[RFI] Re: Radio Frequency Interference (RFI) Digest V4 #56
scameron
scameron <scameron@austin.rr.com>
Thu, 28 Jun 2001 10:13:34 -0500
The only thing that has worked for me on our and a neighbor's touch lamps is a 120
micorhenry RF choke in series with a 1.8k ohm resistor at the circuit board end of the
sense lead.
March 1988 QST Technical Correspondence page 42 had a nice article on this. 3 lamps were
discussed. the cures:
1. A 4.7 millihenry, 100 milliamp RF choke in series with a 1.8k resistor. (this one
worked for me)
2. Same as #1 plus 7 turns of the power cord on a 2.5 inch Amidon FT-240-43 toroid.
Raising the resistor value above 1.8k to the highest value possible while still allowing
touch operation will provides the highest attenuation.
3. A 9.4 millihenry RF Choke in series with a 3.3kohm resistor plus a Radio Shack power
line filter.
January 1986 QST had another article, saying a 100 microhenry RF choke in series with a
1.8kohm resistor worked.
Skip W5GAI
"Experiment trumps theory." -- Dave Leeson W6NL
------------
"Radio Frequency Interference (RFI) Digest" wrote:
> Radio Frequency Interference (RFI) Digest Tuesday, June 26 2001 Volume 04 : Number 056
>
> In this issue:
>
> [RFI] Touch Light Update #3
> RE: [RFI] Touch Light Update #3
> RE: [RFI] Touch Light Update #3
> RE: [RFI] Touch Light Update #3
> RE: [RFI] Touch Light Update #3
> RE: [RFI] Touch Light Update #3
> [RFI] Coffee Pot RFI!
> Re: [RFI] Coffee Pot RFI!
> Re: [RFI] Coffee Pot RFI!
> Re: [RFI] Coffee Pot RFI!
> [RFI] Touch Light Update #3
>
> See the end of the digest for information about rfi-digest
>
> ----------------------------------------------------------------------
>
> Date: Tue, 26 Jun 2001 07:31:18 -0500
> From: Jon Ogden <jon.ogden@cain-forlaw.com>
> Subject: [RFI] Touch Light Update #3
>
> Hi all,
>
> Yet again another update to my under cabinet touch lighting situation.
>
> To refresh your memory, on 20m I am having problems with my RF turning the
> lights on and stepping them through their various dimmer stages.
>
> The lighting system consists of a dimmer unit which contains the sensing
> circuitry and a switching power supply unit which takes the AC voltage
> output of the dimmer unit and steps it down to 12 V DC or less.
>
> Here is where I am now. I have successfully eliminated the interference on
> all amateur bands from my lighting system when it is uninstalled. This
> solution consisted of wrapping the cord going to the AC mains around a large
> Amidon torroid (I forget the material number - but it's correct for HF) and
> wrapping the cord going between the dimmer unit and the power supply unit
> the same way. I've tested on all bands but 160M and I have no interference
> to the light.
>
> I did not need any bypass caps or anything like I thought I might.
>
> The current unit I have been messing with gets mounted above a fan hood.
> The hood is basically a big stainless steel box (simplest way to describe
> it). The lighting circuitry is mounted above it. The sensing line is then
> attached to the metal hood. This way whenever the hood is touched, the
> lighting system is activated. With the sensing line attached to the hood, I
> get my 20m interference problem again. The hood is acting like a big
> antenna. The hood is not grounded but isolated from DC ground since
> grounding the hood when then ground the sense line and the switching would
> not work.
>
> I've tried adding a .01 uF cap (and other values too) from the sensing lead
> to ground. So far no matter what value I have tried, adding the cap ends up
> loading the oscillator in the dimmer unit to the point that it is no longer
> sensitive to touch. I've also tried winding the sensing line around a
> torroid. If I get too many wraps, I again destroy the sensitivity of the
> sensing line and it no longer does it's job. And anyhow, it still doesn't
> stop my RF problem. I've tried resistors in series with the sensing line to
> the hood. Above a few 100 Ohms and I lose my sensitivity just like with the
> torroid.
>
> So far, I have found no good way to RF bypass the sensing line. What I want
> to do is basically shunt all HF energy to ground on that line, but I can't
> load down the line otherwise the sensing circuitry won't help.
>
> Does this make sense and does anyone have any ideas?
>
> Thanks es 73,
>
> Jon
> NA9D
>
> ------------------------------
>
> Date: Tue, 26 Jun 2001 10:01:27 -0500
> From: "EDWARDS, EDDIE J" <eedwards@oppd.com>
> Subject: RE: [RFI] Touch Light Update #3
>
> > -----Original Message-----
> > From: Jon Ogden
> > Here is where I am now. I have successfully eliminated the interference
> > on
> > all amateur bands from my lighting system when it is uninstalled.
