More Questions About the Maximum Useable Range for Part 15 AM

Here is a suggestion for anyone who wants facts they can see and hear about range. This one you won't have to worry about here say. Its called Youtube and search for AM Transmitter Range Test. Also the part 15 AM and FM facebook group has actual audio/video tests of Range. One has a man who took his Radio outside and you can see and hear the range of his transmitter as he walks. I'd like to see more video's where someone has a speedometer in their car showing the starting mileage and ending mileage when the signal fades out or is no longer listenable. That is the Real range test. NEC graphics are nice, but does not actually give you an audio experience of what you'll expect. If I could see better I'd do this to show you the range of my Talking House AM Transmitter on the wire. Then compare it to Station8's new antenna. I'm working on getting someone to help me cross the street and video tape me as I walk with my Grundig 450 Radio. I'll have them focus on the meter of the Radio while tuned to The Legacy at 1630 Khz. I'll show some of the neighborhood minus my house for safety reasons. Honestly I don't need to have someone at my door uninvited. But I'll show the public land marks near my place as I walk. If copyright is an issue and Youtube kills the audio I'll do another one and repeat my Album Rock ID over and over through out the range test. Its just my voice with a gunshot through a voice changer saying “True Album Rock here on The Legacy” and a growly aggressive voice like Album Rock stations did around 1979. There will be no doubt as to who is doing the beta test work and no one else can claim what I'm doing with Station 8. Plus there should be watermarks all over the video too with The Legacy and the web site to my station as well as Antenna manufactured by Station8 of the ALPB. Again this way there is no doubt as to who is doing this work. Part 15 dot US should also be mentioned through out the video so as to show the world who is making the difference for Hobby Broadcasting. I'll see if I can get this done because I don't know how to water mark a video like I have imagined. You need to see the speedometer, but have the video so that no one else can claim credit for the Range that is about to happen. Maybe if I repeat it myself every 30-60 seconds. But if someone kills the audio credit won't go to where it should.

We can thank the folks on the Facebook group Part 15 AM and FM group for this nice article about ground conductivity numbers and how that helps your signal.  Plus another antenna design was mentioned.  AFAIK it does not break any FCC Rules and should be all legit here.

http://lowpowerradio.blogspot.com/2012/05/low-power-am-broadcasters-can-improve.html

What is the typical noise floor in terms of uv/m for both urban and rural environments?

As probably expected, the answer to that question is not simple.

The graphics in the paper linked below might be useful, in some cases.

https://www.itu.int/dms_pubrec/itu-r/rec/p/R-REC-P.372-8-200304-S!!PDF-E.pdf

I appreciate your thoughts and efforts, but as I've mentioned before all these sorts of tests are relying on a never ending list of variables and in fact would only show a very limited in scope "range test".

For example, walking down the street with the radio playing and shooting a video.  This shows the range in that particular neighborhood, with it's particular noise floor.  It shows reception on that particular radio and in that exact direction only. It demonstrates the range to that radio, in that direction, with that particular transmitter installation.  It would show nothing of real value to any other person. What happens if the same guy walks down a different road in a different direction?  What happens is he uses a different radio, either more or less sensitive?  What happens if I buy that transmitter and only hear half as far in my noisier neighborhood with a different radio?  How does it work inside a house? Or are potential listeners expected to sit out in the street to listen.  If you're testing an AM station, is he walking a mile? That would make a pretty long video!

As for showing the speedometer in the car as you drive and listen.  Which car? I own 4 cars. Range is about the same on two of them, close on one, and MUCH less on the 4th.  A co-worker who lives a couple blocks away can't hear my station to the end of the block in his car.  But he can also barely hear the 5000 watt station 7 miles away. So if he were showing his test he'd be showing how all transmitters are awful because all the AM transmmitters would have a range of two blocks or less due to the horrible factory radio in his car.  So, again, the extreme variables in car radios would make such tests anectedotal at best. As for watching the speedometer, only valid if your transmitter is located on a street where you can drive away in a straight line until the signal fades out.  My regular test spot is 7100 feet away from my trasmitter as determined by GPS and verified and mapped out on Google maps and Google satellite view. But when I DRIVE to this spot my speedometer shows a bit over two miles. It's not a straight road to that spot.  So, by your plan my range is about 2.1 miles, rather than the 1.34 miles is actually is in a straight line. Of course my range is a lot less once the sun goes down as noise and skip comes rolling in and I get lost in the noise. 

