EDACS MA/COM signal measurements

[SCPD]

Hello. I am glad I found this forum, because I need some help. I am doing an unscientific study of 800 MHz radio signal strength for the fire department I work for. I am going to use a Jaguar 700Pi portable that has the FCC menu enabled. This gives a reading of the system in -dB. What I need to know is a simple explanation to interpret the reading. For example, a -65 dB reading for this system, according to system tech's correlates to a very strong signal, whereas, -110 dB is poor, and on the fringes of an unusable signal. Is this measurement really dBm's? Or, can I simply explain the reading as a signal loss measurement? Really, the comparison of readings from outside buildings, inside and from structure to structure is what I'm really after, but I'd like to learn more about what the negative dB reading means. Thanks in advance. I might not be able to get back and check the board soon and I need this info. pretty fast, so if anyone wants to reply, feel free to "ping" my personal email:

tmbevtfd@tampabay.rr.com

Again, Thanks!

TB, Florida

 

[SCPD]

Loosely speaking, think of the negative number like the exponent of a decimal number written in scientific notation.

In scientific notation ...

1.0 x 10^1 = 0.1
1.0 x 10^3 = 0.001
1.0 x 10^6 = 0.000001

As you can see, the more negative the exponent (the number just after the "^"), the smaller the number.

So yeah, -90 db (or dbm) would represent be a tiny (and weak) signal while -70 db would be relatively much, much stronger.

-rick

 

[N_Jay]

You need to check with M/A-COM as to the exact meaning, and accuracy.

I am guessing that those numbers are the signal strength in dBm (refference a 1 milliwatt signal) at the antenna port.

I will give you a gentle warning;

Interpreting signal levels and coverage is a VERY scientific subject.

A "non-scientific" study is very likely to be near meaningless, and worse yet confusing and misleading.

Depending on what you want to do, there may be some easy ways to make sure you are collecting valid information.

PM me if you want some help with this.

 

[CSHIFTLT]

I believe you also need to make sure it is on the freq of your control channell, which is changed also in the menu, good luck it is nice to use but a pain to get there.
cshiftlt

 

[SCPD]

Thanks to all for your replies. N_Jay, I understand what you mean about signal measurements being very scientific, however, with all else being approximately the same, if I've got a reading of -88 dB outside a building, and -110 dB inside the same building, though the accuracy of whether it's really -88 or -110 might be questioned, the fact of the matter is there is a significant signal drop in that scenario. And yes, I am monitoring signal on a control channel.

Another question: What does anyone think good, fair, poor and critically poor -dB values would be in your typical ericsson-M/A-COM trunked system. Techs are telling me that anything below -90 dB is OK, but upwards of -90 is questionable. 90-100 poor, and upwards of -110 almost unusable. I'd like a source to cite in my report, does anyone know any links to research this data? I've Googled it until I'm blue in the face, and cannot find it..

Thanks.

TB

 

[N_Jay]

Thanks to all for your replies. N_Jay, I understand what you mean about signal measurements being very scientific, however, with all else being approximately the same, if I've got a reading of -88 dB outside a building, and -110 dB inside the same building, though the accuracy of whether it's really -88 or -110 might be questioned, the fact of the matter is there is a significant signal drop in that scenario. And yes, I am monitoring signal on a control channel.

Another question: What does anyone think good, fair, poor and critically poor -dB values would be in your typical ericsson-M/A-COM trunked system. Techs are telling me that anything below -90 dB is OK, but upwards of -90 is questionable. 90-100 poor, and upwards of -110 almost unusable. I'd like a source to cite in my report, does anyone know any links to research this data? I've Googled it until I'm blue in the face, and cannot find it..

Thanks.

TB

It sounds like you are trying to test your existing system.
Either to show it does not meet the promissed level om coverage or to show you need a new system.

In order to be statisticaly valid you need to take several samples in a small area while moving.

Lets say 20 samples over a 6 to 12 foot area.
You would thien average those to get one data point.

I would have the radio tested on a bench and find out what signal is required for at least 12 dB SINAD, or 20 dB Quieting.
I would use that as a reference. You brobabaly want 6 to 20 DB above that to show a reasonable amount of margin. I don't know what statistical reliability you are shooting for (90%, 95%, etc.)

