Re: [time-nuts] DDS'ery narrow scoped.
IMHO, that would require a sine table with a steerable number of entries. Very problematic for a tunable DDS, but doable for a fixed frequency application, although address mirroring for ROM size reduction would require real address comparators instead just using the 2 MSBs as a selector. The table could also be in RAM instead of ROM without large increase of the cost in an FPGA, so with some processor support one might approach tunable. regards, Gerhard It crossed my mind of messing somehow with the phase accumulator metrics but did not figure a way... that is a good suggestion I will investigate in that direction... (or maybe... if you do have a bit of free time to drop me a couple of lines more, could you please detail a bit more as so far I did not caught the idea clearly enough to start coding...) On 7/21/2011 9:11 AM, Magnus Danielson wrote: You want to consider a phase-accumulator with a steerable or suitable sequence length. That way you can match up the ratio to form a suitable for the frequency you want and the spurioses will become harmonics so to speak. Such a phase-accumulator gets shortend and takes some comparision of phase-state to translate state at the end of the sequence to the next period. A bit more logic, but comes with some nice properties. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] DDS'ery
There is an excellent article about cordic on http://www.andraka.com/files/crdcsrvy.pdf There are a lot of other good publications on Ray Andraka's web site. I have published a accurate sine/cosine function on www.opencores.org underhttp://opencores.org/project,sincos It is VHDL only. The test bed is a DDS and it can write the generated waves to files for inspection with Matlab. I think I have caught all these off-by-1-LSBs by now. The sine function is ROM-based with size reduction by symmetry. Getting a cos at the same time is free wrt ROMs, just 2 adders more. Pipelining can be selected from combinatorial to 10 stages, depending on your speed requirements. Amplitude and phase resolution is automatically determined by the connected bus. feedback welcome. regards, Gerhard - Original Nachricht Von: li...@lazygranch.com An: Discussion of precise time and frequency measurement time-nuts@febo.com Datum: 20.06.2011 22:26 Betreff: Re: [time-nuts] DDS'ery With the coordic (yeah, sometimes cordic), you need to build it a few more bits wider than the DAC. Then it closely matches the lookup table. One of the best references for the coordic I found was a PhD dissertation at ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] cordic
So then, it's a trade between a big ROM LUT or a bunch o'gates for CORDIC. And for big N the bunch o'gates is probably going to be easier: 16 bit phase and wanting 16 bits out would be a 64kbit ROM (assuming you didn't do the usual thing of only needing 1/4 cycle).. There is also the Sunderland technique that can reduce the table size by a factor of 12 to 50 by splitting the table into 3 small ones and combining them with simple arith. Gerhard ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] An (unknown?) nasty feature of the DDS principle for time nuts applications
Don't forget that your HP3325 is DDS-based, too, so it adds its own phase error sawtooth. 73, Gerhard dk4xp ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] An (unknown?) nasty feature of the DDS principle for time nuts applications
Don't forget that your HP3325 is DDS-based, too, so it adds its own phase error sawtooth. 73, Gerhard dk4xp ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] what is the best way to multiply a 10 Mhz signal?
Von: Stephen Farthing squir...@gmail.com Betreff: [time-nuts] what is the best way to multiply a 10 Mhz signal? I want to multiply the output from my Efratom 101 (10Mhz) to clock a DDS at 70 Mhz. Has anyone tried this? I did 5 MHz * 7 = 35 which is about the same, with CMOS gates and filtering. ( in the style propagated by Wenzel) This took a lot of filtering to get rid of the last spurii. Too much ado. I recommend a 70 MHz VCXO and locking this to the 10 MHz source. regrds, Gerhard ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] New Zealand, Iceland, Haiti
Betreff: Re: [time-nuts] New Zealand, Iceland, Haiti In message 4c8651e7.1080...@att.net, Brooke Clarke writes: All the subject locations are on the edge of the Pacific plate. Iceland ? On the edge of the *Pacific* plate ? Have I missed some serious tektonic activity last night ? Haiti? Gerhard ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Phase noise measurement (was - no subject)
Von: Bob Camp li...@rtty.us If you start with a mixer that runs 500 mV / radian (an RPD-1 at the typical 8 mV / degree + 10%) then -180 below that would be 0.5 nV. Since noise it coherent close in, the DSB to SSB process nets you 1 nV out when you have -180 dbc noise. Adding the two sidebands may double the power, but not the voltage? 73, Gerhard ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Phase noise measurement (was - no subject)
