Re: [time-nuts] Sysclock source for AD9912

2013-12-31 Thread Grant Hodgson

Anders

You can set the overall PLL divider to any even value between 4 and 66 
as there is a fixed /2 prescaler preceding the programmable divider, so 
with a 20MHz reference (from a 10MHz source) set the overall divider to 
50 to give 1GHz - not sure if you set N to 50 or 25 in the Eval. 
software, but it's easy to do.


regards
Grant



Anders wrote :-

Thanks for all replies so far!

It looks like I will play around with the evaluation board some more, and
see if I can get the on-chip PLL to behave better.
The settings with 2x edge-detector and 60x PLL were the only ones I could
find where the output frequency setting in the software corresponded to the
actual output frequency - hence I tested only with 10MHz x120 = 1200 MHz
sysclock. I have asked about this on the AD forum, but no replies yet.

If that doesn't work the suggested ADF4351 (or similar) evaluation board
looks like the most straightforward option.

thanks,
Anders

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Re: [time-nuts] sysclock source for AD9912 DDS?

2013-12-30 Thread Grant Hodgson

Anders

I've used the AD9912 Eval board with great success - spurs with the 
on-chip clock multiplier were -60dBc, IIRC, maybe better.


My guess is that you are pushing the on-chip VCO too high - do you 
really need a 1200MHz system clock?  The AD9912 is only specified for a 
sys. clock of 1000MHz, and the on-chip VCO is also only specified to 
1000MHz - yes, I know that the Eval software allows other values, but 
the VCO actually has quite a narrow frequency range (10%) in order to 
improve phase noise, and uses switchable on-chip inductors to select the 
correct output frequency range, the highest being 900-1000MHz.  I'd be 
surprised if it locks at 1200MHz.


First thing is to try a 1000MHz clock.

regards
Grant Hodgson

From: Anders Wallin anders.e.e.wal...@gmail.com
To: Discussion of precise time and frequency measurement
time-nuts@febo.com
Subject: [time-nuts] sysclock source for AD9912 DDS?

I've tested the AD9912 evaluation board:
http://www.anderswallin.net/wp-content/uploads/2013/12/dds_test_2013-12-30.png

I want to use it with a 10MHz external input clock, but it looks like the
on-board PLL that generates a 1200MHz sample clock from my input isn't that
great, since I get strong side-bands on the output that are only 18-20 dB
down from the fundamental.

So it looks like I need to supply a clean 800-1000MHz clock to the DDS to
get a clean output. Any ideas/suggestions for generating this from a 10 MHz
sine?
Driving the DDS system clock from an expensive RF generator (e.g. HP 8648A)
would be possible but I'd prefer a PLL from 10MHz if it's doable
simply/cheaply.

Anders
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Re: [time-nuts] GPS antenna??

2013-04-09 Thread Grant Hodgson

Alan

As has already been stated by others, if the purpose of the GPS signal  
is for a GPSDO, then putting an active patch next to a SW facing  
window should work fine.  No need to re-radiate.  You only need to  
receive 1 satellite in order to get a timing signal - more satellites  
will give better (lower) jitter/ADEV, but if you just want an accurate  
frequency source for a counter or signal generator then the setup you  
describe should be fine.


If that's the case, then it might be worth taking a Rubidium source as  
a higher-performance back-up than the GPSDO in holdover, although some  
GPSDOs are more equal than others in holdover performance.


regards
Grant

Quoting time-nuts-requ...@febo.com:


Hi all an interesting problem you may have encountered, I want to use a GPS
frequency standard inside a building with no opening windows (opening
windows are known as air conditioning in the UK :-))  )
This is part of a two day amateur microwave conference so we should have the
expertise.

I intend to try and pass the signal through a a double glazed glass window
unit (hopefully not metalised) using a couple of patch antennas. The outer
GPS antenna is active so will need  a 5v supply via an inserter. Inner patch
active, outer patch passive to avoid problems of feedback. Main antenna can
be shielded from the coupling either physically or with a slab of
absorber.

Has anyone tried this? does it work?.any gotchas?

