On Saturday, October 6, 2018 at 2:03:44 AM UTC-4, 69883925...@nospam.org wrote:> I have, and this is REAL fun, a bug detector from ebay, > it will beep if any RF in the GHz range is detected, > very similar to this one: > https://www.ebay.com/itm//372193315564> < 8$ free shipping! Wideband spectrum analyzer my foot!A spectrum analyzer can detect very weak signals and tell you their frequency. It is also very useful for other measurements. You can get an HP 8566B on eBay for around $1,500. It spans 100Hz to 22Ghz. The problem with your detector is it doesn't specify the frequency range so you don't knowwhere it cuts off. You can make your own that goes from 1MHz to 10GHz with 55dB dynamic range. It is available for $7.37 at Arrow. https://octopart.com/search?q=ad8317&start=0
really fast buffers
Started by ●October 3, 2018
Reply by ●October 6, 20182018-10-06
Reply by ●October 6, 20182018-10-06
On a sunny day (Fri, 5 Oct 2018 23:41:03 -0700 (PDT)) it happened Steve Wilson <9fe142ac@gmail.com> wrote in <445ed56b-7f23-441c-87e9-d7d8dcf2d37a@googlegroups.com>:>On Saturday, October 6, 2018 at 2:03:44 AM UTC-4, 69883925...@nospam.org wrote: > >> I have, and this is REAL fun, a bug detector from ebay, >> it will beep if any RF in the GHz range is detected, >> very similar to this one: >> https://www.ebay.com/itm//372193315564 > >> < 8$ free shipping! Wideband spectrum analyzer my foot! > >A spectrum analyzer can detect very weak signals and tell you their frequency. It is also very useful for other measurements. >You can get an HP 8566B on eBay for around $1,500. It spans 100Hz to 22Ghz.Yes, I have an rtl-sdr: https://www.ebay.com/itm/272411458376 based spectrum analyzer and wrote the software for that: http://panteltje.com/panteltje/xpsa/index.html Also build a mixer to extend the range http://panteltje.com/pub/2.4_GHz_to_1.5_GHz_mixer_in_box_IMG_4661.JPG It is not hard to build mixers up to several GHz with modern 'tronincs.>The problem with your detector is it doesn't specify the frequency range so you don't knowwhere it cuts off.sigh, what do you even mean with that? read the specs, it is good to 6 GHz>You can make your >own that goes from 1MHz to 10GHz with 55dB dynamic range. It is available for $7.37 at Arrow. > >https://octopart.com/search?q=ad8317&start=0It is the user, not the tool, that often sets what can be done. To detect 'if something is oscillating' that is the issue here, the ebay thing is world class, has adjustable threshold, and you can set it so sensitive that if 2 houses down the road a light switch is flipped it beeps. That chip you refer to is no better, and something like that is maybe even in it :-) (I had it open, glued the beeper back in place after I dropped it, forgot to look up the detector, as it works OK) but now add the cost of housing, battery, potmeter, antenna, beeper .... plus the camera lens detection thing it has, magnetic compass, what not. What RF detectors have you designed and build? China has won again! LOL spectrum analyzer my foot
Reply by ●October 6, 20182018-10-06
On 10/5/18 7:42 PM, Steve Wilson wrote:> John Larkin <jjlarkin@highland_snip_technology.com> wrote: > >> On Fri, 05 Oct 2018 03:12:42 GMT, Steve Wilson <no@spam.com> wrote: > >>> John Larkin <jjlarkin@highland_snip_technology.com> wrote: > >>>> On Fri, 5 Oct 2018 09:26:17 +1000, Clifford Heath <no.spam@please.net> >>>> wrote: > >>>>> How does an emitter follower do anything useful if the base is tied to >>>>> ground? > >>>> I said "bypassed to ground." But an emitter follower can certainly >>>> work, and oscillate, if its base is really grounded. > >>> How? There's no signal on the base. > >> Just pull the emitter negative with a resistor or a current sink. That >> can make a nice UHF oscillator. > > Might as well just ground the base. But that's not an emitter follower, as > you stated in your first post. There's no place to put a signal.The signal doesn't have to be fast, and the bypass doesn't have to be slow. Its impedance only matters up near the instability. And reset circuits and cap multipliers are very useful.> > Just put a proper value resistor in series with the base. It won't oscillate. > But it's still not an emitter follower. >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 ●October 6, 20182018-10-06
