Why X-RAY FM be so noiseyyyyy?????

feedback.pdxradio.com forums feedback.pdxradio.com forums Portland Radio Why X-RAY FM be so noiseyyyyy?????

Tagged: ,

This topic contains 13 replies, has 6 voices, and was last updated by  Andy Brown 4 years, 9 months ago.

Viewing 14 posts - 1 through 14 (of 14 total)
  • Author
    Posts
  • #6669

    Jay Bozich
    Participant

    Constant static.

    I didn’t think it was happening on 91.1 but it turns out, 91.1 is broadcasting audio in mono, stereo pilot on.
    107.1 is more obvious cause it’s broadcasting in ((stereo))

    What’s happening?
    Where are we?
    What are these bugs?

    #6677

    Andy Brown
    Participant

    Your analysis is remiss. Since 107.1 is a translator that rebroadcasts the signal from 91.1 on Rocky Butte in a composite fashion (received signal is not demodulated and remodulated as L and R, it is simply stripped off of the 91.1 carrier and remodulated as a whole (see explanation below) onto the 107.1 carrier, it will carry the same stereo status. That is to say if, as you state, “91.1 is broadcasting audio in mono, stereo pilot on” then 107.1 would also be broadcasting in mono and the stereo pilot would be on. However you state that 107.1 is in stereo. The conditions as you present them are not possible from the broadcast end, they are indicative of your receiving location and equipment.

    KXRY has had issues in the past with obtaining a clean signal at the translator site at Stonehenge in Healey Heights and had solved that a few months ago by relocating the receiving antenna which is pointed at Rocky Butte. Perhaps those issues have returned, but in no way would the translator be able to create stereo if it is receiving a mono signal, as it is required to be fed “off air.”

    If you are listening at a distant location from 91.1, you may indeed be only able to pick up the mono part of the signal. Since the translator has better coverage, you may from your location, be able to pick up the stereo signal on 107.1 but the content may be in mono because it (the receiver in the translator) is having trouble receiving stereo. Remember, FM stereo and mono are both receivable when a station broadcasts in the stereo mode. This was devised to keep mono receivers compatible back when the service was incepted.

    My guess is you are too far from Rocky Butte to pick up the 7 watt signal in stereo and your receiver keeps itself in the mono mode. Usually the pilot (stereo) light will then go out, but many consumer receivers don’t always show that the receiver has gone to mono mode, showing only that the stereo pilot is still detectable even though the required L-R stereo sideband (FM stereo is actually broadcast in mono (L+R) and stereo difference (L-R) ) is not there in sufficient amount. The mono signal is the most robust as it is closest to the center of the channel. The pilot is second closest and the stereo difference part is the farthest from center, so it is the most easily damaged by propagation obstructions and unavoidable free space loss (attenuation due to distance from the antenna).

    At this moment I am too far from Rocky Butte to pick up the direct signal, and yes, the translator is noisier then normal. It definitely sounds like the translator is having issues again picking up a robust signal from Rocky Butte, so it is rebroadcasting a noisy signal on 107.1 even though the 107.1 signal strength shows up just fine.

    #6686

    Alfredo_T
    Participant

    I have noticed that on some days, the signal received by the Healy Heights translator is relatively noise-free but is noisy at other times. I’ve wondered whether weather conditions cause the received strength of the 91.1 MHz signal to fluctuate. Or, maybe the receive antenna has a loose connection. Or, maybe there are wires or other metallic objects near the receive antenna that form a diode-like contact when they get wet.

    I am pleasantly surprised that this translator setup works at all. The RF front end of the translator has to contend with extremely strong signals that are close-in in frequency (90.7 MHz and 92.3 MHz) plus 93.9 MHz, 95.5 MHz, 97.1 MHz, and 105.1 MHz. If that is not enough, there are also very strong signals on 93.1 MHz, 94.7 MHz, and 104.1 MHz. 90.7 has IBOC, so very sharp selectivity is required to reject that station’s digital sidebands, which are dangerously close to the desired 91.1 MHz signal. I doubt that any stock home hi-fi tuner could gracefully perform under these extreme conditions.

    #6710

    semoochie
    Participant

    105.1 is at Skyline. Did you mean 99.5?

    #6732

    Alfredo_T
    Participant

    I mistyped. The list I was working from is here:

    http://www.sbe124.org/Tours/Portland/Stonehenge/

    That is an RF madhouse!

    #6734

    Andy Brown
    Participant

    “RF madhouse”

    Which is one of the issues in trying to receive KXRY’s primary signal which is well below 60 dBu. Add to that the potential for less than 20 dB overhead above the multitude of nA+mB-oC combinations that could land on or near 91.1 MHz would literally take software to figure out. Although the signal from the main antenna on Stonehenge is shooting over the top, it’s downward lobes still do exist and can mix with other fundamentals and harmonics. Moving the translator east off the hill gives up westside coverage, moving it north along the ridge won’t solve the problem as the further away from Stonehenge you go to get out of the RF jungle, the closer to the Sylvan towers you get. Moving it south is just getting further from KXRY on Rocky Butte. They have to make it work where it is. This is a receiving antenna performance challenge. If what they bought off the shelf isn’t cutting it, get one custom wound.

