Local RFI (From me)

[W7SOE]

My HB rig is interfering with my neighbors baby monitor.  I may be interfering with others, I don't know.  He reported the interference (politely) after the first time I had it on the air, about 10 minutes.

I REALLY don't want to antagonize the neighbors.  I was operating well off the resonant frequency of the antenna, I imagine this would make it worse.

My question is this, would switching back to coax feedline help?

Thanks

Rich

[Steve - WB3HUZ]

I REALLY don't want to antagonize the neighbors.  I was operating well off the resonant frequency of the antenna, I imagine this would make it worse.

Probably not. The antenna is radiating. If you are using open-wire line, the system is at resonance or it wouldn't take power from your transmitter.

My question is this, would switching back to coax feedline help?

Once again, probably not. If your feedline is radiating, due to some unbalance, then coax may help.

[k4kyv]

Chances are, the baby monitor is a piece of crap that is picking up your signal because it won't tolerate an rf environment.

I would try to be polite and diplomatic with them, and try to help resolve the problem, but would not let some piece of Part 15 junk keep me off the air.

I have a wireless PLC (power line carrier) intercom that operates on about 250 kHz, to communicate between the house and shack, but my transmitter doesn't bother it.  I can sometimes faintly hear harmonics from the thing, but they have never been strong enough to cause me any trouble.

My motto regarding rfi has always been "co-operate but operate".

[Tom WA3KLR]

What frequency and mode is the baby monitor on?  The baby monitor is not supposed to be a ham receiver, but it is.

What frequency are you transmitting on?

The problem might not be your fault, might be the baby monitor, in which case no matter how clean your signal is, you will interfere unless you go QRP.

 

[ve6pg]

...likely just rf swamping the area....but...if you are 40 metres, simple math states  7Mhz X 7 = 49Mhz...that's where these things are, and are FM ..sk....

[W7SOE]

I was transmitting on 3870, the baby monitor is 900 MHz (ish?)

Rich

[KD6VXI]

I was transmitting on 3870, the baby monitor is 900 MHz (ish?)

Rich

2 ways to fix...  Mine, with the rx on batteries, is fine.  I plug in the AC wall wart, and I come through fine business.  Cure, filter the DC input.

Or, fire up a big amp.  Problem solved.


--Shane

[WA2TTP Steve]

Your AM signal may be getting into the baby monitor transmitter and modulating it. These things have  very high gain mic amps and are powered by a wall wart most of the time. Maybe wrapping the power lead thru a ferrite choke right up close to the baby monitor transmitter may keep the signal out of it. I would wrap as many turns as will fit on it.

I agree with Don that I wouldn't stay off the air due to a Part 15 device.

Steve
WA2TTP

[w5rkl]

Here's a link from the FCC's website that contains the
labeling requirements plus information about interference
issues with part 15 devices

http://www.fcc.gov/oet/info/rules/part15/part15-9-20-07.pdf

This is a common problem with quite a number of part 15 devices.
Most customers never read the label and most often they have
no idea what part 15 is and how it applies to interference issues
with their part 15 device. If the device has 2 parts, a master
and slave so to speak, the label is required to be printed on the
master station. The label states the device must accept
any interference, even interference that may cause undesirable
operation and the device must not cause any interference.

73's
Mike

[KF1Z]

I've never heard of a baby monitor being on 900mhz... (doesn't mean it isn't of course.)

Mine are on 49.870, and 49.820 mhz.  FM

We.ve tried several models .... all were crap....

If conditions are right, you can hear other people's kids whining from miles away.

The RX end of the monitor I use now is about 15 feet from the transmitter...

It sure does interfere!!  the monitor just gets a loud burst of static every time I key up...

Have toyed with the idea of hooking in a TX mute to the monitor, so I can still transmit while my kid is still taking a nap....
But that seems over the top!!


I'm not sure that there is anything you could do to eliminate interfering with it.....

As others have said.... it's actually the monitor's "fault"....
Telling the neighbors that may not end happily though.....

[Steve - WB3HUZ]

Baby monitors operate at 900 Mhz, 2.4 and 5.8 GHz these days.

[K3ZS]

My son had a 49 Mhz baby monitor and also some type of phone extension that ran through the power lines to connect his TIVO unit.   After moving to an area with a bunch of radio and TV towers nearby, both units are now just trash.

[KD6VXI]

I've never heard of a baby monitor being on 900mhz... (doesn't mean it isn't of course.)

I can't remember the brand of mine, but it is on 2.4 gig.  I had to move my wifi home network to the channel 1, and place this thing on the highest channel it had available (didn't say what they where, all in letters, instead of "numerical" notation.

Mine has vid and audio, IR night vision, etc.  Nice little unit, set me back about 45 dollars at geeks.com (shameless plug of my favorite version of overstock.com but geared towards geeks).  As I said, wrapping the wart with ferrite did the trick, or battery operation does, too.

--Shane
(edited to correct freq of 802.11)

[Steve - WB3HUZ]

If Wifi = 802.11 (which it should) then the frequency is 2.4 GHz.

[VE7 Kilohertz]

I had the same problem a few years back. The transmitted AM signal gets picked up by the walwart cord and then gets rectified inside the baby TX and sent out as FM to the RX. The other possibility is that the baby TX cct components are picking up directly and again, rectifying the signal and sending out to the RX.

