Prop Studies

[emtunderwood]

I been using towercoverage prop studies for years and it has worked somewhat ok. I'm just wondering if it is close to the 90% accuracy it claims. The Rx threshold seems to be a huge factor. Some people have told me just set it -90 and run if its bad find a different location. Also, been told set it to the noise floor of your repeater which I'm guessing is around -125 to -119dbm and the antenna patterns on the site and manually entering them become horrendous. Can someone ellaborate on the Rx threshold of a prop study and what it should be and places to get .ant files that work with towercoverage if there are.

Thanks

 

[lenk911]

Can someone elaborate on the Rx threshold of a prop study and what it should be and places to get .ant files that work with towercoverage if there are.

I am not familiar with towercoverage software and how in-depth it may or may not be. A professional grade software package that addresses all the pertinent parameters for coverage will cost you thousands of dollars and serious schooling. You add to this 30-meter accuracy land elevation and land use data.

Your "noise floor" is more like the native sensitivity of the receiver.

You adjust the native receiver sensitivity by considering the following factors-

1. Manmade noise: Manmade noise is very frequency band dependent.
   1. On 150 MHZ it varies from 3-25 db depending on the environment the fixed station and the subscribers operate in.
      1. This is primarily caused by solid state lighting and their controls plus transformer-less power supplies (buck converters i.e. wall warts).
   2. 40 MHZ band is a real crap shoot. You have manmade plus natural noise. The old saying about low band applies, " on a good day you can talk forever. On a bad day you cannot talk at all.
2. Other receiver sensitivity degrading factors: Besides ambient noise you have other factors that need to be addressed beyond the native receiver sensitivity. You need to adjust the net as follows:
   1. TSB-88 losses per the industry standard if the modulation is digital.
   2. Reliability loss: Radio signals are not stable--they vary (Rayleigh Fading). You need to add a threshold margin loss in the equation.
   3. Interference losses: Co-channel stations, sideband noise desense from nearby channel occupancy.
   4. Antenna system gain/losses
   5. Simulcast issues
   6. Losses imposed by regulatory organizations and agencies.
   7. Miscellaneous losses
   8. Subscriber gains/losses. Building penetration losses. Clutter and Foliage losses
   9. Coverage: Unless you are calculating paging, coverage analysis is two calculations, talk out and talk back. The worst case of the two is the facility's usable range.
3. Antenna patterns: The vendors share their antenna pattern plots with professionals. Software packages use different formats. One of the more common formats is Planet. Professional grade coverage packages use both the azimuth and the elevation patterns. If the antenna is side mounted on a tower...that's where you use the degree you got from the school of hard knocks to make adjustments.
4. The mechanism of electromagnetic wave coverage prediction is really an unknown phenomenon. The formulas created by scientists are from curve fitting observation data into formulas. They have created 4-5 different models each providing differing results. The formulas have limited valid ranges.
   1. So, you need lots of real-world experience to validate what the software is telling you. It is not cookbook. Old Murphy of Murphy's law fame resides here. He will humble you while you are getting a degree from the school of hard knocks! It's taken me a lifetime of battering from Murphy to gain some gut confidence to go or no-go with the software results.