> >
> > The current unit I have been messing with gets mounted above a fan hood.
> > The hood is basically a big stainless steel box (simplest way to describe
> > it). The lighting circuitry is mounted above it. The sensing line is
> > then
> > attached to the metal hood. This way whenever the hood is touched, the
> > lighting system is activated. With the sensing line attached to the hood,
> > I
> > get my 20m interference problem again. The hood is acting like a big
> > antenna. The hood is not grounded but isolated from DC ground since
> > grounding the hood when then ground the sense line and the switching would
> > not work.
> >
> > I've tried adding a .01 uF cap (and other values too) from the sensing
> > lead
> > to ground. So far no matter what value I have tried, adding the cap ends
> > up
> > loading the oscillator in the dimmer unit to the point that it is no
> > longer
> > sensitive to touch. I've also tried winding the sensing line around a
> > torroid. If I get too many wraps, I again destroy the sensitivity of the
> > sensing line and it no longer does it's job. And anyhow, it still doesn't
> > stop my RF problem. I've tried resistors in series with the sensing line
> > to
> > the hood. Above a few 100 Ohms and I lose my sensitivity just like with
> > the
> > torroid.
> >
> Have you tried a "micro" Henry choke on the sense line? Something
> from 1-10 micro Henries is what is recommended. I don't think the resistor
> is really needed since this is a very low current application (high current
> would be bad for the human contact!). This is a very small inductance
> (don't use the Radio Shack 100milliH choke!) and should not be much
> reactance to the free running oscillator's sense line.
>
> Assuming the oscillator is around 170 Khz like most touch lamps (see
> if you can find out), that would be only 11 ohms inductive reactance (for 10
> microH) while providing 880 ohms at 14 Mhz; a factor of 80. Don't use 10
> milliH since the inductive reactance to the sensing circuit at 170Khz would
> be almost 11Kohm and probably would shut it down. If 10 microH is too much
> try 1 microH. That'd be only 1.1 ohms at 170Khz (assuming that is the
> oscillator's freq!?). It may take experimenting with several values to get
> it close. Also mount the inductor as close as possible to the circuit.
>
> > So far, I have found no good way to RF bypass the sensing line. What I
> > want
> > to do is basically shunt all HF energy to ground on that line, but I can't
> > load down the line otherwise the sensing circuitry won't help.
> >
> Perhaps you could use a capacitor to pass the 14Mhz on the hood to
> ground while, at the right value could look like a higher reactance to the
> sensing line's capacitance. Cap of 0.01 microF would give 1.1 ohms at 14
> Mhz & 93 ohms at 170Khz. So connect the cap to the hood somewhere or at a
> couple of places, then gorund the other end of the cap(s).
>
> The problem is that the sensing line is operating on a
> "Change-of-Capacitance" to change the operating state. The 14Mhz bypass to
> ground might desense the "sensing line" enough to kill it. I think that's
> what you've found already. So we're back to getting the RF choke right.
> This all depends alot on the free running oscillator's operating frequency.
> Is it spec'ed anywhere?
>
> 73,
> de ed -K0iL
>
> ------------------------------
>
> Date: Tue, 26 Jun 2001 10:23:11 -0500
> From: Jon Ogden <jon.ogden@cain-forlaw.com>
> Subject: RE: [RFI] Touch Light Update #3
>
> > Have you tried a "micro" Henry choke on the sense line?
> > Something
> > from 1-10 micro Henries is what is recommended. I don't
> > think the resistor
> > is really needed since this is a very low current application
> > (high current
> > would be bad for the human contact!).
>
> No I have not. I had assumed that the sense line wrapped around the torroid
> would end up looking similar to using a choke in series in the line.
> Perhaps I am mistaken. Ten turns of the wire around an FT-50B-77 (half inch
> torroid using the 77 material) didn't do much to solve the problem. Maybe
> it's not the same as a choke actually in series with the line.
>
> >> So far, I have found no good way to RF bypass the sensing
> >>line. What I want to do is basically shunt all HF energy to ground on
> that
> >>line, but I can't load down the line otherwise the sensing circuitry won't
> help.
> >
> > Perhaps you could use a capacitor to pass the 14Mhz on
> > the hood to
> > ground while, at the right value could look like a higher
> > reactance to the
> > sensing line's capacitance. Cap of 0.01 microF would give
> > 1.1 ohms at 14
> > Mhz & 93 ohms at 170Khz. So connect the cap to the hood
> > somewhere or at a
> > couple of places, then gorund the other end of the cap(s).
