Certification Requirements

John Mouw (wdcx) should be able to help, as I believe he used to work in that area.

Clip from the OP:

Somewhere ... Is a complete chart or list of specifications that must be met to obtain certification for a Part 15 FM transmitter.  ...  Darned if I can find it.

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TIB -

Below is a link that may be useful:

https://www.fcc.gov/general/equipment-authorization-measurement-procedures

I did manage to find what I'm looking for.

A fascinating array of FM transmitter tests/reviews coming up in the next few weeks.

Stay tuned.

TIB

Sweet.  I'd like to find out if you ever find one that is right on the money at 250 uV/M @ 3 meters.  If you do what thpe of range will you get to a Car Radio and to a Good Digital Radio (Grundig 450 DLX, Tecsun 310, 880, Yamaha, Dennon, Carver, Luxman, Pannasonic, Sony).  Let us know.

... I'd like to find out if you ever find one that is right on the money at 250 uV/M @ 3 meters. ...

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Just to note that for other things equal, the field intensity near the earth 3 meters away from an FCC "Part 15 FM" transmit system mainly depends on the azimuth and elevation at which it exists, and the radiation pattern/polarization of the transmit antenna system.

A system producing a field intensity of about 250 µV/m at 3 meters from the transmit antenna for one set of conditions will not necessarily limit its fields to about 250 µV/m at 3 meters for all, or even most other sets of conditions.

Very true indeed. In fact, in some of my tests last year I clearly demonstrated that various simply changes around the transmitter resulted in pretty big swings in field strength.  Without moving the transmitter or metering equipment simply moving the power cable from one side to the other, adding an audio cable, etc made quite a difference. And that was in the wide open test field.

In a more realistic test I moved the transmitter into the house and set up the FIM in the yard. Simply setting something near the transmitter on the window sill would change the reading. Most likely it was changing the pattern of the radiated signal, as I didn't move around the yard with the meter to check.

But when Uncle Charlie comes knocking he's just been standing in range of your signal either with his Potomac FIM or his Z-Tech 506 and getting a reading.  He's not taking into account the metal railing he's leaning on, or the fact that your power cable is stretched out across the room to the power outlet, or that your audio cable is plugged, or that the signal is reflecting off your steel garage door. 

At least me "field tests" are done in exactly the same field, with the transmitter and meter set in the same locations each time, so from test to test the results are somewhat able to be directly compared. 

I did do most (if not all) of my tests last year with the transmmitter antennas both in vertical and horizontal polarization.  The test meter is set up for horizontal.  Naturally the signal was much stronger when both were oriented the same. 

But at least I am doing the tests under consistent conditions so the machines can be compared.

TIB

Yes, two very good examples of why the Part 15.239 rule is unrealistic thanks to the information from Rich and Tim.

As there are any number of variables which affect field measurement of field strength as explained it is unreasonable to expect compliance tolerances as evidenced to some NOUO actions.

Rather, transmitter input power and antenna spec such as Part 15.219 would be more realistic and attainable.

Agreed.

Canada does put power into the BETS-1 rules for FM - under a microwatt, but then still has field strength as the ultimate measure of compliance.

If they wanted to be smart about it, just specify power.  It's the antenna+ground+feedline requirements for AM that causes the endless debates on AM.