In the Hillsboro area, some houses have Yagi rooftop antennas with elements that look shorter than those on standard UHF television Yagis. Judging by the size of the elements, I would guess that they are designed for frequencies around 1 GHz. For what service are or were these antennas used?

The original HBO service via microwave.

Vertical or horizontal polarization ? Are they all pointed in approx same direction? Can you give the approximate location of one, so I could take a look ?
I still see a few yagis around Hillsboro pointed SE, left over from the old KECH-22 subscription days.

Edit: most of the HBO yagis that I remember used disk directors, but a parabolic type antenna was usually used in Hillsboro, because of the weak signal level. Snow coasters and coffee cans were sometimes used

They are horizontally polarized and pointed southeast. I'd initially suspected that they were channel 22 antennas, but the elements look a bit short.

I have seen a few of the "dish" microwave antennas. The reflector is dish-shaped, but it is made out of metal bars, rather than a solid piece of metal. However, these dish antennas typically sit on a very tall mast, whereas the yagis are just above roof level.

Could it be some big WiFi test going on?

In the Hillsboro area the KECH-22 Yagis were usually mounted on short masts (4-5 ft) and braced with 2 metal straps (no guy wires). The Yagis were only about 8-10 elements, and mounted so that all of the elements were on one side of the mast, toward the transmitter. A small box (booster or down-converter?) was usually mounted just below the antenna.

Intel uses an unlicensed wireless broadband between its Hillsboro campuses and some area employees homes. 2.4 GHz, I think.

For us non-engineers, Yagi is "smarter than the average bear," right?

A year or so after they shut down the KECH-22 PPV movies, you could go to Cascade Surplus on N.Denver Avenue and find, in the back corner, a bunch of the converter boxes and a bunch of those antennas, complete with amplifier. I bought one antenna and amp for about $5, I think. For what?????? Why did I buy anything in there? It was a Friday afternoon treasure hunt!!!

When CH32 started up, I put the antenna on my roof, pointed it towards their transmitter location fired up the amp and voila!!!! it works just fine for CH32. It is still on the roof and still functioning perfectly ...... in Troutdale.

Alfredo_t:
Found a good example of an original KECH-22 antenna on NE 6th between Jackson and Lincoln (west of a school on a blue house). Pointed SE, 10 elements, little amp box and metal braces, like I remembered.

During the KECH-22 subscription days, there were hundreds of these around town.

If TV/FM reception in Jellystone was poor, Yogi might have used a Yagi.

Here's a question for you guys.
I've got a long yagi here,judging by the distance of the elements,it appears to be for approx 2.6Ghz. (didn't work so well at 2.4Ghz,as a wifi antenna.)
A metal can enclosure at one end,with I think,a small folded-dipole in there,as the feed element.The 'boom' is a long rod,with some spacers,and "discs" on it..very much like the homebrew "Cantenna" Yagi's for Wifi...About 34 inches long,with 32 sections (discs).

My friend says it was probably part of the old HBO setup,but is sorta unsure.

I also used to have a white dish,about 2.5 feet across,with a PVC tube coming out of the center.
I think it used to be an antenna for the HBO thing,but i'm not sure. No idea what freq. it was for or anything.

Any ideas? Probably old HBO equipment,or?

There was bunch of people using something similar to receive HBO (i think) in the 80's. HBO (?) sent out roving observers to document all of the addresses of houses where they could see the antennas, and then had their lawyers send a little note to the suspect addresses.
I don't know whatever happen with that. An arguement was you have a right to receive anything being transmitted onto your property.

Thatonedude:
The old HBO transmitter was in the 2.2 to 2.4 GHZ range, so the antenna *might* work at 2.4 ghz. Are there any active circuits inside the can? If I remember correctly, some of these units had a down-converter in the can, that converted the microwave signal to ch 3 or 4. DC voltage was supplied up the coax to power (and fine tune) the converter. You would have to remove/bypass any convertor circuits to use the antenna for wi-fi.

No, the can just had an antenna attached to an N-Connector. From there, Most had a barrel N connector to a box. That box either hung from that "can" or it was mounted to the mast and connected by a short piece of coax. The down converter was in that box. A DC voltage was sent up the regular coax (RG-6 or RG-59) Adjusting that voltage would tune the unit.
Home brew models were mounted to something similar or to an old parabolic UHF antenna (from Monkey Wards catalog) with a mesh screen attached. Rough tuning was accomplished by using a razor blade to cut stripes on circuit boards. If you cut too much, solder a piece of wire back on.

There were all kinds of things used back then.
All experiments in the interest of science. They could also be used for Amateur Radio (hams) television.

Ah! that would be an easy way to tell... if the can has an "N" connector, it is just an antenna, If it has a "F" connector there is likely to be a down-converter inside the can that must be removed before the device could be used as a WiFi antenna.

Around Hillsboro I am also seeing some of these "disk Yagis" that are about 1/2 the size (disk diameter and length) of the old HBO antennas. These are mostly in industrial parks. There must be some data links around 5 GHZ (or so)?

A yagi is a type of antenna. Co-inventer: Hidetsugu Yagi. Patented in 1926.

See http://en.wikipedia.org/wiki/Yagi_antenna

Thanks for the tip, Jr_tech. I looked at the antenna on the house across the street from the school. This one definitely looks like a UHF television antenna, judging by the length of the elements. I'll have to make a closer comparison between this and the other ones, as I think they have shorter elements and no amplifier/downconverter box.

"Thanks for the tip, Jr_tech."
Indeed!
The yagi I have here appears to just be an antenna.Peeking through the water drainage? holes with a flashlight reveals a (mostly) empty can.It does have an N-connector.

If you look real hard at the other end of the N connector (on the inside), you will probably see a little stub about an inch or so long That is the pickup point for the antenna. It is soldered on the center conductor on the inside of the can. I forget the exact length and I also forget the distance from the back of the can. We used to make them out of old (Folgers) coffee cans. I hauled my last "commercial" one to the dump 4 months ago. it was getting in the way just taking up space in the garage. The downconverter died years ago.