On 8/4/20 12:39 pm, Gerhard Hoffmann wrote:> Am 08.04.20 um 03:05 schrieb Clifford Heath: >> On 7/4/20 11:03 pm, George Herold wrote: >>> On Monday, April 6, 2020 at 7:32:00 PM UTC-4, Clifford Heath wrote: >>>> George, I'm trying to understand this. What do you need 20 zeners for? >>>> >>>> FWIW, I'm currently making a broadband noise source for testing filters >>>> up to 1.5GHz. Still scratching around for the best source to put before >>>> a string of ERA-3 MMIC amplifiers. >>>> >>>> The BFR93A data sheet says abs max Vbe is 2V, but it doesn't zener at >>>> 5V. Although avalanche zeners produce much more noise, I'd rather not >>>> boost my 5V supply (though I might need to). I wonder how much reverse >>>> current a microwave Shottky diodes (say HSMS-286) would survive. Abs >>>> max >>>> peak reverse voltage is 4V, so it might withstand 5V anyway... >>>> >>>> Any better suggestions for a device I might have in the drawer already? >>>> >>>> Clifford Heath. >>> >>> Arghh! typo. sorry a 20V zener! Run near the knee you get these big >>> avalanche spikes, with ~1us rise/ fall times. >>> >>> 1 GHz noise sounds hard. >> >> It doesn't look hard, a lot of people have done it. I've built the >> amplifier, I just need a noise diode that will give me me 20db ENR or >> better to feed into it. The only zeners I can easily get are 1W and >> above, so have big capacitance, only good for audio. I need a >> physically small device that will have low capacitance. That's why I >> started with a GHz transistor. >> >> I've thought about trying an HSMS286 series microwave Schottky, which >> break down at about 4V (if the data sheet is to be believed). The >> literature says that devices with a sharp breakdown curve last longer >> - a soft curve indicates partial breakdown at the edge of the die, >> which leads to early failure. So I'll need to evaluate the sharpness >> of the breakdown to see if it's likely to last a while. >> >> But first I'm going to crank the Vbe on this BFR93A to see where it >> really breaks down. If I can get it to zener on w 12v supply, that'll >> probably do. >> >> I'd prefer not to need a higher supply voltage, but I might have to >> compromise on that. Pure zener noise (low voltage) is much lower >> amplitude than higher-voltage devices which have avalanche >> multiplication. > > I have done that thing with the BFR93A many years ago...> Today I would not use a "Zener" source. If you have them, spend > 2 more ERAs and amplify the noise of a 50 Ohm resistor. Yes, they > have a noise figure of a few dB but you know it and it's flat. > More flat than a BFR93A breakdown, and much better than any > Z-diode with its huge capacitance. 1K may produce more voltage noise, > but @ 50 Ohms you know that the ERAs will behave.Well I've done quite a bit of mucking around with 4 ERA-3's (96dB gain!) and nothing I've tried will stop it from oscillating. Because I used 33nF coupling caps, with the 50R matched impedance it oscillates about 200-300kHz. During the few occasions where it was well-behaved I got really nice looking noise from the resistor source, with most of the density within 20mV of the origin, and a scope trace that barely changed in appearance between 10ms/div right up to 5ns/div. It was all looking pretty ok for a while actually, until I noticed some noise spikes from the fan in my PSU getting to the output, so in addition to the 220nF decoupling caps on each stage, I added a 10uF aluminium electrolytic - and since I added that it takes off like a rocket at any bias level above 15mA. I had to reduce the bias current below the recommended 40mA, because the maximum input level (13dBm) is just below the maximum output level (13.6dBm), and when it oscillates at full power that was enough to blow up MMIC 3&4 in the chain. Reduced current stopped them expiring, but doesn't stop the oscillation. I tried a small can over the first stage but suspect the feedback path is on the board. An inductor in series with the first stage bias might help? Pictures here (the noise is with the zener source): <https://www.dropbox.com/sh/v9h6p7ajtvyllng/AAD9Y69UpRU1o1yMQgUuxMpxa?dl=0> You can see I used generic grid-punch prototyping PCB, with adhesive copper foil to make a ground plane on the back. I think I'll just drop back to the zener source, two stages, and call it done... unless someone else has a better idea? Clifford Heath.
Favourite parts with off-label uses?
