S.A.- CPS vehicle with roof mounted yagi

[davidbond21]

On the way back to work from our lunch, me and my buddy saw a CPS Expedition slowly pass us the coming the other way on Nakoma by 281. It was driving down the middle of the road, barely staying on its side of the road, occasionally slowing to almost a full stop then moving up the road and slowing to a stop again. It was using the little tiny alternating white flashers in/by the headlights, but on the roof, where you would sometimes see a spotlight mounted, there was a log periodic yagi instead, rising about 6-8 inches above the roof top. The yagi's reflector(or rearmost) was about 14-16 in long and the front director was maybe 4 in long, not exactly sure what band this would be used for though.

OK. Question time. I was posting this because a) I have never seen a vehicle mounted yagi, or even seen pictures(though I haven't looked) of one; b) what would be the utility of having a vehicle mounted yagi like that, at least as far as putting it on a city/utility vehicle; and c) for the San Antonio folks, what exactly(or what do you guess) would City Public Services be using this setup for?

I might have gotten some pictures of this, but I didn't try very hard to convince my coworker/carpool driver to turn around.

[j0nnyb1aze]

The first thing that comes to mind when I hear vehicle mounted yagi is "foxhunt" or direction finding. You would use this to find the location of a transmitter. This would have some LE applications, as well as SAR. This could also be used to locate, say a downed weather balloon or something of the sort(though I'm sure if their equipment is that important to them they would incorporate GPS into it, but you get the point).

As far as the band goes, to make an educated guess one would use the length of the "driven element", or the one that's actually connected to the feedline.

****
Driven element is assuming it's a yagi, as opposed to log periodic, which is a slightly more complex design where the length of all the elements is a log(remember trig class) function. Hence the name. But I digress.

[davidbond21]

That's what I had originally thought, "direction-finding," but this was on an otherwise plain-jane though normally marked as a City Public Service vehicle is(CPS is San Antonio's Energy Company). I'm not sure what an energy provider would be using this for.

Yes, it wasn't a log periodic. I was trying to lock up and get out of work earlier and wasn't sure what to call it quickly.

[milf]

Does San Antonio CPS have radio gear on any of their service devices such as the substation boxes, meters, transformer gear? Or could they have been looking for a RF signal interference created by one of their devices/distribution systems?

[FFPM571]

We have water meters that are on a UHF freq.. Once a month a utility truck will drive down the block with a UHF gain on the roof and a laptop mounted in it.

[texasemt13]

Originally Posted by FFPM571

We have water meters that are on a UHF freq.. Once a month a utility truck will drive down the block with a UHF gain on the roof and a laptop mounted in it.

San Marcos has the same type but, I usually see about a 20 ft. mast with a yagi mounted on top to transmit a certain direction at the location of the meter itself. I've seen the yagi that davidbond is talking about and they are not similar to the water meter yagis we have in San Marcos (supposing they are the same thing).


Checking the RR db here these ranges are most used:
453.1500-453.9500
458.1500-458.9500
467.7500-467.9250
809.8375-813.8625
854.8375-858.8625

I see a few patterns. The 453.XXXX is probably coupled with the corresponding 458.XXXX as output/input. I would bet the same holds true for the 809-813 & 854-858 output/input.

[texasemt13]

I will try to get a picture this weekend of the local transmitters in San Marcos.

[nd5y]

Not being from San Antonio I don't know what CPS is.
Was this an electric utility truck?
If so, the antenna might be a for an impulse noise receiver for locating faulty power line hardware.

Several years ago I had something making line noise in my neighborhood that wiped out HF and some of my over the air TV channels.
I called the electric company and they sent an engineer out with a hand held wide band noise receiver with a LP antenna. I watched him point it around and found the noise was coming from a damaged arcing insulator on the primary in my back yard.

[j0nnyb1aze]

Hmm, I would have expected each meter to have a unique ID, and the fact that they are relatively close to the meter itself, I wouldn't have thought that they would need a directional antenna.

[tunnelmot]

Me too,
I have seen either the handheld readers, or the truck mounted laptops. But even the mobile readers use just an average NMO antenna.

My curiosity is raised also.

DF for meter reading seems unrelible as far as keeping accounts separate. Maybe the companies radio/tele shop checking operation of telemetry equipment?

Kinda stumped.

Rich

[davidbond21]

Thank y'all for the replies and suggestions. I am really regretting not getting any pictures of this thing to put up on here.

[MaxTracker]

could be point-to-point data when the vehicle is stationary and conducting work.