplifier, then 1/4 wave 75 ohm lines from them to a final combiner/resistor in an enclosure & Input/output relays/LPF & SWR/power bridge. This will keep my runs as short as possible for the topography that I have.
    Now, I plan to tune each pallet for the 2M band, right at 146 Mhz (Even though they are broadband, there is an input tuning cap for trimming the SWR. If there is any output SWR, I may pull one of the output caps & experiment with a variable cap to come to a best final value of the output cap.
    Now, how much bandwidth should I get out of the 75 ohm splitter/combiner lines? I would love to cover the whole band.
    Most splitter/combiner articles are for HF or UHF/microwave. Of course, the HF ones can do 1-30 & sometimes, 50 Mhz. Ln the UHF/microwave ones, they state narrow bandwidth, but up there it could be 10 Mhz-2 Ghz (Just throwing numbers out).
    What kind of bandwidth can I expect out of a 90* phased TL Wilkinson splitter/combiner set at 146 Mhz? I have found no difinitave answer. If anyone can direct me to articles of the sort, I would appreciate it. I already have several pages of math in my notebook & would like to get an equation for this in a 2:1 SWR bandwidth scenario (Or 3db, whatever is more useful).

    Planning stage is going well. Most modules of the system have been tested. Just waiting on the slow boat from China.
    Ordered more junk from Ebay, too...

    Thank you all for the valuable input,
    AF6LJ likes this.
  8. W0AAT

    W0AAT XML Subscriber QRZ Page

    Why full band coverage? For repeater use it is not needed(or wanted because you will be keying every repeater on that pair in a 100 mile radius!) plus not many verticals can handle that power level. Coverage from 144.00 to 144.500 should be plenty.
  9. AA7QQ

    AA7QQ Ham Member QRZ Page

    Well, there are some Simplex calling frequencies up to the 147 Mhz range & I was thinking about them. I was looking to use something like the CC 10X10 element yagi, A148-20t. It has a 1KW rating & I expect about 800W total output with 10W drive. If needed, I can always alter the gamma match to take the power if needed.
    At least this is my thinking, if the wilkinsons will have the bandwidth. My Larcan does the whole 6 meter band with a combination of stripline & some LC components.
    Should I be rethinking my goals?

    Thank you,
  10. AF6LJ

    AF6LJ Ham Member QRZ Page

    The two meter band is on the order of 2.5 percent of 146MHZ so my money is on your combiner and splitter will cover the whole band.
    KD2ACO, AA7QQ and K7JEM like this.

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