Then you have the variable of what is considered listenable. I can hear my station quite a bit farther than that, but *I* wouldn't listen to it.  But if I was trying to prove my amazing range I might include the extra distance.

When I first set up my station I did extensive field strength readings to see how my signal fared through the various directions and through buildings, etc. In fact, (hang on I'm counting) I took FS readings at 36 different points, marked down distances (in straight lines, not odometer in the car) and field strengths. Amazing how many different spikes and nulls there are in a signal.  Depending on which way I went this would make a drastic change in my determination of range.

NEC gives you a scientific expectation. Range tests as described give you an expectation of what you'd get under all the EXACT same circumstances.

The ONLY way you can test these sorts of things is with a set of controlled tests. To be honest the folks over at Hobby Broadcaster were certainly on the right track.  Their shootout test is multiple times more accurate than any test described above.  Granted I have a few issues with the methodology over there in the AM Shootout (and even more so in their older FM tests) but it's still a thousand times more telling that any walk or drive around test.

Remember too in AM the level of modulation has quite an effect on range. If one guy gets x range and he's modulating 130% positve, and his simply cranks his modulation down to a peak of 80% there will be a marked drop in range. This is why I always point out that a compareson between two transmitters must include accurately monitored modulation tests. Just a plain unmodulated signal is one thing, but in use if one modulates to 75% and one modulates to 125 the range will be quite different. This was one of my problems with the shootout. Just plain signal.  In this instance the Procaster would have probably beat the Rangemaster simply because the Procaster has built in (and adjustable) processing that easily gives me 125% modulation, whereas the Rangemaster required the purchase of an external processor (the recommend the inovonics 222, which is a fine device for the job) but roughly double the cost -- a new 222 costs about the same as a new Rangemaster). So a stock Procaster I believe would clearly have beat a stock Rangemaster were modulation figured into the test. Bang for the buck I give the edge to the Procaster. 

With the test described above a guy could clearly show that he's loud and clear at 1.5 miles. So another guy goes out and buys that same transmitter and he's pissed that he barely gets 1/4 mile. Of course maybe he's only modulating 75% and the other guy was at 130%.  And the guy in the video showed 1.5 miles but the road had several turns in it and he was only 3/4 of a mile away as the crow (or radio signal) files.  And this other guy lives down the block from a brake drum manufaturing plant that puts a ton of electric static into the air and the guy doing the test lived on a farm in Iowa. And the guy on the test video had a really good radio and the guy who bought the transmitter based on the test video has a crummy radio.  Too many variables for any of these test to actually mean anything. 

If you want to know, for fact, how effective this new antenna design might be you need to do an actual field test.  You need to setup a transmitter and do a field strength reading.  Actual accuracy in the number is not even important. Decide on a transmitter and install it somewhere where it won't be affected as much by outside influences if you can. Remember, in AM you're not worried about a field strength limitation in the rules, and you strictly want to compare and see how much difference JUST this degisn can make. You will need an actual field strength meter, NOT a radio with a signal strength meter, etc.  You need much more sensitivity and accuracy. 

Set it up, decide on a distance, say 100 feet. Fire up the transmitter, take a field strength reading.  Then, changing ONLY the antenna, take a second reading and see what the improvement is.  As long as all other factors stay the same you have a valid test.  If you get 2.2 mV at 100 feet with the stock antenna, and 2.8 mV with the new design, and NOTHING ELSE changed you know you've made an improvement. You don't need to go driving and walking around doing random range tests that are influenced by a million different things, and it's not a valid test if you're comparing the new antenna on transmitter "A" compared to the range with the stock antenna on transmitter "B".  They need to be the SAME transmitter.  You don't need to modulate. You're not testing range.  You want to test actual signal in the air.  You're not testing the transmitter, you're testing the antenna. 

