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In another thread http://www.part15.us/forum/part15-forums/regulations-law/pirates-remain-priority#forum-topic-top a graph was posted with the comment that at 1 mile a legally operated AM station per 15.219 would produce an field strength below the ambient noise at most receive locations. While the graph predicts this it does not reflect my experience nor that of others who operate such a station.
The ambient noise in a car environment is expected to be less than that of a home environment and the signal to noise ratio is expected to be better since the receive antenna is outdoors and the signal is not attenuated by building materials.
The other factor affecting range which is not accounted by the graph is that conductors such as power and telephone lines can act as receive antennas and by induction couple a signal to a mobile receiver. This effect has been observed by me with both my station’s signal and those of very remote commercial stations where the signals and listenability improve with proximity to power lines.
Such calculations and graphs are a good starting point for range determination but fail to account for other factors which affect reception of weak AM signals.
Neil
Total posts : 45366Neil wrote: … a graph was posted with the comment that at 1 mile a legally operated AM station per 15.219 would produce an field strength below the ambient noise at most receive locations. While the graph predicts this it does not reflect my experience nor that of others who operate such a station. …
However that graph was based on the conditions shown there, which are not the same as the system Neil is using. That graph and performance applies only to that set of conditions.
I modeled Neil’s ground-mounted Part 15 AM system using his Class E transmitter in NEC4 back when he first described it. The differences are:
- Uses 12 buried radials as an r-f ground reference rather than a single 8′ ground rod
- Earth conductivity is 8 mS/m rather than 5 mS/m
- Frequency is 1670 kHz rather than 1650 kHz
The groundwave field calculated by NEC4.2 at 1 mile for Neil’s conditions is about 110 µV/m — which is more than 11 dB greater than the 30 µV/m minimum field for the set of conditions in my original graph.
A 110 µV/m field in the AM broadcast band can produce useful reception on a sensitive AM receive setup, in the absence of local r-f noise and with no other interfering stations.
I can listen to the daytime groundwave of WHO in Des Moines on a clock radio inside my home, and WHO has a groundwave field here of about 100 µV/m.
A 30 µV/m field would have a very poor signal-noise ratio in the AM broadcast band, that few tolerate for very long.
Total posts : 45366What you say now doesn’t track with things said in the Chart & Graph Exhibit being discussed:
“Below is a graphic showing the groundwave fields existing at a radius of just 1 mile from a transmit antenna system, for the other conditions shown.”
“The only system configuration there that actually is _compliant_ with all of FCC §15.219 is shown at the intersection of the X and Y axes, at the bottom left of the graph.”
“The 30 µV/m field strength that configuration can produce at 1 mile for those compliant conditions probably is below the ambient r-f noise level at most receive locations — regardless of the receive system located there.”
“Receive systems 3x more distant would be even less likely to receive consistently/reliably useful signals, unless those transmit systems were non-compliant with FCC §15.219 — as illustrated by the fields at 1 mile produced when using the longer lengths of vertical conductors shown along the X (horizontal) axis in the graph.”
My Comments Start Here: “For the other conditions shown” is unspecified since no detailed conditions were stated in Part 15 Engineer’s original post.”
“The only system configuration there that actually is _compliant_ with all of FCC §15.219 is shown at…” Where is “there“? What is meant by “all of FCC 15.219“?
“Probably is below the ambient r-f noise level” is an imprecise guess and not a definite fact. You could also say “may or may not be below the ambient r-f noise floor.”
Saying “less likely” is not the same as saying unlikely.
Most important of my comments at this time: “…unless those transmit systems were non-compliant with FCC §15.219…” This is a final conclusive judgement and does not leave open the chance that other systems, such as Neil’s, might in fact comply with 15.219.
My advice to readers is to doubt these Charts and Graphs until they are carefully examined for the accuracy they claim.
Total posts : 45366charts. they lay out a simple fictional scenario that leave out many environmental factors. it is in fact possible to recieve a legal part 15.219 setup at a distance of 3 miles. a friend of mine who has a compliant 15.219 system i installed for him myself gets out 2-3 miles to a car radio in some directions with no issues during the day time. at night he is trashed and doesn’t get down the block.
the system located in central NJ consists of a optimod 9100A2 driving a hamilton rangemaster on a 4 ft mast with 8 x 10ft radials in his backyard tuned for 100mW but heres the kicker it is 15ft from the back of his 3 story home with aluminum siding exterior on top of having AC lines criss cross his property in proximity to his rangemaster.
Total posts : 45366My Comments Start Here: “For the other conditions shown” is unspecified since no detailed conditions were stated in Part 15 Engineer’s original post.”
