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“Given that variablity, if I used the weak Grundig radio to pump up the FM range to 200-feet then the other radios would pick it up for a mile!”
This clearly illustrates the major problem with the 200 foot suggestion. The conditions of measurement were not specified. It is best to take this 200 foot range as an indication of what to expect rather than a specification to set the transmitter.
The FM situation here is similar to your observation. On three portables the signal is only usable inside the house and perhaps 20 feet or so outside, but car radio provides a usable signal past the curb and beyond. I have adjusted the transmit antenna to give the minimum strength which works with the portables inside the house and this is not a very assuring way to proceed but it is the best I can do without getting a certified unit. It is a dilemma in that I don’t want to invest in a certified unit only to find that it will not work with these particular portables. On the other hand, risking non-compliant operation is also a dilemma.
This whole problem would go away for me if our local broadcasters provided something worth listening to and I could abandon FM transmitting.
At least with AM under 15.219 there is some assurance that compliant operation is doable and perhaps my solution will be to switch to AM since the portables don’t reproduce stereo anyway. But around here the noise level on AM is quite high due to CFLs and dimmers. More study by me is needed on this.