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Can anyone identify what this antenna is, or, more importantly, what it's used for? A local (minor-league) baseball stadium has one and runs a Motorola system, and I assumed it was maybe something like a small-scale repeater setup. But I've seen it on some small shops and several restaurants (including this boarded-up one), which couldn't possibly need a repeater, or even bubblepack FRS radios.
These things are fairly common out here (New England), yet I have no clue what they're for. The places that use them suggest it's something in-house. (Unless restaurants have some sort of secret radio network? Is that what the numbers stations are?)
It's a coaxial dipole. VHF high band, if the scale is what I think it is. The top spike is 1/4 wavelength long, as is the sleeve below it, each being half of the dipole.
High volume restaurants use paging systems to call
customers when their table is ready. I was in an
Olive Garden earlier this week in Virginia that had one.
What band they use I have no idea, but in the DC
area they're in Clyde's and probably many
other similar places.
Tom in D.C. In 1920, the U.S. Post Office Department ruled
that children may not be sent by parcel post.
The large base is the decoupling sleeve for the top radiator, which appears to be low band in frequency range.
In essence, it's a 1/2 wave antenna...similar to the 'elevated' feed antennas so often seen on trunking portables, just larger in relation to frequency, but the basic design remains identical regardless.
The lower decoupling 'stub' keeps RF off the feedline as you do not need the signal on the feedline to be a part of the antenna, the decoupling stub makes this possible as it cancels the RF at the feedpoint so more of the signal is radiated instead of being soaked up in the feedline and wasted as heat.
The MSS I worked for in the 70s referred to those as "Slim Jims." I could be wrong, but it seems to me they were manufactured by Phelps-Dodge, and were quite common public safety base rigs back then.
Many antenna Mfrs. produced similar designs, such as the one pictured...A.S, Circle-M, P/D and Celwave.
Rugged antennas, but ZERO gain in most cases as they were produced as a no groundplane antenna, although many did have some gain, but never more than 3 dB, probably closer to 1-2 dB in real life.
That is one of the nice features of half waves....the lack of a necessary G/P to work against, as the sleeve acts as both decoupling and G/P, with the support tube providing rigidity for mounting on most anything, motorcycles included.
AEC wrote:Many antenna Mfrs. produced similar designs, such as the one pictured...A.S, Circle-M, P/D and Celwave.
Rugged antennas, but ZERO gain in most cases as they were produced as a no groundplane antenna, although many did have some gain, but never more than 3 dB, probably closer to 1-2 dB in real life.
That is one of the nice features of half waves....the lack of a necessary G/P to work against, as the sleeve acts as both decoupling and G/P, with the support tube providing rigidity for mounting on most anything, motorcycles included.
Indeed. As long as you got them high enough, they produced pretty good results. My favorite thing about them was that they were relatively easy to replace in the dead of a midwest winter, on the rare occasion that one of them took a dump.
If you're seeing the same antenna like that in multiple places in a certain town or community or region, it's possible they are voting receivers for something...
d119 wrote:If you're seeing the same antenna like that in multiple places in a certain town or community or region, it's possible they are voting receivers for something...
I was seeing it on things like the Home Depot, the Cracker Barrel, and the car dealer, all of them more or less next to each other. I just found it really odd that so many neighboring businesses would have the exact same antenna, when their radio needs aren't at all alike.
You'd be surprised. All of those businesses have similar radio needs.
Basic two-way comms between employees with a repeater onsite to boost coverage.
Since many of these stores get their radios from places like Grainger, it's possible an enterprising local radio guy came along and suggested they get low power repeaters and put them up in an attic somewhere.
I notice many CLs and XTNs walking around on people's hips at Costco, Home Depot, OfficeMax, Olive Garden, Lowe's and the like.
Could be part of a region-wide alert system, part of an older alarm system, who knows.
One likely possibility is that it's part of the electric company's telemetry system that either allows them to control things like air conditioning, etc. (load shedding), or less likely it could be telemetry to read the electric meter via radio so a meter reader doesn't have to go out.
My guess is that it's power company load-shedding receivers. IIRC, there was often some sort of incentive offered to commercial customers if they allowed the utility to have control over air conditioners and other equipment that was a major drain on the grid.
Find one on a building that someone you know works in. See if you can get permission to go check it out.
And of course, there's absolutely nothing wrong with going into one of these businesses and asking: "I'm really curious about that antenna on your building. Whats it for?"
