| Author |
Message |
R TERRY
Rating: N/A
Votes: 0 (Vote!) | | Posted on Wednesday, May 04, 2005 - 10:33 pm: | |
Here's an easy one for all you electronics gurus: How do I stop the static interference on the TV when the 12-volt ceiling ventilation fans are running?
Thanks for your help.
R TERRY |
Chuck Newman (Chuck_newman)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Thursday, May 05, 2005 - 12:35 am: | |
Arching is produced within the motor, usually between brushes and rotating pole pieces. An arc or spark is a broad bandwidth radio frequency (RF) generator. It can enter any electronic device via the power conductors, AC or DC; but in the case of a television or radio, most of the impulse noise seen and/or heard on the reception device is due to the antenna receiving wide spectrum RF noise. The input electronics directly downstream of the antenna on most consumer radios and TV's do not have sharp response filters to eliminate most (not all) of the offending interference. This is due to costs of design, and the necessity of somewhat broadly tuned preamps being necessary for a broadcast type signal. Not necessairly so for other types of RF comm equipment. From here it goes into passband, filter Q, notch filters, bandpass filters, high/low pass filters, tuned response curves, etc.
Simply put, the cheaper the motor, generally the more RF noise it produces. In one motorhome I had a cheapo 6" blade bathroom fan and motor that put lots of sparkleys in the TV picture. This was broadband impulse noise generated by the motor.
In another motorhome with Fantastic Vent fans, I had no noise problem. Better quality motor.
This does not mean you need to run out and buy Fantastic (or similar) fans -- though they are great. Try a local electronics store or catalog to find another motor that will fit into your existing fan housing. You can lay a dozen of these small motors side-by-side and they look basically the same, but the quality of windings, brushes, bearings, and connectors vary greatly.
You can try some simple capacitive filters accross the fan leads, but this is usually ineffective due to most of the impulse RF radition being airborn.
Chuck Newman
Oroville, CA |
Chuck Newman (Chuck_newman)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Thursday, May 05, 2005 - 12:44 am: | |
Let me try the last sentence again. ... this is usually ineffective due to most of the impulse RF radiation (it's late) being airborn. And being of a wide bandwidth charastic, is usually not attenuated much by add on high pass / low pass antenna filters. These units are designed primarily for nearby RF emissions of properly operating (non-broadband) transmitters.
Chuck Newman
Oroville, CA |
Chuck Newman (Chuck_newman)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Thursday, May 05, 2005 - 12:46 am: | |
Sorry guys. I normally spell better. I'm packing it in tonight. |
Brian Brown (Fishbowlbrian)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Thursday, May 05, 2005 - 2:16 am: | |
Yur dooin fyne, Chuk!
*grin*
Kidding aside, thanks for the lesson. It's helpful to all.
BB |
DrDave
Rating: N/A
Votes: 0 (Vote!) | | Posted on Thursday, May 05, 2005 - 7:19 am: | |
All that info was fun.. But...
Go to Radio Shack and get some 10 to 20 microfarad electrolytic capacitors ( polarized type ) and place one across the motor leads on the each of the fan motors.
Plus + to + Plus ( be sure! ) and the Negative to ground (-)..
Caps should be rated at 35 volts d.c. or higher.
That should help solve the problem of noise.
Oh..Yeah this is called a filter by us electronerds... |
Gary Stadler (Boogiethecat)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Thursday, May 05, 2005 - 9:32 am: | |
...and because electrolytic capacitors usually have a higher inductance and esr, (electrogeekspeak) and don't do a very good job of filtering out all of the high frequency stuff, also put a .01 mfd ceramic disc capacitor across the leads of the fan motor. No polarity needed with these.
Put both caps as CLOSE to the motor as possible. Any wire between the cap and the motor acts as a noise transmitting antenna. So right on the motor would be best (some manufacturers even put them inside) |
DrDave
Rating: N/A
Votes: 0 (Vote!) | | Posted on Thursday, May 05, 2005 - 3:25 pm: | |
Yup, I forgot about the HF component, Glad you thought of it, That little .01 ceramic disc is important too.
My Brain hurtz..... |
R TERRY
Rating: N/A
Votes: 0 (Vote!) | | Posted on Thursday, May 05, 2005 - 4:25 pm: | |
Uh-huh, that's what I thought!
Translated into RV English, it means turn off the vent fans and turn on the roof A/C.
Right?
That's what I thought.
Really, now... thanks for your very insightful and educational help. Radio Shack, here I come. But first, let me turn on the A/C.
R TERRY |