Text below the horizontal line is from FCC §15.3 (text bolding added).
It would be interesting to learn if the test labs followed this requirement when they recorded the measurements that were submitted to the FCC, and which resulted in grants of certification under §15.239.
Seems doubtful, given the huge increase in radiated fields beyond the §15.239 limit, when an audio cable was added to some of the transmitters in Tim's tests.
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g) Equipment under test shall be positioned and adjusted, using those controls that are readily accessible to or are intended to be accessible to the consumer, in such a manner as to maximize the level of the emissions. For those devices to which wire leads may be attached by the operator, tests shall be performed with wire leads attached. The wire leads shall be of the length to be used with the equipment if that length is known. Otherwise, wire leads one meter in length shall be attached to the equipment. Longer wire leads may be employed if necessary to interconnect to associated peripherals.
The quote from 15.3 quoted above by Rich puts the word "attached" in the foreground.
My first thought was that "attached" meant "hard-wired" or physically part of the transmitter, as Tim pointed out with the C.Crane FM2 which has a physically attached audio cable that does not disconnect from the transmitter.
Looking again we see that 15.3 says something more: For those devices to which wire leads may be attached by the operator.
The Wholehouse 2.0 and many certified FM transmitters come with a separate audio cable which can be attached or detached by the user, but we expect would be the same length audio cable as utilized in the certification process.
The Specification page on the back of the C.Crane FM2 Manual states: Audio Input Cord 5 ft. stereo (extension cords are not recommended).
Although no further explanation is printed in the Manual, we can deduce that an audio cable extension would take the FM2 beyond its certification.
Mr Blare wrote in Reply 2 of this thread, which was his 1st reply in this thread:
... many certified FM transmitters come with a separate audio cable which can be attached or detached by the user, but we expect would be the same length audio cable as utilized in the certification process. ...
The essence of my opening post raised the question as to whether or not the certifying test labs in fact used those audio cables if they were supplied by the manufacturer. Alternately, if the audio cable was not supplied by the manufacturer, did the labs supply and use one of at least one meter in length, as required by FCC Rules?
So far there has been no direct response to that question.
I would suppose that you would have to ask the testing labs that question for each transmitter, as there is no way that anyone here would know the answer. Unless, of course, there is someone here who actually participated in such a test.
I suspect that if the FCC is monitoring this site, and seeing the results to some of the FM testing, they would be asking that same question themselves. And they're the ones who can get an answer from each lab involved.
Artisan Radio posted:
... I would suppose that you would have to ask the testing labs that question for each transmitter, as there is no way that anyone here would know the answer. ...
True, but I thought I'd raise the issue here so that readers might consider it, even if they are unable to give the correct answer.
As Tim's measurements showed, those audio leads can have a strong influence on the performance of Part 15 FM setups -- for which the end user (ultimately) is responsible.
Carl and everyone else who FYI again the FM 2 by C. Crane is lower than the legal limit and is the output uV/m is in the 100's (much less than legal limit)!!! Extending the cable would most likely bring it up to Legal at 250 uV/m @ 3 meters. Maybe the C. Crane company took under consideration one may extend the cable and or the fact that the ground leads to your device you attach to the transmitter which again will increase the field strength as was demonstrated with the Decade CM-10 in the youtube video from both the power source (the lantern battery and cord) and the audio cable. We have learned that this will increase the strength. The C. Crane company was cautious knowing the human nature of us all to use extenders and things of that nature. I could see a user in a car extending the cable not to go beyond the FCC rules, but to simply get the TX out of the way while driving. Or to allow easy access to a device in the car such as a DVD player and yet keeping the TX closer to the car Radio's antenna. That said a common unsuspecting user who knows nothing about electronics would suddenly be transmitting further than the original 25-35 feet. Now they can TX 150 feet and maybe beyond. As I talked about with the transmitter that Winter4w I think his name is and when I talked about extending the audio cable for more range. Since these little $7 transmitters are well under legal limit and the shield is the antenna a 3 foot cable would be the same as a telescoping antenna on a C. Crane and thus give me the 800 Ft range to a good radio and the .5 mile range to a super sensitive car Radio especially on 87.9 Mhz. That is why I have to point this fact out. Plus although we seen simulations we never in real world tests or video's seen a transmitter buried at 100% legal and the range you get to a car Radio, a Tecsun, Grundig, Boombox. As the simulations keep suggesting it is possible to get more than 150 feet on a legal TX and now with 87.9 Mhz allowed we have some possibilities to explore. We need to test transmitters able to to to 87.9 Mhz and when the NEW rules apply to 87.9 Mhz it will definitely open doors to hobby broadcasting. Other sites failed to mention anything about 87.9 Mhz again its a gold mine. I's ever so important that I can TX on 87.9 Mhz now. I'm really thinking hard about the TX for $7 as a temp solution till I get a better one. But maybe its not a real lost cause as was $54. Its a hit and miss. I really want the Ramsey but can't afford that and I really want the Whole House FM transmitter 3.0 for its nice sound but it can't do 87.9 Mhz what to do?
Up above member Rich said: "The essence of my opening post raised the question as to whether or not the certifying test labs in fact used those audio cables if they were supplied by the manufacturer. Alternately, if the audio cable was not supplied by the manufacturer, did the labs supply and use one of at least one meter in length, as required by FCC Rules? So far there has been no direct response to that question."
As Artisan was quick to point out, the reason your question wasn't directly addressed was because it is obviously rhetorical. All I did was build on the questional aspect of it.
In the end we have nothing but unanswerable questions, as Tim has shown that certified transmitters are above or below 15.239, meaning we have no way of obtaining compliant equipment.
Until the FCC invents an achievable way the common Part 15 user can assure compliance with 15.239 we are all sitting rubber duckies.
If someone is worried about their power and audio leads radiating, looping them through a ferrite a couple times should help suppress any RF radiation from the audio or ground leads.
At one point, I thought I wanted to do as much as I could to bring the RF ground out of the transmitter so I could attach a proper counterpoise to it to boost my FM signal. Then I came to the personal conclusion doing anything to up my range on FM would be inviting FCC scrutiny that I did not want to deal with.
I got an assortment of ferrite bits from all electronics and alltronics. When I get my FM transmitter up on the roof, the power and audio leads are going to be choked right next to the transmitter and a couple times as they go down to the ground as some defense against the leads radiating. I am going to put it on a fiberglass mast so the mounting is as RF transparent as possible.
The frustrating reality is we don’t know what our transmitters are doing out of the box. It might be 100uv/m at 3m. It might be 400uv/m at 3m. Buying something on ebay with free shipping from china that works on 87.7 and 87.9 would make the part 15 complaint sticker questionable. On the other hand, getting something from a reputable manufacturer would make me hope it is 250uv/m at 3m or less.
I got a c crane 2, and after the latest testing, I feel that is pretty safe. All I really want to do is cover my yard with FM for when I am mowing the lawn.
The FM2 has a 5 or 6 ft hardwired audio cable.
If it were to break and need replacing would that void certification because you changed the type of cable or length?
Mark
Mark I bet it would. But the C. Crane is well under the limit of 250 uV/m @ 3 meters. This leave lots of room and if you didn't turn up the pot you could simply wire a jack into the unit and use regular cable. C. Crane was being ultra conservative so I'd say if it needs fixing go for it and by happy. So much rhetoric would make a normal non tech savvy person throw their hands up and say Forget it! If you live in a police state like CT or where Pirate Radio is a huge issue its not likely to be even the slightest issue. Again no matter what anyone says here on the forum its up to the operator to do what they feel is safe. There comes a time when we get into the overkill category here.