KPIJ interfering with KAVE?

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    I frequently drive to Oakridge. While there I tune to 88.5 KAVE (a KRVM translator). I’ve noticed a lot of fuzzy reception of KAVE, even within a couple hundred yards of the transmitter.

    Driving up to Hills Creek Dam, only a few miles from Oakridge, KAVE suddenly drops out and is replaced by KPIJ, also 88.5. KPIJ comes in very strong, almost like a local. KPIJ is in Junction City, about 60 miles from Oakridge, at only 550W.

    Driving to Oakridge on Hwy 58, KPIJ comes in quite well up to a few miles from Oakridge. Reception starts flipping between KPIJ and KAVE, then settles on KAVE at a couple miles out but KAVE is still fuzzy.

    One time I was in Oakridge when KAVE was down due to weather-related issues. With KAVE down, KPIJ came in loud and strong in Oakridge.

    I’m convinced the fuzzy reception on KAVE is interference from KPIJ. Looking at KPIJ’s 60db contour map it doesn’t extend anywhere east of I-5. Yet the signal reaches Oakridge, 30+ miles east of I-5, with no trouble at all. Also KPIJ uses directional antennas with the strongest lobe being southeast, in the direction of Oakridge.

    How can this not be illegal interference by KPIJ on KAVE? How can only 550W in Junction City possibly reach Oakridge and audibly interfere with KAVE’s 400W signal?

    Apologies in advance if I’ve used any incorrect technical terminology.


    Probably because 550 watts directional goes a long ways when your stick is 3400 feet high on a mountain in the coast range.

    Don’t confuse the city of license with the transmitter site. Two entirely different things.


    KPIJ’s transmitter is in Alsea, northwest of Junction City. Thus it’s even farther away from Oakridge than I thought.

    I understand what’s happening. My question is how can KPIJ be legally allowed to interfere with KAVE. This seems wrong from an engineering and regulatory perspective.

    According to their FCC correspondence file, KPIJ has been messing with their directional antenna and transmitter power over the last 2-3 years. An interesting coincidence.

    Is an interference complaint required to be filed by the party being interfered with (KAVE/KRVM)? Or can anyone file a complaint and expect it to be taken seriously. Who has the burden of proof?

    Again I reference KPIJ’s 60db contour which Oakridge is far beyond. It doesn’t even include Eugene.



    Andy Brown

    First, KAVE is not a translator. It is a Class A FM that is fed by satellite. Translators have call signs like K255JX or W296AZ.

    Second, KAVE is in a hole. It’s HAAT (height above average terrain) which is what sets class and ERP (effective radiated power) is highly negative coming in at -392 meters (1286 feet) and the antenna is pretty close to the ground at 18 m (60 feet). From the transmitter site to the area by the Hills Creek Dam is uphill for the first 1.35 km and then drops down. This hill blocks any appreciable coverage between said hill and the dam about another 3 km south and east. Just because that area is inside the FCC 60 dBu contour doesn’t mean reception is guaranteed. The FCC predictions use old data from 1927 where the elevation points are further apart then in a more modern coverage analysis. In other words, no one is interfering with the signal, there just isn’t any signal there to receive so the radio grabs hold of a much weaker but present signal from KPIJ. There never was any intention of covering the area by the dam or they wouldn’t have put the transmitter in a deep hole surrounded by higher elevations. The elevation profile in the second image below shows the transmitter location on the left and the dam on the right. You can easily see why there is no signal out by the dam. Never ever assume the FCC 60 dBu curve is wholly accurate without looking at topography. Again, any ‘complaint’ about this is baseless. Your issue has nothing to do with KPIJ’s pattern. Click on images for larger version.


    I appreciate your technical analysis.

    I guess what bugs me is that when KAVE was down, KPIJ came in so well in Oakridge proper. That just seems like an unintended but real problem.

    Just out of curiosity how difficult (expensive) would it be to change KAVE to a different frequency in Oakridge? 88.3 and 88.7 seem to be wide open there. Although admittedly I haven’t researched it.

    Thanks again.

    Andy Brown

    “seems like an unintended but real problem.”

    No. It is the physics of propagation and reception. It is not a ‘problem.’ When there’s nothing else nearby on the channel, even a tiny bit of signal is enough to be received. Given another signal that is stronger and closer totally hides the smaller signal. Nope, no problem there at all.

    “how difficult (expensive) would it be to change KAVE to a different frequency in Oakridge?”

    Whatever the cost, it’s unnecessary. There still won’t be any coverage towards the dam if they don’t relocate the antenna and as far as ‘Oakridge proper’ if a different frequency was available, and they went ‘down’ some other co channel not too far away would be easily heard.

