K3: 6M SSB audio hash
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Jim, > My point is that what you have described is ALSO WRONG. That > short jumper can cause common impedance coupling, as the voltage > drop across it is added to circuit common. That "short jumper" > has inductance, and at some frequency, and/or at some power level, > the voltage drop across it becomes strong enough to cause RFI. I'm aware that a short jumper is "wrong" from the purist point of view. However, it is much better than mic return that is held above ground by an RF choke! Most of the rigs I've seen have relatively good grounding for the "PTT ground" - the jumper is 1 cm or less or the circuit board layout includes the "PTT Ground" pin in a wide (large) ground plane. Fortunately, most amateur equipment is not operated in strong (multi hundred KW ERP) UHF fields. Yes, the best connection would be to tin the mic cable braid and clamp it and jumpers to both the "PTT ground" and "Mic ground" pins in the cable clamp of the Foster plug. Unfortunately, the manufacturers have not chosen to do so. > On my website are photographs of very high quality (and very > expensive, German-made) condenser mics with serious RFI problems. Which article? I used many of the Neuman and AKG mics 30 years ago in the recording studio. Of course, the "purists" were not about to give up their Nuvistor preamplifiers <G>. > One piece of good news -- the front panel mic connector on the K3 > IS mounted directly to the shielding enclosure. So are all the RF > connectors. Unfortunately, neither the front panel nor the KIO3 have good shielding connections to the rest of the radio - at least not with my factory assembled K3. I measure between 5.5 and 6.0 Ohms from the shell/ring of the Foster jack to the grounding lug and RF (antenna) connectors on the rear panel. I also measure between 5.5 and 6.0 Ohms from the sleeve of the rear panel (3.2 mm) Mic jack to the ground terminal and about 24 Ohms from the sleeve of the Line in and Line Out jacks to the ground terminal. 73, ... Joe, W4TV > -----Original Message----- > From: [hidden email] > [mailto:[hidden email]] On Behalf Of Jim Brown > Sent: Sunday, June 08, 2008 4:17 PM > To: Elecraft List > Subject: RE: [Elecraft] K3: 6M SSB audio hash > > > On Sun, 8 Jun 2008 14:28:45 -0400, Joe Subich, W4TV wrote: > > >Then I should not have said "PTT Ground" but that is how Icom, > >Kenwood and Yaesu all label their mic connectors. In all three > >brands, the "PTT ground" is DC return and is, in fact, chassis > >ground - usually a short jumper from the "PTT Ground" pin to > >the chassis or the ground trace on a circuit board which contains > >mic connector which is tied to chassis with multiple grounding > >and mounting screws. > > Joe, > > Thanks for hanging in on this issue, because it is VERY important. > > My point is that what you have described is ALSO WRONG. That > short jumper > can cause common impedance coupling, as the voltage drop across it is > added to circuit common. That "short jumper" has inductance, > and at some > frequency, and/or at some power level, the voltage drop > across it becomes > strong enough to cause RFI. > > On my website are photographs of very high quality (and very > expensive, > German-made) condenser mics with serious RFI problems. In one > of them, > the cable shield goes to the shell of the mic with a jumper > less than one > inch long. In downtown Chicago, where TV transmitters are on tall > buildings, that mic begins to detect TV broadcast stations at > roughly 180 > MHz. An older mic from the same manufacturer begins detecting at TV > channel 2 (54-60 MHz) and FM broadcast! Mics with shorter > jumpers begin > having trouble only on higher UHF channels. They ALL have > trouble with > cell phones. Documentation of this, along with the extensive > testing I've > performed, are on my website. > > http://audiosystemsgroup.com/publish > > The voltage drop across that inductance is proportional to frequency, > inversely proportional to distance between the victim > equipment and the > transmitting antenna, and proportional to the square root of the > transmitter power! > > I will keep repeating this until it becomes clear. The ONLY > good place to > terminate a cable shield is to the shielding enclosure DIRECTLY. Any > other connection sets up the possibility of common impedance > coupling -- > what pro audio folks call "the pin 1 problem." > > >The whole point is that all of the "big three" manufacturers use > >the shield in their microphones improperly by connecting it to an > >ungrounded mic return instead of the chassis ("PTT Ground"). In > >the schematics I have checked, every one provides a DC return for > >the mic/preamp using an RF choke but connects the mic shield to > >the mic return instead of the chassis. > > I also see this, and I strongly agree with you that it is > VERY WRONG, and > is often the cause of RFI into the ham rig (what we call RF > feedback). > This improper connection of cable shields is the primary > cause of RFI of > all types, including RF in the shack. Add to this the US > members of that > group, which should more properly be called the big five. The > K2 and the > K3 have improperly terminated shields at some connectors. So > does my Ten > Tec Omni V. > > One piece of good news -- the front panel mic connector on the K3 IS > mounted directly to the shielding enclosure. So are all the RF > connectors. > > n Sun, 8 Jun 2008 09:39:20 -0700, Brian Lloyd wrote: > > >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. > > YES! > > 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 _______________________________________________ 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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Hmmm. I measure 0.2 to 0.4 ohms from shell of Foster jack to grounding
