Just because you can divide two things that are in the same units, and convert the result to bits, doesn't mean you should!
-- John Larkin Highland Technology, Inc jlarkin att highlandtechnology dott com http://www.highlandtechnology.com
Yes, but they can do this without having to eat every 5 minutes.
-- Rick
Interestingly, the cheapest - Mouser sells if for $18 one off - Analog Devices DDS chip that can accept a 155.52MHz reference frequency input
does offer a non-binary modulus. The application note doesn't spell out how you work out what to use - the reader is referred to AN-953 - but the accumulator is 32-bits wide, so there won't be any long term phase creep.
Your $18 only buys you a 10-bit DAC, but for a situation where the stair-case approximation to the desired 10MHz sine wave only has 15.552 steps per cycle - ie either 15 or 16 with slightly more 16 than 15 -
10-bits should be plenty.A single pole low pass filter will turn the steps into exponential segments. Adding a second pole could allow you to add enough ringing to improve this - perhaps down to the noise floor imposed by the 10-bit DAC accuracy.
-- Bill Sloman, Sydney
Curiously, I found John Miles' (KE5FX) website looking for microwave stuff, and he's posted data on excess noise added by a 74AC04 ... about 12dB.
The tutorial looks promising, but the equations are rendered as ASCII integers.
The base-Q-loading doesn't apply for VHF oscillators--they're common-base.
At great personal peril, for the benefit of the group I descended into the dungeon, fetched the Matthys articles, and fled.
Matthys and another guy, Belcher, report loaded, in-circuit Qs of 70K - 80K for 5th-overtone 100MHz quartz crystal harmonic oscillators.
The technique is to run the rock series-resonant, and load it with a common-base stage's emitter. Drive comes to the xtal's other terminal from the collector via a simple network.
The effective resistance of the load being super-low, the ESR (namely, the dissipative loss) added to the crystal is minimized, and Q maintained.
I scanned Matthys' articles to .PDF, if anyone wants them. [1] Crystal Oscillator Circuits for VHF, Robert Matthys, RF Designm May/June 1983 p62 [2] A High-Performance VHF Crystal Oscillator Circuit, Robert Matthys, RF Design, March 1987, p31-38
Here's a web-accessible example from Wenzel:
(Wenzel's main site (and business) is full of the finest XO's made:
(John could just talk to Wenzel for the VCXO and / or crystal.)
Given VCOs with resonators of Q>=70K+, that translates to a crystal 3dB passband on the order of 2-3KHz @ 155MHz. I'm not immediately sure if that means 80KHz phase comparisons are enough to keep it on track, but at least it doesn't look ridiculous...
I mentioned microwave bricks...KE5FX has a schematic for one here:
(thanks KE5FX !)
It uses an ovenized VHF crystal XO to drive an SRD + schottky-sampler phase detector, which samples the 10GHz cavity oscillator.
Putting those pieces together, if the VCXO is up to it, with a little twist that could translate into this architecture to solve John's problem:
Master Oscillator 80 .- - - - - - - - - - - - - -. .----. KHz | |
10MHz >---|/125|------------. ' '----' | v VCXO | ' .---. .---. .---. ' | .->|_/_|-->|LPF|->| ~ |-+---> 155.52MHz | | '---' '---' '---' | | ' | sampler | ' | '-----------------------' | '- - - - - - - - - - - - - -' Croven's website has a brutally cute version using a 74ac240 as a sampler!As Gerhard said though, the schottky sampler's noise would be a lot lower than the 74ac240. As I recall, it's hard to beat a schottky mixer for anything, ever, period.
Okay, that's more than enough food for thought!
Cheers, James Arthur
Indeed I should, hence the curiosity! :-)
Cheers, James
In general, I agree that the most practical way to get a filter design is to use the standard closed form techniques. I have many of them built into SuperSpice. Press the button and it places the filter on the schematic.
However... I have come across research in evolution genetic algorithms that have "designed" impressive filters by that select, replicate, random variation, process. Component connection topologies pop up in the most unusual configurations.
Modern filter theory came about by the objective of obtaining closed form solutions to construct filters of arbitrary order, before computers were available. It turns out, that selecting a topology, then running an optimiser to get the component values to get a filter response to match a given frequency/phase profile, will, essentially, always get you a better match than a standard filter. Standard filters are mainly used for convenience.