Started by ●April 4, 2020
Reply by ●April 13, 20202020-04-13
Reply by ●April 13, 20202020-04-13
On 13/04/2020 08:12, Ricky C wrote:> On Sunday, April 12, 2020 at 6:03:01 PM UTC-4, Jasen Betts wrote: >> On 2020-04-12, George Herold <ggherold@gmail.com> wrote: >>> On Saturday, April 11, 2020 at 5:38:40 PM UTC-4, Joe Gwinn wrote: >>>> On Tue, 7 Apr 2020 07:55:27 -0400, Phil Hobbs >>>> <pcdhSpamMeSenseless@electrooptical.net> wrote: >>>> >>>>> On 2020-04-06 21:35, jlarkin@highlandsniptechnology.com wrote: >>>>>> On Mon, 6 Apr 2020 17:43:46 -0400, Phil Hobbs >>>> [snip] >>>>>> >>>>>> I guess the seive would soak up humidity and reduce the pressure >>>>>> inside, so a tiny flow through the seals would introduce a little more >>>>>> humidity. Wouldn't that eventually get to zero humidity and zero >>>>>> pressure differential? >>>>>> >>>>>> I guess atmospheric changes would still pump the system slightly. >>>>> >>>>> Simon's the seal expert at this point. A sufficiently stiff box, with >>>>> enough screws holding the lid on, and hermetic connectors, ought to be >>>>> able to stay sealed pretty well. The pressure changes are nontrivial >>>>> though--our box is about 3 x 5 inches, so a 7% pressure change amounts >>>>> to about 15 pounds over the surface of the lid. They're also fairly >>>>> slow, so it doesn't take much of a leak rate to equalize the pressure. >>>>> >>>>> We're using a cable gland rather than a hermetic connector, primarily >>>>> for cost reasons. I suspect that enough air will flow inside the cable >>>>> to manage the vent job, but we'll probably have to measure that to find out. >>>> >>>> A traditional alternative is a long thin tube whose volume is >>>> sufficient to ensure that no inside air gets out or outside air gets >>>> in, despite the +/- 7% variation in ambient air pressure. Invented by >>>> Louis Pasteur in 1859. >>>> >>>> .<https://en.wikipedia.org/wiki/Swan_neck_flask> >>>> >>>> >>>> Joe Gwinn >>> >>> Nice, I was trying to express this idea, but I was more focused on >>> keeping the length of the tube long to limit diffusion of the H2O. >>> >>> George H. >> >> >> With minimally vented or imperfectly sealed enclosure you have the >> problem that if it gets splashed with cold water on a hot day it >> cools rapdily and the air inside contracts and sucks surface water >> in. >> >> Using the cable to vent the enclosure seems like a good scheme, >> assuming that air flows freely enough and it terminates in a dry >> location. > > Talking with hams it seems they never trust sealing to keep an enclosure free of moisture. After reading about a defect in a auto brake pressure switch impacting something else at the other end of the car I realized why. The pressure switch was sealed, but the switch itself developed a leak, not to the outside, but to the also enclosed space with the wire which wicked it into the spaces between the strands. The brake fluid was carried to the other end of the vehicle where it came in contact with something that it then messed up. > > So if you have any insulated wires exiting a sealed enclosure, in the long term it is not sealed. I guess that's why they use those through the bulkhead solid pins to pass signals in and out of a sealed box. >You can get cable with all of the spaces between the strands etc. filled not with air, but with some sort of gel. Very messy but probably worthwhile if you need a cable to be buried and want it to stay free of liquid water.