On 10/5/18 9:36 PM, George Herold wrote:> On Friday, October 5, 2018 at 5:26:37 PM UTC-4, John Larkin wrote: >> On Fri, 5 Oct 2018 10:40:12 -0400, Phil Hobbs >> <pcdhSpamMeSenseless@electrooptical.net> wrote: >> >>> On 10/4/18 11:09 PM, Steve Wilson wrote: >>>> John Larkin <jjlarkin@highland_snip_technology.com> wrote: >>>> >>>>> On Thu, 4 Oct 2018 08:39:11 -0700 (PDT), Steve Wilson >>>>> <9fe142ac@gmail.com> wrote: >>>>>> I hope that anyone playing with 42GHz GBW would automatically add a base >>>>>> resistor to kill parasitic oscillations. Even a lowly 2N3904 can go into >>>>>> parasitics with a long base lead. >>>> >>>>> Or as an emitter follower with the base well bypassed to ground. The >>>>> wire bonds inside are nice high-Q inductors. >>>> >>>> How do you make an emitter follower when the base is bypassed to ground? >>>> Where do you put the signal? >>>> >>> >>> The classical example is the one-transistor !RESET generator, which is a >>> slow RC with an emitter follower. >> > It oscillates because of a slow edge and no hysteresis?If you put a resistor in series with the emitter, the reflected impedance at the base is a negative resistance. If that becomes larger than the extrinsic base resistance, the thing becomes unstable. The parasitic Ls and Cs help set the oscillation frequency, but even without them, the transistor becomes a relaxation oscillator.> Is it similar to cap. multiplier oscillations? > (do all single transistor circuits map onto each other?)It is precisely a cap multiplier. ;) 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 ●October 6, 20182018-10-06
On 10/5/18 10:28 PM, Steve Wilson wrote:> George Herold <gherold@teachspin.com> wrote: > >> It oscillates because of a slow edge and no hysteresis? > > It oscillates because of inductance in the base lead. Along with the base- > emitter capacitance and capacitance from the emitter to ground, this forms > a Colpitts oscillator, which is one of the most vigorous oscillators known. > It can accept an extremely wide range of parameters and still oscillate. > > The purpose of the resistor in the base lead is to dampen the Q of the tank > so oscillations are no longer possible. > >> Is it similar to cap. multiplier oscillations? > > Could be. Any place where you have some inductance in the base and > capacitance from the emitter to ground could form a Colpitts, especially > where you have some inductance in the emitter lead.The key ingredient is negative input resistance. 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 ●October 6, 20182018-10-06
Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net> wrote:> On 10/5/18 10:28 PM, Steve Wilson wrote: >> George Herold <gherold@teachspin.com> wrote:>>> It oscillates because of a slow edge and no hysteresis?>> It oscillates because of inductance in the base lead. Along with the >> base- emitter capacitance and capacitance from the emitter to ground, >> this forms a Colpitts oscillator, which is one of the most vigorous >> oscillators known. It can accept an extremely wide range of parameters >> and still oscillate.>> The purpose of the resistor in the base lead is to dampen the Q of the >> tank so oscillations are no longer possible.>>> Is it similar to cap. multiplier oscillations?>> Could be. Any place where you have some inductance in the base and >> capacitance from the emitter to ground could form a Colpitts, >> especially where you have some inductance in the emitter lead.> The key ingredient is negative input resistance.That term always bothered me. Negative input resistance to what? If you look a the base input impedance, it is always positive. When the oscillations get going, the transistor is cut off most of the time. Where is the negative input impedance then? The key ingredient is positive feedback. Say the emitter generates a voltage that is fed into the tank. The capacitive divider generates a voltage on the base that is higher than the emitter. The emitter follower operation means the voltage fed to the capacitive divider is larger than the original. Positive feedback. Oscillations ensue.> Cheers> Phil Hobbs
Reply by ●October 6, 20182018-10-06
