15.239 compliant FM signal reaches into a typical dwelling?

If we knew the loss of a signal passing through different materials in the FM band, we could calculate an estimated field strength if we had distance from the transmitter to the receiver. If we had the sensitivity of the receiver and the gain of the receiving antenna, we could make educated guesses about reception.

From HDTV calculations, a number of 20dB loss for an indoor antenna comes to mind, unfortunately I do not have a source and I am unsure of the specifics of what frequency range, what building materials, and if that was specific to building materials that were wet or dry.

Just using -20dB for building penetration, the range is reduced by an order of magnitude. A 20dB loss is a power loss of 100. The field at a given distance is proportional to the square root of power. A 100x reduction in power would correspond to a sqrt(100) or 10x loss in range. So if a radio could receive the part 15 signal at 800ft from the transmitter outside, inside it would only receive it 80ft from the transmitter.

The signal strength display on my Tecsun PL-880 with its whip antenna fully extended in the vertical plane reads the same maximum (18 dBu) when tuned to an FM station 60 miles from me whether the radio is inside my brick/frame home, or outside it.

The signal strength reading is less than 18 dBu depending on the exact location of the receiver whether inside or outside, but that is normal for VHF signals (due to multipath).

The field intensity of that FM station at 30 feet AGL at my location for that 60-mile path would be on the order of 30 uV/m.

So you may figure that a signal to a sensitive Radio that could hear my station 800 Ft outside may only hear the station 80 feet?  That may get you from one house to next door.  Makes me wonder.  Since AM has a stronger field strength legally would it be as dramatic for part 15 AM.  I mean really I may not be heard by anyone inside a building.  Only if their in their car and parked while eating out.  Or if their sitting in front of the library listening.  So even if someone with a good sensitive Radio heard my station 1/4 mile you take that same Radio and take it inside I may only be heard less than half that distance.  It really makes me wonder if I am really being received at all inside the wood houses?  Has anyone who ran part 15 FM and took requests ever got calls from the neighbors?  This could calculate if your even going to be heard.

Probably both my AM and FM signals get into the very nearby houses on either side, but the residents are never going to call and make a request.

The neighbor on the east is following sports on ESPN or making cell phone calls, the neighbor on the west is watching Matlock reruns or making cellphone calls.

Besides, if one of them made a request I would need to turn them down because I make my own requests.

As part of a promotional tool to get more locals to find my station and when they are out of range of it to tune to my Website and Download the Andorid app to hear my station it seems that I'm not getting anyone doing that.  I may have got a few Carolina listeners I think one and it was on the other side of the state.  Its had to tell if he drove by and stopped for a bite to eat and heard my station and took down the website and later tuned to the station or rather he found me on one if the internet radio directories.  It sure would have been nice to hear from a local just so I would know my station is getting out in the first place.  When I get my HTC 610 phone which has a FM Radio I'm gonna go inside the library and listen with headphones to see if I can be heard in the building accross the street from my station and see what that does.  I hope it has a sensitive FM Radio on it.  It may give me a clue.

FM goes where AM can't. A normal wood or brick house will not hinder AM much except in the basement. BUT....have a portable radio outside on a LOCAL AM station and then walk into a school, hospital, office building, apartment building, a mall, etc, and you'll loose it!....the signal can't get into large buildings with steel grid structure. But FM will get in fine!

I once stayed at a cottage resort a while back and the cottage was with metal siding all around....AM with a GE superadio dead! FM was fine....even enclosed in metal!

The same way blue yellow and red visable light will see glass as transparent, but ultra-violet, which is just beyond the "visible" portion of the spectrum won't go through glass...FM goes into where AM won't. Different parts of the spectrum.

Mark

You make an important point Mark and I am a strong believer in using EVERY part 15 avenue out there... AM, FM, shortwave, and odd in-between frequencies, because something might hit the ... excuse the expression... "mark."

ALSO, I suspect that neighbors on the same water pipeline and electic service will receive your AM signal just fine in the basement (assuming your ground is attached to all that).

LPFM’s were finding that 100W had problems with building penetration.

Licensed FM stations have a set power (ERP) for a given height above average terrain (HAAT). If they have more HAAT than their station class’s reference facilities, they lose some ERP. Power costs money, so stations were putting up their antennas really high, but the drop in ERP was hurting their building penetration. So stations started looking for a good compromise of having antennas above obstructions, keeping the power bill low, and having enough power density to get signals into buildings.

The super powered translators (250W, as much HAAT as they can get while staying within the service contour of the parent FM/AM or not interfering with another station) have no building penetration. Some of them have a service contour the size of a class A licenses station, but they are unlistenable inside of buildings near the edge of their service contour. That is okay though, because the target audience is probably people listening to car radios.

To stay legal, we are limited to a very tiny field strength. I have no visions of using FM to cover my neighborhood. I can cover my yard nicely which is great for mowing the lawn with a pocket radio. Doing some LR modeling, a useful signal may penetrate the house on either side of me and across the street. On the other hand, similar LR modeling tells me I am covering a dozen yards with enough signal for a good radio to pick up.

The construction of a building will greatly impact radio wave propagation. If a building is dry for the most part radio waves should pass through okay. On the other hand, if there is a layer of moisture trapped between the building wrap and the siding that moisture will attenuate RF pretty bad.

I read somewhere part of the reason cell phone companies want UHF spectrum is the waves nicely fit through the size of a typical window. On the other hand, part of the problem with DTV on VHF-low is the waves do not easily penetrate buildings. Early on, HD radio realized the best way to improve the home user HD radio experience was for the home user to put up an outside antenna. HD radio had a problem with building penetration that was only sort of solved with a power increase.

If a 15.239 field strength increase were to be asked for, it would be reasonable to expect it to have some stipulation such as the transmitter must be indoors and the field strength must be attenuated by some specified amount between the inside and the outside of the building, similar to the initial rules for some wifi in the 5GHz band.

Hi Mark: I Had a General Electric 3-5280B radio back in the 1980's and still have to this day and it works.

Are house we had in upstate, New York was all Alumium siding all around the house and we also had a basement and lived in the country on old farm land. 

I received all these station with NO external antenna of any kind.

I agree on a normal wood or brick home you won't have much issues on the am signal.

We had a tiny sandycreek pulaski am station and i still pick it up in our house with alumium siding and also as well in the basment with not much issues at all.

Depends on what am station you listen too and it's location to the building you could receive the station in a school or with a building with steel grid construction as long you did not go deep into the building But stay near the entrance or near bulildings edge area.

When i was in the house section with the alumium siding in the living room i tuned in 660,770 & 880 am radio in New York, New York which was about 267 miles away during the day around noon time est time from me with the General Electric 3-5280B radio and did not have any issue on the signal coming in on all 3 station they came in about the same .

As Fm goes i have seen the signal get effected by heavy steel grid construction.

I seen all this stuff done above also on the General Electric super turner II radio as well.

I thought i let you know how my radio received, I know allot of factors can be involved on radio receiver in different areas.

Just so you know when i tried to transmit a part 15 Am station out of the basement no luck on range,But when i moved the transmitter in a wood shack about 50 feet away from the house what a big difference i got in range.

As for the General Electric 3-5280B and the 7-2880 series radio goes these are some of the best radio i seen ever made and still can kick some of these newer radios down to size.

I tried to put jpeg picture of the General Electric radios up with no luck.

station 8

The AM from your basemnt doesn't get out very far 'cause the ground around you absorbes all the signal. FM will still get out pretty well.

Mark