Reply by ●April 13, 20202020-04-13
On 2020-04-04 20:49, pcdhobbs@gmail.com wrote:> Following up on blocher's sterling work,(*) > > Many of us use parts off-label, often very successfully. A few examples: > > SAV-551+ pHEMTs make very good wideband bootstraps. Their f_max is around 12 GHz, but they're amazingly stable. > > 74HC4352s make good flying-capacitor diff amp front ends. > > TMUX1511s make very nice analogue lock-ins--their Coff*Ron FOM is almost in a class with relays, but 1E5 times faster. > > Zero-ohm jumpers have about the right resistance to stabilize LDO regulators with ceramic output caps. (It's good to be able to disconnect the supplies during bring-up, and putting the jumper between the reg and the output cap has this additional benefit. > > Your faves?Back when there were more analogue RF building-block chips available, I used to get about 40X speedup by cascoding their RSSI current outputs. I made an interesting lidar-style 3D scanner that way, using current-tuning of a diode laser plus a diffraction-grating gizmo to provide both a fast fine scan (20 pixels worth) and a triangle-wave FM waveform. The tri wave lets you measure both time-of-flight and Doppler, because their frequency offsets add on one slope and subtract on the other. In lots of situations you can get excellent results by connecting a photodiode directly to the input of an MMIC amp with no coupling cap. The input is usually within a factor of 2 of 50 ohms, and the noise temperature may be as low as 100K. Cascoding a solar cell can get you up to about 100 kHz bandwidth with unbeatable detection area and good linearity at high current. Gate drivers are good for running small Cockroft-Walton generators for PMTs or APDs. Some depletion pHEMTs will self-bias with the gate below the source, so you can use them with no bias resistors. For the lowest-noise applications, that saves some input capacitance, which helps. (You can't get them anymore, unfortunately.) The monitor photodiode of a diode laser can be used as a temperature sensor--it's brazed to the same header as the laser, so it's super fast. A quadrant photodiode will give a nice beam position indicator that's independent of the laser power if you just add and subtract diagonally opposite pairs of open circuit voltages. 1 | 2 ----- 3 | 4 X = (1-4) - (2-3) Y = (1-4) + (2-3) 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 ●April 13, 20202020-04-13
On Mon, 13 Apr 2020 11:34:41 -0400, Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net> wrote:>On 2020-04-04 20:49, pcdhobbs@gmail.com wrote: >> Following up on blocher's sterling work,(*) >> >> Many of us use parts off-label, often very successfully. A few examples: >> >> SAV-551+ pHEMTs make very good wideband bootstraps. Their f_max is around 12 GHz, but they're amazingly stable. >> >> 74HC4352s make good flying-capacitor diff amp front ends. >> >> TMUX1511s make very nice analogue lock-ins--their Coff*Ron FOM is almost in a class with relays, but 1E5 times faster. >> >> Zero-ohm jumpers have about the right resistance to stabilize LDO regulators with ceramic output caps. (It's good to be able to disconnect the supplies during bring-up, and putting the jumper between the reg and the output cap has this additional benefit. >> >> Your faves? > >Back when there were more analogue RF building-block chips available, I >used to get about 40X speedup by cascoding their RSSI current outputs. > >I made an interesting lidar-style 3D scanner that way, using >current-tuning of a diode laser plus a diffraction-grating gizmo to >provide both a fast fine scan (20 pixels worth) and a triangle-wave FM >waveform. >The tri wave lets you measure both time-of-flight and Doppler, because >their frequency offsets add on one slope and subtract on the other.WWII vintage bomber radio altimeters worked that way. Send a CW carrier that's triangle FM modulated, and mix the transmit and ground echo signals. The beat frequency is proportional to altitude.> >In lots of situations you can get excellent results by connecting a >photodiode directly to the input of an MMIC amp with no coupling cap. >The input is usually within a factor of 2 of 50 ohms, and the noise >temperature may be as low as 100K.I just did that in my new GHz o/e converter. The DC behavior of the MMIC is dreadful, so I have a separate low-frequency gain path to get clean DC-coupled step response. MMICs have a lot of personality. You've got to test them to find out what. And hope MiniCircuits doesn't switch fabs. -- John Larkin Highland Technology, Inc Science teaches us to doubt. Claude Bernard
Reply by ●April 14, 20202020-04-14
