Before I decided to take out the batteries and pack up the FIM-71 until the next project comes along, and list the CM-10 on eBay I thought I'd pop out to the front yard and shoot a quick demonstration video of this transmitter in action, and also show the extreme variabilities in Part 15 transmitters. The variations you will see were similar with the WH 3.0.
Note this was NOT done in an "open field" but how many Part 15 broadcasters do you know that put their transmitters in open fields? Further, how many NOUO's have you see where the operator got to tell the FCC agent "But wait, lets take my transmitter over to the fieid over there..."
No, this is in the front yard. Next to a big ol' pine tree (that actually absorbs signal).
Note also that the readings you see on the meter are NOT the actual field strengh readings. Per the graphs in the FIM-71 manual, at the test frequency, to determine actual field strength the reading must be multiplied by the antenna factor for the frequency. In this case that is 2.25. So that reading of 5 mV (yes, that's mV not uV) is actually more like 11 mV, or 11,000 uV/m. You can do your own math for the other readings demonstrated in the video. A LEGAL reading at this frequency would be roughly 111 uV/m.
Now I realize there are those who will say "that can't possibly be right" even when seeing the meter for themselves. Personally, I don't much care. As far as I'm concerned, for someone who has no intention of ever using a Part 15 FM transmitter, my work here is done. And I challange others who may feel so inclined to do such testing to not only report actual numbers, but demonstrate them. I trust big city engineers also have access to video recorders.
Even accounting for various variables we're WAY past the limits here.
See:
TIB
Good video, and valid conclusions. Well done, Tim.
IIRC, field measurements made and posted by "others" claiming to be expert(s) did not report fields that were GREATLY non-compliant with FCC §15.239.
Even though the tests in your front yard were not made in an uncluttered environment, that environment could not possibly account for the HUGE difference between the fields you measured, and those permitted by §15.239.
It will be interesting now to compare your measured results with the next measured results of others -- hopefully made with the same authenticity and documentation you used.
What a nice thorough video explaining it all even for a lame person to understand what is going on and how the Patomac FIM-71 works. You have a very clear and concise Radio voice too so folks should understand what it is that concerns the FCC when you operate at this overpowered level with the Decade CM-10 (Nothing more than an overpriced modified SainSonic AX-05B or CZH-05B or Failsafe CZH-05B or Rangemaster FM Transmitter). And the meter almost went full scale at 3 meters. The audio was clear too so as you said its a dandy transmitter but note its still over the limit so if your gonna use it you should live outside the Metro area and do note it doesn't make it legal its just that you are less likely to be under the radar all things considered. Thanks again Tim.
Tim, you did a superb job narrating and demonstrating the process of properly measuring a Part 15 FM transmitter for compliance with 15.239.
Your effort makes us more aware of what's going on with these "certified" FM transmitters than all our talk and conjecture could ever achieve.
It would be very enlightening to hear the strategy meetings at the maker and distributor level that ultimately result in over-powered transmitters put on the market.
Back to conjecture, but I'll bet the return rate of legally set transmitters is too great to bear, the only solution being a cheat to grab for "customer satisfaction."
Maybe the transmitter execs had lunch with the Volswagen guy.
Nice job Tim. It does not take a rocket scientist to see the unit is clearly over the limit. Thanks for taking the time to debunk the myth-busters. 🙂