K2 cellphone interference
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Our K2 appears inordinately sensitive to radiation from my GSM phone.
It occurs with the audio gain turned all the way down so it appears that this problem might be with the audio amp stage. Have others experienced this and, if so, has anyone come up with a fix? -- Brian Lloyd Granite Bay Montessori brian AT gbmontessori DOT com 9330 Sierra College Blvd. +1.916.367.2131 (voice) Roseville, CA 95661, USA http://www.gbmontessori.com I fly because it releases my mind from the tyranny of petty things . . . — Antoine de Saint-Exupéry PGP key ID: 12095C52A32A1B6C PGP key fingerprint: 3B1D BA11 4913 3254 B6E0 CC09 1209 5C52 A32A 1B6C _______________________________________________ Elecraft mailing list Post to: [hidden email] You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com |
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Yes, same thing here. It doesn't do it with the K3 at all however. I'm
sure it's breakthrough directly into the audio stages. It's never bothered me too much as most of the time my cellphone is in the car or in a jacket pocket somewhere. Some judicious decoupling somewhere would no doubt help. 73 Stephen G4SJP On 08/06/2008 13:00, "Brian Lloyd" <[hidden email]> wrote: > Our K2 appears inordinately sensitive to radiation from my GSM phone. > It occurs with the audio gain turned all the way down so it appears > that this problem might be with the audio amp stage. Have others > experienced this and, if so, has anyone come up with a fix? > > -- > > Brian Lloyd Granite Bay Montessori > brian AT gbmontessori DOT com 9330 Sierra College Blvd. > +1.916.367.2131 (voice) Roseville, CA 95661, USA > http://www.gbmontessori.com > > I fly because it releases my mind from the tyranny of petty things . . . > Antoine de Saint-Exupéry > > PGP key ID: 12095C52A32A1B6C > PGP key fingerprint: 3B1D BA11 4913 3254 B6E0 CC09 1209 5C52 A32A 1B6C > > > > > > _______________________________________________ > Elecraft mailing list > Post to: [hidden email] > You must be a subscriber to post to the list. > Subscriber Info (Addr. Change, sub, unsub etc.): > http://mailman.qth.net/mailman/listinfo/elecraft > > Help: http://mailman.qth.net/subscribers.htm > Elecraft web page: http://www.elecraft.com > _______________________________________________ Elecraft mailing list Post to: [hidden email] You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com |
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In reply to this post by Brian Lloyd-6
Brian,
I have heard another report of this noise, but no analysis of the effect. Yes, the fact that the level does not depend on your audio gain setting indicates that it is confined to the AF Amplifier. Note that the K2 uses the LM380N BYPASS pin (8) for sidetone input. Normally, the BYPASS pin is used to increase the power supply rejection capabilities of the LM380 and many designs simply ignore it (nothing connected) because the "power source is well filtered for ripple". As a quick test, try grounding the negative side of Control Board C32 with a very short (low inductance) wire and see if that improves the situation. If so, it could be that the power supply wiring in the K2 is picking up the radiation and feeding it to the audio amp. Understand that this is just a guess, but it would be nice to know if this is the source of the interference. Of course, the real problem is the phone - if it radiates that much, I wonder just how well it meets other radiation requirements. Note that your sidetone will not work with the test wire I suggested in place - I did say it was a test! If one would want to implement adding the bypass capacitor as a permanent fix, then a different method of sidetone injection would have to be created. A quick look at the K1 audio may provide some ideas (add an LM386 ahead of the LM380N for more AF gain and isolation of the AF stream from the sidetone - no, I do not have time to design and test and document it, it is just a thought). 73, Don W3FPR Brian Lloyd wrote: > Our K2 appears inordinately sensitive to radiation from my GSM phone. > It occurs with the audio gain turned all the way down so it appears > that this problem might be with the audio amp stage. Have others > experienced this and, if so, has anyone come up with a fix? > > -- > > Brian Lloyd Granite Bay Montessori > _______________________________________________ Elecraft mailing list Post to: [hidden email] You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com |
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In reply to this post by Brian Lloyd-6
On Sun, 8 Jun 2008 05:00:16 -0700, Brian Lloyd wrote:
>Our K2 appears inordinately sensitive to radiation from my GSM >phone. This is a VERY common problem in the audio world. Cell phones and Blackberrys have interrupted hearings on Capitol Hill when they got into the sound systems in hearing rooms! Manufacturers of mics and other audio gear were caught with their pants down. I did some consulting work on that project. I've also consulted with mic mfrs on fixing their mic designs. GSM phones and Nextel phones are part of a broad group of phones that use TDMA -- Time Division Multiplex of the radio channel. That means that they transmit square waves with a very small duty cycle, because many conversations are sharing a channel, each transmitting for only 1-2% of their cycle. A phone with 50 mW average power out may have a peak RF output of 1-2 watts! To make matters worse, the repetition rate is 210 Hz, so the harmonics are right in the middle of the audio spectrum, making them VERY audible. So what you are hearing is that modulation (those square waves). About four years ago, I published an AES paper showing how the cell phone can be