Effective Service Range

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Effective Service Range

What exactly does that phrase mean? "effective service range"?..

Back in 1978 an indepth study was released that looked into several methods which could be utilized during times of emergency to provide the public information. The conclusions came down to using TIS and CBs, but Part 15 also was considered:

"In addition to TIS systems as defined by FCC's Rules and Regulations, similar devices can be operated under Part 15 of the the Rules and Regulations without licences if their output is restricted to 100 milliwatts. These unlicensed stations have an advantage over TIS systems because they can be operated on any frequency between 510 and 1,600 kHz. They can be operated with conventional or cable antennas. Their effective range is under 0.8 kiometer (0.5 mile) with a monopole antenna. Their short range makes them unsuitable for general emergency use." http://https//

I wish I had saved every reference I had come across in official documents that had provided effective service range estimates for part 15 AM transmitters (withon the last 40 years), because none of them say anything so ridiculuos as the FCCs public notice stating 200 feet.Even the FCC's own John Reed (who had wrote the Part15 rules) said concerning that public notice while in correspondence with R Fry:

"..Yes, I know that a Public Notice was released saying that unlicensed AM and FM transmitters have 200 feet of range... same applies to range estimates for operation in the AM band. (That same Public Notice also incorrectly stated that you can have 50 mW ERP in the AM band and 10 uW in the FM band..) This is why our rules do not specify a range - it's a relative term that is completely dependent on the environment.. The non-technical author of the notice should have checked with the engineers before writing this. Note that the numbers in this Public Notice are not binding - the equipment must meet the standards in the actual regulations.).."Source:

I have been researching in the last week or two trying to track down what part15 transmitters where being manufactured and certified under the alternative rule during the early 1970's (which by the way havent found any yet), that had concerned the FCC so much back then,  and though I haven't found what I was looking for, a lot of interesting bits like this have been revealed. Most of this I wrote anout in a couple threads at HB, but I mentioned the same here and at ALPB when I was beginning, but didn't it didn't seem to generate much interest.

Anyway, none of what I found has been much help, but it is interesting to note that the ground lead rule was not wrote into the rules, nor did the FCC propose to eliminate 15.219 from the rules for manufactured units until the studies and considerations of creating a TIS classification had begun.. The time periods corelate exactly.

In the 80 years of part 15, this was the only time the rules underwent any major modification (other than adding the alternate rule being added in 1957). Therefore it's hard not to conclude the TIS station creation somehow directly influenced the ground lead rule being created for part 15.

Also of note is that certain documents stated that prior to the creation of a new TIS classification in 1978, all TIS stations operated under part 15.. However, I couldn't find any other documentation to confirm this.. Other documents make it clear that prior to 1976 only some TIS stations operated part 15, but most of them operated under FCC expiremental licences going back as far as the 1940's.. The story goes on and on.. but I still haven't found what I was looking for, which is manufactured part 15 transmitters in the early 1970's..

Someone, somewhere, must have a lead to follow, cause I have hit a dead end.

Well, looks like I compleately drifted the topic of my own post!


Seems to me

Seems to me that effective service range is the coverage area of a station including part 15/BETS-1 that can be recieved with listenable quality on a typical radio....the best receivers of course will extend that effective service range but only on those receivers.



That makes perfect sense.

That makes perfect sense.

Rich Powers Part15, Take 2..

Just to attempt to make

Just to attempt to make things a bit more precise...

I know that there are classifications for FM signals using field strength, such as 'city grade', etc.  I'm not aware of any for AM, but that doesn't mean anything.  Perhaps, though, effective service range is the range from the transmitting antenna at which the field strength remains 'city grade'.

Let me add to the observations..

To expand on Artisan's accurate comments: "Full Queting."

Druid Hills Radio AM-1710- Dade City, FL. Unlicensed operation authorized by the Part 15 Department of the FCC and our Resident Hobby Agent.  

AM Broadcast Field Intensity Needed

From Reply 4:  ... there are classifications for FM signals using field strength, such as 'city grade', etc.  I'm not aware of any for AM, ...

Below is a clip on this topic from Radio Engineers Handbook (1943) by F. E. Terman.

