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I'm designing a 300W power amplifier using the MRF300AN from NXP targeting a center frequency of 146 MHz.

Obviously I need to keep my fingers out of it and test into a dummy load, but generally speaking when testing an amp design, how do you do it safely to prevent:

  • RF burn
  • Excess radiation
  • Spurious emissions
  • Other considerations?
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  • $\begingroup$ I hope if this can help: microwaves101.com/encyclopedias/ldmos $\endgroup$
    – hesham_EE
    Jan 2 at 4:46
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    $\begingroup$ What frequency is this for? Not to make light of a 300 W solid state amplifier, it's an impressive project, but if it's for 2-15 MHz, that's probably closer, in terms of danger to people, to a 300 W audio amplifier, than something like a microwave oven, which really would be scary. $\endgroup$
    – tomnexus
    Jan 3 at 7:01
  • $\begingroup$ When you go to use this amp, you need to make sure SWR on your antenna system is as low as possible. 1.2 may be too high. Most coax arcs at 600v, at 300w it's not hard to get there with just a little swr. You may need higher grade feed line too. $\endgroup$
    – user10489
    Jan 3 at 12:14
  • $\begingroup$ @tomnexus, its for the 2m band centered at 146 MHz. $\endgroup$
    – KJ7LNW
    Jan 7 at 20:21
  • $\begingroup$ @user10489, I'll make sure to lookup the voltage withstand spec for the cable. We'll use LMR400 for long runs, some say RG58 should be able do 1.5kW at 26:1 SWR according to this page, but others report RG58 arcing at 1.5kW=~274Vrms: forums.qrz.com/index.php?threads/coax-and-corrosion.491219/… $\endgroup$
    – KJ7LNW
    Jan 7 at 20:41

2 Answers 2

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  1. Get yourself a dummy load.
  2. If your gut is telling you your doing something stupid you're doing something stupid.
  3. Keep the power supply switch near by.
  4. Always assume it's live.
  5. If you have doubts about a mod or an idea don't do it unless someone more experienced helps you with it or gives you advice.
  6. Assume your capacitors are still charged, check them every once in awhile.
  7. Ground your bench properly.
  8. Take your tests in increments. Adjust slowly up but quickly down.
  9. Treat the project like your spouse or friends and it won't hurt you back.
  10. Handle any tubes with care and keep your hands clean free of oils when touching them.
  11. Turn off the project when you leave it for long periods of time.
  12. Have a list of emergency back up numbers incase you didn't listen to your gut.
  13. If it has fuses take them out when working on your project.
  14. Unplug what you are working on before you reach for wires.
  15. Don't use tools that have metal handles.
  16. Use your brain.
  17. Get some fresh air after some soldering work.
  18. Keep yourself focused on what you are doing,
  19. If your project is smoking, unplug the power supply.
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    $\begingroup$ 13.b. if it doesn't have fuses, put in fuses, then revisit 13. 19.b. see 13.b. $\endgroup$
    – webmarc
    Jan 10 at 19:06
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If you do have to stick a scope probe or adjustment tool into it, take off all your rings, watches, bracelets, necklaces, etc., before reaching into anything (or around any uncovered circuitry) that might be powered with a high current power supply or high amperage battery.

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  • $\begingroup$ Agreed, but silicone rings are much safer than metal ones for machinists or folks working around electricity. $\endgroup$
    – chicks
    Jan 7 at 17:36
  • $\begingroup$ I'm saying that silicone rings are a much safer option for people who stick their fingers in dangerous places. There are times when your dearly beloved would prefer for you to keep your metal ring in a safe place and having a $1 backup silicone ring will help you feel less naked. $\endgroup$
    – chicks
    Jan 8 at 1:10

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