Ok whats up with 107.7-107.9? WiFi interference? Dying power transformers?

I have had this problem off and on (and noticed it with others) for
about two years now. It appears that everytime I get near a strong
wireless signal there is this loud buzzing noise on the high FM radio
frequencies. At first I thought it was power line interference but
then I've noticed it in places where the power was entirely
underground. Although I suppose RF *could* be emitted and strong
enough to go through concrete and disrupt radio signal.

I have heard from a lineman that when power transformers go they start
emitting RF at different frequencies. I am not completely ruling out
power interference...

I don't know much about harmonic frequencies but I seem to recall from
school something about harmonic distortion. Something to the effect
of if 2.4ghz is divisible down to 107.7-9 that there could be
interference. Although I won't stake anything on this theory.


Any 2c on this one?

Thanks

"foo" <(E-Mail Removed)> hath wroth:

>I have had this problem off and on (and noticed it with others) for
>about two years now. It appears that everytime I get near a strong
>wireless signal there is this loud buzzing noise on the high FM radio
>frequencies.

One possibility of what you're hearing are the harmonics of the clock
oscillator that runs the access point, or the clock oscillators that
run the computah to which the wireless device is connected. You'll
have similar interference, although at different frequencies, with a
fax machine, digital clock, calculator, or any device that has a clock
oscillator.

Another possibility is entry directly into the audio circuitry. You
noted that it's from 107.7 to 107.9MHz, so this is probably NOT what
you're hearing, but does happen (to my cheapo hi-fi). The audio
amplifiers have very little RF bypassing and will respond to almost
any nearby RF signal. The SSID broadcast interval of the typical
802.11b/g access point is 10 times per second. I can hear that on my
cheapo hi-fi as a raspy buzz. Moving the access point away solved
that problem.

If you change the DTIM interval (or data beacon rate) on your access
point and the rate of the loud buzz changes, then you're picking up
the 2.4Ghz RF directly, or possibly one of the clock frequencies used
to generate the 2.4GHz, and not the clock oscillator as I previously
guessed. Note that todays 2.4GHz chipsets are all digital (no mixers
or local oscillators) which offer plenty of clock signals to radiate.

Wanna disclose what make and model of hardware is causing the problem
or is it every wireless device that you bring your radio near?

The RF that the lineman was referring to are harmonics of 60Hz. What
happens is that the AC power line waveform is normally fairly low
distortion and shows few harmonics. When the transformer core
saturates or a turn shorts, the waveform becomes distorted and starts
to show harmonics, which can easily extend into the RF region. Mostly,
you'll hear it on AM broacast band (1MHz) frequencies. However, I
don't think these will extend into the FM broacast band.

--
Jeff Liebermann (E-Mail Removed)
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558

On 8 Jan 2006, in the Usenet newsgroup alt.internet.wireless, in article
<(E-Mail Removed). com>, foo wrote:

>I have heard from a lineman that when power transformers go they start
>emitting RF at different frequencies. I am not completely ruling out
>power interference...

Normally, that's the result of arcing - sparks if you wish. This is
the mechanism originally used to generate RF in the early part of
the _last_ century (think the transmitter on the RMS Titanic). The
interference is usually much more noticeable at low (AM broadcast)
frequencies than VHF or above, Also the design of FM receivers is such
that the effect of impulse or amplitude modulated RF is minimized.

>Something to the effect of if 2.4ghz is divisible down to 107.7-9 that
>there could be interference.

Normally, it's the other way around - the desired stuff is generated at
lower frequencies, and multiplied up to the working frequency. Here,
2450/108.8 is about 22.7:1 which isn't a logical number. 20 (4 x 5)
or 24 ( 2 x 3 x 2 x 2) are more common multiples.

Old guy

I think my local CATV system uses a signal on the cable at 107.9 to
check for leaks in the cable system.

I know that the local techs tell me that they can hear a leak by
driving around with their truck FM radio tuned to 107.9 and listen for
noise,

Just a thought,,


Bob Smith
Robert Smith Consutling
NA6T - ARRL Life Member


On 8 Jan 2006 08:07:44 -0800, "foo" <(E-Mail Removed)> wrote:

>I have had this problem off and on (and noticed it with others) for
>about two years now. It appears that everytime I get near a strong
>wireless signal there is this loud buzzing noise on the high FM radio
>frequencies. At first I thought it was power line interference but
>then I've noticed it in places where the power was entirely
>underground. Although I suppose RF *could* be emitted and strong
>enough to go through concrete and disrupt radio signal.
>
>I have heard from a lineman that when power transformers go they start
>emitting RF at different frequencies. I am not completely ruling out
>power interference...
>
>I don't know much about harmonic frequencies but I seem to recall from
>school something about harmonic distortion. Something to the effect
>of if 2.4ghz is divisible down to 107.7-9 that there could be
>interference. Although I won't stake anything on this theory.
>
>
>Any 2c on this one?
>
>Thanks

Wow great info thanks!

I haven't been able to figure out which access points do this but I
know that a cheapo linksys firewall/wifi b/g unit has done this.

Bob Smith <(E-Mail Removed)> hath wroth:

>I think my local CATV system uses a signal on the cable at 107.9 to
>check for leaks in the cable system.
>
>I know that the local techs tell me that they can hear a leak by
>driving around with their truck FM radio tuned to 107.9 and listen for
>noise,
>
>Just a thought,,

It's 107.75 which is the audio carrier for CATV channel 97:
http://www.qsl.net/atn/library/Broadcast_freqs.htm
However, most AM/FM car radios will only tune to 0.2Mhz channel
spacing and cannot tune exactly to this frequency. 107.7 is usually
close enough.

Most CATV leakage testers work in the aircraft bands.
http://www.fcc.gov/mb/engineering/611.html
There is no standard test frequency as current models offer a wide
range of frequencies:
http://www.comsonics.com/pro_sentinel.html


--
Jeff Liebermann (E-Mail Removed)
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558