John, WDCX, your shorthanded comment isn't clear.
In what way has this thread drifted into pirate radio?"
Talking about Part 74 of the FCC Rules and the Comtek Transmitter is above board and legitimate discussion.
Talking about transmitting sound effects is permitted speech.
Your message is not being recieved.
See Post #7
And now the FCC has stated 1,000 Feet on FM is Legal!! Do I have to say it again LEGAL LEGAL LEGAL LEGAL LEGAL!! Now if its a mistake too bad so sad for the FCC. So as everyone has taken part 15:239 at face value and preached it like a preacher preaches the END OF THE WORLD IS coming save yourselves you sinners!! so too now we have something to throw at the old 250 feet rule of thumb. Truth is the FCC is swaying and the NAB doesn't want to admit it. Now if that is Pirate Radio the NAB has more bigger fish to fry. Even the one who is a well known anti FMer has stated in Radio World that if the NAB or licensed broadcasters are afraid of a little 100mW AM station or a station going that short of distance taking away their precious listeners they have bigger fish to fry. All I wanted to know about the Scoche and its 900Ft (Again legal less than 1,000 feet do the math) was how it sounded and what model number it was. It could have been a good back up to the SainSonic AX-05B. The gray area would be me modifying it to run on electric instead of batteries. I'm sorry if I sound like a psycho wild child here, but I think a certain person who stated this is right. Though it was more about AM the statement should hold true to FM as well. A real Pirate is NOT even going to buy a SainSonic AX-05B when they could go and often will go for a transmitter with 50 Watts to as low as 15 Watts. Hell a 7 Watt transmitter will carry further than 6 miles even on a telescoping antenna. I thought in America we have FREE speech? I guess we always have to be certain we don't offend anyone in anything we say these days. Its like I like Atrains Rants. Now I am on my rant. Get over the notion that anyone reaching outside their yard on FM is a PIRATE its not true and even looks very unprofessional. A professional moderator of a site should agree. Now if the FCC wants to clarify this well lets hear from them. Why can't we have a spokes person on our side? I get AM gets more range with less power and I'm willing to give it a try too. But in the daytime when there is no temperature inversion I'm still going to use FM.
Scosche could not have added 87.7, 87.9 because of the Part 74 rules because the sticker on the transmitter says "Part 15," not part 74.
You know what they say, though... those who protest too much are probably doing it (piracy).
Did I miss something? When did the FCC say Part 15 FM at 1000 feet is legal?
EDIT: I found it.
So Part 15.239 field strength is
250 uv/M at 3 meters... Is this right?
So extrapolating it out (forgive my bad
grammar etc.) this comes out to the
following?
about 125 uV/M at 6 meters
about 62.5 uV/M at 12 meters
about 31 uV/M at 24 meters
about 16 uV/M at 48 meters
about 8 uV/M at 96 meters
about 4 uV/M at 192 meters
about 2 uV/M at 384 meters
- and that's about 1260 feet.
So... a really good FM radio should
have sensitivity around 2uV for some
kind of quieting. 20 dB????? I have no
idea.
But my Tecsun PL-380 can hear meteor
scatters pings during a meteor shower.
Just with the whip antenna (out in the
backyard.)
So I know this isn't quite right -
I just want to get this down in
general to see if I'm close to right about
the way this works. Do I have it
correct? I'm not an engineer - just a
radio dude.
So with a really good radio - about 1000
feet - I guess.
With a McIntosh (sp.) MR-78
or a Sony XDR-F1HD (apparently
the most sensitive and selective
FM tuner ever made)
and a roof
antenna - even farther.
???
Brooce, WLP
P.S. On this Part 74 thing - I bet there
are some people that are using that transmitter
on 87.7 MHz. It's a a very expensive unit - but
SOMEBODY out there must be using it. They
just aren't telling us about it.
I have a channel 6 LPTV HD (Bleh) TV station
not too far from here, so technically - I'm out.
So how far would a VHF LPTV HD station go?
About 1/2 mile? Yuk Yuk.
My Tecsun 380 goes down to around 76 MHz.
I think my Kaito 1130 radio does also.
There is one other thing:
In the Part 15 station video where they
used frog noises - was that what it was?
Well anyhow - once upon a time there was
a little 10 watt FM college station that had
no listeners. (Pretty much, I guess.)
So they started broadcasting the sound of
waves crashing on the beach - a nice sound -
I guess. They did this overnight. After a while,
a real lot of people in the town listened to them
every night. You know - nice noises to help you
fall asleep. This was way before you could go out
and buy a sound effects generator for 50 bucks that
could do the same thing. Or a computer program or
download or stream.
It does sound nice, doesn't it?
Maybe I'll figure something like that
out and hook it up to one of my Part 15
FM transmitters.
