KFXX

[W7PAT]

Sounds like KFXX is having some transmitter problems. For the past week or so the signal is barely above the noise level at night here in Aloha. Today driving, I tuned in and there was a bad squeal on the signal, much like KPAM used to get. I had to tune over to 99.5 HD-2 to listen.

[Alfredo_T]

At my location in Hillsboro, I am noting that the signal is weak. I was recently hearing a fair amount of interference from 1090. I do not hear the heterodyne, however.

[jr_tech]

How is it today? The signal strength that I am seeing is about 40 dB over s9 on my Icom, same as I “measured” about a year ago. Unfortunately, I did not log the nighttime signal strength at that time, but last night it was about 10 dB lower than I am seeing now. Last night, my wife did not hear a squeal, even using Sony 7056 headphones.

[Alfredo_T]

I wish that I had thought to compare the signal strength on 1080 to that on 910. I will try to remember to do that tonight.

[W7PAT]

The daytime signal is strong and no squeal today. Last night is was still weak.

[e_dawg]

I wonder if KFXX could raise their nighttime power to 20kw or add another tower to make 50kw at night, since their nighttime power is noisy around the metro area.

[Andy Brown]

No and no.

[W7PAT]

Driving around this afternoon, I discovered that the “squeal” is coming from something on the telephone poles. Driving up Allen Blvd it was pretty bad. Going into the neighborhoods where the lines are underground, the squeal went away.

[Andy Brown]

“Something on the telephone poles” are the power transmission lines. Notorious for screwing up directional antenna patterns by reradiating the RF. It also results in inter mod manifested as the “squeal” you heard.

http://www.arrl.org/power-line-noise

[Alfredo_T]

I have run into the RFI problems in the vicinity of Allen Blvd. They are pretty severe, but I have no way of discerning whether it is cable company or telephone company equipment that is to blame.

There is a stretch in downtown Beaverton, parallel to the train tracks, where the new street lights emit near 1000 kHz. This causes heterodynes of varying pitches when listening to KOMO.

I am building up a table of approximate relative signal strengths, both predicted (using the V-Soft Zip Signal page) and measured to be posted here later on. Zip Signal predicts that KFXX’s night signal will be 6dB lower than its day signal.

[Andy Brown]

“but I have no way of discerning whether it is cable company or telephone company equipment that is to blame.”

It’s a no brainer. The primary feed (top wire) has 12 kV (usually but can be upwards of 33 kV) of 60 Hz. The telephone “wires” are mostly fiber optics these days, but either as copper or fiber or coax, do not carry anything in terms of voltage or frequency that can induce noise in a car radio. If anything they (the telecom wires) carry the noise and hum into your connected service on the secondary wires (120 V). When mobile, the emf around the primary wires can pick up and carry information from the telecom wires to your car radio. However, without the primary wire field, that would not happen. The more poorly shielded the electronics at an intersection are, the more likely they will be ride the wave from the power primary transmission. That’s why the radio picks it up. Turn off the power on that top primary wire and all that noise would disappear. The local electronics don’t have any other way to carry through the air more than a few feet if that far.

[Alfredo_T]

From the sounds that I’m hearing here, I don’t think that the primary feed lines are playing a part. About 20 years ago, I lived in Alabama, where the summer humidity would cause discharge and the associated RFI problems. That type of RFI had a very different characteristic than what I hear today.

I mentioned cable TV because today’s bi-directional cable systems use many amplifiers, and something must be powering them.

I mentioned telecom because DSL, though on the way out, is still around. I also see canisters that I think are T-1 repeaters (though I could be wrong).

[Alfredo_T]

When I measured nighttime signal strengths yesterday, I noted that there was a fair amount of selective fading taking place on 1080. I could hear it in the audio, and I could observe the carrier level going up and down on the Rycom selective level meter.

Test setup: A home built outdoor amplified loop antenna was connected to a monitoring receiver and a Rycom selective level meter (to measure carrier level). The antenna was oriented east-west, and its preselector was tuned for maximum signal strength on the desired station. The antenna is not a calibrated instrument, so no guarantees are made about its gain flatness across frequency. My location was Hillsboro, about 1/2 mile south of the Tuality Hospital MAX station.

--Predicted Signal Strength
(relative to 1080 day signal)--
Freq.    Day    Night
910    -9.5dB  -3.8dB
970    +3.4dB  +2.8dB
1080      0dB  -6.0dB
[Prediction data taken from
V-Soft Zip Signal website.]

--Measured Signal Strength
(relative to 1080 day signal)--
Freq.    Day    Night
910    -3.9dB  +0.3dB
970   +11.2dB +11.6dB
1080      0dB  -9.9dB

Please take my measured data with a big grain of salt. [Note: edits were made to improve formatting of data table.]

[jr_tech]

Just a quick check 10 minutes ago, using the tiny meter on my Icom, I “measure” relative to daytime 1080:
910 -14dB
970 +3dB
A couple of nights ago, I “measured” nightime 1080 about 10dB below what I am seeing today.
I am using a 100 ft “longwire” stretched nw to sw, about a mile north of downtown Hillsboro.

[Alfredo_T]

I need to mention that my neighbors and I all have overhead power drops, and at least one of my neighbors has an overhead cable TV drop. This may be affecting my results.

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