Savage said:
Well, BigA, a couple of things. First of all, there is no such thing as "ERP" in AM broadcasting. Effective Radiated Power is an abstraction used to determine FM class and has nothing to do with AM. The power of an AM station is simply measured as the base current into the tower in a nondirectional system or the common-point current in a DA. HD has no effect on either.
If "ERP" is not used in AM broadcasting, then when you have a directional array, and are quoting the power that would be required to produce the same field at a particular azimuth with a non-directional antenna (assuming you're using one of the existing towers), what term do you use? For example, there's a station 9.3 miles north of me on 1170 that runs 50kW daytime. They run the equivalent of 112kW toward me, and about 200kW in their main southwest lobe.
Also could something similar apply when talking about antennas of varying efficiency? For example a 1/4-wave over a ground plane does about 305 mV/m @ 1 km for 1 kW applied power, a 1/2-wave does about 380 mV/m, a 5/8-wave does about 440 mV/m, and the Franklin at KSTP (179.4° stacked on another 179.4°, insulated & fed at the center) does 511.7 mV/m at 1 km for 1 kW of applied power.
Speaking of which, this may be a little OT, but if R Fry is reading this, what may be the efficiency, in mV/m @ 1 km for 1 kW of applied power, for an antenna that is functionally compliant with 15.219(b)?
On topic for HD stations interfering with analog, I've been trying to come up with a way of allowing analog-only stations to compensate for the interference from HD stations. One idea I had was allowing the analog stations to increase their transmit power output (without needing to notify the FCC or get a permit, and even if their TPO would exceed 50kW) to compensate. The station would find out where the HD signal is the strongest within their coverage, including the fringe (even out to the 0dB above quietest atmospheric noise, even if that means using the ground conductivity maps and groundwave charts to determine the distance, not making actual field measurements). Then, they would increase their TPO (without changing their antenna pattern) so the signal-to-noise ratio of their unmodulated carrier over the strongest HD signal (wherever it was in their coverage area - wouldn't necessarily have to be at the extreme fringe) was equivalent to what their S/N ratio of their 125% modulated carrier would be over the noise level if that was an electrically quiet location approximately 20,000+ km from the nearest AC power grid and thunderstorm activity. Only analog stations would be permitted to do this, though - HD stations would be disqualified.
Also, if HD continues to be allowed, how about allowing analog stations to increase their bandwidth to +/- 15 kHz (or such that the RMS value of their splatter is the same as that of an HD station)?
(Alternately, though, I'd prefer to require devices that emit RF that aren't intended to be received on an analog broadcast receiver to have field strengths so low, when measured at the surface of the device with any end-user-removable covers/shields removed, to not even register on a FIM in a screen room, even when that FIM is capable of measuring the noise floor in that room. Exceptions could be made for devices that are intended for testing radios, for example, or some hobby kits as long as they're not used unattended for extended periods of time, like more than a few minutes to a couple hours or so.)
Another thing (maybe I should find another topic to piggyback this onto) ... I'd like better receiver standards mandated. One example would be to require better IF filters - for example if a radio (or a device that includes a radio) has an MSRP of over, say, $20, then require the -60dB IF bandwidth to be no more than 2x as wide as the the -6dB bandwidth (which can be no wider than the audio bandwidth), and require stop-band attenuation to be at least 90dB and no more than 3x the -6dB bandwidth on AM, and at least match the Tecsun DSP radios on FM. For radios costing upwards of $60, $150, $250 or more, the filters would need to be much better. (A $150+ radio, for example, should be able to receive a weak but usable signal of a station near the atmospheric noise floor, splatter-free, while at the occupational/controlled maximum permissible exposure contour of a first-adjacent strong signal, and allowing the full analog bandwidth of the desired signal, if at all possible.)