new antenna construction at DMV Glen Burnie

[ka3jjz]

Eating my lunch this afternoon in my condo, I noticed a cherry picker with a couple of men working on the old antenna tower at the DMV. There's always been a pair of folded dipoles at the top, but some new antennas are being put there now.

Looking at it through a handscope, there are 2 cross beams, each sporting a new vertical antenna, which would appear to be for VHF (at least, the stinger at the end of each is about the right size for VHF). In addition, there's a new cross beam, with a boom coming out of it. Assuming that looking at the tower from my condo is zero degrees, the boom is pointed at roughly 130 degrees; that would take the signal away from Annapolis, but straight down a line toward the Harbor Tunnel and Ft. Mc Henry, or perhaps to the Inner Harbor. There is no beam on the boom as yet (I assume that is what will be mounted there) so I have no clue as to the frequency to be used. Of course, looking at the antennas with a scope it's difficult to be certain about the freq ranges on those verticals, but it seems likely.

The only thing I could think of - and this is very much a WAG - is some new VHF allocation, maybe narrowband; but for what? I did hear some whispers about MSP starting to use VHF narrowband in some places, and that MSP Glen Burnie would be closing shortly. Maybe it's for this?

Anyone have any ideas? I would try Close Call on my 396, but likely as not they'll be testing during the week while I'm at work, and I would expect it to pick up a lot of the other stuff in the area before it would pick this up.

73 Mike

 

[ka3jjz]

Update: I guess before the men left, I can clearly see that they ran coax to the 2 verticals, but did not install any antennas on the empty boom. That is still a mystery, I guess, for another time.

It's long enough for a very high gain VHF beam, but it could be something else.

73 Mike

 

[Llwellyn]

I'm not sure about the new antennas, but I had heard they were keeping the airport (Glen Burnie) MSP barracks open, because they were closing the Annapolis barracks and moving them all to Glen Burnie. Maybe that has since changed... but if they do close both of them, they must be ready to move them somewhere else close or open a new barracks. I don't see how they could get away with closing both AA County barracks since we have so much highway they patrol; they were doing it as a cost-saving measure and with the price of fuel, I can't see having troopers driving an extra 30 miles to AA every day would save them money over having a barracks open.

 

[trimmerj]

How high is the new tower ? I would think that they need more height to hear the mobiles out near Davidsonville on Rt 50 from GB.

 

[ka3jjz]

It's not a new tower, John. It's the same antenna pole they've had the folded dipoles on since I can remember. I'm going to guess at something around 35 foot or so.

They just added a couple of cross arms and antennas, coax and so forth. I noticed today (I can't believe that they had workers in on a Sunday, but there they were...) that they moved the boom for the presumed beam up higher on the vertical support coming out of one of the cross arms.

Another possibility might be a trunked system for the MTA, although the size of the verticals doesn't suggest UHF. There are several UHF narrowband allocations in the FCC data listing (use the form on the database; there are 2 selections for Maryland Transportation Authority, strangely enough - one all in caps, the other not...). Interestingly the 2 entries don't match up; there are more freqs on one than the other. That might make sense, given the direction (however WAGged) that the boom is pointing.

73 Mike

 

[ka3jjz]

I was able to drive by the antenna pole briefly and take a quick look. The verticals are almost certainly for VHF hi - the stingers coming out of the base look too small to work well on VHF lo. One thing though - one vertical looks like it's mounted a bit lower than the other. If they were trying to feed them to make a cardoid (figure 8) pattern, that's going to be a problem.

Another thing - that boom is pointing in the general direction of the 97/695 split. Perhaps someone is trying to improve their coverage in that area?

It wouldn't surprise me if MSP Glen Burnie were trying to improve their coverage - their antennas are very low, likely because they're close to the airport. It wouldn't be much of a stretch to have a remote site at the DMV.

Still something of a mystery. Could be either MTA or MSP (could be both, too...). More will be gleaned I think once the beam goes on the boom, and it starts transmittting....73 Mike