August 29, 2014 at 7:15 am #767Andy BrownParticipant
Normally referred to as 2A-B IMD.
This is the second most common form of third order intermodulation distortion.
http://www3.alcatel-lucent.com/bstj/vol32-1953/articles/bstj32-1-63.pdf (second page down)
Receiver intermodulation occurs as the results of two or more high-level off-channel signals overloading the receiver’s RF amplifier causing it to operate in it’s nonlinear region thus acting as a mixer. Older radios may not employ an RF amp and go straight into the first mixer.
It may be difficult to determine where intermodulation is occurring because the new frequencies being generated are precisely the same whether they are generated in the receiver front end, transmitter PA or some other non-linearity. Inserting a 6 db. attenuator in the receiver front-end will attenuate “transmitter” intermod by 6 db. “Receiver” intermod will be attenuated more rapidly because both signals A & B are simultaneously reduced by 6 db each.
Are the 103.7 and 102.3 transmitters close to each other? See:August 29, 2014 at 7:49 am #768jr_techParticipant
Both appear to be on the same tower, about 22 meters apart.August 29, 2014 at 7:57 am #769Randy_in_EugeneParticipant
Both are listed at the same coordinates on Blanton Heights in south Eugene. I am located just over 3 miles away, with small nearby hill to attenuate the signals a bit, but it’s still a great place for front-end overload.
However, the 103.7 (KNRQ) license to cover the move from Lebanon to Harrisburg was granted on 9-4-13, yet I have not noted this particular problem until now. My receivers are a Yamaha T-85 and a Sony XDR-F1HD, which have both served me fairly well in this hot RF environment. If it had just popped up on only one receiver I would first suspect that to be a possible culprit, but appearing on two receivers at the same time…I dunno.
Perhaps a little attenuation would do me good anyway.
I also have a Pioneer SX-850 and a Pioneer TX-980, which have always been totally hammered with overload at my location.August 29, 2014 at 11:56 pm #770
In a failed effort to bring in Portland and Seattle stations, I installed an expensive FM signal booster. The Fail part is KZEL and 1 or 2 other strong locals started popping up at other frequencies. Sony XDR-F1HD with directional antenna aimed north.August 30, 2014 at 6:06 am #771Randy_in_EugeneParticipant
I’ve never known a signal booster to work satisfactorily except in deep fringe to ALL received signals. Boosters built into tiny, undersized antennas are universally garbage.September 3, 2014 at 2:51 am #772
Cumulus Eugene doings… KZEL HD is on again. KUJZ was dead air at least part of Labor Day. And today KNRQ’s audio level is about half what it normally is. Very low.
Meanwhile, anyone notice that KRVM FM sounds like they’re using more aggressive (read: obnoxious) audio processing lately? More compressed, less dynamic range. Or am I imagining it? More aggressive Optimod settings? I could be wrong but everything suddenly sounds “dirtier” to me.September 3, 2014 at 8:17 pm #774the_radio_guyParticipant
KRVM-FM uses an Omnia.
The harmonic which is now very strong over 105.1, is illegal interference caused by an issue with 102.3 and 103.7. The engineer needs to work on this!September 3, 2014 at 8:31 pm #775Andy BrownParticipant
Finding where the spur is being generated is not an easy task, and may not be in the HPA’s of the A or B transmitters.
We had a spur once in Portland when 103.3 came on the air, caused by an A+B-C where none of the transmitters were co located, being 2 to 10 miles apart. (106.7 + 103.3 – 97.1 = 112.9) Modulation detected was 106.7’s but the mixing was taking place in the 97.1 HPA. 103.3 had to pay for a filter on 97.1. It took engineers from all three stations and some guys at PDX airport to pin it down.September 3, 2014 at 11:13 pm #776
103.7 KNRQ has been intermittently up and down numerous times today.
Edit: 105.1 is indeed a mixing 103.7 and 102.3September 3, 2014 at 11:45 pm #777jr_techParticipant
Do you hear the same mix products on 100.9 as well?September 3, 2014 at 11:51 pm #778
No, only getting 100.9 K265DF K-Love translator in EugeneSeptember 5, 2014 at 1:39 am #779
Turns out Cumulus *is* aware of the 105.1 issue. Dead passband filter on 103.7. New one coming.September 5, 2014 at 5:06 pm #780W7PATParticipant
840 KKNX was sure coming in strong in the Portland area last night. Normally we don’t hear much on 840, other than a mix of garbage.September 13, 2014 at 4:37 am #781
What happened to Justin Myers at KNRQ & KUJZ? Seems like he’s suddenly just gone. One of my favorite Eugene air personalities.
Edit, maybe moved to ESPN Seattle?September 16, 2014 at 3:15 pm #782
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