The local r-f noise, co- and adjacent-channel interference levels can be a lot higher now than they were in 1943.

Has anyone ever attemped to

Has anyone ever attemped to update this to the 21st century? I am aware of generalizations.

Druid Hills Radio AM-1710- Dade City, FL. Unlicensed operation authorized by the Part 15 Department of the FCC and our Resident Hobby Agent.  

Some one had emailed me the

Some one had emailed me the following last week:

...minimum usable signal strength in the AM band. I am going to say that for licensed stations it is probably 0.5mV/meter (500uV/m). I have seen this figure used in talk about the protected contour of a broadcast station. I believe this would also be in the ballpark of what one could expect to receive at a distance of perhaps 250' using a compliant Part 15.219 transmitting system having no long ground lead.

I'm still researching the subject, but came across this FCC record from 1987 that I wanted to pass along to you FCC Record The interesting stuff is on the 3rd page (#5016 in the original document).The Commission presently requires that an FM translator be installed within the 2mV/m contour or 25 miles from the AM's antenna, so it's possible they've upped what they consider to be a usable signal in response to increasing man-made noise levels. Or, they might just have a tighter definition of service area.

Rich Powers Part15, Take 2..

The whole point of my -kind

The whole point of my -kind of question, was really in regard to the nonsense 200 foot estimate..  The answers you've all given has been interesting, but in all honesty I don't have much comprehension on how to directly relate to it. I wasn't really so much asking a question, but more so trying to illustrate a point.. but oddly enough there was no real point to be made - other than I considered the phrase "effective service range" to be extremely vaque (IMO).

 By the way, concerning what I was talking about concerning TIS station operating primarily all operting under part15 prior to them getting there own classification.. At first I had only been able to fond a songle reference saying that, but since then I have been able to confirm that is actually true.. TIS/HAR really didn't even begin to come into regular use until about 1971 and for years after did exclusively operate unlicensed under part 15 untill 1977.

Just a cool bit of information, which I might have already mentioned here.

Rich Powers Part15, Take 2..

"Effective Service Range"

From the opening post:  What exactly does that phrase mean? "effective service range"?


That is a simple and important question/issue concerning probably all "Part 15" operators.

Unfortunately, producing an _accurate_ answer to that simple question is not simple, at all.

There are many variables contributing to the effective service range of Part 15 (and other) radio stations, some of which are:

  • Frequency
  • RF power radiated toward the receive system
  • Modulation percentage/density of the carrier wave
  • Earth conductivity along the propagation path
  • Terrain profile along the propagation path
  • Co- and adjacent-channel interference at the receive site
  • RF noise at the receive site
  • Receive antenna location, pattern, orientation, and polarization
  • Receiver sensitivity and selectivity

         - and more.

Almost all of those variables applying either specifically to a given Part 15 tx/rx setup, or in general to all of them most likely are unknown.

Simple Translation:

You can hear it with no background noise. Full Quieting.

Druid Hills Radio AM-1710- Dade City, FL. Unlicensed operation authorized by the Part 15 Department of the FCC and our Resident Hobby Agent.  

Background Noise

That depends on all the factors I posted, and more.

Reply to Rich Powers

Yes in Canada 500uV per meter is the minimum field strength a station has protection. This is for AM and FM. Most AM sensitivity specs are given in uV/M but most FM specs are given in microvolts which is different then microvolts per meter. But it would take so many microvolts per meter field strength to get a certain microvolt signal strength to the front end of the FM reciever.

With AM A typical good radio and most hi fi tuners will have an AM sensitivity of 200 to 500 uV/M. The GE Superradio has a sensitivity of 65uV/M. Car radios may be better than that. Even the Carver tuner gives AM at 200uV/M

So your range depends a lot on the quality of the radio being used.

Saw on a website about radio which I can't remember where now, said that 100uV/M is the lowest field strength that a good radio could hear...AM or FM and over 1500uV/M will start to cause  overload and station imaging over the band on lesser quality radios.