I was referrring to the other conditions shown in my NEC graph, nothing else.
“The only system configuration there that actually is _compliant_ with all of FCC §15.219 is shown at…” Where is “there“?
There = contained in my graph.
What is meant by “all of FCC 15.219“?
Self-defining.
Most important of my comments at this time: “…unless those transmit systems were non-compliant with FCC §15.219…” This is a final conclusive judgement and does not leave open the chance that other systems, such as Neil’s, might in fact comply with 15.219.
Never did I write that Neil’s or anyone else’s system could not comply with §15.219 if it didn’t match my NEC model. Why did you conclude that I did?
My advice to readers is to doubt these Charts and Graphs until they are carefully examined for the accuracy they claim.
And understood.
Total posts : 45366Our resident sciolist yells: ‘Never did I write that Neil’s system did not comply with §15.219. Why did you conclude that I did?”
No. You didn’t
No. I didn’t.
That’s not what I meant by what I said.
Total posts : 45366When WRCR on 1700 kHz came on (112
miles from me, remember them?) I
couldn’t get them at my house during the
daytime at all.
But if I took a portable radio and held it
next to the telephone pole behind the
CVS 1/2 mile from my house everything
changed.
Then they were weak but completely
intelligible (sp?) on the portable radio
– – touching the side of the telephone
pole in just the right spot.
I don’t remember the radio I used.
It might have been a Kaito KA-1103.
Brooce
Hi Carl
Total posts : 45366Mr Blare writes, quoting me:
“Never did I write that Neil’s system did not comply with §15.219. Why did you conclude that I did?”
Blare: ... That’s not what I meant by what I said.
__________
An obvious and unanswered question proceeds from that reply of Mr Blare, which is:
Then what DID you mean?
Total posts : 45366What I wrote is understandable at an average reading level.
Any pretense toward misinterpretation is specious.
Total posts : 45366(Blare) … Please stop the games!
________
Just to note that Mr Blare is the person playing games here, by trying to evade knowledgeable and technically provable responses to the questions he is asked here.
Total posts : 45366Rich, before you jumped the trigger and responded I changed my post and removed the game element.
Total posts : 45366Mr Blare posted: … I changed my post and removed the game element.
_______
So what?
Does that dismiss your need to prove your point of view?
Total posts : 45366Rich, at this stage I would have to say that you are running a game by pretending there’s something I need to prove.
You know how to irritate but let’s get back to basics.
This is a forum website about part 15 radio.
We post whatever it is we have to say, others post their responses, we reply, and so on.
For some reason you become disgruntled by my responses to your posts.
You didn’t show disdain or disrespect toward Neil when he posted a critical review of your chart and graph.
Therefore you are discriminating against me.
Total posts : 45366For some reason you become disgruntled by my responses to your posts.
Mr Blare: I posted my reason(s) here, which apparently you did not comprehend.
You didn’t show disdain or disrespect toward Neil when he posted a critical review of your chart and graph. Therefore you are discriminating against me.
The difference being, that so far Neil has not responded negatively and without understanding of the comments in my earlier posts in this thread, whereas you (Mr Blare) have done so.
Total posts : 45366I became tired of reading all these back and forth responses, and reread the original post in question.
It was stated in another thread that a there have been instances of a Part 15 compliant transmitter having a 3 mile range. Rich then posted his chart (while quoting that 3 mile statement), which appeared to show – or at least it was inferred – that a legally compliant Part 15 transmitter could barely achieve a range of a mile. Which is how Neal read it, and how I read it as well, at least at first glance. Of course, that was with the assumptions/conditions given, but I have to wonder, why those assumptions? And why weren’t those assumptions more clearly explained?
Neal’s installation conditions could just as easily have been chosen for that graph, and with a field strength of 110uv/m at 1 mile, it would certainly be possible to receive his signal well beyond that one mile mark with a sensitive receiver (i.e., better than a clock radio). I suspect that Neal can probably receive his signal in a car in some directions for up to 2 miles and maybe even more, even if the signal is weak. I also suspect that it might be possible to maybe get 3 miles range under ideal conditions with a better ground system (such as more radials). I haven’t seen that chart yet (i.e., a chart that shows the absolute maximum range a legal Part 15 AM transmitter could achieve, under ideal conditions).
So what was the purpose of the original graph in the first place?
These graphs have their place. But they don’t take the place of a simple, concise and clear explanation. It’s much harder to come up with that explanation than it is to churn out technicalese that few can and want to understand with casual reading.
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