Re: Electric blankets, Gratuitous complexity??

Valve freezing shut.

Do they still make low-wattage electric tape-warmers to wrap around pipes, like in a garage? Maybe that would help.

David

Do you know how much SUGAR (or worse) is in a soft drink?

Likewise caffein.

I used to drink coke like it was water. For years.

Who knows what it did to my innards...

David

...

Please say more about that. Thanks!

They all

What, some kind of impedance matching?

ATU -- what's that?

Thanks!

David

PS: And if you feel like writing a bunch, give us all a tutorial!

Caffeine isn't all bad. It's a natural diuretic.

Early radio stated the wavelength in meters, rather than frequency so it was rather obvious The wavelength at 600 KHz is 300,000,000/600,000 or 500 meters (1640 feet)

Yes, and every installation is a custom design.

ATU= 'Antenna Tuning Unit'. In AM broadcast, it is a custom impedance matching network designed to match the antenna to the transmitter's output impedance of 50 Ohms. They have to handle the transmitters full rated power, and be fairly tolerant of lightning induced flash over conditions.

The old Voice Of America transmitter farm at Bethany Ohio had huge underground vaults for the antenna switches, and remote tuned ATUs. Of course, they could put out up to 500 KW at any frequency from 1.5 to 30 MHz into the directional array to target any point on earth. The WLW site a few miles away could do 500 KW, but since it was designed for a single frequency it was much smaller. Both of those sites date back to the early days of radio, and the VOA site is now a golf course. :(

AM radios use a ferrite cored coil antenna that picks up the magnetic component of the RF wave, so they don't have to be sized to the wavelength like FM and TV antennas.

I built an audio-band VLF radio receiver as a kid with a large folding air-core coil antenna made from a scrapped TV yoke.

The antenna should look like a pure resistance that absorbs (and radiates) the incoming signal completely. SWR or Standing Wave Ratio is an indication of how far out it is.

It's difficult to write a simple, intuitive but accurate explanation of this stuff. Thus I practice. The principles of AC circuits do not relate to everyday experience. I was surprised by how well the mathematics of the "imaginary" square root of -1 describe inductive and capacitive circuits.

There is no sugar in most soft drinks. It is all that corn surp subistute. A new study just out says that the high frutose (however you spell it) does not cut off parts of the brain like the pure sugar does so you keep eating and gitting fatter.

The artifical sweetner is even worse for what some of them can do to your brain.

Idid not know all of this, but never drank many soft drinks. Mostly tea sweetened with sugar.

Yup. It's an impedance match / transformation arrangement, which matches the impedance of the antenna (often far off resonance in these cases) to the impedance of the transmission line.

Although the antenna by itself is not resonant, the antenna + matching circuit is.

Antenna Tuning Unit. A big impedance L/C impedance matcher.

If you're really interested in this topic, may I suggest looking through Laport's classic text from the 1950s, "Radio Antenna Engineering"? Lots of information, and some very nice photos of long- and medium-wave antenna setups (military and commercial).

Although original copies are few and far between (and rather expensive) these days, the book's copyright expired a few years ago and it reverted to the public domain. I scanned it, and you can download a copy at no charge.

Done, in an hour and a half on dialup, and thank you VERY much! jsw

They don't use 'high fructose corn syrup' in softdrinks in NZ. that hasn't made much difference to obesity figures.

Since the radiation from a horizontal wire close (in terms of wavelength) to the ground will cancel out due to the ground "mirror" reflection, only vertical polarization makes sense at frequencies below about 1 MHz (300 m wavelength).

There are two practical ways to generate vertical signals, either by using a 1/2 wave radiator, isolated from ground and fed from the middle or using a 1/4 radiator and a *good* ground plane.

An example of the first approach was the LW tower in Poland

If you are not willing to build such high structures, the alternative is to use 1/4 antennas (requiring *good* ground planes). In order to reduce the masts even further, various top capacitance hat structures, such as T and Z constructs could be used, but this reduced the radiation resistance. Look for instance of the antenna structures of the Titanic, the 500 kHz (600 m) would have required 150 m masts, but in reality, there were several antenna conductors along the ship at lower altitude, forming a top hat capacitance as a T-antenna. The actual radiation occurred from the vertical line going from the radio hut to these horizontal wires.

There are two issues.

In order to radiate effectively, the antenna_system_ must be resonant (i.e. purely resistive) at the transmission frequency with top hat capacitances and loading coils at the transmitter end.

Monopole antennas that are much smaller than the 1/4 wavelength. have a radiation resistance well below the text book 37 ohms, perhaps an ohm or even a milliohm.

To be usable, a transmitter+antenna combination must

In some (most) cases this can be done with a 2-3 component antenna tuner unit (ATU), but the losses may be huge and flashovers and smoke may occur.

One can only bask in that possible outcome imagery...

Ahh... so it is the lack of oxygen to the brain then...

I knew there was a reason for the behavior.

You would certainly understand that, AlwaysWrong. However the issue is quite the opposite. If course, if you knew anything, you wouldn't be AlwaysWrong.

Simple. You're such a charmer, AlwaysWrong.

And retarded punks like you are immediately transparent, which is why I never liked you, and you have always simply been your-asshole-self to me (and everyone else).

OTOH, we're not always wrong, AlwaysWrong.

Oh stop crying, DimBulb. What a pussy!