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It certainly poses an interesting question. In the context of this article I ran a quick search for any registered stations in the Portland area using 90.5 FM a

It certainly poses an interesting question. In the context of this article I ran a quick search for any registered stations in the Portland area using 90.5 FM and I didn't find anything. Not saying that there isn't, but nothing I could find quickly. Also, I don't know many pirate stations that would broadcast solely for the purpose of disrupting another station. My understanding was that most pirate broadcasters do so in order to send their own message, and so finding open signal space would seem to be key.

jacquesm 4y ago
Check the harmonics too.
RF_Enthusiast 4y ago
This station was interfering with KBOO on 90.7 and a licensed low power FM on 90.3. The shoulders of the analog signal on 90.5 overlap the signals on 90.3 and 90.7.
- pstuart 4y ago
  Is this interference avoidable if using the right gear correctly?
  - Ekaros 4y ago
    200 kHz isn't that much. One can easily observe the effect by slightly tuning off radio and still hearing something.
  - RF_Enthusiast 4y ago
    No, the analog signals would overlap. In this case, KBOO on 90.7 is running HD format, which puts the lower digital shoulder at 90.5 MHz. So this station was operating on top of KBOO, compromising the KBOO signal. 90.5 - 90.6 MHz contained two signals, although the pirate operator didn't know that, as the digital hash sounds like static to the untrained ear.
- colinsane 3y ago
  isn’t this the usual spacing of these bands: 200 kHz apart? like 101.3, 101.5, 101.7 were all distinct stations growing up IIRC. does KBOO have a right to 90.5 being unoccupied? e.g. did they purchase double the spectrum as those higher-frequency stations?
  - RF_Enthusiast 3y ago
    KBOO's signal, centered at 90.7, starts at 90.5 MHz. The edge of the digital HD signal touches 90.500 MHz. By a pirate operating on 90.5, half of the pirate analog signal is directly over the KBOO signal. KBOO did not purchase spectrum as they are a noncommercial station, and those stations are not subject to application or regulatory fees. KBOO has the same rights to the 200 kHz for analog and the additional digital bandwidth on either side, as any licensed FM station in the US has (expect for perhaps some FM translators). As for analog vs. analog on adjacent frequencies, they interfere with each other, because there's a little bit of overlap. Analog signals don't have that "cliff" that the band edge that digital signals have. Analog FM can fit right next to digital, because the digital signal stops right at the edge. But the little bit of overlap of a 101.3 signal onto 101.5 is doubled when you consider the little bit of overlap from 101.5 to 101.3. It's significant interference on a receiver. If you look at the lineup of licensed stations in any one location, you'll notice that stations are spaced by at least one vacant channel. For example, in most cities you'll see an alignment like this: 101.3 (full power), 101.7 (low power or distant), 102.1 (full power), 102.5 (low power or distant). A full power station can't be in the same vicinity as another full power station for 3 adjacent channels. That is probably overkill, as it's made with consideration for receivers made decades ago that are no longer in use.
  - Johnythree 3y ago
    > did they purchase double the spectrum as those higher-frequency stations? Pretty much, yes. There are always guard bands allocated, plus careful calculations to avoid harmonics, intermodulation products, images, etc, which could interfere with other services.
    - RF_Enthusiast 3y ago
- pugworthy 3y ago
  Not that it's a critical decision point, but KBOO is rather old and well known in some circles. They aren't powerful but they are respected. When the favorite neighborhood watering hole is disrupted, people may speak up.
  - RF_Enthusiast 3y ago
    Yeah, good point. Those people may have complained directly to the FCC, or a donor may have mentioned to KBOO that they can no longer get the station. Action may have originated on the listener level with a station as loved as KBOO.
alwaysbeconsing 4y ago
There appear to be licensed stations at 90.3 and 90.7, which is close enough to be a problem.
Johnythree 3y ago
That's not how it works: It's not just stations on the same frequency. There a rather complex set of calculations which avoid interference to adjacent stations, plus interference to other services via harmonics, intermodulation products, images etc.

jacquesm 4y ago

Check the harmonics too.

RF_Enthusiast 4y ago

This station was interfering with KBOO on 90.7 and a licensed low power FM on 90.3. The shoulders of the analog signal on 90.5 overlap the signals on 90.3 and 90.7.

pstuart 4y ago
Is this interference avoidable if using the right gear correctly?
- Ekaros 4y ago
  200 kHz isn't that much. One can easily observe the effect by slightly tuning off radio and still hearing something.
- RF_Enthusiast 4y ago
  No, the analog signals would overlap. In this case, KBOO on 90.7 is running HD format, which puts the lower digital shoulder at 90.5 MHz. So this station was operating on top of KBOO, compromising the KBOO signal. 90.5 - 90.6 MHz contained two signals, although the pirate operator didn't know that, as the digital hash sounds like static to the untrained ear.
colinsane 3y ago
isn’t this the usual spacing of these bands: 200 kHz apart? like 101.3, 101.5, 101.7 were all distinct stations growing up IIRC. does KBOO have a right to 90.5 being unoccupied? e.g. did they purchase double the spectrum as those higher-frequency stations?
- RF_Enthusiast 3y ago
  KBOO's signal, centered at 90.7, starts at 90.5 MHz. The edge of the digital HD signal touches 90.500 MHz. By a pirate operating on 90.5, half of the pirate analog signal is directly over the KBOO signal. KBOO did not purchase spectrum as they are a noncommercial station, and those stations are not subject to application or regulatory fees. KBOO has the same rights to the 200 kHz for analog and the additional digital bandwidth on either side, as any licensed FM station in the US has (expect for perhaps some FM translators). As for analog vs. analog on adjacent frequencies, they interfere with each other, because there's a little bit of overlap. Analog signals don't have that "cliff" that the band edge that digital signals have. Analog FM can fit right next to digital, because the digital signal stops right at the edge. But the little bit of overlap of a 101.3 signal onto 101.5 is doubled when you consider the little bit of overlap from 101.5 to 101.3. It's significant interference on a receiver. If you look at the lineup of licensed stations in any one location, you'll notice that stations are spaced by at least one vacant channel. For example, in most cities you'll see an alignment like this: 101.3 (full power), 101.7 (low power or distant), 102.1 (full power), 102.5 (low power or distant). A full power station can't be in the same vicinity as another full power station for 3 adjacent channels. That is probably overkill, as it's made with consideration for receivers made decades ago that are no longer in use.
- Johnythree 3y ago
  > did they purchase double the spectrum as those higher-frequency stations? Pretty much, yes. There are always guard bands allocated, plus careful calculations to avoid harmonics, intermodulation products, images, etc, which could interfere with other services.
  - RF_Enthusiast 3y ago
pugworthy 3y ago
Not that it's a critical decision point, but KBOO is rather old and well known in some circles. They aren't powerful but they are respected. When the favorite neighborhood watering hole is disrupted, people may speak up.
- RF_Enthusiast 3y ago
  Yeah, good point. Those people may have complained directly to the FCC, or a donor may have mentioned to KBOO that they can no longer get the station. Action may have originated on the listener level with a station as loved as KBOO.

alwaysbeconsing 4y ago

There appear to be licensed stations at 90.3 and 90.7, which is close enough to be a problem.

Johnythree 3y ago

That's not how it works: It's not just stations on the same frequency. There a rather complex set of calculations which avoid interference to adjacent stations, plus interference to other services via harmonics, intermodulation products, images etc.