Thank You

Rich Powers posted that FCC Inquiry from 1987, and I saved it to my folder. I've read up to 105, and my mind is going in circles. Normally, I'm inclined to squares, rectangles and triangles, but circles is good.

So many issues to discuss...where to begin...well, I'll keep it short. OK:

At 101, they mention an antenna. The "Perimeter Current Antenna". Electrically short, but efficient.  Has anyone done anything with this? I see Part 15 applications right away. Remember, this is 1987, thirty years ago! 

Is this PARAN the Isotron? Or do we have other AM antennas in the works? To be frank, I am not convinced about the Isotron. And up here in New England, the frequency 1500 is clear from Maine to the Carolinas and west to Oklahoma. But there is a night time lobe of noise that extends across the eastern US! 

I am really interested to see if anything has been done with the PARAN. I do not have the facilities to experiment with AM. My FM broadcasts have been cut down to 10mW. This covers me, and my 3 neighbors in this building. You can't even pick it up in the street very well. It disappears at the house next door. That's fine.

Reading that inquiry makes me think this hobby is an uphill battle. NOUOs and NALs are being handed out like candy. Two (or is it three?) states make Pirate Radio a felony. Florida does not recognize Part 15 as I understand it. Unlicensed is unlicensed. Ya goin' ta jail! That was back then. They may have lightened up a bit since...

I'm not totally in the clear at 1500AM. We have 1490 twenty miles from here. That's 10kHz separation. I was at 1560 until I found out about that 50,000 watt blowtorch in New York. And 1610 is taken by a HORRIBLE sounding TIS a couple miles from here, out on the Interstate. That thing should be illegal.

Thanks, Rich. I'm going to read that inquiry in its entirety at my leisure. It answers a lot of questions.


Groundwave Field Intensity vs. Distance and Earth Conductivity

Here is a table showing how groundwave field intensity varies with distance and earth conductivity (other things equal).  The conductivity values range from the best to nearly the worst for the continental U.S. shown on the FCC M3 chart.

If an AM broadcast receive system needs a minimum field intensity of 100 µV/m for acceptable performance, note that this field is produced (or exceeded) at a range of 1 mile from the transmit antenna -- but only for earth conductivities of about 8 mS/m or better.

A 100 µV/m field also is produced for the lowest conductivities in the chart, but at path lengths progressively less than 1 mile.

Useful reception of fields less than 100 µV/m might be possible, depending on the noise tolerance of the listener.


Data Point

In the 3rd paragraph of Reply 3 in the link below, Tim in Bovey reported that he was able to hear a noisy signal from his Part 15 AM station on his car radio at a distance of 7100 feet from the station (1.34 miles away).

He measured the signal strength at that location using a calibrated field intensity meter; it was 60 µV/m.

In other posts he mentioned that the r-f noise level in his community is very low.  That would be a factor in getting this kind of range for/with a field intensity of only 60 µV/m.

Reply to Rich #16

Yes, that's why a station goes so good on a car.....onlly the GE superradio would even come close to that as it has a sensitivity as posted in specs of 65uV/M.

Average radios have sensitivities of about  1500uV/M

Hi-fi tuners are between 500uV/M to 300uV/M generally.

The Tecson model that has the DBu reading, is in the specs 1000uV/M

One of the best moderately priced radios that you can get now that would have decent sensitivities is a few Sangean models and the Grundig S450.

Oh yes Ccrane has one that's supposed to be like the suprradio was.





Tecsun PL-310 MW Performance

"The Tecson model that has the DBu reading, is in the specs 1000uV/M"


I own a Tecsun PL-310 with that "dBu" reading.   The operation manual for it shows its sensitivity on the AM broadcast band is less than 1 mV/m for a S/N ratio of 26 dB.  That audio noise level would be nearly inaudible compared to the program modulation/processing used by most AM broadcast stations.

Using its rather short internal loopstick antenna and inside my home in a city of 42,000, the PL-310 receives the groundwave of radio station WHO from Des Moines, IA -- which has a field intensity here of about 100 µV/m.  The audio is noisy, but listenable.

I also have a cheap, >25-year-old, General Electric 7-4624B clock radio in the house that performs about the same when tuned to WHO as the PL-310.

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