Since it sounds like you are doing an inbuilding test, you probably want to take these samples ar some predetermined locations that are not related to any particular preconceived notion of good or poor coverage spots. This helps prevent skewing the test results.
I would say the corners, crossings and midpoints of each major hallway on each floor in each building.

Like I said before, if you don't do it in a scientific and statistically valid manner, you are just collecting a lot of data that provides no information.
I am not sure who teh target of your paper is, but it will get torn apart as soon as it is presented to anyone with any level of expertiece.

 

[SCPD]

Didn't take your happy pill today, did you, N_Jay... Just kidding. I know what you're saying, and you're right, if we were to approach this exactly scientifically. However, I don't have that level of training or experience in communiations to represent a scientific presentation anyway. And no, we're not trying to dump our present system or show it's not working to our liking. This trunked 800 system has been in service for better than 17 or 18 years now, but our PSA (fire-rescue) is on the known fringe of the system. Communications International came out and did a drive-by signal study and found this was the case. We are simply taking it a bit further. So far, my samplings show EXACTLY that.

Samplings as you suggest are not exactly what I'm doing, but close in regards to different levels or parts of a floor in a building.

Frankly, I don't care if it gets torn apart, because regardless of how anal someone with an engineering degree becomes, I'll just haul them out in the field on a cardiac arrest call, and when we try to key up for assistance and can't get out, I'll make him do mouth to mouth on the patient for awhile. Maybe that'll get the point across.

Thanks again.

TB, Florida

 

[N_Jay]

Didn't take your happy pill today, did you, N_Jay... Just kidding. I know what you're saying, and you're right, if we were to approach this exactly scientifically. However, I don't have that level of training or experience in communiations to represent a scientific presentation anyway. And no, we're not trying to dump our present system or show it's not working to our liking. This trunked 800 system has been in service for better than 17 or 18 years now, but our PSA (fire-rescue) is on the known fringe of the system. Communications International came out and did a drive-by signal study and found this was the case. We are simply taking it a bit further. So far, my samplings show EXACTLY that.

Samplings as you suggest are not exactly what I'm doing, but close in regards to different levels or parts of a floor in a building.

Frankly, I don't care if it gets torn apart, because regardless of how anal someone with an engineering degree becomes, I'll just haul them out in the field on a cardiac arrest call, and when we try to key up for assistance and can't get out, I'll make him do mouth to mouth on the patient for awhile. Maybe that'll get the point across.

Thanks again.

TB, Florida

Been there done that.

Started as an EMT!

Just remember, all the testing in the world won't make it work better.

OIf you had a study done that says the signal is weak in teh streat, then it will be weaker in side. (Maybe unusable).

I guess, I am still a bit confused about what you are trying to show, and what outcome you are trying to drive?

 

[SCPD]

What we are trying to achieve is to establish at least some numbers on signal strength in the service area. We knew all along that we were sitting on the "fringe" of the system, and there's been discussions going on for years on what to do about it. Frankly, the County doesn't want to spend a million dollars or more setting up a tower closer to our service area. And it's not just us. Other agencies on other barrier islands are experiencing the same problem. The fact is, nobody has ever done any sort of study on signal strength, until our police department chief hired C.I.I to do the drive-by study.

So, assuming what the tech's at C.I.I told me is true, and -90dB's on a portable is borderline at best, my numbers jive with what C.I.I's report validates about being on the fringes of the system.

Our service area also lies within the scope of a Motorola digital trunked public safety system, so using a XTS500R with the RSSI feature enabled, we've been recording these numbers too. Not suprisingly, I see the same kind of signal drop with the motorola system as I do our M/A-COM, formerly Ericsson. However, they do not have a antenna pointed directly at us, so I wonder how it would change if they did. Again, the motorola system is not our primary; it's a mutual aid thing that we have those portables at all.

One example in regards to the old Ericsson system we use: Outside a building, -78 dB, not bad. Step into the lobby, and we have -98 dB. This is a 10 story building. On the 5th floor centrally positioned, -118 dB. Wow. So, there are definitive problems that need to be solved.

One solution being batted around is identifying the worst problem buildings, and asking the association that runs the place to purchase BDA's. At $9-12,000 installed per copy, I doubt it. But it may be worth checking into. We have suggested repeaters, but the powers that be who control the 800 system won't allow us to install them. He just doesn't like the idea of us possibly tying up one of his channels for any extended period of time, say on a high-rise operation for example.