On 10/6/18 3:03 PM, Steve Wilson wrote:> Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net> wrote: > >> On 10/5/18 10:28 PM, Steve Wilson wrote: >>> George Herold <gherold@teachspin.com> wrote: > >>>> It oscillates because of a slow edge and no hysteresis? > >>> It oscillates because of inductance in the base lead. Along with >>> the base- emitter capacitance and capacitance from the emitter to >>> ground, this forms a Colpitts oscillator, which is one of the >>> most vigorous oscillators known. It can accept an extremely wide >>> range of parameters and still oscillate. > >>> The purpose of the resistor in the base lead is to dampen the Q >>> of the tank so oscillations are no longer possible. > >>>> Is it similar to cap. multiplier oscillations? > >>> Could be. Any place where you have some inductance in the base >>> and capacitance from the emitter to ground could form a >>> Colpitts, especially where you have some inductance in the >>> emitter lead. > >> The key ingredient is negative input resistance. > > That term always bothered me. Negative input resistance to what? If > you look a the base input impedance, it is always positive.No, it isn't. YCLIU.> When the oscillations get going, the transistor is cut off most of > the time. Where is the negative input impedance then?Present during the conduction angle. The amplitude limits where the average gain around a cycle equals unity.> > The key ingredient is positive feedback. Say the emitter generates a > voltage that is fed into the tank. The capacitive divider generates > a voltage on the base that is higher than the emitter. The emitter > follower operation means the voltage fed to the capacitive divider is > larger than the original. Positive feedback. Oscillations ensue.A Colpitts network is one way of generating a negative input resistance, but it can also happen inside the transistor die. The B-E capacitance and the 1/f dependence of beta put two lags in the R_E -> R_b transformation, so it comes out negative. 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 ●October 6, 20182018-10-06
On Friday, October 5, 2018 at 10:28:43 PM UTC-4, Steve Wilson wrote:> George Herold <gherold@teachspin.com> wrote: > > > It oscillates because of a slow edge and no hysteresis? > > It oscillates because of inductance in the base lead. Along with the base- > emitter capacitance and capacitance from the emitter to ground, this forms > a Colpitts oscillator, which is one of the most vigorous oscillators known. > It can accept an extremely wide range of parameters and still oscillate. > > The purpose of the resistor in the base lead is to dampen the Q of the tank > so oscillations are no longer possible. > > > Is it similar to cap. multiplier oscillations? > > Could be. Any place where you have some inductance in the base and > capacitance from the emitter to ground could form a Colpitts, especially > where you have some inductance in the emitter lead.My first (or second) cap multiplier oscillated and I added a F-bead and 100 ohm resistor on the base lead, through hole hair-pin. No problems since then. George H.> > Other configurations where fast transistors are connected together could > become an oscillator. Some examples are: > > Cascode > Darlington > Sziklai pair > etc > > > (do all single transistor circuits map onto each other?) > > The various configurations of the Colpitts are basically the same. It's > just where you put the ground that makes them look different. > > The difficulty with the Colpitts is it loves to oscillate. The conditions > are layout-dependent and dependent on the gain and bandwidth of the > transistor. The oscillations can completely destroy the desired performance > of the circuit. > > My approach is to assume the circuit will oscillate under the right > conditions, and to include a resistor in the base in all critical circuits > that could be susceptible to parasitics. After a while, you get to know > what value would be appropriate, usually from 5 to 50 ohms. But check > carefully. > > This creates a problem. Often the oscillation frequency is far above the > frequency range of the best equipment available in your lab. To compensate, > you need some way to perturb the circuit and look for any change in the > operating parameters. One method is to use a dental pick which is available > at most pharmacies. This is a small stainless hook imbedded in plastic, > with a cover to fit over the top. You can touch various points in the > circuit an see if you can detect any change in the operataion. > > The best by far is a wideband spectrum analyzer. You can make a small loop > feeding a coax cable to the analyzer. Bring the loop near the circuit. any > oscillation should become visible in the display. > > Of course, with modern transistors, especially SiGe, you need a very high > frequecy specctrum analyzer. These are not cheap. > > > George H.
