One-Way (Half) BDA?

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MotoBill

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I hate to sound ignorant on the subject but I came across some registrations listed on the Part-90 Booster Registration site today having observed thee devices placed at an elementary, middle, and high school all located in a fairly small and somewhat rural community. Accordingly, the registrations were also submitted by the same agency that's responsible for the statewide P25 network.

What was odd, at least to me was that the registrations only listed the frequency band associated with the P25 site downlink band with nothing in the uplink band as I am somewhat accustom to seeing .

I can certainly understand a "One-Way" booster would be beneficial to fill in dead zones in specific buildings with more and more P25 paging becoming common place, but I am not sure how or why such configurations might be placed in three small rural schools. Are boosters configurations common, or might it be that the registration data was incomplete in omitting the uplink band?

Just curious!
 
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EM36

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Betting it's incomplete. Could be one way though. I'd think they would be amplifying the uplink though. You got higher erp on a repeater getting to the portable rather than a 3w peanut whistle getting to the repeater?
 
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Notarola

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Speculation: They may also be just boosting the inside to outside signals. the system signal may be strong enough to penetrate.
 
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MotoBill

MotoBill

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Betting it's incomplete. Could be one way though. I'd think they would be amplifying the uplink though. You got higher erp on a repeater getting to the portable rather than a 3w peanut whistle getting to the repeater?
My thought exactly, but I am not a BDA guy and can't imagine in reality they exist as shown in the registrations!
 

RFI-EMI-GUY

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Back in the late 80's we did a one way TX-RX amp to null fill for a non simulcast, but voted 800 MHz system. The uplink was fine but a shadow existed behind a condo building on downlink. The donor antenna was on one side of the building and a reradiate antenna on the other side. It worked for that limited area.

Funny thing was that if you brought a portable near the re radiate antenna at rooftop level, you could hear a ringing tone from the delay shift caused by the amplifier and filters.
 
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MotoBill

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Funny thing was that if you brought a portable near the re radiate antenna at rooftop level, you could hear a ringing tone from the delay shift caused by the amplifier and filters.

I wonder what that arrangement would look like with P25, simulcast distortion (mucho bit errors)?

This begs a question on my part not having any experience with BDA's. How much of a problem is there when SU's operating in areas (buildings) with BDA's wonder into signal overlap areas? What sort of rules go into the engineering to ensure enough capture within the operational area to keep BER to a minimum where significant overlap occurs?
 

Notarola

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MotoBill: Capture effect math is used to calculate the overlap. The idea on most BDA is to have enough signal to cover the needed area but not so much that it bleeds back out to the normal system coverage areas and causing the issue your asking about. Most BDA setups are providing coverage inside a 'metal box' type of enclosure so by its nature there is a sharp inside/outside difference.
 
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MotoBill

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MotoBill: Capture effect math is used to calculate the overlap. The idea on most BDA is to have enough signal to cover the needed area but not so much that it bleeds back out to the normal system coverage areas and causing the issue your asking about. Most BDA setups are providing coverage inside a 'metal box' type of enclosure so by its nature there is a sharp inside/outside difference.
Would a capture ratio of 6 dB or more represent the target for P25 applications?
 

EM36

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MotoBill: Capture effect math is used to calculate the overlap. The idea on most BDA is to have enough signal to cover the needed area but not so much that it bleeds back out to the normal system coverage areas and causing the issue your asking about. Most BDA setups are providing coverage inside a 'metal box' type of enclosure so by its nature there is a sharp inside/outside difference.
I was just about to say exactly this. Always measure the outside signal first then enable the system inside, do your isolation checks etc then walk the building and verify coverage is the same or less. I find many times checking these that gain level is up too much. 150 rssi is almost saturation to an apx radio. If you keep the coverage internal to the building theres less chance you will see distortion issues going inside to outside and vice versa. High gain settings will only extend how far it gets out. Notarola's comment on a "metal box" is spot on.
 

RFI-EMI-GUY

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I wonder what that arrangement would look like with P25, simulcast distortion (mucho bit errors)?

This begs a question on my part not having any experience with BDA's. How much of a problem is there when SU's operating in areas (buildings) with BDA's wonder into signal overlap areas? What sort of rules go into the engineering to ensure enough capture within the operational area to keep BER to a minimum where significant overlap occurs?
The BDA system needs to serve the very worst locations on the interior of the building, on the absolute lower floors and basements. If you start putting antennas near the exterior or on higher floors, especially near windows you will have that sort of distortion inside and outside at the exterior walls. It can also affect the uplink signal integrity.
 

gsxxr1300r

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I've fought with numerous installers on the proper downlink levels and have in the end won when I clearly show that the radio gets confused in what to listen to. The easy way to see this is to look at the RSSI on the radio as I have seen it plummet when there is a high BER. I don't use the radio to actually document the levels, but it gives a very clear audio able and visual indication when things just aren't right.

Also my limit on above ground floors is typically the 3rd level unless there are issues in and around an elevator, but they are usually so deep into the building it's not seen in the outside world if just the elevator landings have the antennas.
 

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All the high tech stuff is great, but a very good little trick (which should always be used in addition to any other tests in my opinion) is good old analog

At the end of the day, that's what the radio has to listen to also

Listen to the control channel very carefully in analog on a nice radio, XTS5000 is my go-to for this actually, but whatever radio lets you hear plenty of bass with a nice full sound

When the CWID comes on listen super carefully also



High BER-causing conditions don't just happen out of thin air, it starts with the digital modulation sounding messed up to the radio in one way or another.
 
