I talked to Brian of Whole House FM Transmitter 3.0 and told him the Association of Low Power Broadcasters attempt to petition the FCC for increased field strength. However I told Brian that I want to make it mandatory that the extended part 15 transmitters scan before allowing a user to transmit on their intended frequency of choice. Brian said that he would have no issue with that but his concern was it would cost the company an unnecessary expense if I were to make it mandatory for the current part 15 service so that all transmitters have this fail safe built in. Then I said how about having two categories of transmitters? He was more willing to look into that and said he'd have to read all about what we are proposing before they jump on and support us. I gave him this site and the ALPB site and facebook page. He said he'd meet with the other members and discuss this. Next I asked him why some transmitters are putting out more range than others and rather or not they even try and go for the max on each transmitter? Well JUST AS I SUSPECTED they go UNDER the max in case at the mass production line one is over. I asked him if somehow we could get a transmitter that is 250 uV/m to test for range before asking for more because full legal power may already get us a mile. He said one would hafe to be manually tuned and he would have to get extra permission from the rest of the company and the equipment to fine tune the unit to that limit. And yes the output to the final of these units are JUST UNDER 100mW (you read right). So is 100mW legal into a rubber duck? Well as Brian and I talked and I mentioned that a Rubber Duck is no more than a leaky dummy load he laughed and said there is not much these antennas put out. Hence why it takes near 100mW to get the field strength. When they tune the transmitter they shot for close to 200 feet (even though legal field strength can go 800 feet or more). So is the Sainsonic legal? May be now that I found that this transmitter was near 100mW. I also talked about the 87.9 issue and he did say they had to stop allowing their transmitters to go down to 87.9 Mhz because it is not part 15.
I'm so happy I talked with him about this and got some answers. Now we know these transmitters are not 100% 250 uV/M. So we really need to get one that is and see what range we get. Also he did confirm that in an open field you'll get twice the range and height does matter. He was a very nice guy to talk with and it just goes to show that if you present yourself in a professional matter you'll get the answers you need. Now we have a little more data not just theories.
I admire your executive trait of getting right into an issue and talking with the key players.
The conversation you had with Brian at Wholehouse was informative for you and now for us, as we have suspected that the certified FMs are "set low" for reasons we weren't sure about.
It becomes obvious that the stubby antennas on the certified units are playing a part in crippling the field strength, and our hall-monitors and sargents-at-arms who scold us for thinking and talking about "better efficiency" jump all over the idea of trying better antennas with these mini-micro-doll-house-sized-toy-transmitters.
Start jumping, junk-yard-dogs, we are experimenting with improved antennas on certified FM transmitters. Or, we're only talking about it.
Hey, is there a bounty payment if you report something which results in a NOUO?
Of course, in an open field you don't have any listeners 🙂
But if you're testing to see if a transmitter is legal, 3 meters isn't going to require a large open field. You're practically standing right in front of the transmitter. So testing for legal output isn't really effected by this unless you're in an alley between two buildings! And if the FCC hits you up for a violation they're not going to take your transmitter out into a field to test it 🙂
I figured they'd have to make them just under the limit to allow for tolerance in components and manufacturing process, that only makes sense.
Output of 100mw, or 500mw etc is not a deciding factor. It's how that power is transferred to the air through the antenna. An ineffecient antenna can certainly drop a signal down to legal with plenty more output than that.
A rubber duck may be a leaky dummy load, but I hit our ham clubs repeater from 45-50 miles away with a rubber duck and one watt. As I've mentioned before, not all rubber duck antennas are created equal, and they can be built to be frequency specific -- want to reduce your output, just use a horribly unresonant antenna.
So you're saying Part 15 operators would not be intelligent enough to monitor the FM band and seek out an available frequency on the own? How about the autoscan feature on your new transmitter picks up a birdie thrown by a piece of equipment in your house, or some intereference, or a far away station you received through the propagation known as ducting, which can carry a station hundreds of miles? Huge added expense and complication for something you theoretically need to use once. When you find a channel what do you do when a new repeater or translator pops up on your frequency?
When we talk about whether or not a transmitter is legal remember the FCC is not going to test your field strength in lab conditions. There're either going to exterpolate the data from some distance away, or plop down 3 meters from your antenna and see that they get.
When you say "see what kind of range we get" you are again bringing variables into the result, way more than any variables Rich mentioned in my testing plans. Range into what? A sensitive car radio? If that my really good Ford, or my neighbor's Kia that can't hear a darn thing from even local real stations? is that into a boombox on a picnic table, a portable radio in someone's hand, a table radio in a kitchen or on a desk in someones house? or a high end hifi tuner in an audiophiles listening room?
In basic theory, 250 uV/m at 3 meters will give you the same coverage from the same installation location from any transmitter/antenna combination. Field strength is field strength. Now, you may get 250 uV/m by having the necessary power to do it, or having less power and a more efficient antenna, or a bunch of power and a crappy antenna, however you reach that field strength reading is irrelevant.
I certainly believe that to a point, height will help. How much remains to be seen, and needs to be tested. And again the effects will depend a lot of local terrain and structure.
My Decade will be here this week. It won't take long to take it out, fire it up and put the R-506 in place and tell you what the actual rield intensity is at 3 meters. In the meantime I think I'll pop over to AMazon and order up one of these Wholehouse 3.0 jobs and see whats up.