NXP BF862, available from digi-key. Don't these devices have relatively high flicker noise? 1/f corner is well below 100 Hz. Look at the noise voltage plots of that audio guy I cited. My results for the BF862 were the same shape, absolutely somewhat worse in amplitude because I wanted a differential input and less FETs in parallel. Most of my BF862 had abt. 12 mA IDss, btw. The input capacitance is relatively noncritical in this application (phase noise measurement) since it is shunted by the much larger output capacitance of the low pass filter at the mixer IF port. The 300 pF Cin of a single IF3602 could seriously detune the input low pass and the 200 pF feedback capacitance in a stage with substantial voltage gain would destroy the bandwidth unless cascoding is provided. I think, I'll test some Analog Devices ADA9848-2 in parallel. It's hard to beat that combination of noise, 1/f, bandwidth, offset stability and price. Such a preamp can be used as an add-on to a scope or FFT-Analyzer, too, to characterize power supplies, references or oscillator bias circuits. It's fun to enter 60 dB probe gain into a scope channel menu and still see usable traces with uV/div scale factors. ( with a low pass, of course) There are noise nuts, too! ;-) Gerhard One heroic effort for audio is here: http://www.diy-audio-engineering.org/index.php?board=2.0 HPS5.1 ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Phase noise measurement (was - no subject)
I think, I'll test some Analog Devices ADA9848-2 in parallel. It's hard to beat that combination of noise, 1/f, bandwidth, offset stability and price. Oooops, ADA4898-2 http://www.analog.com/en/amplifiers-and-comparators/operational-amplifiers-op-amps/ada4898-2/products/product.html sorry for the confusion, Charles! Gerhard ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Phase noise measurement (was - no subject)
Wenzel Audio Amp referred to in this email. Perfect! I drive with it a 3561A and a 7L5! Works for me. The only problem is getting any more 2SK369. Any recommendations? NXP BF862, available from digi-key. I have used it in a similar hookup with good success. Its virtue is the low noise voltage AND low input capacitance at the same time. You could deploy MANY of them in parallel until you get into the capacitance range of a single Interfet device. One heroic effort for audio is here: http://www.diy-audio-engineering.org/index.php?board=2.0 HPS5.1 I currently use 3 pairs of SSM2210 in front of a AD797. regards, Gerhard ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Phase noise measurement (was - no subject)
to drive a +17 dBm mixer, and then amplify the IF output with a low noise current amplifier like the Linear LT1028. You can easily homebrew low noise _voltage_ ? 73, Gerhard dk4xp ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Notes on the Driscoll VHF Overtone Crystal Oscillator
My understanding is that Chris' variant of this particular Driscoll osc. has been designed specifically for low close-in phase noise, and that is why the phase-shift network has a low-pass response (to try and reduce flicker noise) rather than the more common high-pass network. The NE688xx was chosen for the active devices due to it's claimed low flicker noise; the flicker noise parameters are actually specified on the datasheet for the NE68833 - which is quite unusual. The high Ft may not be desirable, but it seems that is the price to pay for low flicker noise. I've built a couple of oscillators similar to Chris Bartram's design at around 116MHz, albeit with the more conventional 'high-pass' phase shift network, and they seem to perform quite well - certainly no sign of spurious high frequency oscillation, but that may be a function of PCB layout. I'm not aware of anyone yet measuring the close-in phase noise of the Bartram variant of this oscillator, and that's really the only way to verify or otherwise that the new topology gives any advantage in terms of close-in phase noise, compared to a similar, low cost design using similar crystals. When I get a sample in known working condition, I'll stress the friendliness of my customer to get it tested on their signal source analyzer. What we already have seen is that crystals from the same production run may yield up to 15 or 20 dB worse phase noise at 100 Hz than the best. (in the same oscillator) That confirms: Close-in to the carrier, the phase noise is dictated by the resonator. [1] 73, Gerhard DK4XP [1] Grant Moulton: Analysis And Prediction Of Phase Noise In Resonators and Oscillators, HP signal analysis division 1985 http://www.hparchive.com/seminar_notes.htm ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Notes on the Driscoll VHF Overtone Crystal Oscillator