When discussing range I generally am thinking only in the AM realm as it's just not worth wasting time discussing FM.  If you're over 500 feet, you're clearly illegal. To get that far you need x amount of field strength, and its just not going to be legal. Period. So I don't even realistically consider FM as a method of transmitting to more than the house next door. I've tested several FM transmitters over the past few months, even the illegal ones didn't go past 300 feet.  It's proven to me they are useful only for distributing audio within the confines of the studio. 

Field strength meters for AM are not nearly as expensive as those for FM, although they're still not cheap. But it's hundreds rather than thousands. You don't need a FIM-41 from Potomac. I've used a Nems-Clarke 120E for decades for directional AM broadcast radio work. The same machine was also sold under the RCA name and these can be found for less. You might even be able to find someone who would borrow you one, or maybe even track down an engineer who would, out of curiosisty volunteer to come do the test once you have the transmitter set up.  For this particular test your machine wouldn't have to even be accurately calibrated. You're just comparing the difference between two antennas and relative numbers will do the job. 

If I were anywhere near you I'd be glad to come test these things.  But alas, I'm stuck in the frozen north!

TIB

Thenks Tim I did forward your comments to Station8. As I'm doing a very poor man's Radio station I'm not able to do a modulation test. Before I lost everything I had I would have had all the equipment. Sonce I was able to spend 7K on a Bose system I may have been able to buy a FIM 71 for FM and the one for AM as well. I know Station8 was talking about building me a cheap FIM meter for AM just to test the difference in field strength between the wire and his antenna. The difference between indoors and out and the difference in where I place the antenna. That way I could get the highest field strength. He says it should not be hard to make a field strength meter for AM. I gave him your feedback so we can talk about it at the ALPB meeting.

This is for "Relative" observations but can be useful to see the effects of "long radiating" grounds etc.

http://www.mfjenterprises.com/Product.php?productid=MFJ-802B

As my Dad used to say "You know what Einstein always said.  It's all relative". 

The cute little MFJ meter will gladly show you signal in the air.  With absolutely ZERO use for determining actual field strength. Set it up, turn on your transmitter, set the sensitivity for, say, mid-scale, then go tweak your antenna, or ground, or whatever, and it will indeed show you whether you've increased your field strength. At least, in that particular spot. You may have just shifted the pattern into that direction at the loss of signal in another direction 🙂

It will NOT even give you an idea of what you've got radiating in mV/m at all.  And since it's not tuneable at all, you have NO idea if you're picking up all sorts of other stray RF. 

However, for doing some general FS readings, and looking to see the effect of moving or changing an antenna, etc it will at least give you some indication.

Buy the time you bought a meter, a box, a couple antennas, and a few components (very vew) you could build one for about what you'd pay for the MFJ unit above.

Or you could do this:

TIB

I did not say it was good for anything more than relative observations.  And yes  someone can scrounge up a 1N34 germanium diode and a meter and do the same thing. It was simply an example of another way to detect a RF signal and do things for comparison. You could use an O-Scope too as well as many other methods.

On the transmitter end there is only so much that can be done.  The variables the part 15 operator has the least control over are ground conductivity past the property line, obstructions, and the sensitivity/quality of the potential listener’s equipment.  The listeners tolerance for noise will also impact the effective range of the signal.

I may be missing the point of the range question, but in most cases does it really matter?  We use 15.219 because we can’t reasonably buy a FCC license but we don’t want to be pirates.  If someone listens that is great, but they are probably not going to be scanning the AM dial and their radio scan happens to be on our channel at 1 mile and they stop to listen.

On the other hand, I know range is important for a special case of multiple transmitters.  If someone has a bunch of 15.219 complaint transmitters and puts them on the same channel with their carriers synchronized and audio feeds delayed so the overlap is in sync, the range of each transmitter is important; the range of one transmitter determines where the next needs to be located.