used as a simple injection probe to find the path the RF is taking into the victim equipment. While listening to the output of the victim, put the cell phone in transmit mode and move it slowly along each individual wire or cable that is connected to the radio. Since the cell phone is operating in the 800-900 MHz range, you will see wavelength-related effects and find hot spots along the cable(s) that is(are) doing the coupling. Suspect the mic cable and the headphone cable. The most common cause of GSM interference is a pin 1 problem. Another common cause is coupling around the feedback loop of the output stage that drives the headphones or an external speaker. In both cases, the fix is to either correct the pin 1 problem by properly connecting the cable shield to the chassis, not the circuit board, or clamping one or more UHF ferrites onto the cable very close to the point of entry. Fair-Rite #61 is the weapon of choice at cell phone frequencies. These coupling mechanisms are described in detail in a tutorial on my website. It's a free pdf download, no cookies. http://audiosystemsgroup.com/RFI-Ham.pdf Jim Brown K9YC Chair -- Technical Committee on EMC Audio Engineering Society _______________________________________________ Elecraft mailing list Post to: [hidden email] You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com |
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On Jun 8, 2008, at 8:14 AM, Jim Brown wrote: > On Sun, 8 Jun 2008 05:00:16 -0700, Brian Lloyd wrote: > >> Our K2 appears inordinately sensitive to radiation from my GSM >> phone. > > This is a VERY common problem in the audio world. I know. I used to make a living designing high-end audio preamps for audiophiles. EMI through the phono stage was always a problem and dealing with it with an impact on sound quality became an art. Being a ham also meant that my designs were exposed to RF from the get-go so I tended to fix things to my own satisfaction before they every saw the light of day. > About four years ago, I published an AES paper showing how the cell > phone can be used as a simple injection probe to find the path the RF > is taking into the victim equipment. While listening to the output of > the victim, put the cell phone in transmit mode and move it slowly > along each individual wire or cable that is connected to the radio. > Since the cell phone is operating in the 800-900 MHz range, you will > see wavelength-related effects and find hot spots along the cable(s) > that is(are) doing the coupling. Suspect the mic cable and the > headphone cable. Except the problem occurs with mic, external speaker, and antenna disconnected. That leaves either improper shielding or ingress on the power cable. > The most common cause of GSM interference is a pin 1 problem. Another > common cause is coupling around the feedback loop of the output stage > that drives the headphones or an external speaker. I hate to sound stupid but, what is a "pin 1 problem"? I can understand an "improper electrostatic shield problem" or a "common mode RF current problem" but the reference to "pin 1" leaves me confused. Ah, never mind. All I needed was to read your paper listed below. Thank you. OTOH, it is using a term from the audio engineer's lexicon, one that might not be obvious to others outside that discipline. (It certainly was to me and I was already aware of the problem.) > In both cases, the fix is to either correct the pin 1 problem by > properly connecting the cable shield to the chassis, not the circuit > board, or clamping one or more UHF ferrites onto the cable very close > to the point of entry. Fair-Rite #61 is the weapon of choice at cell > phone frequencies. > > These coupling mechanisms are described in detail in a tutorial on my > website. It's a free pdf download, no cookies. > > http://audiosystemsgroup.com/RFI-Ham.pdf I guess that people forget that, in shielding equipment, they are building a Faraday cage around it. That means that you need to terminate your shield at the OUTSIDE of the equipment, not inside. One wants to continue the Faraday cage all the way out to the input device. This means that the shield of any wire needs to be attached to the chassis externally. That isn't hard to understand. I know that I solved the problem in my designs by using shielded twisted-pair for phono cartridge input and tying the shield to the chassis. Now, having said that, it doesn't appear to be coming in on the mic cable or the external speaker cable. I already use my cell phone as a probe and the problem seems to be a function of proximity to the radio on any side. Pickup occurs as much as 8' away from the radio with everything (except power) disconnected. > > > Jim Brown K9YC > Chair -- Technical Committee on EMC > Audio Engineering Society > > > > _______________________________________________ > Elecraft mailing list > Post to: [hidden email] > You must be a subscriber to post to the list. > Subscriber Info (Addr. Change, sub, unsub etc.): > http://mailman.qth.net/mailman/listinfo/elecraft > > Help: http://mailman.qth.net/subscribers.htm > Elecraft web page: http://www.elecraft.com > -- 73 de Brian, WB6RQN Brian Lloyd - brian HYPHEN wb6rqn AT lloyd DOT com _______________________________________________ Elecraft mailing list Post to: [hidden email] You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com |
Re: K2 cellphone interference
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In reply to this post by Don Wilhelm-4
Don Wilhelm wrote:
> > I have heard another report of this noise, but no analysis of the > effect. Yes, the fact that the level does not depend on your audio gain > setting indicates that it is confined to the AF Amplifier. Yes, the K2 does have rather poor uHF EMC properties. You can slightly pull one of the VFO or BFO with a PMR 446 (500mW handheld) close to the left of the case. It also generates clicks on keying, especially close to the speaker grill. (The same rig crashed my PC held at similar distances from the keyboard!) Similar powers on 70cm also have an effect. Part of the problem is that the seams on the case are not continuous. This was compounded on #6123 because not all the screw holes for the 2D connectors had masking tape. That meant that the paint overspray results in quite a high resistance between the blocks and the panels. I fixed this by sanding off the paint around all the blocks. Actually I can still pull the frequency (BFO v VFO on the 7MHz birdy) by about 5Hz, but I need to hold the transmitter in front of front panel, with the antenna parallel and horizontal. Improving those connections means I can't, now, reproduce any frequency pulling, but there is still some audio pickup, which does seem to be post volume control. (The failure to reproduce the frequency shift may be partly due to having a less sensitive test configuration, though. Real high quality EMC design would use some form of conductive gasket, or at least finger stock, but they are expensive in small quantities, difficult to add and, in some cases, compromise the ability to remove covers (e.g. conductive tape). They would also need more extensive removal of overspray. Incidentally, this thread has shades of the pin 1 problem thread, because the K2 case violates the Faraday cage principle at UHF. > source of the interference. Of course, the real problem is the phone - > if it radiates that much, I wonder just how well it meets other > radiation requirements. GSM interference is generally an unintentional receiver issue, not a spurious transmissions one. The TDM envelope gets AM detected by some non-linear element in the circuit (often a semiconductor junction). -- David Woolley "The Elecraft list is a forum for the discussion of topics related to Elecraft products and more general topics related ham radio" List Guidelines <http://www.elecraft.com/elecraft_list_guidelines.htm> _______________________________________________ Elecraft mailing list Post to: [hidden email] You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com |
Re: K2 cellphone interference
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David Woolley (E.L) wrote:
> fixed this by sanding off the paint around all the blocks. Actually I > can still pull the frequency (BFO v VFO on the 7MHz birdy) by about 5Hz, > but I need to hold the transmitter in front of front panel, with the > antenna parallel and horizontal. Sorry, that's 4MHz versus effective receive frequency. I believe when I first tried this, I used a GDO as an external source, rather than the birdy. -- David Woolley Emails are not formal business letters, whatever businesses may want. RFC1855 says there should be an address here, but, in a world of spam, that is no longer good advice, as archive address hiding may not work. _______________________________________________ Elecraft mailing list Post to: [hidden email] You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com |
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On Jun 9, 2008, at 12:51 AM, David Woolley wrote: > David Woolley (E.L) wrote: > >> fixed this by sanding off the paint around all the blocks. >> Actually I can still pull the frequency (BFO v VFO on the 7MHz >> birdy) by about 5Hz, but I need to hold the transmitter in front of >> front panel, with the antenna parallel and horizontal. > > Sorry, that's 4MHz versus effective receive frequency. I believe > when I first tried this, I used a GDO as an external source, rather > than the birdy. Sounds like going back to the K2 and making sure that I am getting good contact at all the corner blocks will improve things. I will try that. Not sure it will help all that much at 1.9GHz but it can't hurt. -- 73 de Brian, WB6RQN Brian Lloyd - brian HYPHEN wb6rqn AT lloyd DOT com _______________________________________________ Elecraft mailing list Post to: [hidden email] You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com |
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In reply to this post by David Woolley (E.L)
On Mon, 09 Jun 2008 08:43:25 +0100, David Woolley (E.L) wrote:
>Incidentally, this thread has shades of the pin 1 problem thread, >because the K2 case violates the Faraday cage principle at UHF. The pin 1 problem and the shielding problem are two VERY different coupling mechanisms, although they have in common antenna action and RF detection. The shielding problem lets the RF in the box, where it couples to internal wiring by antenna action. The pin 1 problem takes RF that has been put on EXTERNAL wiring by antenna action and puts it onto internal wiring because the shield goes inside, not outside. I agree that the seams are the likely open door in the shielding. As noted, the proper hardware to seal the box at these frequencies is not inexpensive. Ham gear need not be "perfect" enough for a high stakes military mission or a flight into space. It must be designed to meet a budget. IMO, the shielding is sufficient for all ham installations I can think of as long as the ham maintains a reasonable distance between the rig and any GSM or TDMA phones. :) The pin 1 problem and the unshielded transformers, however, are another issue. This can readily cause problems at HF and at baseband (hum, buzz, RFI), and should be fixed. Luckily it is easy to do that by modest redesign that can actually REDUCE the cost. 73, Jim Brown K9YC _______________________________________________ Elecraft mailing list Post to: [hidden email] You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com |
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