Thanks
Alan
G3NYK





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Re: [time-nuts] 40MHz source

2013-03-25 Thread Grant Hodgson

Dave

I think you're going down the right road with the Chris Bartram transceiver.

My suggestion for a 40MHz source would be to take a 10MHz source and  
feed it into two successive doublers, with a bit of inter-stage and  
post-stage buffering and filtering.


Frequency doublers can be very simple indeed - as simple as a  
full-wave rectifier.  It's the sort of thing that somebody in the  
local radio club might be interested in building, even if they are  
afraid of the 'scary' microwave stuff.  Lot's of possibilities for  
experimentation there.


As for a 10MHz source - I'd be tempted to go for either a good quality  
OCXO, or maybe a GPSDO such as the Trimble Thunderbolt (which has a  
fairly good 10MHz OCXO inside it).  Many Rubidium sources are designed  
for medium-long term stability, at the expense of close-in phase  
noise, and that might be a problem in this application, as the 10MHz  
oscillators in many rubidium sources don't have as low phase noise as  
the 10MHz oscillators in the good GPSDOs.


A good quality 10MHz frequency standard will also have other uses in  
the lab, of course.


To answer Jim's question - 'inside the box' is an LTC6946-3 integrated  
Frac-N PLL/VCO with an o/p at 5GHz, then feeding into a sub-harmonic  
mixer to get to 10GHz.  The PLL uses a 40MHz reference, which I  
believe is also the PLL comparison frequency.  I think that the  
supplier might be reluctant to change the software to use a lower  
comparison frequency, but I haven't asked.


The loop bandwidth of the PLL is somewhere in the 10kHz-20kHz range,  
so any close-in phase noise from the reference will get multiplied up  
to the final frequency, hence the need for a reference with good phase  
noise.


regards
Grant



Subject: [time-nuts] Are there any rubidiums
programmahttps://mail.google.com/mail/?shva=1#inboxble to 40 MHz?


I'm possibly looking for a 40 MHz source and I know some of the
rubidiums are programmable. But can any of the affordable ones be
programmed to work at 40.0 MHz?

I was looking for a source to drive this 144 MHz - 10 GHz transceiver.

http://www.chris-bartram.co.uk/products.html

The TCXO oscillator is off the board and a separate item, but costs
?40 and then one ideally wants to lock that to a more precise source.
The oscillator will lock to an external 10 MHz source, but then one
needs to buy both a 10 MHz rubidium as well as this 40 MHz TCXO. Hence
I was wondering if there was a cheaper more compact solution, which
just used a rubidium, and dispensed with a TCXO.

Dave
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Re: [time-nuts] GPS at 60,000 feet

2013-02-02 Thread Grant Hodgson
GPS has already flown in space several times; one of the well-publicized 
occurrences is when NASA sponsored an experiment to put a 6-channel 
Trimble receiver on the ill-fated AO-40 amateur radio satellite which 
launched in 2000.


This satellite had a highly elliptical orbit, with perigee of 1000km and 
apogee of 6 km - well outside the GPS constellation.


The GPS experiment was one of the first experiments to be tested on this 
satellite and some useful results were obtained before the satellite was 
lost due to technical failures in 2004.


The results of the experiment have been published :-

ftp://goes.gsfc.nasa.gov/pub/chesters/goesref/Moreau_GPS.pdf

and

http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20030025378_2003025844.pdf

Just google AO-40 GPS for more information.

regards
Grant


On 01/02/2013 14:16, time-nuts-requ...@febo.com wrote:

Message: 6 Date: Fri, 01 Feb 2013 06:14:04 -0800 From: Jim Lux
jim...@earthlink.net To: time-nuts@febo.com Subject: Re: [time-nuts]
GPS at 60,000 feet Message-ID: 510bcdac.8080...@earthlink.net
Content-Type: text/plain; charset=ISO-8859-1; format=flowed On 1/31/13
1:09 PM, Chris Albertson wrote:

I know  for sure my handheld Garmin works at 27000 feet, at
530mph...   ...I was actually surprised it worked up there.
It made me  wonder what the actual limits are.


