On 14.4.20 23:42, DecadentLinuxUserNumeroUno@decadence.org wrote:
> 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.
Sorry, no.
A marker beacon is an A2A modulated 75 MHz signal, sent
directly upward from the beacon station, with a power of
a few watts. The receiver just listens to the signal and
decides, based on the modulating frequency, which of the
marker indicators to light.
--
-TV
Reply by George Herold●April 14, 20202020-04-14
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.
Hmm well not the cable (carrying wires). I was
picturing a long tube on the vent... it could be coiled
inside the box.
So here's a 'back of the envelope' calculation question.
The diffusion constant of H2O in air (STP) is
about 0.3 cm^2/sec.
https://en.wikipedia.org/wiki/Mass_diffusivity#Example_values
So if I have a 10 cm (long) tube the time it takes for
water to diffuse along it is about 200 seconds.
t = len^2/(2*D). So how then do I calculate the number
of water atoms at steady state that are diffusing
along the tube?
Do I calculate the number of water atoms entering the
front area of the tube, in one second. And then divide
by 200?
George H.
>
> --
> Jasen.
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
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.
>
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
> 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)
>
>
> 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 Clifford Heath●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 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 Phil Hobbs●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.nethttp://hobbs-eo.com