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Author Topic: RFI in pellet stove  (Read 12882 times)

Posts: 15

« on: January 21, 2013, 07:02:12 AM »

We have a small house, so I share my shack, of necessity, with the pellet stove that heats this place.  However, on certain frequencies (harmonics of 7) the RFI causes the fan to pulse and the machine to eventually shut down.  Not good on a day like today, when the temperature here in northern New York is not expected to top zero.  What can I do to eliminate this problem?  Would laying in a new circuit dedicated to the radio work, or is RFI entirely independent of that? 

I appreciate your time and consideration.

Posts: 14491

« Reply #1 on: January 21, 2013, 07:26:34 AM »

I expect that the stove has some electronics in it, perhaps to adjust the fan speed. Most likely radiation from your antenna is coupling into the power line feeding the fan circuit. Short of moving the antenna farther away, you will probably have to filter the power line near to the stove connection.

The first thing I'd do is to put a dummy load on the transmitter and run full power on one of the problem frequencies. If no RFI then it shows that radiation from the antenna, or the feed line, is the problem. You could also try reducing the power output to get an indication of how much margin you have (i.e. do you have to drop the power to 1/2, 1/4, etc).

What kind of antenna do you have? Things like off center fed dipoles and end fed half waves have a tendicy to bring common mode RF back down the outside of the coax into the shack (which is close to the stove I presume).


Bob  AA4PB
Garrisonville, VA

Posts: 15

« Reply #2 on: January 21, 2013, 07:50:00 AM »

Thanks for your reply.  Yes indeed, my antenna in use is an off-center 40m - 6m dipole, up about 18 feet, with the coax feed coming to within 8 feet of the stove.  I've tried reducing power, and there is indeed an attenuation of RFI with 25 watts, even more with 5. 

Posts: 2083

« Reply #3 on: January 21, 2013, 11:15:47 AM »

danger, warning, fattening, etc:  fooling with the stove cb can burn up your warranty.

having covered my tailbone... running all wires through the same clip-over ferrite can't hurt.  any sensor-type stuff should be fine if you wire a .001 to .01 ceramic capacitor across it for RF bypass.  put a ferrite snap-over on the AC line to the stove as close as you can get to the stove itself.

off-center dipole feed means there is reflected power on the coax jacket... there are snap-over ferrites for that, too, from places like RF Engineering and MFJ.

and make sure you have a common ground bus connected to all the chassis of your ham equipment; it's something that's been in the handbook since 1799.

Posts: 15

« Reply #4 on: January 21, 2013, 05:28:26 PM »

Hoo boy, is this site ever worth the price of a subscription!  Thanks for the help.  I've had my license for just over a year, and have spent most of my time trying to get my CW past 18 wpm rather than understanding the stuff I'm working with.  

How many ferrite cores should I use?    Sorry about the questions, but after all, I teach SECOND grade, not THIRD.   Tongue
« Last Edit: January 21, 2013, 05:39:01 PM by K2ADK » Logged

Posts: 115

« Reply #5 on: January 23, 2013, 01:30:13 PM »

Emmett,  The Pellet Stove's RF interception can be from one or a combination of causes.  It's likely to have an exhaust pipe that resembles a vertical antenna which may couple to the OCF antenna's coax, perhaps a balanced multi-band antenna like a G5RV may help in this case since it would have less RF radiation from its feedline.  Your OCF dipole will indeed have antenna current flowing on the outside of it coax feedline.   Do you have a method of removing those currents before entry into the 'shack'?   Start with a ground rod, and consider laying a 2-4 radials of 15-30 feet out on the yard (burial of these can wait till spring).  Tie the radials to the ground rod, tie the shield of your feedline to the ground rod.  This can help encourage the RF current not to follow the coax into the 'shack' area by taking a detour onto the ground system.
___That being said, antennas radiate, which means their fields can couple to other objects (you couldn't make a Yagi beam antenna if this weren't true).   So there is still a way to move electrons based on your antenna's radiated signal, the antenna can couple RF to the AC power lines in the house based on how close the antenna is to the wiring.  Ferrites on the AC power cord of the Pellet Stove may help reduce the RF current level flowing on the wiring of the Pellet Stove.  Even then, if the internal sensors and control computer are RF sensitive, the best option may be to try a different antenna placement further away from the house (higher would be great, but all of these changes don't always fit your lot, which makes Ham Radio a lot different than commercial broadcasting).  Best wishes for a simple solution.   73,  Tom Howey  WB1FPA

Posts: 15

« Reply #6 on: January 24, 2013, 04:35:31 PM »

I sincerely appreciate all responses.  All have been helpful.  Ferrite cores don't do the trick, so I'm not using the radio while the stove is on.  Looks like I'll be repositioning the antenna this Spring!



Posts: 3

« Reply #7 on: January 30, 2013, 07:03:23 AM »

Before you give up for the winter, try a dummy load and see if the problem still exists. That is, disconnect the antenna and connect the dummy load in its place. This is a key test. It will tell you whether the problem is due to the antenna/feedline or if the RFI is spreading some other way. If the problem exists when using a dummy load, then be certain you have all your gear bonded together (#12 wire is OK, but keep runs short) and connected to a "ground". Is the stove wired with a ground? 
The concept of "ground" becomes messy very quickly, but in this case the third pin of the power outlet is probably OK (assuming correct house wiring).
Every ham should have a proper dummy load. If you have not acquired one yet, that should be at the top of your list. They are not expensive, but they are a little difficult to neatly construct yourself if you run more than a few watts. (I still have my Heathkit Cantenna after 55+ years, with the original mineral oil in it. Still works OK.)

Bill - W2WO

Posts: 17476

« Reply #8 on: February 14, 2013, 02:12:04 PM »

Do you have a remote thermostat on the stove?  If so, the wire might be acting
as an antenna and picking up the signal, especially if it happens to be resonant
on 40m.  (Ran into that problem in the dorms at college - all the cheap stereo
systems seemed to come with 30' long speaker leads.  Garage door openers have
a similar issues with the remote switch lead.)

You can try filtering that wire using multiple turns though a ferrite core and/or
a bypass capacitor (perhaps 0.01uF) from each side to ground.

The dummy load test will help to determine whether the problem is due to
pickup of signal from the antenna and/or feedline (if so, it should go away)
or is coupled through the AC wiring.  Another test to try is to bring in a
battery to power the rig and see if the stove still acts up:  if it does, then
suspect it is picking up radiation from the antenna.  If not, then running an
extension cord from another AC circuit might make a difference.

How much power are you running?  Is it putting a stress on the AC circuit?
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