Microwave tech, "the blackest of the black arts in analog electronics" as CuriousMarc called it.

I worked a aircraft transponder repair bench in the 70's. The early transponders put out simple pulses at 1090mhz using a tube and a cavity. If the load at the antenna was not 50 ohms the cavity could ring funny and even cause multiple aircraft to be reported at the same location. We used one of those to vary the impedance to see if the transmitter was stable with different loads. The early Narco transponders were prone to this problem. Now I might be wrong, maybe what we had was just a line stretcher. I bet you could build a better transponder than what was availble in the 60 and 70's for $20 from off the shelf components today.

"Back in the day", I used these at my place of work. They are wonderful impedance-matching devices, I believe capable of conjugately-matching any finite and non-zero impedance to any other at any given frequency across the stated frequency range, as long as the impedances have positive real parts, and only subject to the limitation that the conductors of the tuner are not perfect, in that their resistances are greater than zero. The book, Microwave Measurement, edited by A. E. Bailey, shows a waveguide E-H tuner in Figure 9, page 81. A counterpart in coaxial line, identified as a shunt - series coax tuner, is shown in Figure 10, page 82. The Figure 10 tuner is very similar but not quite identical to the Narda 906N because the Figure 10 tuner uses a coaxial line with sliding short in the center rather than a balanced parallel line with sliding short. (The E-H tuner name when applied to the Narda 906N must be a carryover from the waveguide tuner, as the E and H refer to the electric field plane and the magnetic field plane, respectively, of the waveguide.) As you correctly point out, the inner slotted structure with sliding short forms an adjustable series element somewhat like a trombone, such that the transmission line length in series between the source and load can be changed. (However, since the input portion of the line up to the inner sliding short is in proximity to the output portion coming back down from the inner sliding short, this section acts as a balanced coupled line.) The line length is adjusted by moving the sliding short. As long as the effective length of the transmission line can be varied over a half wavelength or more, the impedance can be moved along a closed arc spanning a full 360 degrees when mapped on the Smith chart. This adjustment constitutes one degree of freedom. Another degree of freedom is needed to move the impedance anywhere on the chart from the center to the edge. The other adjustment on the outer coaxial structure accomplishes this. The outer coaxial structure with the outer sliding short forms a transmission line stub, shorted at the far end, and connected in shunt with the main line. This part forms a shunt susceptance that behaves as either a shunt inductance of any desired value or a shunt capacitance of any desired value, depending on the position of the sliding short. When the sliding short is exactly a quarter wavelength (or an odd integer multiple of a quarter wavelength) from the junction, the stub acts like an open circuit -- it is as though the stub is not present at all. When the sliding short is exactly a half wavelength (or integer multiple of a half wavelength) from the junction, it is as though there is a dead short across the transmission line at the junction. Adjusting the position of the sliding short makes the impedance spot mapped onto the Smith chart move in and out while also changing its angle on the Smith chart. Thus, the two adjustments interact, but the two degrees of freedom allow any situation to be conjugately matched, as long as the loss in the lines is not excessive. 🙂

A E-H tuners are commonly known as "Magic T's". Microline was a product line Narda bought from Sperry Rand Corp. I have a similar one (different frequency range) that is labeled Sperry Rand Corp. All of my other Magic T tuners are waveguide types where the E and H adjustable arms are perpendicular to each other.

It's a microwave slide whistle.

I may be all wet, as I've never seen on of these before....From what I see, making the transmission line longer adds inductance. That's one of the sliders. The other slider spreads the split line closer to the large tube which is ground and this spacing becomes a variable capacitor shunt. I think you have a simple L type tuner that is of low pass design. They have just unwound the inductor that you'd find in an HF tuner, and made it linear because the wavelength is so small. Very cool instrument.

5:30 "Gesundheit!"

And at Georgia Tech this is why we called RF, black magic.

From the thumbnail, I thought that looks like small, precision tuning hammer. But not nearly that simple! Coming from that era, I imagine that LSD was likely involved in the conception and design of such a device. And it might be helpful in the subsequent operation. What funky thing! Maybe if you could shine it up nice an pretty, it would be a great addition to your gallery of "guy toys".

homo sapiens and sticks relationship sure has gone a long way

They could have made a fortune selling this Rube Goldberg contraption as the E-H Putter!

Forgive me if I am way off base as RF is not my thing, I'm more of a DC digital guy. It appears this creates a variable serial/parallel inductor connection The inner slide varies the serial inductor (and perhaps capacitance across the inductor), the outer slide varies inductor between transmission and ground.

When the smith chart is matched to a 50 ohm termination (at a fixed frequency) moving each rod from the tuned position should scribe a curve, giving away what it is doing. It will no doubt be adjusting along reactance or susceptance curves, inductive or capacitive following the curves on the chart (noting your analyzer is not displaying the admittance chart, only the more familiar impedance chart).

Let me try and see if I can have a go at this one. It's a tuneable coaxial "cable". If you have a properly tuned antenna you can stick a pin through a coax at the right spot and the RF will act like there's no short. With an impedance mismatch you'll get reflections. If you add a shorting "pin" at the right place you can eat up a reflection but it'll change the impedance the transmitter sees. With a second shorting "pin" you''ll re-reflect that back to the antenna. The transmitter sees the proper impedance and the load sees the proper driving impedance. It's sort of like a capacitive input pi filter that's used on the plate of a class D amplifier. The plate feds into a variable capacitor in parallel, that feeds into a variable series inductor, and that then feeds into another variable capacitor in parallel. The only difference is this is using the distributed inductance and capacitance instead of the bulk inductance and capacitance.

i think iner rode adjusts capacitanc ,outer rode adjusts inductanc.

in my point of view, this is just a parallel plate capacitor. the two segments split inside acts as a capacitor and the shorting point is just a way to put two capacitors in parallel. that is, before the shorting point you have a capacitor and after another capacitor. both will be in parallel. there are some liquid level sensors that resort to a similar effect but by changing the dielectric constant and not the size of the plates. im sure there is also some inductive reactance distributed along the device.

What happened to your recent "not using fancy test equipment" initiative?

God bless you!

Don't you love it when mechanical and electronics design converge?

wow, very nice!!!🤓

a 40 Ohm load? what a weird thing. But so convenient for this demo. Is testing Magic T and other match networks what it was made for?

Had to use a few of those in university some years ago. Yeah they didn't make any intuitive sense.

A microwave impedance matcher?

As a resource to repair the broken one... Maybe a music instrument repair company would be cheaper than an electrical equipment repair company? No joke really intended... HTH

Your analyzer is set for 0 - 10 MHz, but the device is marked 0.95 - 10 GHz ?

Isn't just an adjustable "T" network?

Phase adjuster?

Got a Smith Chart?

___ | | З L1 __|__ | | L2a 3 3 L2.b ____|--||--|____ C1 C1 and L2(a,b) is a inside slider, L1 outside slider.

u do know that the label says microtune not microline right?