New Salem FM

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  • #22092
    Radio Ruminator

    There is going to be a fundraiser on Friday, July 29, for a new FM Station in Salem called the Moon. When does the construction permit end? How many watts will the station have? Will the license be commercial or non Commercial?

    105.5 The Moon Inaugural Event

    Andy Brown

    RR said: “How many watts will the station have?”

    LPFM licenses are granted in the range of power between 1 and 100 watts depending on how high above the average terrain (HAAT) the antenna center of radiation is. LPFM’s whose HAAT is 30 meters (98.4 feet) or less can radiate 100 watts. Anything over 30 meters and the power output must be reduced.

    Note that HAAT is not the same as the height of the antenna above ground (HAG) or the height of the antenna above mean sea level (HAMSL). Usually, HAAT is determined by calculating the HAAT of the tower base location and then adding HAG to it.

    Since you are new to the board, I will explain this. Power is determined by class and height above average terrain.

    Every class of FM service except fill in translators and on channel boosters is assigned its own radius (distance) to the point where their signal strength is 1.0 millivolt per meter (exception Class B, B1). The larger the HAAT, the less actual power is needed to produce this field at the proper distance. The reason for this is that the higher above average terrain you are, the more lower lobes coming off the antenna are able to propagate instead of hitting the ground. You can observe the area of two right triangles formed by the tower, the ground and the radiating lobes. Compare one triangle formed with the entire tower with antenna at top ABC, then a second triangle with only half the tower height FBC being used (ignore the other lines). If the distance along the x axis C (the ground) is constant as it has to be for a single class, you can see the higher antenna has a lot more ‘area’ inside its triangle then the shorter one does. The area is analagous to field strength. For both systems to create the same signal strength at the allowed distance, the lower antenna will need more power since it has less ‘area’ which translates to less radiating power.

    The best coverage for an LPFM is not necessarily one that is licensed for 100 Watts but could be one that has a higher HAAT. It can’t be too high because the FCC will never license any station in any class with a power of less then 1 watt. Of course there are many other factors involved like terrain obstructions and interference.

    Many stations are licensed with less then maximum power because they have height. Contrary to mainstream thought, stations that are higher up with lower power often have superior coverage.

    KISN-LP in Portland, for example, has a very large signal footprint and they are only 2 watts. They are able to be received in many places outside their 1 millivolt primary contour for two reasons, height and low levels of co channel interference. This is true for all classes of station, that is, how well you are received outside your primary contour (which is protected from co channel interference through spacing requirements that all stations must adhere to) depends on height and how much co channel interference is at the receiver input.

    FM radio reception is primarily a line of sight service. Distance receiving (DX) of FM signals bouncing off of various levels of the atmosphere is possible, but other than for its hobby value, plays no role in FM station licensing of power and height. In the AM standard broadcast band, it’s a whole different story.


    Just an FYI; This station may or may not be “owned” and operated by an alumni of this very board.


    This is going to be interesting considering that 105.5 out of Eugene has a strong signal into parts of Salem. Might end up with the same problem as 97.5 did.

    Andy Brown

    “105.5 out of Eugene has a strong signal into parts of Salem”

    Not really. KEUG, Veneta is a Class C3 whose 60 dBu to the north ends in Brownsville. Salem is at their 40 dBu but much of their signal does not penetrate the hills south of Salem. In those few spots that KEUG now can be heard will mostly disappear as it would be inside the proposed 60 dBu resulting in at least 20 dB of headroom and more. I’ve observed this phenomenon here in Portland with several of the LPFM’s that have come on air and the feedback on this board was just like your statement and it turned out to be not true. Radio receivers need a few microvolts on channels with little co channel interference and a full millivolt or more of something else on the same channel simply quashes the weak signal. You know this.

    In other words, just because you can receive a signal doesn’t mean there is a whole heck of a lot of signal there. KEUG is receivable because there is nothing else on channel in those areas where the signal sneaks through the hills but hardly could be considered “strong” in actual field intensity. Also it’s noisy and will be quashed by a new line of sight signal so close in origin. Most of the population in and around Salem won’t have any problem receiving the new station. KEUG does not have line of sight into Salem.

    Also in Salem in a CP for 94.3. Now that’s a situation where KZZR on Mt. Hood does have line of sight right into Keizer and Salem and even though it’s outside their 40 dBu because of line of sight probably has more then the theoretical field strength. Chances are it won’t be successful if built out. 94.3 needs to be used down in Albany or Corvallis if possible.


    I go down to my in-laws in West Salem quite often. Measurements aside, the KEUG signal is quite strong most days at their place on the car radio. Same with 97.5 from Newberg which is on the other side of the hills.
    It’s really a shame that they pile stations on top of each other to the point that the translator in Salem on 97.5 shut down because of the interference from Newberg.
    At this rate, it won’t be long before the FM band won’t be listenable outside of your immediate area.

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