>
> Tried that. The .01 uF cap prevents things from working correctly. That's
> 93 Ohms at 170 KHz and I think that it pulls the circuit to ground too much.
> I think a much, much smaller cap will need to be used.
> >
> > The problem is that the sensing line is operating on a
> > "Change-of-Capacitance" to change the operating state. The
> > 14Mhz bypass to
> > ground might desense the "sensing line" enough to kill it. I
> > think that's
> > what you've found already. So we're back to getting the RF
> > choke right.
> > This all depends alot on the free running oscillator's
> > operating frequency.
> > Is it spec'ed anywhere?
>
> Exactly. No, I don't have a spec on the oscillator frequency. I think I
> will finally puy my O-scope to a useful purpose and try to measure it. Then
> I can try to make some useful sense out of things.
>
> UGH! There has got to be a solution though. So close!
>
> 73,
>
> Jon
> NA9D
>
> ------------------------------
>
> Date: Tue, 26 Jun 2001 11:17:34 -0500
> From: "EDWARDS, EDDIE J" <eedwards@oppd.com>
> Subject: RE: [RFI] Touch Light Update #3
>
> > -----Original Message-----
> > From: Jon Ogden
> > > Have you tried a "micro" Henry choke on the sense line?
> > No I have not. I had assumed that the sense line wrapped around the
> > torroid
> > would end up looking similar to using a choke in series in the line.
> > Perhaps I am mistaken. Ten turns of the wire around an FT-50B-77 (half
> > inch
> > torroid using the 77 material) didn't do much to solve the problem. Maybe
> > it's not the same as a choke actually in series with the line.
> >
> I'm not sure how to calculate the inductance of the FT-50B-77.
> Anyone know if it's the same as the FB-(77)-1024 listed in the ARRL RFI
> book? And if so, what are the "A-sub-L v Mix No." values listed in table
> 2.2? Seems to indicate nanoHenries. So then FB-77-1024 is 5600 nanoH or
> 5.6 microH? For how many turns? One? So many questions! If it is one
> then would've been 10 times 5.6 for 56 milliH. That might be too much
> inductance and reactance for the sensing line. But this is all a complete
> guess without the answers to my questions.
>
> An actual inductance value for the FT-50B-77 would be helpful to
> know for sure.
>
> 73,
> de ed -K0iL
>
> ------------------------------
>
> Date: Tue, 26 Jun 2001 11:35:34 -0500
> From: Jon Ogden <jon.ogden@cain-forlaw.com>
> Subject: RE: [RFI] Touch Light Update #3
>
> According to the Amidon literature I have in front of me, the FT-50B-77 has
> a value of 2160 mH per 1000 turns. So that would mean that 10 turns is
> 21.60 mH. So that's way to big. However, it still didn't stop the 20M RF
> from messing with things.
>
> You'd think it would since it's a rather large impedance at 14 MHz, but it
> didn't.
>
> 73,
>
> Jon
> NA9D
>
> - -------------------------------------
> Jon Ogden
> Sales Engineer
> Cain-Forlaw Company
> 847-202-9898 (Voice)
> 847-202-9896 (Fax)
> jon.ogden@cain-forlaw.com
>
> > -----Original Message-----
> > From: EDWARDS, EDDIE J [mailto:eedwards@oppd.com]
> > Sent: Tuesday, June 26, 2001 11:18 AM
> > To: 'Jon Ogden'; 'RFI'
> > Subject: RE: [RFI] Touch Light Update #3
> >
> >
> > > -----Original Message-----
> > > From: Jon Ogden
> > > > Have you tried a "micro" Henry choke on the sense line?
> > > No I have not. I had assumed that the sense line wrapped around the
> > > torroid
> > > would end up looking similar to using a choke in series in the line.
> > > Perhaps I am mistaken. Ten turns of the wire around an
> > FT-50B-77 (half
> > > inch
> > > torroid using the 77 material) didn't do much to solve the
> > problem. Maybe
> > > it's not the same as a choke actually in series with the line.
> > >
> > I'm not sure how to calculate the inductance of the FT-50B-77.
> > Anyone know if it's the same as the FB-(77)-1024 listed in
> > the ARRL RFI
> > book? And if so, what are the "A-sub-L v Mix No." values
> > listed in table
> > 2.2? Seems to indicate nanoHenries. So then FB-77-1024 is
> > 5600 nanoH or
> > 5.6 microH? For how many turns? One? So many questions!