What are the limits of your hand held unit or what are the limits of
GPS in general.   I think GPS works as long as you are under the orbit
of the satellites.  The company I used to work for placed GPS on some
low orbit spacecraft, so say roughly 200 miles up and 18,000 mph but
I'd guess most hand held units would not work in those conditions





GPS will even (maybe) work at the Moon: with a gain antenna pointed back
at earth.. you're looking at the satellites on the opposite side of the
earth radiating around the limb.  I don't know that anyone has actually
tried it but it's certainly been analyzed to death.

The potential problem with a handheld GPS in space (depending on where
you are) would be whether you can keep track of the constellation and
acquire new s/v's fast enough with lots o'Doppler.

You already have to deal with the Doppler from the S/Vs buzzing around
at 3-4 km/sec.  Whether your receiver can handle the extra 7 km/sec
Doppler in LEO is a good question.  7 km/sec is about 20 ppm, and I
suspect that the receiver can already deal with that much change in the
oscillator frequency.  It might be doppler rate that it would have a
hard time with (because the designer cranked down on the loop bandwidth
for noise reasons)

What are those folks flying GPS on CubeSats using?

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Re: [time-nuts] Is there any way to use a TIC to measure time of reflection on a PCB?

2013-01-24 Thread Grant Hodgson

Dave

Couple of thoughts here :-

1)  A 'real' TDR measurement would require a pulse generator with a  
fast rise/fall time.  The faster the rise/fall, the better.  A  
directional coupler could be used to separate the forward and  
reflected signals, or you may be able to get away with a 3dB splitter  
and use the forward pulse to start the TIC and the reflected pulse to  
stop it.  However - this will only give you a measurement of the  
propagation time of the pulse - using the VNA with a short at the end  
of the microstrip (as has already been described) would give a much  
better result.


So yes, you could use a TIC, but you would need a pulse generator and  
you wouldn't have a better measurement than that already.  Actually, a  
fast 'scope would be better than a TIC as you would be able to see the  
shape of the reflected pulse, which is somewhat more useful than a  
simple time measurement.


2)  Given that the student doesn't have the TDR option on his VNA, it  
would be possible to simulate this using Matlab, Mathcad or one of the  
other analysis packages which are now freely available.  The formatted  
data (in the frequency domain) from the VNA can be read via GPIB,  
inverse FFT'ed, time-gated and FFT'ed back into the frequency domain.   
Excellent learning task for a keen student.


regards
Grant


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Re: [time-nuts] Thermal noise contribution to phase noise

2013-01-19 Thread Grant Hodgson

Joe

Nobody is suggesting that KTB noise is revised.

Bruce's original post quoted two articles that state that the thermal 
contribution to the phase noise floor of a carrier signal is -177dBm/Hz, 
not -174dBm/Hz.  These papers also state that there is an equal 
contribution of amplitude noise which also equals -177dBm/Hz.


So the total thermal noise floor of a carrier signal is -174dBm/Hz - 
half of which contributes to amplitude noise, half of which contributes 
to phase noise.  The quoted articles go some way to demonstrating that 
by both theory and measurement.


regards
Grant





--

Message: 4
Date: Fri, 18 Jan 2013 23:52:37 -0500
From: Joe Leikhim jleik...@leikhim.com
To: time-nuts@febo.com
Subject: Re: [time-nuts] Thermal noise contribution to phase noise
Message-ID: 50fa2695.1030...@leikhim.com
Content-Type: text/plain; charset=ISO-8859-1; format=flowed

I have just sent off an e-mail to David Howe of NIST Metrology
requesting clarification about this assertion that KTB is revised -3dB.



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Re: [time-nuts] 5120A and PM signal

2013-01-14 Thread Grant Hodgson


Filip

What exactly are you trying to measure?

A phase-modulated carrier will have an infinite number of sidebands 
spaced at the modulating frequency, the amplitude of the sidebands 
gradually reducing away from the carrier.   The amplitude of the 1st 
pair of sidebands (closest to the carrier) is a function of the 
modulation index.  In your case the 10MHz carrier signal has it's phase 
modulated by +/- 1 rad, at a rate of 10kHz. Note that the level of the 
carrier is itself a function of the modulation - i.e. as you change the 
level of the peak deviation, the level of the carrier will change.  With 
1 rad deviation, the carrier will be approx. 2.3dB down compared to with 
no modulation.