Kevin Aylward
I would like copies. Can you upload them to some file host?
Thanks
On a sunny day (Fri, 19 Sep 2014 21:58:16 -0700 (PDT)) it happened snipped-for-privacy@yahoo.com wrote in :
Nice.
Microwaves... If you want a free running oscillator, then the litte ceramic pucks in the satellite LNBs are 9.something and 10.something GHz, and have really really low noise. The little yellowish disks on the right:
You can bring these down in frequency by mechanical loading, for example by gluing some parts of a broken one on it. So mechanical vibrations at 10 GHz, and cheap. One project on the table here is converting a standard LNB to a transmitter for the 10.5 GHz ham band, DVB-S. This is done by changing the input and output of the 10 GHz pre-amp so it drives the horn, and is fed from the (ring diode) mixer. Very low power that is. And all is very very low phase noise, even after mixing up with those pucks.
Von Braun went to the moon and back without simulations. There is a large number of companies that try to sell C++ compilers and simulators and what not, kids (say students) - are indoctrinated with it. And where does it go? Not even to the ISS. Inferior color system in the US, most decisions politically based, if not all. Bloatware no end, quad cores to read your email. Side effect of capitalism I guess, production of ever more crap. It WILL collapse.
And those fusion lasers, chances are same as winning the euromillions.
Never the main reason for the set-up - it's actual job, as a opposed to the PR window-dressing, has always been nuclear weapons testing and maintenance.
-- Bill Sloman, Sydney
I never said I understand the design. In fact I have been asking others to explain it. Instead I get idiotic replies like this one from people who are just too dysfunctional to actually be people. I think this point is clearly illustrated by your compulsion to reply with derisive comments rather than just not replying at all or, God forbid, offering some insight into how the circuit actually works.
My previous reply assumed the problem was you didn't understand the circuit either. I guess maybe that is not true, you just can't bring yourself to actually be of some assistance to someone.
-- Rick
On a sunny day (Sat, 20 Sep 2014 20:42:28 +1000) it happened Bill Sloman wrote in :
Now I am curious, how do you test nukes by imploding a pellet of ?? with lasers? US has plenty nukes, some need fresh plutonium I've read.. Maybe some more recent electronics, would make me feel safer. :-)
"Fresh plutonium"? Perhaps tritium but Pt doesn't go "stale" (in hundreds of our lifetimes).
Microsoft nukes? Google nukes? They seem to be fine, just as they are.
Brings a new meaning to the "blue screen of death".
On a sunny day (Sat, 20 Sep 2014 10:33:44 -0400) it happened "Tom Miller" wrote in :
Yep. They already tested that in some warship a while back. it no longer moved.
The Yorktown, an Aegis Cruiser, about 100 miles off Newport News, Virginia.
Immediate cause was that somebody in the Engine Room accidentally entered a zero in a field of a screen about pump performance, causing Windows NT to crash, and take the network down with it.
No propulsion, steering, sensors, or weapons. They were drifting for a few hours. Had to reboot the ship.
No damage to ship or crew. But the Captain still wakes up screaming.
The idea of using Windows NT for anything mission-critical and/or safety-critical died of injuries received in The Yorktown Incident.
Joe Gwinn
.
I was on a flight home from Detroit recently, when a similar thing happened. Just before the pilot pushed back from the gate, there was an engine warning light. After much consultation with the mechanics, they did a cold-restart of the airplane. The problem went away, at least long enough to get me home.
One only hopes.
That's a true statement if I've ever heard one.
ChesterW
On Sat, 20 Sep 2014 10:18:42 -0400, snipped-for-privacy@attt.bizz Gave us:
LANL X-Rays nukes to determine ongoing efficacy claims.
It is a long standing, decades old, regular test program.
On Sat, 20 Sep 2014 11:29:48 -0400, Joe Gwinn Gave us:
An application causing a hard kernel crash? NO!
A workstation locking up a network?
Bet no ship operates its network that way any more.
The trick with LC filters is to use standard value Ls and Cs. That's a good opportuity for massive frobbing.
More fun if you allow series and parallel parts.
-- John Larkin Highland Technology, Inc jlarkin att highlandtechnology dott com http://www.highlandtechnology.com
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