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Thread: RF CO2 laser drive frequency

  1. #11
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    I spent a lot of time the last few days reviving the brain cells I used back in the pirate radio days and getting back up to speed on RF electronics. I tried a bunch of stuff, but in the end, I've built a matching network with 12 turns of #14 magnet wire wound around a 1/2" post and stretched to a bit over an inch long. That gives 0.9 to 1.0uH, not mH like in the diagram. For the cap I used a 100pF silver mica cap in parallel with a 20-80pF mica compression adjustable cap. I can adjust this for better than 1.5:1 SWR, but the tube wont restart afterward. It seems happier with a little more inductance (compress the coil a bit) or a little less capacitance. When I tune for peak output, the SWR is 2 or 2.5:1 so not terrible. According to my power meter, I'm hitting the tube with about 150W. That seems high, but the driver was made for a slightly smaller DEI tube (which, sadly, is up to air). The small tube was part of a vet surgical system that should have made 15W when working.

    Sadly, only 1 of the tubes I have here is working well. It makes 14W average though the power wanders quite a bit (I've seen 12-15.5W). Another does about 8W average and the rest are dead or dying (1-3W) I tried tweaking the alignment on one of the near-zombies with no luck. I didn't move it much since I didn't want to crack the indium.

    BTW, the output beam is as big as the OC mirror - about 1/2" and so not terribly destructive until focused to a smaller spot.

  2. #12
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    Your coil wire gauge and dimensions sound simular to the factory matching coil on the digimark tubes. mH is certainly a mistake. On the batch of Domino tubes I had I found the matching networks would often be out of tune and the tubes would often run much better at a slightly different frequency than the expected 27MHz. The tubes would also tend to make more power at cooler temeratures. I susupect this is true of most CO2 lasers.



    Quote Originally Posted by Junktronix View Post
    I spent a lot of time the last few days reviving the brain cells I used back in the pirate radio days and getting back up to speed on RF electronics. I tried a bunch of stuff, but in the end, I've built a matching network with 12 turns of #14 magnet wire wound around a 1/2" post and stretched to a bit over an inch long. That gives 0.9 to 1.0uH, not mH like in the diagram. For the cap I used a 100pF silver mica cap in parallel with a 20-80pF mica compression adjustable cap. I can adjust this for better than 1.5:1 SWR, but the tube wont restart afterward. It seems happier with a little more inductance (compress the coil a bit) or a little less capacitance. When I tune for peak output, the SWR is 2 or 2.5:1 so not terrible. According to my power meter, I'm hitting the tube with about 150W. That seems high, but the driver was made for a slightly smaller DEI tube (which, sadly, is up to air). The small tube was part of a vet surgical system that should have made 15W when working.

    Sadly, only 1 of the tubes I have here is working well. It makes 14W average though the power wanders quite a bit (I've seen 12-15.5W). Another does about 8W average and the rest are dead or dying (1-3W) I tried tweaking the alignment on one of the near-zombies with no luck. I didn't move it much since I didn't want to crack the indium.

    BTW, the output beam is as big as the OC mirror - about 1/2" and so not terribly destructive until focused to a smaller spot.

  3. #13
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    I think a friend of mine might have the power supply modules for these things. I can check if anyone is interested.

    -Jerry

  4. #14
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    Quote Originally Posted by macona View Post
    I think a friend of mine might have the power supply modules for these things. I can check if anyone is interested.

    -Jerry
    I'd be very much interested!

  5. #15
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    If he's got several, I'd be interested in a stand-alone driver as well. I have a couple of those Domino 7 channel driver boards, but they only produce ~10W per channel. If I decide to slice one of those up, one channel driving a cheapo CB 'linear amplifier' would do the trick also.

  6. #16
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    Anyone happen to have the PS for a Domino DD3? I have a brand new tube from their blue line which lases at 9.3um and puts out 25w cont 40w peak. It has the rf drive built onto the tube heatsink. The thing is it needs somewhere around 80v and a couple amps to drive. I dont have anything that puts out that high of a voltage. Ive been debating selling it since they cost so much $, and ive kinda switched focus from my original plans. But i have to say, these things are so damn cute!!
    Jane

  7. #17
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    According to the spec sheet, the ARF449 transistor used on those tubes needs 150V to produce full power. Also, it's just an amplifier - it needs to be excited by one channel of the 7 channel driver boards that make about 10W @ 27.12MHz. An 'export' CB radio transmitting unmodulated on channel 14 would also work


    Quote Originally Posted by als1980 View Post
    Anyone happen to have the PS for a Domino DD3? I have a brand new tube from their blue line which lases at 9.3um and puts out 25w cont 40w peak. It has the rf drive built onto the tube heatsink. The thing is it needs somewhere around 80v and a couple amps to drive. I dont have anything that puts out that high of a voltage. Ive been debating selling it since they cost so much $, and ive kinda switched focus from my original plans. But i have to say, these things are so damn cute!!
    Jane

  8. #18
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    got to take some pics and post them. From what I dug up on a 3rd party tube maker and looking at my unit it just needs the DC power and a 0-5v mod signal, which is very similar to the Synrad units I have, except they only take 30vDC.