Reply by ●October 6, 20182018-10-06
On Saturday, October 6, 2018 at 2:45:29 PM UTC-4, Phil Hobbs wrote:> On 10/5/18 9:36 PM, George Herold wrote: > > On Friday, October 5, 2018 at 5:26:37 PM UTC-4, John Larkin wrote: > >> On Fri, 5 Oct 2018 10:40:12 -0400, Phil Hobbs > >> <pcdhSpamMeSenseless@electrooptical.net> wrote: > >> > >>> On 10/4/18 11:09 PM, Steve Wilson wrote: > >>>> John Larkin <jjlarkin@highland_snip_technology.com> wrote: > >>>> > >>>>> On Thu, 4 Oct 2018 08:39:11 -0700 (PDT), Steve Wilson > >>>>> <9fe142ac@gmail.com> wrote: > >>>>>> I hope that anyone playing with 42GHz GBW would automatically add a base > >>>>>> resistor to kill parasitic oscillations. Even a lowly 2N3904 can go into > >>>>>> parasitics with a long base lead. > >>>> > >>>>> Or as an emitter follower with the base well bypassed to ground. The > >>>>> wire bonds inside are nice high-Q inductors. > >>>> > >>>> How do you make an emitter follower when the base is bypassed to ground? > >>>> Where do you put the signal? > >>>> > >>> > >>> The classical example is the one-transistor !RESET generator, which is a > >>> slow RC with an emitter follower. > >> > > It oscillates because of a slow edge and no hysteresis? > If you put a resistor in series with the emitter, the reflected > impedance at the base is a negative resistance. If that becomes larger > than the extrinsic base resistance, the thing becomes unstable. The > parasitic Ls and Cs help set the oscillation frequency, but even without > them, the transistor becomes a relaxation oscillator. > > > Is it similar to cap. multiplier oscillations? > > (do all single transistor circuits map onto each other?) > > It is precisely a cap multiplier. ;)Right. cap multiplier is a high-side emitter follower. Thanks, George H.> > 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 ●October 6, 20182018-10-06
Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net> wrote:> On 10/6/18 3:03 PM, Steve Wilson wrote: >> That term always bothered me. Negative input resistance to what? If >> you look a the base input impedance, it is always positive.> No, it isn't. YCLIU.A simple LTspice measurement shows the base impedance is always positive. Can you supply a simple LTspice analysis showing negative input resistance? There are many sites using the term negative input resistance. None of them explain why adding a resistor in series with the tank kills the oscillations. You still haven't defined negative input resistance with respect to any point in the circuit.>> When the oscillations get going, the transistor is cut off most of the >> time. Where is the negative input impedance then?> Present during the conduction angle.LTspice shows the input impedance of the base is positive at the peak of the cycle.> The amplitude limits where the > average gain around a cycle equals unity.You have just confirmed my positive feedback argument. The loop gain goes to unity. Oscillations cease increasing when they hit a limit, such as base voltage above VCC. It can't go any further.>> The key ingredient is positive feedback. Say the emitter generates a >> voltage that is fed into the tank. The capacitive divider generates >> a voltage on the base that is higher than the emitter. The emitter >> follower operation means the voltage fed to the capacitive divider is >> larger than the original. Positive feedback. Oscillations ensue.> A Colpitts network is one way of generating a negative input resistance, > but it can also happen inside the transistor die. The B-E capacitance > and the 1/f dependence of beta put two lags in the R_E -> R_b > transformation, so it comes out negative.You still haven't defined negative input resistance with respect to what? You can add external capacitors to form the tank. The result is the same. The emitter follower signal is in phase with the signal on the base. Consider a 74H04 Pierce oscillator with a LC tank feedback. The input impedance of the 74H04 is capacitive. By the energy equation, E = (CV^2) / 2, the impedance is always positive. Where is the negative input impedance? How do you measure it?> Cheers > > Phil Hobbs >