> > If it is one
> > then would've been 10 times 5.6 for 56 milliH. That might be too much
> > inductance and reactance for the sensing line. But this is
> > all a complete
> > guess without the answers to my questions.
> >
> > An actual inductance value for the FT-50B-77 would be helpful to
> > know for sure.
> >
> > 73,
> > de ed -K0iL
> >
>
> ------------------------------
>
> Date: Tue, 26 Jun 2001 12:06:31 -0500
> From: Jon Ogden <jon.ogden@cain-forlaw.com>
> Subject: RE: [RFI] Touch Light Update #3
>
> I made a mistake here. The inductance is proportional to the square of the
> turns.
>
> Amidon uses the following formula:
>
> Turns = 1000 * Sqrt(desired L (mH)/Al)
>
> Where Al = the inductance value at 1000 turns specified by Amidon
>
> So in my case I have 10 turns. Al = 2160
>
> So the correct amount of inductance is .216 mH or 216 uH.
>
> 73,
>
> Jon
> NA9D
> - -------------------------------------
> Jon Ogden
> Sales Engineer
> Cain-Forlaw Company
> 847-202-9898 (Voice)
> 847-202-9896 (Fax)
> jon.ogden@cain-forlaw.com
>
> > -----Original Message-----
> > From: Jon Ogden [mailto:jon.ogden@cain-forlaw.com]
> > Sent: Tuesday, June 26, 2001 11:36 AM
> > To: 'EDWARDS, EDDIE J'; Jon Ogden; 'RFI'
> > Subject: RE: [RFI] Touch Light Update #3
> >
> >
> >
> > According to the Amidon literature I have in front of me, the
> > FT-50B-77 has
> > a value of 2160 mH per 1000 turns. So that would mean that
> > 10 turns is
> > 21.60 mH. So that's way to big. However, it still didn't
> > stop the 20M RF
> > from messing with things.
> >
> > You'd think it would since it's a rather large impedance at
> > 14 MHz, but it
> > didn't.
> >
> > 73,
> >
> > Jon
> > NA9D
> >
> > -------------------------------------
> > Jon Ogden
> > Sales Engineer
> > Cain-Forlaw Company
> > 847-202-9898 (Voice)
> > 847-202-9896 (Fax)
> > jon.ogden@cain-forlaw.com
> >
> > > -----Original Message-----
> > > From: EDWARDS, EDDIE J [mailto:eedwards@oppd.com]
> > > Sent: Tuesday, June 26, 2001 11:18 AM
> > > To: 'Jon Ogden'; 'RFI'
> > > Subject: RE: [RFI] Touch Light Update #3
> > >
> > >
> > > > -----Original Message-----
> > > > From: Jon Ogden
> > > > > Have you tried a "micro" Henry choke on the sense line?
> > > > No I have not. I had assumed that the sense line wrapped
> > around the
> > > > torroid
> > > > would end up looking similar to using a choke in series
> > in the line.
> > > > Perhaps I am mistaken. Ten turns of the wire around an
> > > FT-50B-77 (half
> > > > inch
> > > > torroid using the 77 material) didn't do much to solve the
> > > problem. Maybe
> > > > it's not the same as a choke actually in series with the line.
> > > >
> > > I'm not sure how to calculate the inductance of the FT-50B-77.
> > > Anyone know if it's the same as the FB-(77)-1024 listed in
> > > the ARRL RFI
> > > book? And if so, what are the "A-sub-L v Mix No." values
> > > listed in table
> > > 2.2? Seems to indicate nanoHenries. So then FB-77-1024 is
> > > 5600 nanoH or
> > > 5.6 microH? For how many turns? One? So many questions!
> > > If it is one
> > > then would've been 10 times 5.6 for 56 milliH. That might
> > be too much
> > > inductance and reactance for the sensing line. But this is
> > > all a complete
> > > guess without the answers to my questions.
> > >
> > > An actual inductance value for the FT-50B-77 would be helpful to
> > > know for sure.
> > >
> > > 73,
> > > de ed -K0iL
> > >
> >
> > --
> > FAQ on WWW: http://www.contesting.com/FAQ/rfi
> > Submissions: rfi@contesting.com
> > Administrative requests: rfi-REQUEST@contesting.com
> > Questions: owner-rfi@contesting.com
> >
>
> ------------------------------
>
> Date: Tue, 26 Jun 2001 18:23:27 -0700
> From: "Mike Lazaroff K3AIR" <k3air@arrl.net>
> Subject: [RFI] Coffee Pot RFI!