lug to UHF connector on back, and from various other connector sleeves/shells to the grounding lug. However, I have no continuity between line in and line out sleeves and chassis ground, which appears to be by design, looking at the schematic. Rear panel mic, speaker and phone commons are tied to chassis ground on the KI03 main board, but not the (xfmr coupled) line in and line out commons. Bob NW8L On Sun, Jun 8, 2008 at 6:33 PM, Joe Subich, W4TV <[hidden email]> wrote: > > > Unfortunately, neither the front panel nor the KIO3 have good > shielding connections to the rest of the radio - at least not > with my factory assembled K3. I measure between 5.5 and 6.0 Ohms > from the shell/ring of the Foster jack to the grounding lug and RF > (antenna) connectors on the rear panel. I also measure between > 5.5 and 6.0 Ohms from the sleeve of the rear panel (3.2 mm) Mic > jack to the ground terminal and about 24 Ohms from the sleeve of > the Line in and Line Out jacks to the ground terminal. > > 73, > > ... Joe, W4TV 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 Joe Subich, W4TV-3
On Sun, 8 Jun 2008 20:33:15 -0400, Joe Subich, W4TV wrote:
>I'm aware that a short jumper is "wrong" from the purist point >of view. However, it is much better than mic return that is >held above ground by an RF choke! Most of the rigs I've seen >have relatively good grounding for the "PTT ground" - the jumper >is 1 cm or less or the circuit board layout includes the "PTT >Ground" pin in a wide (large) ground plane. >Fortunately, most amateur equipment is not operated in strong >(multi hundred KW ERP) UHF fields. This is NOT purist. The cell phone interference being discussed in another thread could easily be the result of a jumper that short. It is in those mics! The field is determined by inverse square law. A 2W radio (cell phone) puts a pretty strong field at 6-12 inches. Back in Chicago, I ran 160M and 80 on a long wire that ended at the transmitter. With only 13W (K2 barefoot) I could lock up the keying loop between the computer and the radio. >Which article? I used many of the Neuman and AKG mics 30 years ago The AES paper on RFI in condenser mics has the greatest detail. I've summarized it and used it tutorially in other publications. 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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I usually avoid public testimonials, but in this thread, I choose to
make an exception. For those who have interest in this discussion, I notice that Jim Brown has been a bit bashful in stating his credentials. Jim has extensive experience with EMC and RFI in both ham radio and pro-audio systems. Take a look at http://www.audiosystemsgroup.com/bio-jb.htm for his professional pro-audio profile, or for something more ham related, look at http://www.audiosystemsgroup.com/K9YC/k9yc-bio.htm. For those interested in his technical publications, they can be seen at http://audiosystemsgroup.com/K9YC.htm - it is an extensive library. I consider Jim's work to represent examples of good engineering practice in the fields of Pro-Audio, EMC and RFI. Keep up the good work Jim - you and your research are a great asset to the amateur radio community. 73, Don W3FPR Jim Brown wrote: > On Sun, 8 Jun 2008 20:33:15 -0400, Joe Subich, W4TV wrote: > > >> I'm aware that a short jumper is "wrong" from the purist point >> of view. However, it is much better than mic return that is >> held above ground by an RF choke! Most of the rigs I've seen >> have relatively good grounding for the "PTT ground" - the jumper >> is 1 cm or less or the circuit board layout includes the "PTT >> Ground" pin in a wide (large) ground plane. >> > > >> Fortunately, most amateur equipment is not operated in strong >> (multi hundred KW ERP) UHF fields. >> > > This is NOT purist. The cell phone interference being discussed in > another thread could easily be the result of a jumper that short. It is > in those mics! The field is determined by inverse square law. A 2W > radio (cell phone) puts a pretty strong field at 6-12 inches. Back in > Chicago, I ran 160M and 80 on a long wire that ended at the transmitter. > With only 13W (K2 barefoot) I could lock up the keying loop between the > computer and the radio. > > >> Which article? I used many of the Neuman and AKG mics 30 years ago >> > > The AES paper on RFI in condenser mics has the greatest detail. I've > summarized it and used it tutorially in other publications. > > 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 > ------------------------------------------------------------------------ > > > No virus found in this incoming message. > Checked by AVG. > Version: 8.0.100 / Virus Database: 270.0.0/1489 - Release Date: 6/7/2008 11:17 AM > 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 Jim Brown-10
