Model formula calculator for RF attenuation over distance - Page 1
Forum section: electronics / projects

author: Wilson__
author_rank: Frequent Contributor
timestamp: May 23, 2024, 08:18:46 pm
content: Any advises for web page or Excel spread sheet or formula for calculating RF signal attenuation over distance in real world situation (not free space)?Antenna height in single-digit meters, distance of 'zero' to 2km, residential area (no high building), 800 to 900MHz.Many thanks.

author: shabaz
author_rank: Frequent Contributor
timestamp: May 23, 2024, 10:21:59 pm
content: Some of the semiconductor manufacturers offer calculator tools, e.g. Silabs website has a downloadable spreadsheet with models for free range and office environment.Matlab has capability too:https://uk.mathworks.com/help/comm/ref/propagationmodel.html(not free, but low-ish cost for a home license). You can select quite a few propagation models. I've not used that function myself so I cannot comment.However, you mention you're interested in 800-900 MHz, and part of that may be in an ISM band, so you can just try it out for real at an allowed frequency. I've done that in the past; simply get a couple of RF chip dev-boards, and modify the demo code to send packets (and display reception with even just an LED, it's not even essential to have a digit/text display), and just go for a walk with the other board, and see how far you get. That's very feasible at 868/915 MHz, and will give you a more realistic feel for what is possible with what antenna and location.

author: LaserSteve
author_rank: Super Contributor
timestamp: June 30, 2025, 03:24:52 pm
content: Your looking for Broadcom, Avago, HP ---> "Appcad" for a simple free Frijs calculator with many other useful RF features. It is a tiny Windows executable, however.Microwaves 101 has an on-line freebie as well.I have not tried this one from TL, but here is a link for a popular Excel spread sheet.https://www.ti.com/tool/RF-RANGE-ESTIMATORSteve

author: tggzzz
author_rank: Super Contributor
timestamp: June 30, 2025, 03:29:06 pm
content: Quote from: Wilson__ on May 23, 2024, 08:18:46 pmIn general this is averycomplex topic, and you will only get statistical probabilities - and even those can be very questionable.Entire careers and companies have been founded on understanding the topic.Onekey point is the consequences of multipath reception - without multipath, modern cellphone systems wouldn't work.

author: LaserSteve
author_rank: Super Contributor
timestamp: June 30, 2025, 03:41:02 pm
content: Yes, that equation is known to work very well mostly when used by a fellow named Harold T. Frijs,only when at Bell Labs former Homdel test range,, and on Antennas with a very good front to back ratio, such as the modestly sized Western Electric KS-15676 microwave antenna, on dry evenings with a full moon. I'm still glad he published it though.A more through treatment for truly long distance systems at UHF and above is in the various updated Linkurt texts titled "Engineering Considerations for Microwave Communications Systems" and articles in the "Bell Labs Technical Journal"Link:https://www.worldradiohistory.com/Archive-Company-Publications/Lenkurt-Demodulator/Lenkurt-Engineering-Considerations-for-Microwave-1972.pdfI've never found anything effective outside of academic papers, BTSJ, some Telstra / UK GPO, and serious amateur radio publications (RSGB etc.) for very short-range systems. About 60% of the RF academic papers I've read, and in some cases, tested, would have best been published in the "Journal of Irreproducible Results"Model->Build->Measure, Repeat, is a good idea when working at RF.Steve

author: antenna
author_rank: Frequent Contributor
timestamp: June 30, 2025, 04:02:04 pm
content: Assume line of sight for microwaves. The important part isn't just a straight line though, its the fresnel zone between them, an elliptical region encompassing both TX and RX antennas.This website shows terrain between two stations given locations and antenna heights and the path lights up green when there is line of sight.https://www.scadacore.com/tools/rf-path/rf-line-of-sight/edit: for example, a station 20 miles apart will have a first fresnel radius at the midpoint of about 100 feet. That first fresnel zone needs to be at least 60% clear for reliable comms. So if line of sight touches the ground somewhere along the path, that cuts into that first fresnel zone and that can increase interference from diffraction and reflection which increases attenuation and affects reliability. Tropospheric propagation may hide these effects. Traveling along a straight line between the two antennas, the first fresnel radius F= sqrt(wavelength*D1*D2/(D1+D2)) where D1 and D2 are the distances from each antenna (equal at midpoint).