>
> Here's a great (and true!) story about our FD operation this year:
>
> When operating 80m phone, all of a sudden we were overwhelmed with 40 db
> over 9 buzzing QRM up and down the band. The noise was barely audible on
> 40m, and not at all on the other bands. It just appeared suddenly, so we
> figured somebody turned on something that didn't like 80m. We checked our
> power supplies, laptops, etc., figuring it had to be one of them. Nope.
>
> After checking all around the campsite, we discovered that when the coffee
> pot in the "dining area" was turned on, the RFI appeared. When it was off,
> the RFI was gone.
>
> We survived just fine without (hot) coffee.
>
> Anyone else ever experience this???
>
> 73 and hope everyone enjoyed Field Day,
> Mike K3AIR
>
> ------------------------------
>
> Date: Tue, 26 Jun 2001 20:10:03 -0400
> From: "K4LDR" <k4ldr@hitter.net>
> Subject: Re: [RFI] Coffee Pot RFI!
>
> Ahoy there Mike:
>
> That is really gud RFI experience and info to know and maintain in our
> mental file. What
> brand/model coffee pot was that? If u tell us, that wud be a great service
> to readers and it may well save some teeth gnashing at a future
> time.
>
> 73, Pete K4LDR Citrus County, FL
>
> ------------------------------
>
> Date: Tue, 26 Jun 2001 20:32:54 EDT
> From: W2YR@aol.com
> Subject: Re: [RFI] Coffee Pot RFI!
>
> - --part1_69.174003b8.286a83b6_boundary
> Content-Type: text/plain; charset="US-ASCII"
> Content-Transfer-Encoding: 7bit
>
> Mike,
>
> You asked if anyone else experienced anything like this? Well, at N2MO in
> Spring Lake, NJ our field day microwave oven generated lots of hash on the 20
> meter band. Thankfully, it was only short duration till another member
> finished cooking his meal!
>
> 73,
> John - W2YR
>
> - --part1_69.174003b8.286a83b6_boundary
> Content-Type: text/html; charset="US-ASCII"
> Content-Transfer-Encoding: 7bit
>
> <HTML><FONT FACE=arial,helvetica><FONT SIZE=3>Mike,
> <BR>
> <BR>You asked if anyone else experienced anything like this? Well, at N2MO in
> <BR>Spring Lake, NJ our field day microwave oven generated lots of hash on the 20
> <BR>meter band. Thankfully, it was only short duration till another member
> <BR>finished cooking his meal!
> <BR>
> <BR>73,
> <BR>John - W2YR</FONT></HTML>
>
> - --part1_69.174003b8.286a83b6_boundary--
>
> ------------------------------
>
> Date: Tue, 26 Jun 2001 21:37:43 -0400
> From: Pete Smith <n4zr@contesting.com>
> Subject: Re: [RFI] Coffee Pot RFI!
>
> At 06:23 PM 6/26/01 -0700, Mike Lazaroff K3AIR wrote:
> >
> >Here's a great (and true!) story about our FD operation this year:
> >
> >When operating 80m phone, all of a sudden we were overwhelmed with 40 db
> >over 9 buzzing QRM up and down the band. The noise was barely audible on
> >40m, and not at all on the other bands. It just appeared suddenly, so we
> >figured somebody turned on something that didn't like 80m. We checked our
> >power supplies, laptops, etc., figuring it had to be one of them. Nope.
> >
> >After checking all around the campsite, we discovered that when the coffee
> >pot in the "dining area" was turned on, the RFI appeared. When it was off,
> >the RFI was gone.
> >
> >We survived just fine without (hot) coffee.
> >
> >Anyone else ever experience this???
>
> Sounds like a close cousin to the electrically-heated dog dish we
> discovered at a neighbor's house.
>
> 73, Pete N4ZR
> No, no ... that's WEST Virginia
>
> ------------------------------
>
> Date: Tue, 26 Jun 2001 23:36:48 -0400
> From: Palomar Engineers <Palomar@compuserve.com>
> Subject: [RFI] Touch Light Update #3
>
> F50B-77 is 2400 mH/1000t so the 10 turns is 216 uH. But 77 material is
> quite lossy at 14 MHz and inductance is too high anyway. Better to use
> about 15 turns on a T50-6 to get 1 uH with good "Q". -- If you are stuck
> with the F50B-77 just slip it over the wire (one turn) to suppress the 14
> MHz. -- Jack, K6NY, Palomar Engineers
>
> ------------------------------
>
> End of Radio Frequency Interference (RFI) Digest V4 #56
> *******************************************************
>
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