On a sunny day (Thu, 09 Mar 2023 09:56:12 -0800) it happened John Larkin <jlarkin@highlandSNIPMEtechnology.com> wrote in <ta7k0i5j95lqorlq6a41ushch2b3dss5fl@4ax.com>:>On Thu, 09 Mar 2023 06:54:56 GMT, Jan Panteltje <alien@comet.invalid> >wrote: > >>PS >>about that right side MOSFET with the high value series resistor in the gate: >>try using your smartphone next to it... >>It REALLY needs decoupling caps. >> >>That gate input, when not in a 100% shielded housing, will react to any RF, >>if the signal is big enough unexpected things may happen. > >I doubt it. Fet capacitances will keep gate RF levels down to >millivolts.That M7 MOSFET with the 1M or so gate resistor is a low power MOSFET I think, or should be: few pF It forms a feeaking antenna in this circuit.
MOSFET Needed
Started by ●March 8, 2023
Reply by ●March 10, 20232023-03-10
Reply by ●March 10, 20232023-03-10
On Fri, 10 Mar 2023 07:28:52 GMT, Jan Panteltje <alien@comet.invalid> wrote:>On a sunny day (Thu, 09 Mar 2023 09:56:12 -0800) it happened John Larkin ><jlarkin@highlandSNIPMEtechnology.com> wrote in ><ta7k0i5j95lqorlq6a41ushch2b3dss5fl@4ax.com>: > >>On Thu, 09 Mar 2023 06:54:56 GMT, Jan Panteltje <alien@comet.invalid> >>wrote: >> >>>PS >>>about that right side MOSFET with the high value series resistor in the gate: >>>try using your smartphone next to it... >>>It REALLY needs decoupling caps. >>> >>>That gate input, when not in a 100% shielded housing, will react to any RF, >>>if the signal is big enough unexpected things may happen. >> >>I doubt it. Fet capacitances will keep gate RF levels down to >>millivolts. > >That M7 MOSFET with the 1M or so gate resistor is a low power MOSFET I think, >or should be: > few pF > >It forms a feeaking antenna in this circuit.Well, try it. Put a small mosfet on a PC board with a 1M gate resistor to ground, with a reasonable layout, and see if a cell phone will turn it on. I'm guessing it won't. A 2N7002 is 20 pF typical Cin.
Reply by ●March 10, 20232023-03-10
On 2023-03-10 10:12, John Larkin wrote:> On Fri, 10 Mar 2023 07:28:52 GMT, Jan Panteltje <alien@comet.invalid> > wrote: > >> On a sunny day (Thu, 09 Mar 2023 09:56:12 -0800) it happened John Larkin >> <jlarkin@highlandSNIPMEtechnology.com> wrote in >> <ta7k0i5j95lqorlq6a41ushch2b3dss5fl@4ax.com>: >> >>> On Thu, 09 Mar 2023 06:54:56 GMT, Jan Panteltje <alien@comet.invalid> >>> wrote: >>> >>>> PS >>>> about that right side MOSFET with the high value series resistor in the gate: >>>> try using your smartphone next to it... >>>> It REALLY needs decoupling caps. >>>> >>>> That gate input, when not in a 100% shielded housing, will react to any RF, >>>> if the signal is big enough unexpected things may happen. >>> >>> I doubt it. Fet capacitances will keep gate RF levels down to >>> millivolts. >> >> That M7 MOSFET with the 1M or so gate resistor is a low power MOSFET I think, >> or should be: >> few pF >> >> It forms a feeaking antenna in this circuit. > > Well, try it. Put a small mosfet on a PC board with a 1M gate resistor > to ground, with a reasonable layout, and see if a cell phone will turn > it on. I'm guessing it won't. > > A 2N7002 is 20 pF typical Cin. >Not to mention the Miller capacitance--the stage is running at maximum voltage gain. Cheers Phil Hobbs -- Dr Philip C D Hobbs Principal Consultant ElectroOptical Innovations LLC / Hobbs ElectroOptics Optics, Electro-optics, Photonics, Analog Electronics Briarcliff Manor NY 10510 http://electrooptical.net http://hobbs-eo.com