So, if you want to measure the phase noise of the 2024, then you should 
turn off the modulation.


Are you getting confused about the dBc/Hz measurement?  'dBc' means 'dB 
relative to the carrier' - that's why it's called dBc.  dBc/Hz is 
usually used for noise measurements only, and means the level of noise, 
relative to the un-modulated carrier (in dB), if measured in a 1Hz 
bandwidth, at a given offset from the carrier.


The level of modulation sidebands is independent of measurement bandwidth.

I may have missed something here - please could you give more details of 
what you are trying to do?


regards
Grant



Date: Mon, 14 Jan 2013 11:35:02 +0100
From: Filip Amator filip.ama...@gmail.com
To: time-nuts@febo.com
Subject: [time-nuts] 5120A and PM singal
Message-ID:
cabztljcz+vht+ehijzgm0uky_lio9yzphogxngmg7yap4rt...@mail.gmail.com
Content-Type: text/plain; charset=ISO-8859-1

Hello,

I made a simple measurement using Symmetricon 5120A phase noise
measurement set and a Marconi 2024 signal generator and I don't
understand the results. I measured the phase noise of 10 MHz signal
with 1 Rad phase modulation at 10 kHz, and I got from mesurement peak
at 10 kHz with level about -26dBc/Hz. According to the current
definition of dBc/Hz, the value of -26dBc/Hz should be considered as a
-26dB of modulation relative to 1 Rad. But I would expect that the
peak level will be at 0 dBc at 10 kHz. Does anyone knows how to
explain this difference?


Filip Ozimek



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End of time-nuts Digest, Vol 102, Issue 51
**



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Re: [time-nuts] Orbital time-delayed angular momentum

2012-07-20 Thread Grant Hodgson
If the signal is delayed in time by the dish, then there will be no phase
coherency, and it is the phase coherent properties of a parababoid that make
it the most commonly used type of reflector for microwave signals.

A direct analogy between optical signals propogating in a fiber and RF signals
propogating in free space is not possible - the best analogy would be to
compare light in a fibre with RF in a circular waveguide - which somwehat
limits the applications of orbital angular momentum for RF/microwave systems.

regards
Grant



 From: Michael Baker mp...@clanbaker.org
 To: time-nuts@febo.com
 Subject: Re: [time-nuts] Orbital time-delayed angular momentum
   phasing???!!
 Message-ID: 5008c114.2090...@clanbaker.org
 Content-Type: text/plain; charset=ISO-8859-1; format=flowed
 
 Time-nutters--
 
 Didier Juges asked:
   What does that do to the focussing properties
   of the dish?
 
 
 I have seen several descriptions of how the dish
 needs to be shaped in order to develop the orbital
 time-delayed angular momentum signal and still
 achieve an integral focus point.   I am not sure that
 I can describe it, but as I understand it, the dish
 is not just split and bent into a cork-screw, but that
 the surface of the dish is also continuously shaped so
 as to provide a good focus   It is just that the
 signal striking parts of the dish which are increasingly
 displaced along the axis of the bore-sight are time
 delayed more or less with respect to other surfaces
 of the dish.   The only way I can see for this to work is
 for the dish surface to deviate from a true parabolic
 shape incrementally as each particular area is displaced
 closer or further away from the focal point.   It is a
 little hard to visualize and a lot harder to find the
 right words to adequately describe!
 
 Mike Baker
 ---
 




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Re: [time-nuts] HP 53310A modulation domain analyzer

2011-07-27 Thread Grant Hodgson
Jose

As with most things, it depends.  The 53310A was designed and marketed at the
RF design community where there was a need to be able to display parameters
such as settling time of PLLs and to display frequency-based modulation modes
in the time domain.  To this end, the 53310A is a superb instrument.  It
performs these functions by acting as a time interval counter, but has the
rather interesting feature of a very large display, combined with X and Y 
markers.