    #6737

    jr_tech
    Participant

    Wouldn’t they be using a few traps to reduce the signals from the problem stations *before* they can get to the 91.1 receiver? Anybody know for sure what receiver they are using… perhaps just one built in to the transmitter, as in a Crown FM100R?

    #6759

    Jay Bozich
    Participant

    My listening device is car radios.
    One is a Ford 3 nights a week, the other is a Toyota 1 night a week.

    I drive around the entire city for hours on end.
    When I get into the sweet spot of reception for 91.1 I can then A/B the 2 stations.

    Both instances the pilot is on.

    91.1 distinctly sounds mono on the last time I did this, in the Toyota.

    The noise is louder on 107.1 because it seems to be in the L-R sideband, when I listened really carefully I could hear the noise on 91.1 but because it seemed to be in mono, the noise wasn’t as pronounced.
    Keep in mind I’m still driving around.
    Not stationary.

    #6760

    Andy Brown
    Participant

    Sounds like you have a receiver issue in the Toyota. Last I checked 91.1 inside their primary reception area, the signal sounded fine. I’ll check it again tomorrow when I’m out that way. As far as the noise on 107.1, that’s what the discussion above your recent post is addressing. Again, the translator is in Healey Heights and that is significantly outside the primary reception of the source on Rocky Butte, so it is subject to interference which diminishes the signal to noise ratio of the information being translated.

    #6762

    radiogeek
    Participant

    To feed K296FT directly from an internet feed would take a license change, right? Is there a category of license that would match the current location and power? In other words, what type of filing window would XRAY have to wait for to convert the service to what they need?

    #6763

    Andy Brown
    Participant

    Off air is the only way for this situation.

    If the translator was on Ch. 220 or below and if they (Common Frequency in Davis, CA.) owned it, they could use alternative delivery means. But it is not below 91.9 and they don’t own it.

    Non-fill-in noncommercial educational translators on Channels 221 through 300 are prohibited from any alternative methods of signal delivery, including programming feeds by satellite. See 47 CFR Section 74.1231(b).

    http://tinyurl.com/ltgq2ox

    #6775

    radiogeek
    Participant

    Right. I get that. The current rules and license don’t allow it.

    What I’m asking is … that frequency is clear for the location and power used without messing with any other license. So if it were possible to leave the actual equipment in place with 28W, what would that license (not the current translator license) be called? Does such a license type exist that could be used for non profit entities as primary service, and be feed other than over the air?

    #6781

    Andy Brown
    Participant

    ” that frequency is clear for the location and power used without messing with any other license. So if it were possible to leave the actual equipment in place with 28W, what would that license (not the current translator license) be called?”

    It only works as a Class D translator secondary service assignment. It does not qualify as a Class A primary service station for numerous reasons and an LPFM in its place would have to reduce power. There is no other “license” that “exists” that would work at that power, frequency, location and height above average terrain. Period.

    #6823

    Andy Brown
    Participant

    Today I rode along SE 82nd south from SE Woodstock to SE Johnson Creek Road and parked in the Fred Meyer parking lot at Johnson Creek Road. 91.1 comes in fine there, even though it is outside the 60 dBu contour. The signal was definitely in stereo. The pilot lamp indicator was steady and the material was in full stereo, which I checked on several songs by rotating the balance from left to right and noting the differences. The K296FT translator has good field strength (this is inside its 60 dBu contour) but clearly has a noisy signal being received from 91.1 Rocky Butte to try and relay.

    As I said earlier this issue is about marginal reception at the translator of the primary signal. The off the shelf antenna being used is doing as good as it can. As I discussed a year ago on this board, a custom antenna can be built tuned specifically and only to 91.1 with side rejection that might even be better then the one in use, or two off the shelf units can be stacked. As I also said a year ago, it’s just about how much money do you want to spend on the problem. If it was me, I wouldn’t have wasted a thousand bucks on a generic full band antenna, knowing what an RF nightmare and long distance to the primary signal the location has. I would have been on the horn to all the antenna makers getting bids on something a little more exotic, with maximum gain and rejection of everything but the primary frequency in the forward direction. But hey, that’s just me. I”m sure their engineering staff is doing the best they can with what they have to work with. It’s easy to armchair quarterback the problem, but as far is the first post in the thread is concerned, their is nothing wrong with the primary signal. Fix your car radio.

Viewing 14 posts - 1 through 14 (of 14 total)

You must be logged in to reply to this topic.