Reply by ●March 10, 20232023-03-10
On Fri, 10 Mar 2023 10:18:51 -0500, Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net> wrote:>On 2023-03-10 10:12, John Larkin wrote: >> On Fri, 10 Mar 2023 07:28:52 GMT, Jan Panteltje <alien@comet.invalid> >> wrote: >> >>> On a sunny day (Thu, 09 Mar 2023 09:56:12 -0800) it happened John Larkin >>> <jlarkin@highlandSNIPMEtechnology.com> wrote in >>> <ta7k0i5j95lqorlq6a41ushch2b3dss5fl@4ax.com>: >>> >>>> On Thu, 09 Mar 2023 06:54:56 GMT, Jan Panteltje <alien@comet.invalid> >>>> wrote: >>>> >>>>> PS >>>>> about that right side MOSFET with the high value series resistor in the gate: >>>>> try using your smartphone next to it... >>>>> It REALLY needs decoupling caps. >>>>> >>>>> That gate input, when not in a 100% shielded housing, will react to any RF, >>>>> if the signal is big enough unexpected things may happen. >>>> >>>> I doubt it. Fet capacitances will keep gate RF levels down to >>>> millivolts. >>> >>> That M7 MOSFET with the 1M or so gate resistor is a low power MOSFET I think, >>> or should be: >>> few pF >>> >>> It forms a feeaking antenna in this circuit. >> >> Well, try it. Put a small mosfet on a PC board with a 1M gate resistor >> to ground, with a reasonable layout, and see if a cell phone will turn >> it on. I'm guessing it won't. >> >> A 2N7002 is 20 pF typical Cin. >> > >Not to mention the Miller capacitance--the stage is running at maximum >voltage gain. > >Cheers > >Phil HobbsAll our boards have a ground plane on layer 2. I can imagine a haywire 2-layer board with a grand-tour autorouted gate trace resonating at a cell phone frequency. Don't do that.
Reply by ●March 10, 20232023-03-10
On a sunny day (Fri, 10 Mar 2023 07:12:59 -0800) it happened John Larkin <jlarkin@highlandSNIPMEtechnology.com> wrote in <90im0i1shrf91q085uihf98ifps19e6m8l@4ax.com>:>On Fri, 10 Mar 2023 07:28:52 GMT, Jan Panteltje <alien@comet.invalid> >wrote: > >>On a sunny day (Thu, 09 Mar 2023 09:56:12 -0800) it happened John Larkin >><jlarkin@highlandSNIPMEtechnology.com> wrote in >><ta7k0i5j95lqorlq6a41ushch2b3dss5fl@4ax.com>: >> >>>On Thu, 09 Mar 2023 06:54:56 GMT, Jan Panteltje <alien@comet.invalid> >>>wrote: >>> >>>>PS >>>>about that right side MOSFET with the high value series resistor in the gate: >>>>try using your smartphone next to it... >>>>It REALLY needs decoupling caps. >>>> >>>>That gate input, when not in a 100% shielded housing, will react to any RF, >>>>if the signal is big enough unexpected things may happen. >>> >>>I doubt it. Fet capacitances will keep gate RF levels down to >>>millivolts. >> >>That M7 MOSFET with the 1M or so gate resistor is a low power MOSFET I think, >>or should be: >> few pF >> >>It forms a feeaking antenna in this circuit. > >Well, try it. Put a small mosfet on a PC board with a 1M gate resistor >to ground, with a reasonable layout, and see if a cell phone will turn >it on. I'm guessing it won't. > >A 2N7002 is 20 pF typical Cin.Maybe you can try with your few pF scope probe next to your smartphone and your gigglehertz scope? Just call somebody...