- Original Nachricht Von: Bruce Griffiths bruce.griffi...@xtra.co.nz An: Discussion of precise time and frequency measurement time-nuts@febo.com Datum: 28.12.2009 06:52 An inductor in series with the 220 ohm emitter resistor will improve the phase noise floor. In theory, yes. But already with only 220 Ohms, Q3 will oscillate wildly at a few hundred MHz. The mechanism is this: Somewhat hot RF transistor NE688, collector at RF ground, emitter at high-ish impedance --- When you measure into the base, you see a negative resistance in series with a few pF. Add L6 = 82 nH with the other side at RF ground and you have built the usual negative-impedance VCO for VHF/UHF. The crystal and the intended feedback network just don't matter any more. I should have re-read my own Dubus article on oscillator simulations from 6 years ago before I tried the Distaw. :-( Other people have observed the wild oscillations, too. The MMIC output amplifier has a wider bandwidth than necessary and doesn't have a particularly high reverse isolation. Also, it has 20 dB gain, that alone guarantees a less than ideal far-off noise level. The BAS70 clips at less than 1 V pp, this should be more. Could be easily done in the Rohde style with a decoupled DC divider and one Schottky that points from the divider to the collector circuit. I have changed my own locked VHF crystal oscillator back to Butler - this time single stage with 3* cheap NXP BF862 in parallel, common gate. The gate can be grounded directly, needs no voltage divider and decoupling. Input impedance of the 3 FETs is abt. 7 Ohms, which brings us close to the point of diminishing returns for the usual 45 Ohm crystal. The BF862 works to 700 MHz, so it is just fast enough and won't surprise me at 3 GHz. regards, Gerhard dk4xp ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Notes on the Driscoll VHF Overtone Crystal (time-nuts Digest, Vol 65, Issue 114)
Von: Magnus Lindahl sm4...@telia.com Do you have schematics, PCB-design etc. to share on your design with 3* BF862? I will publish the results in Dubus. (www.dubus.org) board size is 1.5 * 2.5 inch for oscillator, buffer, reference conditioner and PLL. No soldering without a microscope, however. Lots of SSOP16, sot-336, 0603 friends. I wanted to make a VHF crystal oscillator that could be locked to a 10 MHz reference and be used for the usual transverter designs. That required a locking grid of 333 or 500 KHz. Furthermore, I wanted to avoid microcontrollers and other stuff that had to be programmed. I wanted just normal stuff from Digi-Key and your favorite crystal supplier. (Also, I wanted a nice clock source for state-of-the-Art 16 bit ADCs) The fine locking grid has a devastating influence on the design. Either one compares at 500 KHz, then locking to small error will take months, the pull-in range is ridiculous (I don't want an oven for the 100MHz) or one compares to a harmonic of the 500 KHz, then the phase comparator gain is ridiculous and the PLL kills the 100 MHz phase noise. Probably I'll give in and stay with a 10 MHz grid. That will help hams who want to multiply to 100 GHz and above. I now have limited access to an Agilent signal source analyzer that does the three cornered hat thing with cross correlation to 2 precision oscillators close to real time. I'm still stuck at -135 dB@ 100Hz @100 MHz, but without Rohde's limiter. (only antiparallel Schottky across tank circuit and with BFG196 emitter follower) I'll test w/o the follower and with the new limiter in week 1/2010 There are many things still to explore: thin film vs thick film resistors, influence of emitter/source resistors, amplitude clamps, crystals, ... regards, Gerhard DK4XP U.L.Rohde/David P. Newkirk: RF/Microwave Circuit Design For Wireless Applications, page 762++ Wiley, ISBN 0-471-29818-2 ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] homebrew 13 dBm distribution amplifier based on NIST design 5 to 100 MHz
I've done a redesign of the distribution amplifier without transformers or other ferrite (apart of dc filters). This required 2 transistor chains in parallel or 96 mA at 24V / Channel. It runs quite hot but looks like it could work from KHz to 600 MHz+. Harmonics are down 40 dB at 250 MHz/13 dBm including SMPD signal generator and the 54846B scope digitizers. AF decoupling is in again as well as Bruce's base divider caps. http://www.hoffmann-hochfrequenz.de/downloads/IMG_0499__Q73.jpg I had quite a lot of stability problems in the last stage; it liked to oscillate at 1.5 to 3 GHz. I had to use 33R base stoppers for the pnp transistors and tried a week's evenings with Genesys to get rid of them to no avail. I even tried 0603 base decoupling caps right _through_ the board from the base pad to the ground plane 0.5mm / 20 mil away. There is still a lot to do optimizing the voltage drops per stage and characterizing that thing. Any idea of more harmless pnp wideband transistors with Ptot = 1W? Maybe I could run this with -24V and use more NPNs and the pnp only in the CC stage. The efficiency might be improved with a 10 uH choke from the final collectors to gnd. That could be accomplished without ferrite or at least with a large air gap. regards, Gerhard dk4xp ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
