=  NOW 40 WPM  =  
LINE OR TO THE DETECTOR.  THE SENSITIVE DETECTOR CAN NOT ONLY SHOW THE
STANDING WAVE PATTERN ON THE COAX OR WAVEGUIDE TRANSMISSION LINE, BUT ALSO
PROBE A RADIATED FIELD PATTERN.  SUMMARY  WITH SIMPLE EQUIPMENT, WE ARE
ABLE TO VISUALIZE MICROWAVES IN BOTH COAX AND WAVEGUIDE, AND AROUND AN
ANTENNA.  THIS INSIGHT MAY REMOVE SOME OF THE MYSTERY AND MAGICAL ASPECTS
FROM MICROWAVES, SO GIVE IT A TRY.  THIS RUDIMENTARY TEST EQUIPMENT MAY NOT
BE AS ACCURATE AS EXPENSIVE PROFESSIONAL

MICROWAVELENGTHS PAUL WADE, W1GHZ, W1GHZ ARRL. ORG  VISUALIZING MICROWAVES,
PART 2 WAVEGUIDE VISUALIZING MICROWAVES ON A COAXIAL LINE, AS SHOWN IN THE
OCTOBER 2019 MICROWAVELENGTHS COLUMN, CAN BE ILLUMINATING, BUT WAVEGUIDE IS
EVEN MORE INTERESTING.  WAVEGUIDE OPERATION IS FAR FROM INTUITIVE, BECAUSE
RF ENERGY TRAVELS THROUGH A HOLLOW METAL TUBE WITH NO CONDUCTORS, LEADING
SOME HAMS TO CONSIDER WAVEGUIDE MAGIC.  BECAUSE IT IS HARD TO SEE OR PROBE
THROUGH THE SOLID METAL WALLS OF A STANDARD WAVEGUIDE, I CONSTRUCTED A
WAVEGUIDE SHOWN IN FIGURE 1 USING COPPER MESH SHEET AMACOS WIREFORM METAL
MESH IN COPPER, OFTEN USED BY ARTISTS.  I LEFT A LENGTHWISE SLOT IN THE
CENTER OF THE BROAD WALL OF THE WAVEGUIDE, BECAUSE THE MAXIMUM ELECTRIC
FIELD, WHICH WE CAN DETECT AS VOLTAGE, IS IN THE CENTER SEE FIGURE 2.  IF
THE SLOT IS EXACTLY IN THE CENTER, THE VOLTAGE ON EACH SIDE OF THE SLOT IS
THE SAME AND THERE IS NO RADIATION FROM THE SLOT.  THE SLOT DOES NOT AFFECT
WAVEGUIDE OPERATION, AND WE CAN PROBE THROUGH THE SLOT WITH LITTLE
DISTURBANCE.  WE CAN SEE IN FIGURE 2 THAT THE ELECTRIC FIELD VOLTAGE AT THE
SIDES OF THE WAVEGUIDE IS ZERO, BECAUSE THE SIDE WALLS CONDUCT AND CREATE A
SHORT CIRCUIT.  THIS IS ONLY POSSIBLE IF THE WIDTH OF THE WAVEGUIDE IS MORE
THAN A HALFWAVELENGTH.  THE LOWEST FREQUENCY WHERE THIS OCCURS IS CALLED
THE CUTOFF FREQUENCY, BELOW WHICH NO ENERGY CAN TRAVEL THROUGH THE GUIDE.

A WAVEGUIDE FOR 1296 MHZ WOULD BE QUITE LARGE.  I CHOSE TO MAKE THE MESH
WAVEGUIDE WR 229 SIZE 2R29 X 1R145 INCHES VISIT WWW. WA1MBA. ORG/ WAVEGD.
HTM FOR A TABLE OF WAVEGUIDE SIZES, COVERING 3R3 TO 4R9 GHZ, BECAUSE I HAD
A SURPLUS PIECE TO HOLD THE MESH IN SHAPE AND A COAX TO WAVEGUIDE
TRANSITION TO EXCITE IT.  THE SETUP, SHOWN IN FIGURE 3, USES THE SAME
CHINESE SYNTHESIZER AS THE COAXIAL LINE FOR A SOURCE, RETUNED TO 3456 MHZ,
BUT ANY SIGNAL GENERATOR, TRANSVERTER, OR EVEN A SIMPLE OSCILLATOR WILL DO.
FOR SAFETY, KEEP THE POWER LEVEL LOW A FEW MILLIWATTS IS PLENTY.  THE SAME
SENSITIVE RF DETECTOR IS USED.  I MADE A NEW LONGER, THINNER PROBE AND
INSULATED IT WITH A BIT OF WIRE INSULATION TO PROBE THROUGH OPENINGS IN THE
COPPER MESH.  PROBING THE OPEN COAXIAL LINE AT 3456 MHZ SHOWED MINIMUM
VOLTAGE AT 16R4, 20R6, AND 25 CENTIMETERS, MINIMA SPACED ABOUT 4R3
CENTIMETERS AS EXPECTED, FOR A WAVELENGTH OF ABOUT 8R6 CENTIMETERS.  WITH A
SHORT CIRCUIT PLATE AT THE END OF THE WAVEGUIDE, PROBING ALONG THE SLOT IN
THE WAVEGUIDE SHOWED MINIMUM VOLTAGE AT 8R5 AND 15 CENTIMETERS, FOR A GUIDE
WAVELENGTH OF 13 CENTIMETERS.  THIS DIFFERENCE IN WAVELENGTH AT THE SAME
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