Brooce., WLP
Sorry - I guess this all should be in
the FM transmitters thread - but I
just want it to all tie together.
If you have a Part 15 FM transmitter that
only goes 30 feet to a good receiver in
a free space path - then you have
more room to transmit and be heard
legally I guess. We are working with
such low power levels. I don't think
we know enough about reflection, phase
cancellation, attenuation in certain materials,
etc etc. Now this becomes a very cool science
experiment.
There are some very talented people over there
at KDX radio that have been working with phase
and/or horizontal/vertical polarization for Part 15 FM.
Ask them. Ask for Phlotilla. Wait a minute. Carl
Blare knows a lot more on the subject.
Brooce, WLP
RE: Reply #21 (fields vs distance)
Field intensity is inversely related purely to distance only for paths having no obstructions and reflections. But this isn't true for Part 15 FM transmit systems located near the surface of the earth.
This is apparent in the graphic below, which for that configuration shows a maximum field of 218 µV/m at horizontal distance of 3 meters and an elevation of about 2.8 meters above the earth. However the field at a horizontal distance of 100 meters and 2.8 meters elevation is about 1.5 µV/m.
By inverse distance alone, that 218 µV/m field at 3 meters would be about 6.5 µV/m at 100 meters, rather than the 1.5 µV/m shown in the graphic.
As an example, showing that the tiny fm transmitter for $9 could in fact do 900 feet by itself with no real antenna on 87.7 Mhz. I had no idea that young man was going to get so flustered about this.
I for one would love to get my hands on a Comtek doing 50 mW below 88 mhz, but if i could afford the Comtek , I would pass on that transmitter since my only vehicle needs new tires so badly.
For reference, here is the old post about the Scosche FMT-4
http://www.part15.us/blogs/rock95seven/scosche-fmt-4-review
It was part of a sworn statement during a pirate bust in Tampa a while back.
Ah, I'm finally getting what you're saying, Rich. Thanks for persisting.
Now, I wonder at what transmitter height you would get a 6.5uv/m at 100 meters field intensity? Or at least approaching that linear inverse distance relationship? 5 meters? 10 meters? 20?
Your graphic for a transmitter at a height of 2.8 meters explains why Tim could only get a range of about 200 feet or so in his initial test. His field test measurements will verify how close to theory the actual results are.
Tim, if you're reading this, I'm wondering if it would be possible to do a second set of readings with the transmitter(s) mounted higher, say at 5 meters or even higher? And Rich, perhaps you could do additional simulations for field intensity for a transmitter mounted at additional heights, say 5, 10 & 15 meters?
It may be that those who say that you can only get 200 feet range with a Part 15 legal transmitter (even with a sensitive receiver) and those who say that you can get 800+ feet range are BOTH CORRECT - it all depends on the height of the transmitter and antenna (assuming a fixed antenna attached to that transmitter).
Obviously there are infinite variations to this theme, but below is a comparison of the fields for a transmit antenna radiation center of 10 meters AGL.
The graphic shown earlier this thread was for a radiation center of 2-1/4 meters. So these two graphics should show what might be expected at the limits of the most common range of heights used by Part 15 operators.
The maximum field in free space produced by this dipole with 11.43 nW of applied power is 250 µV/m.
That same power was used to generate the plots below, when the dipole was close to the earth.
Really interesting.
I;ll be back.
Brooce, WLP
OK so the left side of the graph is how high the antenna is and the right side is the distance? I'm not sure what I'm looking at. I know I dont have good eyesight but according to the graph your talking 229 feet and we know we can do better than that. Also the distance of over 1300 feet is almost 1/4 mile. It still is less than what the SainSonic does advertise (hate to keep bringing this up). There is a reason I bring it up because it could for all purposes be legally within the limit. But their low power is far less than most folks are reporting out of box on the C. Crane and Whole House FM Transmitter. There are times I only want to reach just my yard when I do audio tune ups or want to broadcast the ALPB meeting just to my own house and don't want to transmit that 1/4 mile. In ham you learn (though I don't yet have a license) that you want to only use the power needed to communicate. So SainSonic's low power is too low, but if they only had a middle ground I'd been happier with the TX. 200 Ft on low power I'd be jumping for joy. Its just enough I could walk away and do a nature call and still hear the meeting. Or if I want to walk to the porch just for a minute to just enjoy the fresh air but again still hear the meeting. And when I do audio checks I don't need to have that go out when I'm saying Testing Testing and playing a song a number of times and adjusting the EQ. The Scoche is still not a bad TX if it goes 75-150 Ft. At $9 if they still made it and 87.7 Mhz would not get me into trouble I'd do that as a link between the TX and the AM TX if I put that one upstairs. At night I can't TX on 96.3 or anywhere else as the distant stations won't allow that.