I found that winding the walwart cord around a 1.5" torroid fixed the problem.

Today, still in the country but closer to my neighbours, I am getting into the cheap phones at 2 neighbours. Have wound ferrites and put in the Z100 filters but no joy.

Am now rereading the ARRL RFI books.

Good luck.

Cheers

Paul

[W7SOE]

I had the same problem a few years back. The transmitted AM signal gets picked up by the walwart cord and then gets rectified inside the baby TX and sent out as FM to the RX. The other possibility is that the baby TX cct components are picking up directly and again, rectifying the signal and sending out to the RX.

I found that winding the walwart cord around a 1.5" torroid fixed the problem.

Today, still in the country but closer to my neighbours, I am getting into the cheap phones at 2 neighbours. Have wound ferrites and put in the Z100 filters but no joy.

Am now rereading the ARRL RFI books.

Good luck.

Cheers

Paul

I will start with the toroid, fingers crossed.......

Rich

[KD6VXI]

If Wifi = 802.11 (which it should) then the frequency is 2.4 GHz.

It is 2.4 gig, but 802.11 also encompasses other frequencies, besides 2.4 gig.  I corrected my post once I read it (you know, we don't see our mistakes in the proofread window, only after they are published for the world to see lol), and of course, I saw yours while waiting for it to load


--Shane

[WA1GFZ]

download the link W2DU posted on baluns plenty of common mode filters

[KD6VXI]

I had the same problem a few years back. The transmitted AM signal gets picked up by the walwart cord and then gets rectified inside the baby TX and sent out as FM to the RX. The other possibility is that the baby TX cct components are picking up directly and again, rectifying the signal and sending out to the RX.

I found that winding the walwart cord around a 1.5" torroid fixed the problem.

Today, still in the country but closer to my neighbours, I am getting into the cheap phones at 2 neighbours. Have wound ferrites and put in the Z100 filters but no joy.

Am now rereading the ARRL RFI books.

Good luck.

Cheers

Paul

Paul,
Check the NID (network interface box outside the house).  Usually these have 2 or 4 wires going onto brass screws.  Electrolysis can cause rectification of the AM / SSB signal there.  No amount of filtering will do any good (except maybe a huge electrolytic) after the AC is rectified.

Easy way to check, try FM.  If you don't have problems on FM, more than likely, your envelope is being detected, rectified and bastardized into the telephones.

Also, if your neighbors are totally cooperative, have them unplug every phone in the house, plugging in one at a time while you are TXing.  This can show the culprit, too.  I had a neighbor in Texas that had a VCR that every time he would plug in the AC cord, I tore up nearly everything in his house.  Unplug that one VCR, and he had no problems.  This was with a 750 watt carrier.

Unfortunately, even offering to purchase him a new VCR wasn't enough.  Instead, all my help was greeted one day with a copy of part 93, part 95 and about 4 or 5 readings about RFI.  I have to hand it to the guy, at least he did his homework, but he was assinine about it, and insisted it was my fault.

I waited for the sold sign to go on his house, a year later, before I took my station down and moved.  Fire with fire?  You bet..  Mo Fire in da Wire.

--Shane

[Steve - WB3HUZ]

Yes, 5 GHz too (802.11a).

If Wifi = 802.11 (which it should) then the frequency is 2.4 GHz.

It is 2.4 gig, but 802.11 also encompasses other frequencies, besides 2.4 gig.  I corrected my post once I read it (you know, we don't see our mistakes in the proofread window, only after they are published for the world to see lol), and of course, I saw yours while waiting for it to load


--Shane

[flintstone mop]

YUP
Sounds familiar. We had the same "fundamental overload" with our 49mhz cordless phome until we switched to a microwave cordless phome.
That leaves you in a strange predictament. (And the problem cannot be fixed) I know there are notices all over, and even on the product that state it might receive interference from other devices, and that's life, BUT your neighbor knows it's you. If it were SSB he'd never figure it out.

Fred

[VE7 Kilohertz]

Shane thanks, I'll check out the box on the house...forgot about that one

Fred, monkey muffins, my neighbours ID'ed me in a second on SSB..said they couldn't tell what I was saying but recognised the tone of my voice.  Mmmm. Going to have to change short sizes.

Paul

[N3DRB The Derb]

The only solution is to buy them a new one.....one that has been de-RFI-ed by you. Baby monitors are cheap. Offer to get them a different new one, but that they must use the one you give them. WORK ON IT until you can operate with it right next to your transmitter while dropping atomic yaellos.  Mention NOTHING to them about the work you have done on it. NOTHING. EVER.  if they ask about anything, tell them you tested some new fixes for the problem in your transmitter.

These cases always wind up in court someday. By buying them a new monitor, you are cutting them off at the pass. A judge will look kindly upon your actions. You will have proven that you have cared 'for the children' and most of any case they have ( and dont kid yourself, they will do that unless it's fixed) will vanish.

[Jeff W9GY]

I'd do what I could to resolve the issue, but the baby monitor manufacturer owns this problem!

[N3DRB The Derb]

yeah, tell the doting parents that. The kid gloves will come off quick. After all , YOUR RADIO is threatening their sweet little angels safety!