Strong Signal Margin DB ??

[Murphy625]

Trying to wrap my head around something.

Using the Radio Mobile online website software, it wants me to fill in a spec for "Strong Signal Margin" in (db).

Now I understand that the higher the db, the stronger the signal needs to be in order for the software to consider the map area as green..

But what is considered a strong signal margin in real life on the 2 meter bands? I've tried looking up information on it and it would seem that a lot of this has to do with the noise floor.. If you're in the middle of the pacific ocean where I'd imagine the noise floor is low, then perhaps a Strong Signal Margin of 7db would be appropriate? But what about in suburbia outside a major city?

Its my understanding that the Strong Signal spec in db is an absolute value that doesn't change.. but what does change is how far above the ambient noise your signal needs to be in order for speech to be audibly recognizable.

That is what the Radio Mobile is asking for correct? Its asking for an absolute value right? Or does Radio Mobile take into account the noise floor in the area its mapping? And what should I set it at?

 

[prcguy]

Are they asking in dBm or dB? Not sure what a strong signal margin is but a strong signal level in the VHF/UHF range might be -80dBm or higher.

Trying to wrap my head around something.

Using the Radio Mobile online website software, it wants me to fill in a spec for "Strong Signal Margin" in (db).

Now I understand that the higher the db, the stronger the signal needs to be in order for the software to consider the map area as green..

But what is considered a strong signal margin in real life on the 2 meter bands? I've tried looking up information on it and it would seem that a lot of this has to do with the noise floor.. If you're in the middle of the pacific ocean where I'd imagine the noise floor is low, then perhaps a Strong Signal Margin of 7db would be appropriate? But what about in suburbia outside a major city?

Its my understanding that the Strong Signal spec in db is an absolute value that doesn't change.. but what does change is how far above the ambient noise your signal needs to be in order for speech to be audibly recognizable.

That is what the Radio Mobile is asking for correct? Its asking for an absolute value right? Or does Radio Mobile take into account the noise floor in the area its mapping? And what should I set it at?

 

[Murphy625]

Are they asking in dBm or dB? Not sure what a strong signal margin is but a strong signal level in the VHF/UHF range might be -80dBm or higher.

THAT is what I wanted. Thank you.. -80dBm = around a signal meter reading of 8.

 

[RFI-EMI-GUY]

THAT is what I wanted. Thank you.. -80dBm = around a signal meter reading of 8.

whoa!!!! \

These programs are terrific but they are "GIGO".

Actually, you really need to refer to TSB-88 Table A-1 and TSB 88 in its entirety.

If you want a "Public Safety" grade delivered audio quality of DAQ 3.4 and you have a +/- 5.0 KHz modulation you need 20 dB of margin.

Example: a receiver of -119 dBm sensitivity has an inferred noise floor of (-119 dBm - 5 dB (12 dB SINAD) = -124 dBm)

So you add 20 dB (DAQ 3.4) to -124 dBm = -104 dBm minimum threshold.

You can also go for "utility grade DAQ 3.0 and use 17 dB of margin. (It will sound worse, but have bigger footprint!)

Additional losses for portable antenna factor and in building loss need to be applied as well.

Then you have to consider this. Are you modeling for a 100 watt repeater and a 5 watt portable? Then you must consider the 5 watt portable is the limiting factor, unless of course you have satellite receivers or diversity.

And yes as well the local noise floor at VHF comes into play. In which case if you measure it, you determine how much it degrades the receiver and it becomes the noise floor for the DAQ calculations.

 

[Murphy625]

whoa!!!! \

These programs are terrific but they are "GIGO".

Actually, you really need to refer to TSB-88 Table A-1 and TSB 88 in its entirety.

If you want a "Public Safety" grade delivered audio quality of DAQ 3.4 and you have a +/- 5.0 KHz modulation you need 20 dB of margin.

Example: a receiver of -119 dBm sensitivity has an inferred noise floor of (-119 dBm - 5 dB (12 dB SINAD) = -124 dBm)

So you add 20 dB (DAQ 3.4) to -124 dBm = -104 dBm minimum threshold.

You can also go for "utility grade DAQ 3.0 and use 17 dB of margin. (It will sound worse, but have bigger footprint!)

Additional losses for portable antenna factor and in building loss need to be applied as well.

Then you have to consider this. Are you modeling for a 100 watt repeater and a 5 watt portable? Then you must consider the 5 watt portable is the limiting factor, unless of course you have satellite receivers or diversity.

And yes as well the local noise floor at VHF comes into play. In which case if you measure it, you determine how much it degrades the receiver and it becomes the noise floor for the DAQ calculations.

I know you're speaking English because I can read the words, but I think its going to take me 3 hours and a lot of googling to figure out what the heck you just said.

Now I know how my 5 year old feels when I try to explain things to her and her eyes glaze over.

 

[RFI-EMI-GUY]

It took me years to learn all this. The document TSB88 was published by TIA to deal exactly with the situation you ask about. It is about 300 pages! Unfortunately you have to pay real money to buy a copy and take a peek.

These programs like radio mobile are great and based on sound principals but they ask for variables that most people don't know the answer to. Unless you quantify the desired audio quality and reliability you desire you can only draw pretty pictures with them. Until about 20 years ago, the major radio vendors could not agree what 800 MHz radio coverage should look like. You had Motorola bidding 6 sites and GE bidding three sites. Plus you have the building penetration loss and portable antenna loss.

If you are just doing Ham stuff and want to know where a repeater peters out at 1/2 Microvolt, then no harm. But if you really want to know the reliability and sound quality , the variables need to be defined.

I know you're speaking English because I can read the words, but I think its going to take me 3 hours and a lot of googling to figure out what the heck you just said.

Now I know how my 5 year old feels when I try to explain things to her and her eyes glaze over.

Sent from my SM-T350 using Tapatalk

 

[Murphy625]

For the past two or three weeks, I have probably run 400 simulations on the Radio Mobile website at 145 Mhz to simulate various antenna heights, coax losses, RF power, and a host of other variables.

I'd input my variables and then run ten simulations while changing the TX antenna height only. Or the same and change the RX antenna height only.

Of even more interest, was running the sims and changing the strong signal margin incrementally and watching the map change.

Eventually, and with a ton of help here, and a lot of hours of reading and watching youtube, I came to a set of variables that I thought would most accurately reflect what my setup would be.

With the help of a neighbor today, we did a short test this afternoon. Two of the N9TAX antenna's, one at 50 feet (top of antenna), and the other at around 24 feet to the top of the antenna. We were separated by 13 miles over hilly (wavy) terrain, farm, and forest land.

At just 5 watts, we got a somewhat clear signal.that I would estimate, using all of my 3 weeks of experience, of being a R4 and S5. I could clearly hear what she was saying and the signal was certainly above the noise floor, but not by much.

What surprised me most was that Radio Mobile was spot on.. and I mean spot on. When I set the strong signal margin to a 6 in the Radio Mobile site, her exact location was yellow surrounded by a 60% green - 40% yellow mix, but when I set it to a 5, her location turned green and was surrounded by much more green than yellow.
And it seems that is exactly what we experienced.

I have to say, I look at tall trees very differently now! LOL