All we've really learned is that they do manufacture them to be "under" the limit, but by how much? And even if they were 20% under (which is a heck of a lot of tolerance) would still be 200 uV/m and thet additional 50 is in no way capable of taking coverage of 800 feet or more (to a sensitive car radio) to a mile.
I'm very anxious to get some actual numbers on these buggers.
Clearly I'm going to have some FM transmitters to sell at a discount in a few weeks 🙂
Tim in Bovey
And worth keeping in mind, there plan to get less than 250 uV/m may count on using their included bad antenna. Simple antenna upgrade will tell us how much you can increase field strength by simply connecting a dipole, or at least a prooper length, tuned whip antenna. I suspect we'll find the transmitter itself has plenty of power, and changing antennas will easily make it illegal.
TIB
... And yes the output to the final of these units are JUST UNDER 100mW (you read right). ...
An output power of 100 mW from any "Part 15 FM" transmitter would have to be attentuated by about 70 dB before being radiated by a 1/2-wave, center-fed dipole, in order to meeet FCC §15.239 in free space.
If a "rubber duck" antenna used with that transmitter had 20 dB less gain than a 1/2-wave dipole (1/100th that of the dipole), then only 50 dB attenuation of the 100 mW transmitter output power would be needed to meet §15.239.
But still, what is the point of generating an output power of 100 mW in an FCC Part 15 certified FM transmitter only to attenuate that power by 50 dB or more within the transmitter hardware (for those wanting to comply with Part 15)?
Thelegacy -- as you have set up a connection with Brian at Whole House, would you be willing to ask him about this, and report back?
Not 5 minutes ago the FedEx man brought me a Decade CM-10 stereo transmitter.
Took less than 60 seconds to have it out of the box and transmitting on 98.5 (what it was set at).
Disappointed to see not one shred of documentation in the box. No instructions, no setup advice, not one work. Invoices and FCC certification papers are with it, but apparently no further information is needed? Odd.
Probably won't have time to do any sort of testing for a few days, but I'll have it playing music in minutes.
Tim in Bovey
Not 5 minutes ago the FedEx man brought me a Decade CM-10 stereo transmitter.
Took less than 60 seconds to have it out of the box and transmitting on 98.5 (what it was set at).
Disappointed to see not one shred of documentation in the box. No instructions, no setup advice, not one work. Invoices and FCC certification papers are with it, but apparently no further information is needed? Odd.
Probably won't have time to do any sort of testing for a few days, but I'll have it playing music in minutes.
Tim in Bovey
While talking to Brian I Quickly learned that the company wanted to make the transmitter as cost effective to the company as possible. I'm getting the impression that the field strength they have these things emitting is 50% less than the full allowed. When I brought up the NAB and interference he confirmed to me it was a huge issue. I think another reason is to not anger the FCC so many companies volunteered to lower the field strength lower than allowed (Although he simply said it is easier and cheaper for the company to have as he says plenty of room). It tells us they don't even measure the field strength or if they do they want to be certain these buggers won't come close to the max. So you see when on the C.Crane you max the VR2 your probably in actuality closer to full legal. Hence all the 90,000 hackers a day doing it to the transmitters neve got NOUO's in my opinion. Looking at the SainSonic AX-05B and their rubber duck which is fatter at the bottom than on top. I was told by a Ham that this rubber duck is a really poor design. So possibly this unit is still legal (Even at high power) which won't matter if Johnny Punk don't stop the dead carriers around here. I'm sure now we all learned something.
As reported TheLegacy is observing dead carriers on his radio that pop up and then disappear.
Setting aside the idea that these are anti-FM operatives trying to prevent TheLegacy from running a station under 15.239, what might be pruducing such phantom carriers?
I've been a ham since 1969. Never learned to identify a "good" rubber duck antenna by it's diameter or shape. In fact, that's not actually possible. See:
https://en.wikipedia.org/wiki/Rubber_ducky_antenna
Tim in Bovey
Nice work! That conversation with wholehouse was very informative and learned a few things. Now we know even at part 15 they could be underpowered and could really go more distance legally than is thought. Yes you're right the Ccrane is under powered(45 to 70 ft) and turning the pot inside and extending the antenna would bring it to the max allowed.
At Decade, Michael told me that they measure them there and their transmitters are at max when sent out. Even the CM-10 is right at the limit for BETS or part15.
Mark
... Start jumping, junk-yard-dogs, we are experimenting with improved antennas on certified FM transmitters. ...
The only thing that legally matters for anyone interested in compliance with Part 15 FM is the field intensity produced by their transmit system, as measured/extrapolated by the FCC.
Of course those who don't care about such compliance and/or misunderstand its variables are free to do as they wish, but not with some risk of FCC action.
With reference to Reply #9 above:
... what might be pruducing such phantom carriers? ...
Here is one possibility:
http://dictionary.cambridge.org/us/dictionary/american-english/phantom
The FCC spokesperson said: "Of course those who don't care about such compliance and/or misunderstand its variables are free to do as they wish, but not with some risk of FCC action."
I simply talked about improving the antennas used with 15.239, but in no way spoke of exceeding the rule...
... yet you jumped.
... I simply talked about improving the antennas used with 15.239, but in no way spoke of exceeding the rule ...
Please develop your quote above when it applies to unlicensed systems exactly compliant with FCC §15.239.