AoE x-Chapters, High-Speed op-amps section, DRAFT

On a sunny day (Tue, 16 Jul 2019 06:56:47 -0700) it happened John Larkin wrote in :

Mega Watt? not kW? What frequency is that?

Long ago I lived not so far away from a TV tower:

Tested my ham transmitter with a neon bulb in the garden :-)

I would not want to live right next to such a tower, all your electronic experiments will be affected by it.

Theoretically yes but it cannot handle the transients at the onset. When that stuff is on a die it can take uncontrolled paths, and from what I experienced seems to do so. Large output amplitudes.

And each would probably cost $2M+ on the market, leaky plumbing or not. No 10 horses would drag me to live in S.F.

IME such small bypass cap values make no sense at all. Definitely not in the days of MLCC. 0.01uF to 0.1uf in 0603 is fine. It's the layout that counts, plus the proper use of large planes as "free" bypass capacitors. This is part of my daily bread, helping engineers route and place vias properly. "But that's less than 1/10th of an inch!" ... "Yes, but it does matter here".

Yes. 70's era stereo amps are a classic example.

As for example circuits that is a good idea but the only entities who'd have a business case to build some are EMC consultancies and labs that teach classes. Small market

I use 1 uF 0805 caps by default. Scattered around a power plane, close to a ground plane, they work fine.

The oft-repeated "analysis" of paralleled, stepped-value bypass caps, is nonsense. Lots of signal-integrity lore is nonsense.

Megawatts.

Everything. On a spactrum analyzer, the AM, FM, and TV bands are about full. And the tower is used for police and fire comms too. It overlooks the entire city, and then some.

Here's my Pockels Cell driver:

My company is about 2 miles away, in a wooden building in plain sight of the tower, and we get a lot of RFI effects.

I love this place. Most visitors see the parts of the city that we never go to.

I have a mostly inaccessable/hidden loft outside of my office. I bet I could put up a big, 100 sq feet at least, resonated loop antenna and get enough RF to light up an LED. Some LEDs are visible in room light at 1 uA, and in the dark at a few nA.

Can a loop antenna be multiple wavelengths long and do any good? The "resonance" would actually be multiple cycles of transmission line delay. That should work. What polarization to AM/FM/TV transmitters use? Antennas are complicated.

But it always makes for a good scare story, just like a lot of the theories about global w... ...... bit my tongue here :-)

I've seen absurd papers about bypassing... authored by capacitor makers. There is one so co-authored paper, with someone from Xilinx, that recommends three caps for *each* power ball on an FPGA. Hundreds of caps per chip.

Modern FPGAs and CPUs have on-chip capacitance for the fast stuff. They don't need heroic bypassing.

I saw one board being assembled in Japan, in an open-air pick-and-place shop, that was putting 3000 bypass caps on each board.

On a sunny day (Tue, 16 Jul 2019 08:26:17 -0700) it happened John Larkin wrote in :

That scares me.

Yes, we discussed that before, just do not put the neon _in_ the coil, it may scatter pieces of glass, I killed one that way, was lucky, was a dual envelope neon tuning indicator... Maybe from some radar..

In the TV studio building the roofs were metal to keep RFI out. Then at some point we got interference from the electric trains, there is a train station next to those studios. Ground loops, miles and miles of coax, 6 TV studios in one big building. Probably more now, have not been there in ages. But it was quite far from the TV tower.

S.F. has deteriorated a lot. Sometimes you have to step over people sleeping on the sidewalk, occasionally over some barf, et cetera. Sacramento is heading in that direction a well, fast, and for obvious reasons. Well, not obvious to certain politicians which are unfortunately in the absolute majority right now.

I like a more rural setting such as our area in the Sierra foothills. And it's not hick town, there is high-tech going on. I just came back from a dog walk and right in front of our driveway had a chat with a neighbor's dad. He said his company needs EMC consulting pretty soon for some big switch mode converters. I guess stuff like that only happens in the US.

Yes.

In your area you may have the sparks flying if the ends of your loop antenna get too close.

AM in the US is usually vertically polarized because they use a very tall tower fed at the bottom. In other countries that sort of expense isn't always palatable so they sometimes use dipoles strung between a couple of high points and then it's horizontal. Horizontal has the downside of nulls in two directions, making the range non-circular and that's bad for listener numbers and thus advertizing revenue.

FM is also vertical but that gets bent along the path, especially when looking at car antennas.

TV is generally horizontal with very few exceptions, for example in mountainous regions.

Stick an NE-2 in a microwave oven. Fun.

That's downtown. We don't go downtown.

SF has decided that "homeless" people who live in cars and trucks and RVs need support too. So we'll have free full-service RV parks all over town. That's going to get interesting.

It'll spread fast. When I visited you guys on Otis Street and we walked to Zeitgeist there were several folks sleeping on the sidewalks.

Ever since some judge declared it ok that they can camp just about anywhere they ... just do that. Parts of Sacramento have become so bad that people start avoiding those areas. Which will ultimately result in business failures. Even where we live it's becoming worse. There is one shopping area we don't use anymore, where people now occasionally use trash cans as open air outhouses.

Just one nickel-plated connector could cause some havoc. ;)

Cheers

Phil Hobbs

Nope. The 22 MegaWatts might be the EIRP (Equivalent Isotropically Radiated Power), which is the transmitter RF output power, minus any coax cable or waveguide loss, times the antenna gain. The antenna gain is achieved by reducing the vertical beamwidth. Such high power levels may have some exposure relevance at the altitude of the antenna, but not on the ground, which is well outside the main lobe.

Also, the 22 MegWatt number seems much too high.

Total: 6,931.2 kW EIRP or about 7 MegaWatts

"The maximum RF exposure level measured at any of the 212 locations surrounding Sutro Tower was 6.0% of the most restrictive FCC public exposure limit."

"The radiation from Sutro Tower is 8.4% of the FCC limit at the point of maximum exposure under normal conditions."

"When broadcasters use their auxiliary antennas, which are located lower on the tower than their primary antennas, the maximum radiation level can rise, but is never more than 15% of the FCC limit."

If the light was in the main lob of the antennas, I could probably cook my dinner. However, on the ground, at 8.4% of the FCC limit, methinks not.

The highest public exposure allowed by the FCC in the VHF/UHF FM and TV bands is a power density of 0.2 mW/cm^2 or 2 watts/sq-meter. 8.4% (maximum measures) is 0.016 mW/cm^2 or 0.16 watts/sq-meter.

That's the base insulator from what appears to be an AM broadcast station. The tower is the transmit antenna and is NOT grounded. Judging by the size of the sparks, my guess(tm) is about 20,000 volts across the base insulator (based on 30kV/cm). The weeds are full of water and make a fairly good conductor. Usually, cleaning the weeds and debris from around the tower is done with the transmitter turned off, or at a greatly reduced power level. The "burns" on his hands were caused either by the heating of the water in the weeds burning his hands or by the RF arcing through the gloves, causing local spot heating in the gloves.