Eric's Weekly Post #3 (Warning, science enclosed. Do not fold or bend.)

At least in the US, an EPIRB is legal only on a boat, while an ELT (Emergency Landing Transmitter) is on an airplane. You can have a personal locator beacon in your backpack, or in the trunk of your car.

The basic Yagi (pronounced: yargee) array has three elements:

1) The dipole, which is connected to the co-ax, and is thus "driven" as Ned said.

2) The reflector, which is longer than the dipole, and collects radio waves, working rather like a dish does on a parabolic antenna, by reflecting the received waves back to the dipole.

3) The concentrator, which is shorter than the dipole, and has the effect of producing a more directional beam, thus increasing gain, or sensitivity.

Often, there are several concentrators, and sometimes multiple reflectors are employed. I have never seen a Yagi antenna with multiple dipoles.

The result is a directional antenna, which should be pointed in the direction of the transmitter (or receiver, if the antenna is used to transmit). Again, as Ned says, they are the most popular form of TV antenna.

Actually, a Yagi is a fairly narrow band -- they generally won't cover more than one TV channel. Most TV antennas are LPDAs to cover the whole band.

Back in the period 1969-73 I was using a Yagi antenna that had at least a dozen V-shaped tubules that got progressively shorter in the direction of the radio source. It was called an Allied Colorset and was used to catch popular songs from an FM station over 60 miles away. The antenna was rotatable with a motor and compass arrangement. It was probably 10 feet long by 5 feet (max) wide. (3m x 1.5m).

Back in the period 1969-73 I was using a Yagi antenna that had at least a dozen V-shaped tubules that got progressively shorter in the direction of the radio source. It was called an Allied Colorset and was used to catch popular songs from an FM station over 60 miles away. The antenna was rotatable with a motor and compass arrangement. It was probably 10 feet long by 5 feet (max) wide. (3m x 1.5m).

If this was a true Yagi, then only one element was driven, and the elements were all within about 5% of the same length. For FM broadcast, I'd expect the last element to be about 4' 9" (150 cm) and the shortest to be close to 4' (120 cm).

If this was a log-periodic dipole array, the shortest element would have been much shorter -- maybe as small as about 2 feet (60 cm).

TV antennas are often hard to figure out because they're really two antennas on one boom.

TV antennas are often hard to figure out because they're really two antennas on one boom.

TV antennas are often hard to figure out because they're really two antennas on one boom.

Can you explain that one in a little more detail please, Ned? You've got me puzzled.

TV antennas are often hard to figure out because they're really two antennas on one boom.

Can you explain that one in a little more detail please, Ned? You've got me puzzled.

In the U.S. (I suspect much of the world is similar, but not the same), channels 2 through 13 are between 55 and 213 MHz. 14 through 69 are between 471 and 801 MHz.

So a typical broadcast TV antenna is usually a broadband VHF antenna, and a broadband UHF antenna fed with the same feedline. Usually the VHF part is at the back, and the UHF part is at the front, but they can be interleaved -- you'd have long elements and short elements all the way down the boom.

The long elements are one antenna (VHF), and the short elements are a different antenna (UHF).

Aussie TV sets usually come ready to use with several systems, and nobody I have asked knows the A/V separation, though I suspect they use the 6 MHz system.

Nope.
Australia is PAL B/G so a 5.5MHz separation between sound & video.

Well Japan is using NTSC and so I think they use a 6MHz separation also.

Well Japan is using NTSC and so I think they use a 6MHz separation also.

Which, for the record, stands for "Never The Same Color" (or, in Oz, Colour).

Actually in reality It stands for "National Technical Standards Committee", If You want to get technical that is. ;)

One of the classics in that department is TWAIN (Windows legacy scanning layer), which stands for:

Tool Without An Interesting Name.

As for european TV antennae and frequencies, we use UHF and VHF both, and PAL B/G (along with DVB-T, recently, which requires a different antenna - seems to be vertically polarized with much shorter wavelength).

Hope the staff are closer to figuring out where the interference pattern in Multibeam data is coming from, good luck on that.

Regards,
Simon.
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Hope the staff are closer to figuring out where the interference pattern in Multibeam data is coming from, good luck on that.

Hope the staff are closer to figuring out where the interference pattern in Multibeam data is coming from, good luck on that.

I think we went a tad off topic.

OOPS!

Never mind, the subject has been most illuminating. :)

Anyway, There is mention of the RFI matter in HERE

It shows up in both polarizations (and the polarizations are linear, but it would be possible to derive circular polarizations from the data stream.)