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Thread: Coherent GEM CO2 laser RF cable lengths.

  1. #21
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    I contacted photovac and they quoted me a pretty good price, it was discounted though I am not sure why, maybe because of my work email. My friend that I got the laser from found the original RF cable and I tried that. Welp, I don't need to send it in after all.

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    So apparently length or type is really critical with these. The cable is 2.35m long and made with LMR-400 which I had guessed, the plenum version though. I have some of the flexible version coming tomorrow and see if that works too.

  2. #22
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    Looks like a winner!

  3. #23
    mixedgas's Avatar
    mixedgas is offline Creaky Old Award Winning Bastard Technologist
    Infinitus Excellentia Ion Laser Dominatus
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    VSWR sensor is overly sensitive or they are doing something weird with the matching networks.
    Glad to see you have it working.

    Steve
    Qui habet Christos, habet Vitam!
    I should have rented the space under my name for advertising.
    When I still could have...

  4. #24
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    I had ordered some LMR400UF to make a flexible cable since the stock cable is horrible to work with since it has a solid core. So I made the new one exactly the same length.

    Doesn't work.

    Argh.

    So I picked up one of those cheap VNAs, I had been meaning to for a while anyway. I connected it to the original cable and it shows the cable appears to have an open impedance going by the smith chart at 100MHz.

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    I connect the new cable I made, and yep, its different giving about 45 degrees of phase difference and appearing to have about 5 ohms of impedance, so it looks like the cable is too short by about 6-8". Crud. Ordered some more cable and connectors, this time ill put one end on and cut the cable to match. This power supply is way too sensitive.

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  5. #25
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    Feb 2019
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    Hello.
    I have also a coherent gem-50 with deos d600 rf psu without rf cable.
    I tried an rf cable from a synrad laser but it didn't work.
    What cable/connectors worked for you?
    I think i have the manual for this laser but iam not sure.

    Also i have rofin scx30 (300w) and made for this laser a random length rf cable(4m)
    with 7/16 connectors and worked ok.

  6. #26
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    The stock cable I have is 2.35 meters long and made from LMR-400-LLPL. I have not gotten another cable working. I have the parts ordered and will try making a new cable again next week.

  7. #27
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    2.35m with the connectors included or not?
    Thanks for the info i will try with a 2.35m cable

  8. #28
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    Ok, so using the NanoVNA I put a connector on one end of the cable and started cutting pieces of cable off till I got to what appeared to be a perfect open at 100MHZ on the smith chart. Cut a touch more off to compensate for the center pin and crimped it all up. And it works. Finally. This is using LMR-400-UF which has a stranded copper core and it more flexible than the standard LMR-400. Total length from end of connector to end of connector is 2495mm

  9. #29
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    So must get LMR-400-UF 2495mm ..
    What connectors you used at both ends ?
    Your RF PSU is Deos D600 ?

  10. #30
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    I used these.

    https://www.rfparts.com/r161075040.html

    You will need a crimper to use these connections. There are crimpless types of connectors too, just more expensive.

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