Reply by ●March 10, 20232023-03-10
On Fri, 10 Mar 2023 16:01:23 GMT, Jan Panteltje <alien@comet.invalid> wrote:>On a sunny day (Fri, 10 Mar 2023 07:12:59 -0800) it happened John Larkin ><jlarkin@highlandSNIPMEtechnology.com> wrote in ><90im0i1shrf91q085uihf98ifps19e6m8l@4ax.com>: > >>On Fri, 10 Mar 2023 07:28:52 GMT, Jan Panteltje <alien@comet.invalid> >>wrote: >> >>>On a sunny day (Thu, 09 Mar 2023 09:56:12 -0800) it happened John Larkin >>><jlarkin@highlandSNIPMEtechnology.com> wrote in >>><ta7k0i5j95lqorlq6a41ushch2b3dss5fl@4ax.com>: >>> >>>>On Thu, 09 Mar 2023 06:54:56 GMT, Jan Panteltje <alien@comet.invalid> >>>>wrote: >>>> >>>>>PS >>>>>about that right side MOSFET with the high value series resistor in the gate: >>>>>try using your smartphone next to it... >>>>>It REALLY needs decoupling caps. >>>>> >>>>>That gate input, when not in a 100% shielded housing, will react to any RF, >>>>>if the signal is big enough unexpected things may happen. >>>> >>>>I doubt it. Fet capacitances will keep gate RF levels down to >>>>millivolts. >>> >>>That M7 MOSFET with the 1M or so gate resistor is a low power MOSFET I think, >>>or should be: >>> few pF >>> >>>It forms a feeaking antenna in this circuit. >> >>Well, try it. Put a small mosfet on a PC board with a 1M gate resistor >>to ground, with a reasonable layout, and see if a cell phone will turn >>it on. I'm guessing it won't. >> >>A 2N7002 is 20 pF typical Cin. > >Maybe you can try with your few pF scope probe next to your smartphone and your gigglehertz scope? >Just call somebody...Of course a fast scope will see RF near a phone. But will the phone turn on a mosfet on a PC board? Lots of opamps are RF sensitive, so I'd imagine that a phone close to something sensitive, like a thermocouple front end, could cause problems. EMI-hardened opamps and diffamps are becoming common now. Our fastest realtime scope is 7 GHz. What frequencies are cell phones these days? I guess they send short bursty packets. That would be cool on a scope.
Reply by ●March 10, 20232023-03-10
fredag den 10. marts 2023 kl. 18.33.13 UTC+1 skrev John Larkin:> On Fri, 10 Mar 2023 16:01:23 GMT, Jan Panteltje <al...@comet.invalid> > wrote: > > >On a sunny day (Fri, 10 Mar 2023 07:12:59 -0800) it happened John Larkin > ><jla...@highlandSNIPMEtechnology.com> wrote in > ><90im0i1shrf91q085...@4ax.com>: > > > >>On Fri, 10 Mar 2023 07:28:52 GMT, Jan Panteltje <al...@comet.invalid> > >>wrote: > >> > >>>On a sunny day (Thu, 09 Mar 2023 09:56:12 -0800) it happened John Larkin > >>><jla...@highlandSNIPMEtechnology.com> wrote in > >>><ta7k0i5j95lqorlq6...@4ax.com>: > >>> > >>>>On Thu, 09 Mar 2023 06:54:56 GMT, Jan Panteltje <al...@comet.invalid> > >>>>wrote: > >>>> > >>>>>PS > >>>>>about that right side MOSFET with the high value series resistor in the gate: > >>>>>try using your smartphone next to it... > >>>>>It REALLY needs decoupling caps. > >>>>> > >>>>>That gate input, when not in a 100% shielded housing, will react to any RF, > >>>>>if the signal is big enough unexpected things may happen. > >>>> > >>>>I doubt it. Fet capacitances will keep gate RF levels down to > >>>>millivolts. > >>> > >>>That M7 MOSFET with the 1M or so gate resistor is a low power MOSFET I think, > >>>or should be: > >>> few pF > >>> > >>>It forms a feeaking antenna in this circuit. > >> > >>Well, try it. Put a small mosfet on a PC board with a 1M gate resistor > >>to ground, with a reasonable layout, and see if a cell phone will turn > >>it on. I'm guessing it won't. > >> > >>A 2N7002 is 20 pF typical Cin. > > > >Maybe you can try