Coax and N-type to Probe Pieces

TOF work took up most of this week, but I have been working on the problems:

  1. Better Coax – Thanks to Kevin who sent me a link to the “Air Dielectric Cable” and it can handle much higher power then the LMR-400.  I have been trying to track down a source for it in Canada.  Part of the problem is that the bending radius of LMR-400 is 1″, already pretty stiff, and the Air Dielectric cable is 5″ which might be too stiff.  Actually, now that I think about it some more, it doesn’t matter if the cable was completely solid, as long as it can swing with ease, it would still be easier to move a few centimetres than moving a heavy shelf with all the fans, magnetron, waveguides, circulator and water on it.  Coax it is!  Maybe I can find a freely rotatable waveguide transition piece in amongst all those spare parts at the university, hmm…
  2. Better N-Type connector – this is going to be more difficult and here is what I am trying:
    • I am getting a quote from the Canadian division of Richardson Electronics for another Wavguide to N-type transition.  However, the spec makes clear it can only handle a paltry 0.3 KW which is much too low.  I’m guessing they will want $300 to $600 for it anyway..
    • I also have a call into Gerling Applied Engineering, Inc. who has been helpful in the past.  They also make the transitions and might be able to sell or help me solve the problem.
    • It might be possible to use the dielectric from one of the waveguide-to-n-type transitions at the university to replace the one we burned up.  I’m guessing that whatever that dielectric material is made of, it is much better then the one we had because the waveguide-to-N-type connector at the top of the coax has not burned up yet (hmm, I should check, I never looked there for smoke!) It should also be possible to purchase just the dielectric and replace the one we burned because everything else including the probe looks fine.
    • I am desperate enough that I have emailed Shawyer to ask him what probe-to-N-type transition he used and you have been bcc’d.

Another possible solution is to move the probe which leads to a question – Even from our own simulations, it is apparent that the highest power is going to exist within the coax-to-probe conversion point:

The big red arrows are a bad thing!  Is it possible to locate the probe at a different point and decrease the amount of power it sees?  I will try that test on the simulator when I get back from vacation in July.

Unfortunately, eBay has been all but useless in this endeavor…

Magnetron Probe mount

I decided, since I am using the probe from the commercial waveguide in the cavity, to use the waveguide as the magnetron probe mount.  I cut the existing mount off and now have to enlarge the hole to fit the magnetron probe.  I will be up at the university tomorrow to mount it.  It turns out the center of the hole is 33mm from the back short which is exactly what we modeled and built for the pyramid antenna. (In the picture below it may not look the same because the hole in the pyramid antenna is larger and they are at different angles to the camera)

(Although interesting, but not related – the ink on the “Property of Levitee” tag shown on waveguide must be heat activated because after I finished grinding the surface smooth, it turned black in a nice arc.)

Shelf FInished, Bubbles Removed from Circulator

I got the shelf installed and started fixing the leaks and bubbles in the circulator setup.  The pictures below are from my phone and I will get better quality ones next week:

I still need to fix one leak and tighten down the barbed nozzles on the circulator.  I left the setup next to the sink for the weekend.

I need the extension cord to for the water pump’s power supply and you can also see the end of the coax, the leads for the magnetron and the fan.  The fan, used to cool the magnetron, will setup air currents inside the Faraday cage, but I will create a cowling if anything does move.

Have a good weekend!


Built Shelf for Microwave Source

I brought the cavity up to the lab today and hooked it up to the cable, both now hanging in the Faraday cage. I am now building a shelf, parts of which are sitting on the soldering lab bench, which will hold up the µw source assembly (magnetron, circulator, waveguide-to-n).

I tried the barbed nozzles and they fit the circulator (3/8″ sized hole it turns out), but the barbed nozzles fit 3/8″ size tubing but the tubing on my pump/radiator is 1/4″ in diameter which means I need 3/8″ sized threading and 1/4″ sized barbs. I will check Home Depot this afternoon and if they do not have any, I have an alternative solution ready.

I will be up tomorrow (Friday) to fix the shelf to the side of the Faraday cage and wire everything up.

My last task is to then build the magnetron probe to waveguide mount (8.6cm wide, 4.3 high and 8cm long).

I am taking the pyramid antenna back home to use as a guide. If TOF work doesn’t come up, I should have everything ready to go by the middle of next week.

Oh, and I scavenged another 1KW microwave. Not sure what is busted on it though.



Copper Horn Resonator Finished

The resonator is finished:

It looks a bit messy, but it is because I got flux on my gloves and the outside oxidized a bit.

Here is a shot of the interior before I sealed it up:

Brazing with flux and solder worked excellent and it did not warp unlike sheet metal.

I will be up at the university today (Thursday) to try out the barbed nozzles with the circulator and start getting everything setup.  I will have to bring some type of shelving in order to mount the magnetron/circulator/waveguide-to-N near the roof of the faraday cage.

Update on work:

  • Purchase 2m of LMR-400 cable
  • Make the cavity and solder the seams
  • Make the probe mount and solder it to the cavity (I ended up using a copper block, the aluminum one would not braze)
  • Make the launcher for the magnetron probe and solder the seams.
  • Get proper barbed nozzles for the circulator for water cooling (got another set to try that are smaller and should fit this time) – test them.
  • Assemble the magnetron/circulator/waveguide-to-n assembly and mount a shelf for it.
  • Setup the water pump and radiator for the circulator.

Time flies…

LMR-400 and Probe Mount Finished

I moved the project ahead a bit today and got the LMR-400 cable and the probe mount finished:

I went with an aluminum block because that is what the original waveguide, where I got the probe, is made from.  The commercial waveguide to N piece I have is actually made from aluminum and anodized with what looks like a thin layer of brass.  Aluminum is also easy to work with and light.  I tried soldering the mount to the waveguide here but my soldering iron is not hot enough, in part because the copper conducts the heat away too fast.

Below is a list with all the things to do and things not yet crossed out have yet to be finished.

  • Purchase 2m of LMR-400 cable
  • Make the cavity and solder the seams
  • Make the probe mount and solder it to the cavity
  • Make the launcher for the magnetron probe and solder the seams.
  • Get proper barbed nozzles for the circulator for water cooling.

Sorry the build is taking longer then normal, but this is the busy season for TechOnFoot.  I am also making sure that I have all the tools and sources of metal necessary to make building the next set of cavities easier.