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MotoBill

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It appears to me from a learning perspective that any planning (engineering) should begin with a detailed field intensity survey at all possible SU operational locations within a given complex (building) before any deign or installation work begins. It would then seem there is a hell of a lot more to this than just purchasing the equipment and hiring a contractor slap in together.

I appreciate the insight gained of those that have responded.
 

Notarola

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MotoBill. Unless there is a overriding concern there is no real need to engineer all aspects of a install.

I have found that typical BDA installs follow a similar set up and configuration pattern. This eliminates a lot of reinventing the wheel R&D.
You loose about 40-60db inside the structure. This gets worse as you go deeper into the structure as would be expected. The same applies for going below ground level. Knowing this you select your BDA settings to output about 70-80% of the loss (25-45db). This will give you a good RSSI on the radios and thus a good BER. BUT not so much you are saturating the units or creating potential 'doubling' distortion situation(s). With this in mind you can tweak the various BDA nodes to firm up the signal levels. This is where understanding the math comes in. You want to stay in that sweet spot of a good RSSI without overlapping or radiating RF all over the place. EM36 is indeed a wizard on these type of installs and if I needed specific advice I would be first in line to ask his opinions.
 
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MotoBill

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One of the main reasons that this subject is of particular interest to me personally is because that I see a lot of Fire & EMS Paging going over
to 800 Mhz P25 in rural areas of the state and it makes me wonder how reliable this will be in areas where the RFSS sites are 12-15 miles or greater in separation.

There are some pretty geographically large counties in the state where there is an ever increasing number of migrations off of VHF and over to the statewide 700/800 MHz P25 network with no new sites being added to insure signal delivery to the pagers.
 

EM36

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It appears to me from a learning perspective that any planning (engineering) should begin with a detailed field intensity survey at all possible SU operational locations within a given complex (building) before any deign or installation work begins. It would then seem there is a hell of a lot more to this than just purchasing the equipment and hiring a contractor slap in together.

I appreciate the insight gained of those that have responded.
First thing is always a rf test and then a roof test of control channel rssi. It is critical to know up front what kind of gains will be required in the system. You don't want to waste time putting a .5w unit in if it requires a 2w and vice versa. You will pat yourself on the back when you get to the end and do an isolation test knowing that your gain isn't allowing the system to come close to oscillating. The standard rule of thumb is 15dbm more isolation than required gain...I use 20dbm as do many others.

Notorola tnx but I'm a hack with a bridgeport lol.

"You want to stay in that sweet spot of a good RSSI without overlapping or radiating RF all over the place"

No better words could be said. All this goes back to the system design. Losses should be calculated and listed on the submittal, it should be clearly evident to follow. Studying this you can start to form a mental picture of what the rf coverage will be in the building. I've caught alot of fuckups doing this. That mental image should translate through to the final product or something close when you walk it later on. An actual heat map will do this for you. I don't own a program but wish I did. I've always gotten by doing this stuff old school.
 
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EM36

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One of the main reasons that this subject is of particular interest to me personally is because that I see a lot of Fire & EMS Paging going over
to 800 Mhz P25 in rural areas of the state and it makes me wonder how reliable this will be in areas where the RFSS sites are 12-15 miles or greater in separation.

There are some pretty geographically large counties in the state where there is an ever increasing number of migrations off of VHF and over to the statewide 700/800 MHz P25 network with no new sites being added to insure signal delivery to the pagers.

Whats going to make it or break it is your isolation levels. You can work with this though by keeping your donor antennas as shaded to das as possible, keep them so they're pointing off the building not over it. Sometimes things like elevator shafts etc can be used to your advantage to add blocking.
 

Notarola

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I approach all BDA and simulcast type issues with the same mental image. Think of the system antennas a series of light bulbs. You want even lighting with minimal shadows and overlapping. Think of walls and other obstructions of being made of glass. The thicker the glass the more it block the light bulbs and cast shadows. Simulcast can be thought of as a BDA with no walls. Many simulcast systems 800 especially tend to over compensate with too many sites or power for the coverage area needed. Again math is your friend decide on a reasonable RSSI level and then do your site radiation pattern calculations base on that and not saturation levels. Too much is Too much its like listening to music. You want a volume where you can enjoy it with out blowing your and your neighbors eardrums out - but load enough you can hear the lyrics and melody with out straining.
 

EM36

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I approach all BDA and simulcast type issues with the same mental image. Think of the system antennas a series of light bulbs. You want even lighting with minimal shadows and overlapping. Think of walls and other obstructions of being made of glass. The thicker the glass the more it block the light bulbs and cast shadows. Simulcast can be thought of as a BDA with no walls. Many simulcast systems 800 especially tend to over compensate with too many sites or power for the coverage area needed. Again math is your friend decide on a reasonable RSSI level and then do your site radiation pattern calculations base on that and not saturation levels. Too much is Too much its like listening to music. You want a volume where you can enjoy it with out blowing your and your neighbors eardrums out - but load enough you can hear the lyrics and melody with out straining.
Well said. IF MORE TECHS APPROACHED THESE WITH THIS VIEW....you wouldn't see alot of the problems that are seen today like oscillation issues, agc shutback etc. All signal related..usually too much.
 
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