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Author Topic: "Wandering" birdies - what causes them?  (Read 4714 times)
KI6JPE
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Posts: 2




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« on: June 25, 2011, 10:26:29 AM »

I live in an apartment - and I have a homebrewed bug-catcher style antenna out on my 2nd floor porch.

I can be listening to a strong signal on 80m, 40m or 20m and all is good, but then there will be what I can best describe as a wandering birdie - a bit of RFI that swings through the frequency I'm listening to, rising in pitch until it passes by.

Strange thing is, I took my rig off commercial power and went to the top of a nearby mountain (Mt. Diablo in northern CA) and all during my operating session I did not hear this at all.

My rig is a Kenwood TS870S, connected to an Astron SS-25M

I don't know if I'm getting junk here from the power lines, building power or what.  Any advice on what the cause might be and how I can filter it out?  I'm suspecting it's some issue with the power connection since it went away when connected direct to 12V batteries.

TNX & 73

Dave - KI6JPE
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W1AEX
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Posts: 69


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« Reply #1 on: June 25, 2011, 11:57:49 AM »

Hi Dave,

Unfortunately, the wandering birdies are prolifically generated by many consumer products found in most homes. Anything using switching wall supplies could be suspect: phone chargers, computer peripherals, portable DVD players, power tool chargers, and the list goes on-and-on. The noise may be directly radiated, or it may propagate along the AC wiring of a dwelling. High density population areas such as apartments and condominiums are often saturated with HF birdies and other aggravating noise. Using a separate receive antenna can sometimes offer some relief. Loops can often be positioned to null out some types of HF interference successfully. The rising level of man-made HF noise from dubiously designed appliances certainly increases the challenge, but then again, if it was easy, then anyone could do what we do!

73,

Rob W1AEX
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KI4AX
Member

Posts: 113




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« Reply #2 on: June 26, 2011, 06:06:53 AM »

Dave,
.
I have always pondered this question my self. I, personally, am not convinced that they are caused by house hold electronics. My reason for saying this is because I have been in the "radio" hobby for about 40 years now and can say that they have always been there (at least as far as my experience is concerned). Also, I notice that they only show up during periods of high propagation. If we are referencing the same noise I would think, that if it was coming from house hold electronics, that it would be present on the bands all the time but this does not seem to be the case. Like I said, I only hear them during periods when there is lots of propagation... and the more propagation the more often I hear them. Sometimes they sound like someone tuning up while changing frequency and zip by the frequency that you are on. Other times they seem to dance around on your frequency for a fraction of a second and then fly away. Strange indeed. One thing I notice that has disappeared from the frequencies are the chopping sound of what I believe was "over the horizon radar" used by the military back during the cold war.

I am very curious as to what you find out.

Dan KI4AX
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WB2WIK
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Posts: 20595




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« Reply #3 on: June 27, 2011, 03:48:19 PM »

I guess it could be spooks but usually it's man made household junk generating signals that aren't particularly stable.  The "stable" RFI I get that never changes frequency is all from crystal-controlled sources like oscillators in computers, modems and other things.  The "drifting" RFI is from non crystal-controlled sources like power supplies and a thousand other things.

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K2CMH
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Posts: 275




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« Reply #4 on: June 28, 2011, 11:03:14 AM »

I have an FT-950 with DMU-2000 RF bandscope.  I have 'seen' these birdies.  They will show up as a very strong spike at the left hand side of the screen (lower frequency) and start moving to the right.  The single strong spike moves left to right within a second or so.  It is not periodic and never 'stays put' on the display.  It does not appear at regular intervals.
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WB4BYQ
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Posts: 179




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« Reply #5 on: June 28, 2011, 02:07:30 PM »

I have seen these birdies as well.  they were not there until the cheap switching power supply showed up.  i have been involved in amateur radio for 41 years myself.  these birdies
come from cell phone chargers and cordless equipment chargers.  i have a car charger in my truck that will move up and down the band on 80/40.  i did hear the same noise in my neighborhood that i lived in for 30 years.  i could tell when the neighbors would charge their
phones.  the rfi is conducted into the house wiring, back to the drop from the pole and it will flow on the ground as well.  i have use a yeasu ft-897d with battery to trace the rfi from the meter base of the home to the pole.  the timewave anc-4 would help with the proper sense
ant, but it is a moving target.  within the last 4 months i have moved to the county part of the city, 5 miles north of the older qth on 5 acres with only 3 neighbors that are not close, and i cannot hear any rfi, not even from my own stuff.  i use the mfj power line filter on most the consumer electronics.

richard wb4byq
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VA2FSQ
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Posts: 511




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« Reply #6 on: August 14, 2011, 12:25:36 PM »

COuld be this:

http://en.wikipedia.org/wiki/Ionosonde
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VA2FSQ
W8JX
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Posts: 5771




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« Reply #7 on: August 15, 2011, 04:29:06 PM »


I agree and I would not rule out distant low frequency back scatter radar too used to defeat stealth.
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AA4PB
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Posts: 12836




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« Reply #8 on: August 16, 2011, 05:22:55 AM »

"I'm suspecting it's some issue with the power connection since it went away when connected direct to 12V batteries."

As I read your post, you made two changes at the same time. You went to battery operation AND you moved the station to a different location. You don't know if it is the power or the location that eliminated the RFI. Try running you station from battery power at the normal location. Try cutting off the main breaker to your house to see if the RFI is being generated from your own house. Then walk around with a portable receiver to see if you can pinpoint the location of the source of the signals.

Switching mode power supplies are notorious for generating RFI that moves in frequency, often as the load current changes. Small chargers, power cubes, or even your own power supply are all possibilities - especially if your antenna is located nearby.

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