RADAR Power and COAX

  1. I am under the impression that a person might be able to use a short (10 foot) piece of coax to run 10 GHz microwave RADAR energy down instead of using WR90 waveguide. Is this even remotely possible? Is there any such coax that can handle the RF peak pulse or AVG power form an old RADAR set from the 50's? I realize the purpose and reasons for waveguide, but its expensive and usually difficult to work with unlike coax. I'm just not versed enough to know if such a thing can work even if there are acceptable drawbacks like a little extra loss. The RADAR I speak of is an old 10kW Bendix airborne RADAR. I use these type relics from eBay to study RADAR and experiment with high power microwaves. Any useful wisdom from some of you more senior microwave types would be very valuable to me in this endeavor. Many thanks and please... Stay Tuned!
  2. jcsd
  3. marcusl

    marcusl 2,114
    Science Advisor
    Gold Member

    The answer is that you should find out for yourself. There are two numbers you need to worry about--the peak voltage, which governs breakdown, and average power, which determines heating. Calculate the peak voltage in the line and compare it to the maximum voltage handling spec of your coax. You'll see that the V rating depends on the cable type, frequency, and altitude. Do the same with average power. Be sure to also look at the rating for the connectors, since they need to be special high-voltage types. Start with standard old RG-8, then look at specialty coax like Heliax from Andrew Corp.

    BTW, hope you aren't radiating when performing your radar experiments. Unlicensed radiation is illegal, and can create hazards to and interference with legitimate equipment that is used for communications, aircraft navigation, weather observation, etc. Really, if you are not versed enough in electronics and microwaves to know about power handling, I propose that you may be putting yourself and others nearby at significant risk by attempting to experiment with this equipment.
    Last edited: Aug 13, 2014

  4. Thanks for your concern but it's unfounded. I know more about microwaves than that. I have proper dummy loads and antennas and output on that band is nearly unregulated. You're not required to go and get a license to operate a marine or aviation radar. They don't exist. I'm intimately aware of exposure limits of RF emissions. On the other hand, thanks for your ideas on the coax. I thought as much but wondered and still do why you never see coax used for this moderate and low AVG pwr. Heliax I know well. There are these exotic coax types that have many thousands of volts of stand off. These magnetrons run around several KV pulses so I guess that's the number to use. Ultimately, my inspiration is ease of use and low cost as well as great flexibility rather than these miles of heavy waveguide I have been using. Thanks for your reply!
  5. Last edited: Aug 13, 2014
  6. Don't forget about the voltage rating of the N connectors and potential VSWR. Sometimes the connector rating is less than the coax.
  7. marcusl

    marcusl 2,114
    Science Advisor
    Gold Member

    N connector has exposed center conductor and low breakdown voltage.
  8. Is it the best connector for 10ghz power? No, but they can handle 5kW at HF and several hundred at X-band easily with proper matching.
  9. Baluncore

    Baluncore 2,705
    Science Advisor

    Wave guide is used because it has very low loss compared with coax.
    The TR switch is usually integrated into the coupling at the bottom end of the waveguide.
    When waveguides arc over, they do not burn like the dielectric in a coaxial cable.
    You would need to use “airline” coax to reduce loss. It is more expensive than waveguide.

    “Type approved” equipment does not need individual licensing. The manufacturer has demonstrated to the appropriate authorities that the equipment, as inspected, satisfied the regulations. A type approval certificate was then issued to the manufacturer for that version of the equipment.

    Changing from waveguide to coaxial cable will certainly void any type approval on the equipment.
  10. sophiecentaur

    sophiecentaur 13,695
    Science Advisor
    Gold Member

    The 7mm precision connectors work up to 18GHz or so and will take 2500V RMS, I believe. Better than type N in many respects - except for price!
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