Waiting to see the results of your readings....wish I had this meter to test mine for Canadian strength.
Mark
... There's something off kilter there. At 200 feet, a maximum Part 15 legal field strength of 250uv/m at 3 metes should be 12.5uv/m. ...
Note in the graphic below that the field intensity for those conditions at an elevation of about 1.5 meters and an h-distance of 3 meters is about 140 µV/m, but is only about 1.5 µV/m for that elevation at an h-distance of 100 meters.
A 1.5 µV/m field arriving at the receive antennas of most consumer-level FM receive systems would not provide very useful service.
Also notice in the graphic below the considerable variation of the calculated field 3 meters away from this system at h-plane elevations between 0 and 10 meters -- which show the effects of reflections of the transmitted signal from the earth, at that distance.
I would either have to be converted to AM if 250 uV/M @ 3 meters would only get me at best 150-200 feet on a Car Radio with high sensitivity. Its useless at a range of 50 feet to a Digital boom box. As I said when I had my SainSonic AX-05B on Low power I barely got out of my house to the porch. If that is my legal limit (For the Love Of God No) then I can see why all micro FM stations in that other websites mind is (well you know what some call it). It is no way something I'll even tolerate let alone accept. I'd be REALLY trying to raise that field strength. The AM conversion will be short lived if it comes to that. I already may have to use AM after 6 PM because of the temperature inversions here. But trust me I'll do all I can and I suspect a lot of pissed off real Micro broadcasters who won't stand for spending money on a transmitter only for the flies in the house to hear your station. So think about it. I'm not one who will throw my hard earned money away on stupidity as 50 feet is more than plain stupid, its insane at best and again I'm surprised if this is 100% true that anyone in America would take this lying down like a ball baby b&tch boy. Well I will say this I'm not anybody's b*tch for no amount of money or lack of common sense. So if this is true I'll try and start a campaign like none other. That is unless somehow I could get AM to have an Album Rock sound even though mono and get listeners to try my part 15 station on the AM side where I can legally get out a mile to 2 or more. Sorry if I sound offensive, but I think the ALPB is for improving Radio. You can't do that with only 50 foot to a Digital boom box. Its time we find out soon but yes my mind races and my blood is boiling in the meantime. I am preparing for a fight. This certainly will inform us so we know what we are dealing with.
I'm not sure I understand the simulation, Rich. Is the field strength at 3 meters 140uv/m or 250uv/m?
I received email last evening that the Wholehouse 3.0 transmitter I ordered from Amazon has been shipped. I'm going to wait until it arrives then I can get readings from both the Wholehouse and the Decade. Mostly because I don't want to set up the gear twice, when I can just wait. Heck, it might be here by the weekend anyway.
Then I got to thinking -- I was going to head out into the open field to do the testing, which I think to get actual figures is fine. But if the FCC was testing your signal and was exterpolating the readings (like they seem to always do) I'm certain they have no formula to account for reflections, etc. I don't think they're going to let you defend yourself by meeting them in an open field with your transmitter to take readings to ensure no reflections from buildings, etc. Anyway, just more overthinking. But I suspect testing in a lab and testing in the real world would yield differing results. But actual inuse variations wold be different for every transmitter in every situation and I'm sure in real life results in signals stronger one way, less in others, etc.
Tim in Bovey
RE #19 above... Is the field strength at 3 meters 140uv/m or 250uv/m?
The fields shown in Reply #17 for an h-distance of 3 meters are those from a 1/2-wave, center-fed, vertical dipole with a radiation center 2-1/4 meters above earth of average conductivity. The power applied to the feedpoint of the dipole is 11.43 nW.
When that dipole is located in free space it produces the fields below, at a distance of three meters. Note that the maximum field is 250 µV/m, which is the limit given in FCC §15.239. Free space here means there are no other objects near the dipole in any direction throughout the sphere of radiation.
When that vertical dipole is located near the earth then reflections from the earth modify the free space pattern, as shown in reply 17. In this example the maximum field drops to 218 µV/m, at an elevation of about 2.8 meters above the earth.
The maximum field for a given path length, and its elevation above the earth will vary with the height of the radiation center of the dipole above the earth, earth conductivity, and obstructions/reflections from other conductors/surfaces along the propagation path.
to see your results.
Where do you get these meters that can measure in micro-volts?
Don't know if I want to see price!
$15k new.
$1k on eBay.
You get them either used from engineers who retire, or stumble upon a deal. The ZTechnology R-506 currently sells for $11,500.00. Then you will need to add $1150.00 for a calibrated antenna/cable combination, then accessorize from there. This is the combination I have. It's exactly what is used by the FCC (which they also interface with a computer to store the data, and a GPS unit that stores location information that facilitates exterpolating the field strength to where they are measuring from). I happened into a deal on mine from the estate of an engineer who passed away, and instead of waiting to sell off his equipment with help of someone who knew what things were, they just started selling. I have the complete R-506 outfit, complete with GPS interface but I do not own a proper PC laptop to use those extra things, and are not needed for my purposes.
You can also use a Potomac FIM-71, which is also used by the FCC and broadcast engineers. I also own one of these. They haven't been manufactured for decades, but do include an attached calibrated antenna. They read out on a very accurate traditional meter. You can often find a used one for about $4000 and up, but since they're accurate and relatively simple to operate, and still in use by broadcast engineers, they're hard to come by.
Remember field strength and field intensity are two different things. To measure field intensity (that's what the 250 uV/m is) you need the metering device AND a calibrated antenna/cable combination.
For AM there are many vintage units that will do the job. There's the Potomac FIM-41 -- which also has a larger frequency range good for checking harmonics for a broadcast station, as well as the Nems Clarke 120D, 120 E, etc, or the identical Potomac model (they bought out Nems-Clarke and continued to sell the units under their name, then continued to calibrate and service them, although they don't any more). Then there's the RCA WX2 which is also the Nems Clarke with a different name on it. These are vintage, have tubes, and require hard to get batteries. I have a Nems Clarke unit that I use regularly in my station engineering work, and it works for Part 15 AM too, although it technically doesn't cover to 1620 AM, it does work fine at that frequency. You can find these for a few hundred dollars up to a few thousand, depending on who is selling it, and it's condition. A new Potomac unit for AM is about 15K.
Spectrum analyzers, radios with dbu meters, signal meters, etc are all fine for looking at RELATIVE signal strength, but will not give you actual field intensity numbers.
Tim in Bovey
I forgot the concept of a spectrum analyzer with a calibrated antenna. But you'd never pull it off with a cheap one! These are what? $5000+antenna? (I'm kinda guessing there) but far more versatile than the units I have.
Tim in Bovey
Thanks for info.....as I thought, didn't want to see price.
Mark
For compliance measurements you can say sweep from 30 to 200 mHz using a biconical dipole. Plug the antenna correction factors in including cable loss, set the SA to peak hold, rotate the EUT, move the receive antenna up and down and viola! You have the maximum radiated emissions recorded! Repeat this proceedure in the opposite antenna polarization and you're good or not good to go. Above 200 mHz depending on the kind of test you may want to use adjustable dipoles.
Tim: That's pretty close. You should be able to find one used for about $4K. However, what you have is more than most. I have a couple of ancient Eaton receivers with antennas. Kinda big to lug around though. 🙂