The Siren Board

Discussion of Outdoor Warning Systems
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PostPosted: Mon Apr 19, 2021 12:10 am 
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Real Name: Thomas Manchester
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Hello everyone I hope you're having a great day! I'm currently wondering what type of antennas does Dane County use? Specifically the type in the images below, any reply/answer helps helps. Thank you!


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PostPosted: Wed Apr 21, 2021 5:40 pm 
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They look a lot like double dipole antennas

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So... Never heard a siren before :(


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PostPosted: Fri Apr 30, 2021 1:46 pm 
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mmm, nope; quarter-wave antenna with ground radials. By the size, I'm saying low-band (anywhere from 30 to 50 MHz). Similar to a DB201 antenna. With the turn at the top, it will be a 'hairpin' antenna; DC grounded, since the outer side of the hairpin is attached to the main part of the antenna.

Looks like they at least put a drip loop in the cable, and also some amount of weatherproofing at the connector. Should be routed along that diagonal member to avoid being whipped around by wind, shortening its life.

Looks like it's been up a long time, but still sturdy.


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PostPosted: Mon May 03, 2021 4:26 pm 
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kb4mdz, if it helps at all, they're using ATI FSK to activate their sirens, they have ATI Cabinets even though the sirens are T-128's and 2001-130s.


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PostPosted: Mon May 03, 2021 4:34 pm 
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This is another photo of the antenna (I'm trying to identify the larger one with the 4 things sticking out)


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PostPosted: Mon May 03, 2021 8:35 pm 
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oh, my. So is the long straight one the antenna you're interested in? that seems to have no radials attached to that bracket? The lower one in your last photo.

Hazarding a guess, it's probably still low-band, 30-50 MHz, just based on length, but they are 'depending' on the metal bracket to provide a ground side for the feedpoint. And is this from a different location? This one, the hairpin antenna looks to be mounted directly off the utility pole, not out on an arm.

Sign me, Confused.

Oh, and the signalling scheme (FSK, DTMF, etc.) doesn't matter to the antenna; the radio receiving it cares about its frequency, and the antenna, but once it's demodulated and presented to the decoder - now that matters


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PostPosted: Tue May 04, 2021 12:25 am 
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I'm talking about the hairpin still, This is in a different location as well. It doesn't look exactly like a DB-201


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PostPosted: Thu May 06, 2021 4:15 pm 
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I work on commercial radio towers so I should be able to answer this question accurately.

The large antenna looks to be a J-Pole with ground radials. The J-pole is upside-down. This antenna should be omni directional when installed correctly. Judging by its size, its most likely used on High Band VHF (148-156 MHz).

As for the small hairpin antenna. That's also for High Band VHF (148-156 MHz). I can almost guarantee it because I own an antenna just like that one made by Motorola and there is no traps along the antennas radial element.

The reason people think its a different band or a different band between the 2 antennas is because there is a difference between antenna wavelength divisions for antennas. For instance, an antenna on High Band VHF (148-156 MHz) would be a full wave at 2 meters long (for all the elements for simplicity sake). If we were to make a 1/2 (Half Wave) antenna, then we would make the elements 1 meter long. If we were making 1/4 (Quarter Wave) then we would make the elements 0.5 meters long.

A thing to remember is, an antennas resonant frequency is lineally equivalent to its length. But, wavelength divisions of 1/2 or 1/4 are also resonant, just with less receive/transmit gain.

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