with your few pF scope probe next to your smartphone and your gigglehertz scope? > >Just call somebody... > Of course a fast scope will see RF near a phone. But will the phone > turn on a mosfet on a PC board? > > Lots of opamps are RF sensitive, so I'd imagine that a phone close to > something sensitive, like a thermocouple front end, could cause > problems. > > EMI-hardened opamps and diffamps are becoming common now. > > Our fastest realtime scope is 7 GHz. > > What frequencies are cell phones these days?depends on the service and where you are in the world, but roughly 700-800-900-1800-2100-2600MHz>I guess they send short > bursty packets.not nearly as bad as old school GSM, https://www.youtube.com/shorts/nZ-gSKWr2RI
Reply by ●March 11, 20232023-03-11
On a sunny day (Fri, 10 Mar 2023 09:32:57 -0800) it happened John Larkin <jlarkin@highlandSNIPMEtechnology.com> wrote in <vjpm0i5gkh5q7d01oo0dha1m856f805p8c@4ax.com>:>On Fri, 10 Mar 2023 16:01:23 GMT, Jan Panteltje <alien@comet.invalid> >wrote: > >>On a sunny day (Fri, 10 Mar 2023 07:12:59 -0800) it happened John Larkin >><jlarkin@highlandSNIPMEtechnology.com> wrote in >><90im0i1shrf91q085uihf98ifps19e6m8l@4ax.com>: >> >>>On Fri, 10 Mar 2023 07:28:52 GMT, Jan Panteltje <alien@comet.invalid> >>>wrote: >>> >>>>On a sunny day (Thu, 09 Mar 2023 09:56:12 -0800) it happened John Larkin >>>><jlarkin@highlandSNIPMEtechnology.com> wrote in >>>><ta7k0i5j95lqorlq6a41ushch2b3dss5fl@4ax.com>: >>>> >>>>>On Thu, 09 Mar 2023 06:54:56 GMT, Jan Panteltje <alien@comet.invalid> >>>>>wrote: >>>>> >>>>>>PS >>>>>>about that right side MOSFET with the high value series resistor in the gate: >>>>>>try using your smartphone next to it... >>>>>>It REALLY needs decoupling caps. >>>>>> >>>>>>That gate input, when not in a 100% shielded housing, will react to any RF, >>>>>>if the signal is big enough unexpected things may happen. >>>>> >>>>>I doubt it. Fet capacitances will keep gate RF levels down to >>>>>millivolts. >>>> >>>>That M7 MOSFET with the 1M or so gate resistor is a low power MOSFET I think, >>>>or should be: >>>> few pF >>>> >>>>It forms a feeaking antenna in this circuit. >>> >>>Well, try it. Put a small mosfet on a PC board with a 1M gate resistor >>>to ground, with a reasonable layout, and see if a cell phone will turn >>>it on. I'm guessing it won't. >>> >>>A 2N7002 is 20 pF typical Cin. >> >>Maybe you can try with your few pF scope probe next to your smartphone and your gigglehertz scope? >>Just call somebody... > >Of course a fast scope will see RF near a phone. But will the phone >turn on a mosfet on a PC board? > >Lots of opamps are RF sensitive, so I'd imagine that a phone close to >something sensitive, like a thermocouple front end, could cause >problems. > >EMI-hardened opamps and diffamps are becoming common now.Many transistor circuits exist that make great unexpected RF detectors (base emitter). I have wondered why you do not RF decouple your walwart power input.. AT the connector. When you are a radio-ham you will notice real fast what a few hunderd - or even tens of Watts can do.>Our fastest realtime scope is 7 GHz.That should do.>What frequencies are cell phones these days? I guess they send short >bursty packets. That would be cool on a scope.From google: 698-806 MHz 700 MHz Band 806- 849 / 851- 896 MHz 800 MHz Band 1850-1910 / 1930-1990 MHz PCS Band 1710-1755 / 2110-2155 MHz AWS Band You can hear those on some FM radios too, I remeber in a train getting interference on my headplugs on my mp3 player from the guy next to me phoning, you could hear those bursts.
