am radio interference

[misteryabut]

I am having problems with radio reception in the 900s. Shutting off various house circuits, I am confident that it is the booster fan of the furnace. Since I prefer to be comfortable while listening to the radio, is there a way to eliminate the interference without freezing? This problem persists regardless of radio brand, circuit, orientation of the radio, or distance from the fan. Thanks

 

[KeepItSimpleStupid]

Now, that should be easy to confirm. Turn on and off the fan with the thermostat and see if the noise starts and goes away with the fan switch state change.

I had issues with the furnace interfering with X-10 power line signals. This https://www.discounthomeautomation....=1295--XPXPF&gclid=CKvlv-jXrrMCFQJx4AodT0UAyg did the trick for me mounted in the furnace.

Watch for 50/60 Hz power line issues when selecting a filter.

 

[dr pepper]

You can get noise filters designed for the mains, sort of a can shape device held on with a stud and spade connectors for in/out.
One of these might sort the problem out if the issue is noise on the mains wiring, that is rf from the motor using the wiring to radiate.
If the noise is comming directly from the motor then thats a little more tricky, if the motor is a universal, ie has brushes then there may be something up with it.

 

[KeepItSimpleStupid]

More modern furnaces use a three phase brushless motor even though the input in single phase and my stupid Carrier furnace had no RFI filter on the mains.

Older furnaces primarily used an induction motor.

"booster fans" are actually duct mounted fans that actually give the air a little more of a push.

There may be a terminology problem here. Blower - inside furnace. Booster fan - inside duct, usually further from the furnace.

 

[Bob Scott]

I have grounded radios with miraculous results in noise reduction in the AM band (and shortwave bands). If your radio does not have a 3 wire AC cord, get a length of wire and connect the battery - terminal to the ground connection of an AC outlet. You can use a grounded AC plug. Just connect the wire to the ground lug only.

 

[MikeMl]

#$%$$# switching power supplies. As a Ham radio operator, I hate the @#$$%$ things.

 

[Externet]

Adding compact fluorescent lamps and dimmers, even from a neighbor, for the same exact ham reason.

 

[misteryabut]

I am really thankful and impressed by everyone's generosity and quick response. Every response was helpful. I do have a booster fan in the duct work that is probably the problem. Although somewhat more cumbersome, my first attempt to solve the problem will be using Bob Scott's suggestion to ground the radio (cheaper). I have noticed that if I cover the front upper right corner of the plastic casing of the radio; the noise is vastly diminished.

Thanks again,

 

[audioguru]

Old fashioned AM radios were designed to pickup interference and produce awful sound.
Use an FM radio instead.

 

[Bob Scott]

#$%$$# switching power supplies. As a Ham radio operator, I hate the @#$$%$ things.

One of my shortwave recievers has a switching circuit for driving the white LED backlight for the LCD display. This circuit interferes with reception. Imagine! A radio that interfere's with itself!

Beware of this model. It is sold on Ebay as a Grundig or Eton brand model S350.

 

[JimB]

One of my shortwave recievers has a switching circuit for driving the white LED backlight for the LCD display. This circuit interferes with reception. Imagine! A radio that interfere's with itself!

It is hard to imagine what was going off in the head of the guy who designed that!
Can the backlight be switched off?
Maybe it was designed correctly with suitable filtering but when it went into production someone thought "we can save 10c per radio if we miss out the filter components".

JimB

On reflection, that radio was probably designed by none other that our very own AG.
After all, he did write:

Old fashioned AM radios were designed to pickup interference and produce awful sound.

 

[audioguru]

On reflection, that radio was probably designed by none other that our very own AG.

My first job was repairing car radios on the Philips production line (the first car radio that used a cassette tape deck) then I was quickly promoted into the engineering department where I designed (copied from the datasheet) and layed out a pcb for an FM stereo decoder.

On another thread a guy is learning about superheterodyne so he is making an AM radio. He wants it to sound good so he wants a wideband IF strip.
I looked for the pre-emphasis curve used by many AM radio stations (+10dB at 9kHz) and found a review of a new Sony AM-FM receiver. It has much better FM spec's than any other receiver but its AM spec's (and sound) are garbage.

 

[JimB]

I looked for the pre-emphasis curve used by many AM radio stations (+10dB at 9kHz)

That sounds not quite right.
The channel spacing of AM long wave and medium wave transmitters is 9kHz (at least in Europe), so having audio components above 4.5kHz is not a good idea unless you want to splatter all over the station on the adjacent channel.

Hey! we all know your feelings about the audio quality of AM (and SSB ) but for those of us who cannot hear much above 5kHz anyway, the discussion is a bit academic.

JimB

Apologies to the OP, we seem to have a bit of thread drift going on here.

 

[audioguru]

That sounds not quite right.
The channel spacing of AM long wave and medium wave transmitters is 9kHz (at least in Europe), so having audio components above 4.5kHz is not a good idea unless you want to splatter all over the station on the adjacent channel.

High audio frequencies do not occur at full blast. They are at a fairly low level. Pre-emphasis makes up for some of the high audio frequency loss of narrow band radios.
The compressor/limiter in the transmitter and the planning of distanced adjacent stations eliminate splatter.

....for those of us who cannot hear much above 5kHz anyway, the discussion is a bit academic.

Most of us who did not play with guns and who did not play much acid rock can still hear to 15kHz or 20kHz. I pity deaf people where everything sounds like an AM radio.

Here is the Canadian government standard for AM radio stations. It is the same for the USA.

 

[JimB]

Most of us who did not play with guns and who did not play much acid rock can still hear to 15kHz or 20kHz.

No guns, no rock concerts, just age.

JimB

 

[audioguru]

I am 67 and can still hear high audio frequencies VERY well. Therefore I still enjoy listening to live and hifi music.
With the new synthetic lenses in my eyes (cataracts surgery) I can see VERY well.
With the new stents in my heart arteries (angioplasty surgery) my heart beats VERY well like a young man.

 

[Bob Scott]

Here is the Canadian government standard for AM radio stations. It is the same for the USA.

Thanks audioguru. This is the first time that I've heard that AM audio uses 75 uS preemphasis, just like FM radio and the old NTSC analog TV sound. Wow. I would have thought that it would have been mentioned in at least one electronics magazine in the last 50 years. But there it is in black and white.......and blue and red.

Glad to hear that you eyes and ears and heart are in good shape. How about teeth?