So, that's it in a nutshell. What's the solution? I don't know. If our neighboring motorola digital trunked system would point an antenna at us and our numbers are then usable, we might consider hopping over to that system and leave the analog world forever.

Thanks again.

TB

 

[N_Jay]

At 800 MHz 20 dB of building loss is not unexpected.
It can easily be 30 or 40 dB.

I doubt just moving an antanna is going to help much, and will probably affect others areas significantly. You would generaly only get a couple of dB increase.

There are only two solutions to inbuilding coverage at 800 MHz.
Proximety to a tower, and properly designed BDAs.

A work around is to use the BDAs on a conventional channel instead of on the system. (no different technically, but might be more sellable politically)

Another option is the installation of a conventional station just for the area or even just for a building.

 

[SCPD]

Ah, we've tossed the conventional channel thought around too. In fact, one suggestion was vehicle repeaters that received on a "talkaround" channel and transmit back out on an operations group. This, too, was shot down. Also, if memory serves, I believe there are some prohibitions on using mutual aid conventional channels for day-to-day operations, but don't quote me on that.

I think, ultimately, that the County ISD Radio management is simply gonna have to set aside one of their channels (I think they have 16 total on the trunked system, but I could be wrong) as a repeater channel. I know that this system is heavily populated by various agencies, but this would solve the problem in my mind. I don't think BDA's are going to fly because what building board of directors in their right mind would authorize that kind of cash to enhance public safety communications. Isn't that why their owners pay taxes?

Well, we'll see what kind of response we get from our numbers. Either way, it should be interesting!

Thanks again for all your responses.

Tom B.

 

[N_Jay]

I hope I am not breaking any RR Forum rules, but;

You may have better luck getting input from the guys at;

http://finance.groups.yahoo.com/group/PrivateWirelessForum
and
http://finance.groups.yahoo.com/group/LMR

They LIVE this stuff!

 

[SCPD]

Thanks. I jist have to remember my yahoo sign-in information... duh, I forgot it...

Tom

 

[N_Jay]

Thanks. I jist have to remember my yahoo sign-in information... duh, I forgot it...

Tom

Just make up a new one!

 

[nhiester]

The other avenue to consider is looking at EMA for funding for building projects. either a site, or the BDA Idea. The local ema easily funded a BDA system for our Mall as well as a hotel. They are classified as a high life safety priority and can be justified under the homeland security monies. The same justification can be made for a site. You may want to try your luck pushing for just a simple recieve site, generally when you talk in building coverage, the problem tends to be the portable getting enough power out to hit the site, not necessairly the site transmitting to the portable. You might also be suprised to find how many business owners might take the cost of the BDA system in stride, espically if they use an 800MHz system and it benefits their maintenance/security as well.
Just food for thought.

 

[emtLarmy15]

I don't think you will find any radio system that is going to have lower in building coverage anywhere. Some buildings are worse then others. Our county (if I am not mistaken) recently passed a county law that requires anyone performing new construction (except a home) to not interfear with the Counties radio system. If the building inspector checks it out, and the coverage is not good enough, I believe they are required to install a BDA system.

I don't necessarily understand why you don't have any talkaround channels to begin with. On our system we have 6. Some of the fire companies around here just have target buildings. If a building is known to have poor coverage, they switch to the talkaround channels, and command just has to have 2 radios... one stays on the system and one off.

Just a thought, maybe your local gov't or even the state might be willing to offer a little of a tax break to target businesses that install BDA's at their own costs. And then there's everyones favorite... Homeland security grants. Right now is the perfect time to apply (March 7-April 7) for the Firefighter Grants. They give alot of money away each year. Might be a little late this year, cause I am sure the grant will take a lil bit to work out the numbers, but it's always worth a try.

Chris

 

[SCPD]

I think the issue with talkaround channels (conventional), if memory serves, is that we were told by the radio administrators that those are only to be used for mutual aid purposes or other situation that warranted it, and not for daily operation. I cannot remember if that was a state thing or a loca thing, I'll have to check into that...

Thanks for the excellent suggestions.

 

[PhaseLockedLunatic]

Have you considered vehicular repeaters as a possible solution?