Episode 1478 let's look at several architectures some coupler math: • Lecture 31---Coupled L... W2AEW video: • #196: How a Directiona... Be a Patron: / imsaiguy
Very good clip, thanks. I did not know about transformer type coupling. In some power amplifiers, they use couplers to sample the output power so they can per-distort the input signal to cancel out non-linearity of the amplifier .
Delicious black magic! For me the tough part is achieving coupling without disturbing too much the main rf path (as well as getting good impedance match)
The electric field around a wire is mostly radial. The part parallel to the wire only generates IV heat losses. The EM field inside the wire decays exponentially beginning at the surface; this is the 'skin effect.'
That thing that looks like ferrite may be a cast carbon resistor. It looks like a high power coupler so the combination of surface area and non-inductive resistance makes a lot of sense for both heat dissipation and bandwidth.
That microstrip coupler on the power amplifier is actually reading the forward output power of the amplifier and is probably used as part of a power control loop.
@15:25 The wide un-plated trace is of unknown impedance. The green trace above it has a 100 Ohm resistor termination, so we know what the impedance (100-Ohm) is very likely to be. It could be a 1:2 ratio, or in the case of Toroid based (low power) couplers with 1 thru-turn through it could be a 1:20 or higher ratio, depending on the Toroid secondary turns ratio. Many QRP SWR meters use Toroids just to get enough voltage to measure... ...but mostly via Op-Amplification of the half-wave rectification.
Check with your DMM if there's continuity between the L-shaped rod and the ground, because the pin going through the ferrite is there to contact the end of the rod. Lovely HF engineering there! It's still all Klingon to me, but hey - I'll learn it someday. Ha.
Imsai Guy, Maybe the blue coupler's ferrite material is really a wideband resistor? That would make more sense since it would follow the typical coupled line construction (i.e. 50 termination on one end). And I suspect the resistor's topology results in very low parasitics, permitting a very high upper frequency.
More RF magic. Doesn't get much better than this! The two transformer based ones are not that difficult to understand. One transformer measures the current on the transmission line and the other measures the voltage. If you do the math as W2AEW did it comes out fairly easily in terms of forward and reflected energy on the line. See his excellent video for details.
The transmission line devices do the same. Capacitive coupling from the center rod to the adjacent rods establishes the voltage on the center conductor and it will be in phase with the voltage of the center conductor. Inductive coupling reveals the current on the center conductor; this coupling turns into a voltage on the parallel rods BUT the phase is reversed. That means one of the sensing rods will take its measure where the induction and capacitance reinforces; the other sensing rod is where the inductance opposes the capacitance. Only in the case the termination is 50 ohms will the resulting current exactly cancel the capacitively coupled voltage. Really that's all it does. It has no idea of "direction" and it isn't, strictly speaking, a directional coupler.
Awesome video. Back in video #749 you made "Improvements" to an old Antenna Tuner. IT had on of the "SWR Bridge" units in it just like the "Archer" unit in this video. SOMEWHERE around my house I have one of these units - I THINK it is a Vanco unit. Main thing I got from this video is the difference between a "Coupler" and a "Detector (like the SWR Bridge) and it made things much easier to differentiate between the two. Have to used the Toroid thye coupler (see #749b) with an Arduino WITHOUT the Log Amp? Did it work ok?
@@IMSAIGuy I gave it a shot, but I don't have the same results (No coupling), the two wires I'm coupling are also the same in length. Maybe the Vpp? Any ideas?
