154.815 in North NJ overlap?

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ZaneBrooklyn

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I live in Maplewood and monitor the PD on 154.815 with a Pl of 114 I think, if memory serves. Ive noticed that a Hunterdon country dispatch uses the same frequency at a different Pl tone, it's so close that on my home base it comes in full scale and on HT about S3. Why would they use the same frequency so close to one another? Isn't it bound to cause some interference?
 

Septa3371CSX1

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I live in Maplewood and monitor the PD on 154.815 with a Pl of 114 I think, if memory serves. Ive noticed that a Hunterdon country dispatch uses the same frequency at a different Pl tone, it's so close that on my home base it comes in full scale and on HT about S3. Why would they use the same frequency so close to one another? Isn't it bound to cause some interference?
They're not that close to one another. The two are a good 40+ miles apart from one another.

Now Hunterdon does have transmitters at higher elevations thus the signal travels a good distance. It likely won't cause too much interference as long as the Maplewood PD has the PL enabled.
 

joemoor

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I experience a similar problem with Sparta PD and Ulster county NY Sheriff. They are on the same freq with different PL's and yes they both have mountain top towers. I live right in the middle in Wantage, NJ and even with PL enabled if they are both transmitting at the same time I get awful intermix making each unintelligible.

I agree that there should be better freq coordination as there is STRONG signal overlap on many freqs in my area because of the fact they are mountaintop repeaters (1500+ feet).
 

SCPD

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According to the data base, Ulster Sheriff is on 155.67 and Sparta is on 155.64. Is it an image your hearing?
 

joemoor

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You are correct, I meant to say Dutchess County. They are on 155.64 with a tower near Poughkeepsie. The way the terrain is here I seem to have valley up the hudson and the signals come right on down. I'm also investigating an Ulster county freq, so that's where I mixed the two up.

Joe
 

kd2pm

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Most locales do not interfere with each other and are usually far enough apart. There are rules in place to prevent interference to each other but obviously not to scanner users. The 88 kilometer rule (or 54.68 miles) is used when 2 agencies are coordinated on the same frequency. If they fall less than that mileage betweeb their transmitter sites both must sign a LOC (letter of concurrence) that neither will interfere with the other with the most recent user being the one that must re-mediate the interference. Depending on the terrain, most cases both parties never hear the other and with PL in place never know one is transmitting when the other is. If the signals are weak enough from the other user, FM capture should never be an issue where the farthest agency overcomes the local agency.
 

W2SJW

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The most recent situation along these lines that drives me nuts is how in the last year or so Monroe County, PA put their EMS Ops repeater from it's previous 151 frequency to 155.400 - the same as Hunterdon County's EMS Ops. BIG heterodyne when they are both transmitting here at my place...
 

johnls7424

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As long as the PL or DPL tone codes are different they should not be hearing each other. Now if your hearing this on your scanner with interference is one thing. If you program a VHF radio with the PD tone code/ output for the repeater and you still hear this then so are the police on their radios. However if the tone codes are different and you don't hear dispatch asking for the unit calling or complaining of interference then most likely it's only you hearing this and not them.
 

W3DMV

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Just a little more info regarding the 155.640 situation

Dutchess County, NY first licensed operation 12/28/2001.

Multiple sites

KEA368 (100W ERP)
East Mountain Poughkeepsi. Elev 1489 ft
Rocky City Elev 744 ft

WPCI339 (120W ERP)
Silver Mountain Millerton Elev 1328 ft
Illinois Mountain Highland Elev !!08 ft

-----
Sparta First licensed 12/21/2004

Site
\KZR693 (50W ERP)
Morning Star Dr Elev 1220 ft

Distance between locations about 62 miles

Stipulation: Sparta license requires use of a directional antenna
utilizing 6DB gain and aimed 270 deg with a minimum F/B ratio of 7 DB.
and a down tilt of 20 deg.

This would help eliminate interference between the two and since the
Dutchess Co operation was licensed first, Sparta is required to provide
the protection at their end.
 