    I don’t think you are taking into consideration how congested the airwaves are nor how receivers are capable of picking up weak signals when there is nothing else on that channel in the vicinity. There is nothing out of the ordinary happening based on the behavior you’ve given.


    Driving in Eugene a couple of years ago noted that KPIJ did not have that good of coverage…multipath issues…maybe that’s when they were having trouble? Mountain top to mountain top…FM RF travels well line of site…especially with the sensitivity of modern day FM car radios.


    My point was not about reception at the dam, except to emphasize how far KPIJ is reaching. My point is about reception in Oakridge, even up close to the KAVE transmitter.

    The day KAVE was down, KPIJ sounded about the same in Oakridge as it typically does in Eugene.

    Is capture ratio the ability of the receiver to discriminate between two signals of different strengths on the same frequency?

    Andy Brown

    “The day KAVE was down, KPIJ sounded about the same in Oakridge as it typically does in Eugene.”

    As long as there is 20 dBu or more of signal strength that will be the case. In fact, even when you are between two signals on the same channel, if one has 20 dB more signal strength then the other you won’t even hear the weaker one. The entire FM service is predicated on that 20 dBu difference.

    “Is capture ratio the ability of the receiver to discriminate between two signals of different strengths on the same frequency?”

    Yes, but that’s a receiver specification that really has little bearing on your questions. The only facts that matter in this case is free space loss.

    Also, don’t get sucked in to the old AM notion that stronger signals sound louder. Loudness on FM is a function of average modulation percentage. As long as there is enough signal to obtain full quieting, the ‘loudness’ will be the same whether you are close to the transmitter or at the edge of useful coverage.


    Duly noted. Thanks again for your input.


    This is today in Oakridge, about 1/4 mile from the KAVE transmitter (water tower in the background). The “fuzzy” reception is KAVE. The cleaner signal is KRVM.

    I shared this with KRVM. Turns out they said they just had an engineering study done. The results show KPIJ is interfering with KAVE. The video helps bolster their claim of interference.

    Driving back to Eugene on Hwy 58 the car radio flipped to KPIJ just past Westfir.

    I did the video in loser portrait mode on purpose to include the horizon & general weather conditions.

    Andy Brown

    They’re on a water tower? Bingo. What else is on that water tower? Cellular?

    Water tower installations are giant IM (intermodulation) generators. Radio towers are always galvanized (dipped in hot zinc) to avoid the skin effect. Water towers are usually just steel with no coating except maybe paint in some cases.

    Unless the “engineering study” found massive problems at other locations not near the water tower, that is the problem. Land mobile antennae have been using water towers for years, and IM is a constant problem.

    Think of it this way, the water tower is allowing the radio frequency energy to run on its outer surface like it was part of the antenna generating all kinds of destructive interference (where the same signal interferes with itself due to phase cancellation). It’s pretty complicated to analyze but it’s been documented.

    Water towers are a poor choice for VHF. UHF can get away with it most of the time.

    This is easy to prove. Turn off the supposed offender and more than likely you will find the same problems still exist only the weaker signal will not be there, just noise and hash.


    I don’t think there’s anything else on the water tower. Certainly not a cellular transmitter. Directional antenna to receive 91.9 in HD, transmitter for 88.5.

    As I noted previously, when KAVE was shut off, KPIJ came in clearly.

    I get that KAVE is not the ideal setup.

    KRVM is talking to KPIJ’s engineer about it. We’ll see what comes of it.


    Went up to Oakridge with an aligned Sony XDR-F1HD and a decent antenna. Premise: The Sony’s astronomical selectivity etc is so good it will have no trouble picking KAVE out of the KPIJ fog. Especially close to the water tower.

    Except it didn’t. Sounded exactly the same as the car radio. Proximity to the KAVE transmitter and antenna orientation on the XDR made no difference at all in the XDR’s fuzzy reception.

    Conclusion: KAVE is broadcasting fuzz. Most likely explanation for that is a problem with the antenna receiving KRVM-HD1 over the air or the coax feeding the XDR’s antenna input.

    Or someone accidentally switched the XDR to Forced Analog mode, but I doubt that.

    My money is on the receiving antenna for KRVM-HD1 or its cabling to the XDR.

    Notwithstanding the above, KPIJ is still strangely strong there. I wouldn’t give up on that avenue of pursuit yet as a secondary problem.

    Fair and Balanced. Relentlessly persisent. OCD. LOL.

    Andy Brown

    “a problem with the antenna receiving KRVM-HD1 over the air or the coax feeding the XDR’s antenna input.”

    It’s quite possible that KAVE input needs to be filtered to eliminate KPIJ.

    In all cases it’s not KPIJ’s responsibility, assuming they are operating at proper power. KAVE has made a poor choice being on a water tower which could be amplifying the signals hitting the receive antenna.

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