It can be used as a stand-alone TIC - I'm not sure how it performs against
other, more popular TICs, such as the SR620, HP5370, CNT-90 etc. etc.  From
memory the single-shot resolution is about an order of magnitude worse than
the 5370 - that may, or may not, be relevant to you.

The 53310A is not generally regarded as an easy instrument to use, certainly
by RF engineers familiar with 'classic' user interfaces such as on HP spectrum
and network analysers.  However, the 53310A has a very useful Auto Scale
feature, which for repetitive waveforms tends to work very well IMHO - simply
connect the signal to be analysed, and the 53310A works out X and Y scaling
factors and DC offset/trigger levels.  From that point it is easy to apply
markers and zoom functions, and otherwise tweak the parameters that were 
auto-set.

The one thing that the 53310A won't do as-is, is display ADEV or related
parameters - to do this you would need to download measured data and
post-process using a PC, just as with most other TICs.

I've never had to use histograms, std dev etc., but my use has been primarily
for PLL measurements.

Option 31 is highly desirable and well worth paying a bit extra for.

Nice instrument, bit quirky to use.

regards

Grant



 
 Does anyone use an HP 53310A modulation domain analyzer (it is like 
 an oscilloscope for frequency - displays frequency in Y and time in 
 X, also does histograms, stdev, etc.)
 
 What are gotchas, drawbacks and advantages using it as a counter, stability
 measurements instead of a simple counter?  It certainly is a nice 
 tool for rf debug of sweepers, plls, etc.
 
 Ebay has a nice one, with 2.5GHz option 031 for 750 or best offer.
 
 --




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[time-nuts] Phase noise measurement (was - no subject)

2010-08-20 Thread Grant Hodgson

Mark

You've come to the right place - well, that is if you want to devote a 
significant amount of your life in the pursuit of ever-more accurate 
time and frequency measurements


If you've only got one source then you need to use the frequency 
discriminator method (aka delay line method) of phase noise measurement. 
 Basically you take the output of the source, split it in two, delay 
one of the signals, re-combine the two and then measure the resultant 
signal on a base-band spectrum analyser.


There are loads of references to this on the web, which describe the 
method in more detail, including :-


The Art of phase noise measurement - Dieter Scherer

and

HP Application Note AN270-2

both available from John Miles web site

www.thegleam.com/ke5fx/gpib/pn.htm

The references at the end of these articles, especially the HP ones, are 
particularly useful.  The operating manual for the HP 11729B or 11729C 
Carrier Noise Test Set is also highly recommended.


Yes, there's some maths, you need to understand the relationship between 
phase and frequency measurements, but you don't necessarily need ALL the 
theory that most of the papers give - don't give up just because of a 
few differential equations :)


The limitation of the frequency discriminator method is that the noise 
floor of the measurement system is often worse than the DUT, especially 
if your DUT is very good, and it's even worse if you're trying to 
measure close-in noise.  The Sherer article gives a good graph 
illustrating this. If you're trying to measure the phase noise of the 
oscillator inside a Tbolt then I don't think that a frequency 
discriminator will be sensitive enough, although I might be wrong.


Despite what you said, you might want to consider buying an HP 10811 
oscillator or similar which you could use in a phase detector 
measurement system which is likely to give superior results.


Hope that helps

regards

Grant

Mark wrote :-

My new GPSDO leaves me with the question of how do I measure the phase 
noise of what is by far the best oscillator I own... without buying a 
better one to compare it to. That question is what brought me to 
time-nuts. I'm starting to read some papers on oscillator 
characterization that are collected together in a technical note from 
NIST that a co-worker pointed me towards, but some of them are giving me 
a math-induced headache.


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Re: [time-nuts] Low cost 6+ GHz Prescaler

2010-03-27 Thread Grant Hodgson
Samuel

Mini-Circuits ADCH-80A is very good and reasonably priced.

Coilcraft also make a couple of very wideband chokes, but cheap - they are not.

regards

Grant


  PS : I'm looking for a source for RF chokes (MMIC Power stage) useable
from DC to 8+ GHz.



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Re: [time-nuts] Low cost 6+ GHz Prescaler

2010-03-26 Thread Grant Hodgson

I've used the RFMD NBB300/310 and they are excellent up to 14GHz.