  9. #19
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    Laser Warning First time forum user.

    So, first time forum user. Please correct if I do something annoying. The point:

    I used to work at the top laser maker in the world, by volume, and made several of their most recent laser offerings. I only did the RESONATORs and don't know jack about rf and impedance matching. On to the issue...I made a really cool new resonator that no-one else has done. It is like a hybrid of three different types of tech. It is RF driven - will be anyway.

    How do I choose the driving frequency? I know about the Paschen curve, and seem to remember someone telling me I have 4 options for driving frequency: 48, 80-something, 106 and 120?. I'm thinking of just using 40 or 50 MHz, but I want to make something that I can commercialize. I found some really nice RF boards from digi-key for $220 off the shelf. But, then the signal generator, matching network, what else.......

    I'd like to buy everything already made, like the RF board I found, link at bottom.

    Can't I just buy a board that has the signal generator, amp, matching network, and just touch the output wire to the electrode? You'll have to forgive me, as I"m an aerospace engineer, and totally have the mechanical side of this with inductance, capacitance, tank circuit, all that, but syncing the RF to it - total dummy.

    I asked my RF coworker that used to work their with me about using a tesla coil to drive it, as I have a declassified Norway paper from 1983 that talks about how they used a large inductor coil wrapped around the electrode to drive it, and I thought that was a clever way to impedance match. I thought it sounded like some kid of tesla coil. But, he said I was the wrong side of what I need. He said I needed small voltage and large current, and a tesla coil is large voltage, small current.

    I just want this think to make plasma right now, and the easiest way is the best way, for now. Any help would be greatly appreciated!

    Best,
    Photon

    P.S> How had noone on this forum taken that name yet!!!!!!! Mine now!

    Quote Originally Posted by mixedgas View Post
    They were sold as OEM parts to Pfizer, Diamond, and several bar code printer companies.

    Never quite pinned down a maker. I did tear one one down. The optics are indium sealed, and the mix has Co, Xe, Co2, N2, and He.
    Lots of Xe from the spectrum I looked at. I sold my other head.

    My friend has one that is different and runs 8-9 microns using Co-Xe-He instead of the 9 to 10.6 Co2 band.

    The cavity is set up to be pretty much mis-alignment tolerant... Tyring to adjust the mirrors very much will crack the indium.

    There is no catalyst in the bore or anything.

    Steve
    https://www.digikey.com/en/products/detail/nxp-usa-inc/MRF101AN-50MHZ/9749136https://www.digikey.com/en/products/detail/nxp-usa-inc/MRF101AN-50MHZ/9749136

  10. #20
    mixedgas's Avatar
    mixedgas is offline Creaky Old Award Winning Bastard Technologist
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    Google ISM frequencies...
    Those are the worldwide (mostly) license free Throwaway Frequencies for industrial, scientific, and medical.

    If your unit is totally shielded, and has RF line filters, and is tested to ensure it complies with emissions regulations, you can get away with just about anything you want except aviation, navigation, and safety of life/destress frequencies.
    That compliance is costly if your RF engineer doesn't know what he/she/it is doing. If they do, compliance is cheap and is mostly sheet metal and a input line filter and some RF chokes. For a laser you need a good RF engineer anyways.
    No, I don't do that anymore, but I have on a small lab scale in the past. Your product gets designed by a good RF engineer, with a 3200$ spectrum analyzer or ~6000$ network analyzer (used price) then approved by a testing lab with hundreds of thousands of Dollars worth of gear. It typically takes two trips to the certified approval shop. You'll end up butting heads against a conducted emissions LISN test, and radiated emissions test anyways.

    Faraday shields, RF line filters, inductors on control and power cables, ferrite chokes, and copper sheet metal fingers for gap sealing are your friends.

    Just say no to Tesla, say yes to an off the shelf RF amp from a place like Communications Concepts or similar. Modern industrial RF sources are amazingly efficient.

    Tesla is a great way to flunk emissions testing before you even get there. Tesla coils spew noise like a volcano, and would be 1920s RF technology, horribly inefficient for what you want to do,

    Find yourself a 1990s copy of the ARRL handbook and start reading on impedance matching and coaxial cable. There are 600,000 Ham Radio operators in the US, and 5-10% of them can do what you need in their sleep in terms of basic design.


    Steve
    Last edited by mixedgas; 02-09-2021 at 07:51.
    Qui habet Christos, habet Vitam!
    I should have rented the space under my name for advertising.
    When I still could have...

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