author: radiolistener
author_rank: Super Contributor
timestamp: June 30, 2025, 04:11:15 pm
content: Most commonly available formula is the Free Space Path Loss (FSPL) equation, but it only account for the idealized case where the signal travels through an unobstructed, lossless environment. FSPL helps estimate how much power will reach the receiving antenna based on distance and frequency, but it doesn't include environmental losses.In real-world situations, especially in residential areas, even when there are no high-rise buildings, various obstacles like trees, walls, and terrain can introduce additional losses that are highly variable and context-dependent. These losses can range from negligible (e.g. open field, dry air) to severe (e.g. metal fences, wet foliage, dense walls).So, there's no single universal formula that accounts for all such real-world obstructions.

author: Terry Bites
author_rank: Super Contributor
timestamp: June 30, 2025, 05:02:47 pm
content: I don't know about your location but all the free space near me has been auctioned off.Much of it stolen by Arqiva. Bloody Canadians!

author: Solder_Junkie
author_rank: Frequent Contributor
timestamp: July 02, 2025, 07:20:38 am
content: This amateur radio site provides coverage predictions on a map. You will need to register in order to use the site, but it is free. You can save the coverage predictions on the site.Being amateur radio related, the nearest frequency to the ones you mention 910 MHz which is within a USA allocation.https://www.ve2dbe.com/rmonline_s.asp

author: ftg
author_rank: Frequent Contributor
timestamp: July 02, 2025, 07:29:48 am
content: Radio Mobile can also be run locally, but the online version is nice.Ubiquiti has recently renamed their AirLink link planing tool to ISPdesign or something, but it still seems to work.https://ispdesign.ui.com/#NanoStation Loco M900 and Rocket M900 are 900MHz and you can set custom antenna gains and output powers.So that might also work for some use cases.

author: berke
author_rank: Frequent Contributor
timestamp: July 02, 2025, 01:24:17 pm
content: Signal-to-noise ratio or packet loss rate might be more useful than pure path loss. Those depend on the transmitter and the receiver.Also, what kind of distance are we talking about here?(Ooops that was in the first message, <2km)Is this for a ballpark estimate or for something more precise?

author: LaserSteve
author_rank: Super Contributor
timestamp: July 02, 2025, 02:51:51 pm
content: I just tested the TI app against some real numbers I have measured for my Church's spread spectrum wireless microphone system. I made an assumption about the modulation protocol, but the TI Excel sheet seems to be pretty good. ** Disclamer, Pretty good for some small subset of pretty good. My numbers were for 500-700 Mhz, so I used the 430 Mhz setting for the frequency.Church noise floor is very high due to a rural cell site with three carriers and a tall tower 50 meters from the church, and 7" of cinder block in the sound booth where 1/2 the receive antennas are, the other antennas are forward of the wall. The calculated data matches what I'd expect.I have Log Periodics in the rafters and high gain rubber duckies on the other diversity port for the receivers.So for high VHF low UHF, the Ti Calculator is certainly useable, and a lot of work went into creating it.For the OP, if you need antennas, I've had very good results with Kent Brittain's YAGI and Log Periodic products:https://wa5vjb.com/products1.htmlSteve

author: Solder_Junkie
author_rank: Frequent Contributor
timestamp: July 02, 2025, 03:01:36 pm
content: “In building” coverage is not practical to predict as it varies significantly depending on materials, and whether you are on the ground floor or by an upstairs window.To make matters worse, metal cladding is used in some “quick build” commercial buildings (eg supermarkets) and aluminium foil backed insulation panels is used in many new house walls. In one of our supermarkets the mobile phone signal is “5 bars” outside and non existent at the back of the store.

author: radiolistener
author_rank: Super Contributor
timestamp: July 03, 2025, 08:37:20 am
content: To simulate real-world signal losses in Excel, including environmental effects and obstructions, you can use the RAND() function to add random variation representing unpredictable attenuation.

author: tggzzz
author_rank: Super Contributor
timestamp: July 03, 2025, 10:20:41 am
content: Quote from: radiolistener on July 03, 2025, 08:37:20 amYes, for some effects, but what magnitude?There are many causes of variation, with differing statistics, e.g. shadowing/log-normal/slow-fading, multipath/Rayleigh/fast-fading, diffraction.... (Ted Rappaport's work is a good starting point)Then you can add in (or more accurately subtract) the effects of having multiple antennas separated by half-wavelengths.Then you can add in the effects of the modulation and coding schemes, e.g. (C)OFDM.