On 13/4/20 4:25 pm, Clifford Heath wrote:> On 8/4/20 12:39 pm, Gerhard Hoffmann wrote: >> Am 08.04.20 um 03:05 schrieb Clifford Heath: >>> On 7/4/20 11:03 pm, George Herold wrote: >>>> On Monday, April 6, 2020 at 7:32:00 PM UTC-4, Clifford Heath wrote: >>>>> George, I'm trying to understand this. What do you need 20 zeners for? >>>>> >>>>> FWIW, I'm currently making a broadband noise source for testing >>>>> filters >>>>> up to 1.5GHz. Still scratching around for the best source to put >>>>> before >>>>> a string of ERA-3 MMIC amplifiers. >>>>> >>>>> The BFR93A data sheet says abs max Vbe is 2V, but it doesn't zener at >>>>> 5V. Although avalanche zeners produce much more noise, I'd rather not >>>>> boost my 5V supply (though I might need to). I wonder how much reverse >>>>> current a microwave Shottky diodes (say HSMS-286) would survive. >>>>> Abs max >>>>> peak reverse voltage is 4V, so it might withstand 5V anyway... >>>>> >>>>> Any better suggestions for a device I might have in the drawer >>>>> already? >>>>> >>>>> Clifford Heath. >>>> >>>> Arghh! typo. sorry a 20V zener! Run near the knee you get these big >>>> avalanche spikes, with ~1us rise/ fall times. >>>> >>>> 1 GHz noise sounds hard. >>> >>> It doesn't look hard, a lot of people have done it. I've built the >>> amplifier, I just need a noise diode that will give me me 20db ENR or >>> better to feed into it. The only zeners I can easily get are 1W and >>> above, so have big capacitance, only good for audio. I need a >>> physically small device that will have low capacitance. That's why I >>> started with a GHz transistor. >>> >>> I've thought about trying an HSMS286 series microwave Schottky, which >>> break down at about 4V (if the data sheet is to be believed). The >>> literature says that devices with a sharp breakdown curve last longer >>> - a soft curve indicates partial breakdown at the edge of the die, >>> which leads to early failure. So I'll need to evaluate the sharpness >>> of the breakdown to see if it's likely to last a while. >>> >>> But first I'm going to crank the Vbe on this BFR93A to see where it >>> really breaks down. If I can get it to zener on w 12v supply, that'll >>> probably do. >>> >>> I'd prefer not to need a higher supply voltage, but I might have to >>> compromise on that. Pure zener noise (low voltage) is much lower >>> amplitude than higher-voltage devices which have avalanche >>> multiplication. >> >> I have done that thing with the BFR93A many years ago... > >> Today I would not use a "Zener" source. If you have them, spend >> 2 more ERAs and amplify the noise of a 50 Ohm resistor. Yes, they >> have a noise figure of a few dB but you know it and it's flat. >> More flat than a BFR93A breakdown, and much better than any >> Z-diode with its huge capacitance. 1K may produce more voltage noise, >> but @ 50 Ohms you know that the ERAs will behave.> Well I've done quite a bit of mucking around with 4 ERA-3's (96dB gain!) > and nothing I've tried will stop it from oscillating.Oh never mind. It just needed (much) better supply decoupling at the sensitive end. Working a treat now. Spectrum analysis next. Clifford Heath.
Reply by ●April 14, 20202020-04-14
jla...@highlandsniptechnology.com wrote: ---------------------------------------> > WWII vintage bomber radio altimeters worked that way. >** Few WW2 bombers ever had them. Only useful at low altitudes as a blind landing aid. Also for deck landings, which did not involve bombers. .... Phil
Reply by ●April 14, 20202020-04-14
понедельник, 13 апреля 2020 г., 18:34:49 UTC+3 пользователь Phil Hobbs написал:> A quadrant photodiode will give a nice beam position indicator that's > independent of the laser power if you just add and subtract diagonally > opposite pairs of open circuit voltages. > > 1 | 2 > ----- > 3 | 4 > > X = (1-4) - (2-3) > Y = (1-4) + (2-3) >Erratum ? INA330 with current output in simple PID controlled TEC (TO-8) http://ixbt.photo/?id=photo:1337088 Internal gate-source zener FDV301N in zerocross detector 100Hz http://ixbt.photo/?id=photo:1097722 http://ixbt.photo/?id=photo:748178
Reply by ●April 14, 20202020-04-14
On 13.4.20 18:58, jlarkin@highlandsniptechnology.com wrote:> > WWII vintage bomber radio altimeters worked that way. Send a CW > carrier that's triangle FM modulated, and mix the transmit and ground > echo signals. The beat frequency is proportional to altitude.That is how the airliner radio altimeters still work. -- -TV
Reply by ●April 14, 20202020-04-14
Tauno Voipio <tauno.voipio@notused.fi.invalid> wrote in news:r7505i$5on$1@dont-email.me:> On 13.4.20 18:58, jlarkin@highlandsniptechnology.com wrote: >> >> WWII vintage bomber radio altimeters worked that way. Send a CW >> carrier that's triangle FM modulated, and mix the transmit and >> ground echo signals. The beat frequency is proportional to >> altitude. > > > That is how the airliner radio altimeters still work. >Marker beacons are similar but very nearly outmoded by GPS. <https://en.wikipedia.org/wiki/Marker_beacon> They have a sound of each indicator. Pretty cool.
Reply by ●April 14, 20202020-04-14
Laser self-mixing "radar" with triangle injection current Measuring Absolute Distance by Linear Frequency Sweeping https://www.osapublishing.org/aop/fulltext.cfm?uri=aop-7-3-570 Laser feedback interferometry: a tutorial on the self-mixing effect for coherent sensing