Reply by ●March 11, 20232023-03-11
On Sat, 11 Mar 2023 06:47:31 GMT, Jan Panteltje <alien@comet.invalid> wrote:>On a sunny day (Fri, 10 Mar 2023 09:32:57 -0800) it happened John Larkin ><jlarkin@highlandSNIPMEtechnology.com> wrote in ><vjpm0i5gkh5q7d01oo0dha1m856f805p8c@4ax.com>: > >>On Fri, 10 Mar 2023 16:01:23 GMT, Jan Panteltje <alien@comet.invalid> >>wrote: >> >>>On a sunny day (Fri, 10 Mar 2023 07:12:59 -0800) it happened John Larkin >>><jlarkin@highlandSNIPMEtechnology.com> wrote in >>><90im0i1shrf91q085uihf98ifps19e6m8l@4ax.com>: >>> >>>>On Fri, 10 Mar 2023 07:28:52 GMT, Jan Panteltje <alien@comet.invalid> >>>>wrote: >>>> >>>>>On a sunny day (Thu, 09 Mar 2023 09:56:12 -0800) it happened John Larkin >>>>><jlarkin@highlandSNIPMEtechnology.com> wrote in >>>>><ta7k0i5j95lqorlq6a41ushch2b3dss5fl@4ax.com>: >>>>> >>>>>>On Thu, 09 Mar 2023 06:54:56 GMT, Jan Panteltje <alien@comet.invalid> >>>>>>wrote: >>>>>> >>>>>>>PS >>>>>>>about that right side MOSFET with the high value series resistor in the gate: >>>>>>>try using your smartphone next to it... >>>>>>>It REALLY needs decoupling caps. >>>>>>> >>>>>>>That gate input, when not in a 100% shielded housing, will react to any RF, >>>>>>>if the signal is big enough unexpected things may happen. >>>>>> >>>>>>I doubt it. Fet capacitances will keep gate RF levels down to >>>>>>millivolts. >>>>> >>>>>That M7 MOSFET with the 1M or so gate resistor is a low power MOSFET I think, >>>>>or should be: >>>>> few pF >>>>> >>>>>It forms a feeaking antenna in this circuit. >>>> >>>>Well, try it. Put a small mosfet on a PC board with a 1M gate resistor >>>>to ground, with a reasonable layout, and see if a cell phone will turn >>>>it on. I'm guessing it won't. >>>> >>>>A 2N7002 is 20 pF typical Cin. >>> >>>Maybe you can try with your few pF scope probe next to your smartphone and your gigglehertz scope? >>>Just call somebody... >> >>Of course a fast scope will see RF near a phone. But will the phone >>turn on a mosfet on a PC board? >> >>Lots of opamps are RF sensitive, so I'd imagine that a phone close to >>something sensitive, like a thermocouple front end, could cause >>problems. >> >>EMI-hardened opamps and diffamps are becoming common now. > >Many transistor circuits exist that make great unexpected RF detectors (base emitter). >I have wondered why you do not RF decouple your walwart power input.. AT the connector.Our products generally have an EMI filter, a couple of caps and a ferrite bead, and then a polyfuse, TVS, and more caps. I don't bother to do all that on proto boards. We do have an all-facility EMI test system: https://www.dropbox.com/s/tmcpmvqp714c82o/Roof_West.JPG?raw=1
Reply by ●March 11, 20232023-03-11
On a sunny day (Sat, 11 Mar 2023 08:23:45 -0800) it happened John Larkin <jlarkin@highlandSNIPMEtechnology.com> wrote in <kcap0i9kf0tuc35hnlirtoobkqj6u19fgu@4ax.com>:>We do have an all-facility EMI test system: > >https://www.dropbox.com/s/tmcpmvqp714c82o/Roof_West.JPG?raw=1? All I see is a roof with some boxes? Or are you referring to that antenna tower? I remember a discussion about that here some time ago. I have a similar source of RF power here, the radar station just a few km from here. https://panteltje.nl/pub/radar_2kHz_spectrum_burst.gif it works at about 1.35 GHz but sweeps over a wide band. Signal is VERY strong and interferes with satellite reception on some channels as the 1.35 GHz is in the middle of the signal from the LNB down converter.