> This is NOT purist. The cell phone interference being discussed > in another thread could easily be the result of a jumper that > short. It is in those mics! Yes, a jumper that short would respond to 900/1200 MHz within 6" or so. The GSM phones drive TV crews and technicians crazy on a regular basis ... guests on many of the talk/news shows think they ca get away with putting their phones and crackberry devices on silent but they don't know about the polling that happens ever few minutes even if they don't get an e-mail or SMS. I'm still more concerned about the relatively "long" wavelengths up through 55 MHz. > Back in Chicago, I ran 160M and 80 on a long wire that ended at > the transmitter. With only 13W (K2 barefoot) I could lock up > the keying loop between the computer and the radio. That would have been a relatively "long" loop and an end-fed wire would have made the radio part of the antenna. It would have taken a lot of luck to prevent problems there. By the way, I measured the resistance from the Foster to ground lug on my K3 with the power off - it is about 0.5 ohms. There is something strange going on when I turn on the power and have anything connected to the "Aux" (+12 V) Power output. I will need to do some more research to figure out what is going on. 73, ... Joe, W4TV > -----Original Message----- > From: [hidden email] > [mailto:[hidden email]] On Behalf Of Jim Brown > Sent: Sunday, June 08, 2008 11:53 PM > To: Elecraft List > Subject: RE: [Elecraft] K3: 6M SSB audio hash > > > On Sun, 8 Jun 2008 20:33:15 -0400, Joe Subich, W4TV wrote: > > >I'm aware that a short jumper is "wrong" from the purist point > >of view. However, it is much better than mic return that is > >held above ground by an RF choke! Most of the rigs I've seen > >have relatively good grounding for the "PTT ground" - the jumper > >is 1 cm or less or the circuit board layout includes the "PTT > >Ground" pin in a wide (large) ground plane. > > >Fortunately, most amateur equipment is not operated in strong > >(multi hundred KW ERP) UHF fields. > > This is NOT purist. The cell phone interference being discussed in > another thread could easily be the result of a jumper that > short. It is > in those mics! The field is determined by inverse square law. A 2W > radio (cell phone) puts a pretty strong field at 6-12 inches. Back in > Chicago, I ran 160M and 80 on a long wire that ended at the > transmitter. > With only 13W (K2 barefoot) I could lock up the keying loop > between the > computer and the radio. > > >Which article? I used many of the Neuman and AKG mics 30 years ago > > The AES paper on RFI in condenser mics has the greatest detail. I've > summarized it and used it tutorially in other publications. > > 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 _______________________________________________ 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 Mon, 9 Jun 2008 00:51:17 -0400, Joe Subich, W4TV wrote:
>By the way, I measured the resistance from the Foster to ground >lug on my K3 with the power off - it is about 0.5 ohms. What's a Foster? Is that the proper name for the front panel mic jack? If I carefully zero my trusty Fluke 8060A on the lowest R scale (that is, short the probes, then set REL) I measure 0.01 - 0.02 ohms from the shell of the front panel mic jack to the SO239 for ANT1. This is with the power off. Same value, +/- 0.01 ohms to the ground lug. >There is >something strange going on when I turn on the power and have anything >connected to the "Aux" (+12 V) Power output. I will need to do some >more research to figure out what is going on. Yes. With the power on, and the radio in RX mode, there is a small DC gradient from one part of the chassis to another. I can see anywhere from 0.3 to 5mVDC measuring variously between the front panel mic jack and the ANT1 SO239, the ground lug, the front panel mic jack, and the daughterboard coax connectors! These values float around a bit. If you try to measure resistances between these points with the power on, the meter can either increase or go negative, depending on which way you connect the probes. :) That's not at all surprising -- ohm meters are calibrated for un- energized circuits. Although the resistance of the shielding enclosure is small, it isn't zero, so there's some IR drop across it. If we believe the meter inside the K3, the TOTAL current from the power supply is about 800 mA. That's a worst case number for the current on the chassis. 73, Jim _______________________________________________ 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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