coil impedance

Interesting post on Linkedin, a short while ago, highlighting an old audio amplifier trick. This was winding a low value inductor around the body of an aluminum electrolytic can with vinyl insulated wire - something you might have run into in Dynaco kit amplifiers, as an example ('70s)

The <1uH schematic entry, in parallel with 10R, placed in series with the output, was intended to prevent oscillstion driving a capacitive load.

It was pointed out that the aluminum can presented a shorted turn in that configuration.

With an air-cored inductor, the shorted turn didn't have the same dramatic effect it might have had, if wound on a high permeability medium, but did drop inductance by a factor of 3 - 5.

RL

You just shifted the problem to finding a filter with -150 dB distortion.

John Larkin Highland Tech Glen Canyon Design Center Lunatic Fringe Electronics

Below -120 dB, even connectors have distortion.

Low-distortion connectors cost more.

John Larkin Highland Tech Glen Canyon Design Center Lunatic Fringe Electronics

Microwave 'stirring' motors are pretty generic, but unforgiving in form and fit.

Once there's been a fire, the bobbin and terminations are rarely recoverable.

Replaced for a few bucks plus shipping. I keep pull-outs as spares.

RL

Not sure, but the alternative is a rotating reflector, that you can't see unless you take the box apart.

RL

So you wouldn't use ferrite-core inductors to make it, and you might need two made with different components to check if they produced the same result. Twin-T narrow-band filters can be pretty sharp, but you would probably need to twiddle a pot to keep them at the right frequency.

Evidence?

Name one.

You're dreaming! Sure, a shortwave receiver can see 10uV, but it most certainly cannot do that in the presence of a simultaneous

Anyway, 160dB attenuators are fantasy. Leakage from cables and connectors easly exceeds that. Even getting over 70dB needs extra care.

Jeroen Belleman

John Larkin Highland Tech Glen Canyon Design Center Lunatic Fringe Electronics

Google

resistor voltage coefficient

Some common resistors are -1000 PPM/volt.

The best you can buy are around 1 PPM/v. Pots are usually cermet, really bad.

Spice has excellent resistors.

Caps are worse.

John Larkin Highland Tech Glen Canyon Design Center Lunatic Fringe Electronics

John Larkin is a gullible sucker. That ad is aimed at people like him, who don't know that they ought look for evidence supporting implausible claims. The "tri-metal Albaloy coating" may be the greatest thing since sliced bread, but this comes from the same sort of people who used to electroplate silver onto copper and claim that an electroplated layer of silver gave a low skin resistance than the solid copper it was plated onto.

Somebody eventually found a way to measure it, and it didn't. It took decades.

Two-tone intermodulation distortion measurement is even easier to use, the resullts are read directly off a meter. It deserves to be used more often.

It was certainly known in the 1960s in the radar community.

John

It has been used in the human and some animal ears. A healthy cochlea generates intermodulation products that can be measured using a microphone in the ear canal. If the cochlea is diseased the intermodulation products go away. Acoustic time domain reflectometry also works on the ear.

John

google low pim connector

PIM distortion is a serious issue in cell towers. Connectors can have several distortion mechanisms. Even rusty bolts in the structure can be a problem.

In an audio oscillator, even if there are no intermetallic junctions, opamp cmrr and psrr and ESD diode varicap effects will matter.

We have done systems with ca 1 PPM linearity, but that's only 120 dB at DC, not 150dB at KHz.

John Larkin Highland Tech Glen Canyon Design Center Lunatic Fringe Electronics

Some of the nonlinearities are at high power; magnetics, effective arcing, ionization. It affects cell towers too.

Some effects, like oxide film tunneling, happen at low voltages. 150 is a bunch of negative dBs.

John Larkin Highland Tech Glen Canyon Design Center Lunatic Fringe Electronics

What meter goes to -150 dB?

John Larkin Highland Tech Glen Canyon Design Center Lunatic Fringe Electronics

Nice - found this interesting:

The Johnson noise of a 50-ohm resistor at 20 C with 5 Kc/s bandwidth is

-130 dBm. If we take the rail-to-rail output voltage of an op-amp to be about +20 dBm, that gives 150 dB difference. Claims that a device is capable of achieving this sort of figure in any practical situation is stretching the limits of credibility.

If the signal is lower than +20 dBm, you either have to start cooling the device or reducing the measurement bandwidth, otherwise 150 dB S/N ratio is impossible to achieve.