902

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I live in Maplewood and monitor the PD on 154.815 with a Pl of 114 I think, if memory serves. Ive noticed that a Hunterdon country dispatch uses the same frequency at a different Pl tone, it's so close that on my home base it comes in full scale and on HT about S3. Why would they use the same frequency so close to one another? Isn't it bound to cause some interference?
It's not your imagination. I just ran a model on Hunterdon's three repeater sites and Maplewood's two repeater sites. The "service contours" of both come very close to each other - but don't touch - in the eastern tip of Somerset County. The "interference contours" of both intersect with each other.

What about coverage inside the intended areas?

There is no nice way to say this, so I'm just going to say it. I don't mean it in an inflammatory way because this is my hobby too: public safety communications systems are designed to put signal into a defined area. Items like cost and coverage balance at the top of the list of concerns and hobbyists usually don't make that list at all. In other words, if Maplewood gets a good signal inside Maplewood and Hunterdon gets a good signal inside Hunterdon, mission accomplished, regardless of what happens outside.

Seems that there will be interference outside the jurisdictional boundaries, but what's inside is manageable - or at least acceptable to the licensees.

Why do "they" do this?

What I wrote above touches on a very difficult balancing act. VHF spectrum is loaded with legacy users who implemented their system with much larger coverage than is needed. Very big "effective radiated power," very tall antennas. For example, the footprint of Maplewood's two sites not only covers Maplewood, but also most of Essex, part of Passaic, just about all of Hudson and Union, the tip of Somerset, and a good part of eastern Morris Counties. Hunterdon's aggregated service contours cover parts of Lehigh, Northampton, Bucks, Mercer, Middlesex, Somerset, Morrris, and Warren. Radiowaves look like drawn circles and usually defies political boundaries.

New Jersey is one of the most dense environments in the country for VHF high band and UHF spectrum and close-spacing is usually avoided, but sometimes inevitable.

Sometimes this is done because no other frequency will work at a site (combiner limitations or intermod). When an agency says they "have to have this frequency," for whatever reason, another agency can sign a "letter of concurrence" for the frequency coordinators and the restrictions of non-intersecting contours go away.

But 15X.XXXX is clear on my scanner, why don't they use that?

It may be the input to another system somewhere else, it may have a user on it that gets affected worse than whomever is on the frequencies that were ultimately picked. There is a reason, but many times, that reason is not obvious without doing a lot of digging into usage, records, and FCC rules. It also might not work at the site, as I mentioned above. Or, it might be something someone missed or an agency that migrated to another frequency band or on to a larger jurisdiction's 700 or T-Band trunked system but has decided not to "give back" the frequency (which, in that case, it cannot be taken for the greater good).

What happens in the future?

In modern systems, such as Region 8's (Southeastern NY, Northern NJ, and Southwestern CT) 700 MHz plan, a new licensee would have to define where they want to cover. Then there's a small buffer area drawn around it. The engineering proposal has to show how antenna design and placement will keep 80% of the signal inside the jurisdiction and buffer area, or they don't get the frequencies and license. The engineering proposal also has to demonstrate how there will be no signal incursion on co-channel (agencies or county areas who are on the same frequency) or adjacent channel re-use.

These systems concentrate the energy into the defined areas, and these overlaps are proactively controlled. If you plot those out, you will see lots of smaller footprints with directional antennas pointing signals in or notching them from getting out. It's a big change in design strategy. Sometimes all these overlaps inside contribute to simulcast phase distortion and you might hear that on a scanner, although actual public safety radios are designed to minimize the effects, especially in digital modes.

Sometimes special directional patterns are required in VHF, too, to concentrate signals into their intended areas and to "protect" other incumbent licensees. Some states have licensees that are implementing VHF trunking systems or VHF simulcast sites. You'll see exotic antenna patterns on them (look up Bergen County's sites, power levels, and directional patterns on 155.5500).

Sorry I couldn't speak to the specifics, but hope this answers some of the questions of how it's done.

For grins, program in 154.1600 and 155.7300.
 
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