The NLB300 and NLB310 are in plastic packages and are somewhat cheaper 
than the NBBs, but have similar gain characteristics.  They don't do 
strange things when compressed; I've driven them right up to the abs. 
max i/p power level and they survive, and I don't see any evidence of 
harmonic problems when driving a Hittite HMC364 /2 prescaler.


They do exactly what it says on the datasheet.

regards

Grant Hodgson




RFMD seems to produce some nice MMIC, for example the NBB-300
(http://www.rfmd.com/CS/Documents/Nbb-300.pdf), but I never used a RFMD
amplifier. I used Agilent/Avago MMIC since years with great results, but
always with frequencies no more than 3 GHz. 


Anyone have some experience with DC-8/12 GHz MMIC and which's the best ?




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Re: [time-nuts] Notes on the Driscoll VHF Overtone Crystal Oscillator

2009-12-29 Thread Grant Hodgson
I've had several discussions with Chris Bartram about this and similar 
VHF oscillators.


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.


BTW I've tried simulating the phase noise of this oscillator using ADS, 
but wasn't able to get meaningful results from the simulator, and on 
this occasion Agilent technical support were not able to resole the 
issues either.  Maybe Microwave Office or Ansoft Designer would yield 
better results, but I haven't tried them.  (LT Spice is unable to 
simulate phase noise of oscillators).


regards

Grant

 
  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.
 
 
Using a transistor with a higher ft than necessary in an oscillator
circuit isnt usually a good idea.

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Re: [time-nuts] DIY Frequency extension for HP Agilent

2009-02-16 Thread Grant Hodgson
Samuel

The NLB-300 and NBB-300 series MMICs from RFMD work very at up to 13GHz 
or so, certainly far better than a Mini-circuits ERA- whose gain will 
start to roll off at higher frequencies.  Designing a broadband gain 
stage to work up to 12GHz+ may not be as easy as it seems.  However it 
is made somewhat easier by the use of broadband chokes from the likes of 
Mini-Circuits, wideband inductors from Coilcraft and broadband 
capacitors from ATC - to name but three - there may be others as well.

The 4-stage amplifier used by HP not only increases the signal level, it 
increases the slew rate (V/uSec) at lower frequencies.  It's not just 
about signal level, it's about getting fast edges.  The Hittite HMC363 
/8 is a great IC, using static flip-flops, and will work all the way 
down to DC - IF the edges are fast enough.  Ironically it may be the 
case that the lower frequency limit presents more of a challenge than 
the higher frequency limit.

regards

Grant


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Re: [time-nuts] Tbolt with Palisade

2009-01-22 Thread Grant Hodgson
The antenna will be mounted outside with a reasonably clear view to the 
horizon from east-south-west.  But there are times when there could be a 
lot of RF in the area - I design and build high power VHF and UHF PAs, 
amongst other things, and one of the attractions of the quality GPS 
antennas is the fact that they have a built in filter.

But I might try one of the cheap patch antennas as a start with a view 
to upgrading at some point in the future.

regards

Grant

Nigel Wrote :-
 
 -
 Hi Grant
  
 I think this really does depend on where you are, satellites in view etc,  
 and what level of performance you're actually looking for.
  
 I have a few different timing antennas but have found these don't give  very 
 reliable reception indoors.
 Until I can get these mounted outdoors I have been having good results  on 
 various receivers using some small Trimble magnetic patch antennas,  
 specified 
 26dB gain, attached to a steel plate and sitting on a shelf  inside a one 
 level 
 timber framed house on the west coast of Scotland.
 These came via a buy it now from the usual place at $21 for  10 about a year 
 ago.
  
 Driving a pair of Thunderbolts with these and comparing them with an HP  
 53132A counter, either one as reference and the other as input, once  locked 
 I see 
 variations of just a few places around zero in the 10th decimal  place.
 I have used this test on any two units selected from four with  consistent 
 results.
  
 Not a very scientific test perhaps, and nothing else measured, but as  
 regards frequency at least I don't think they're suffering too much  from 
 their 
 lesser antennas:-)
  
 regards
  
 Nigel
 GM8PZR
  
 --

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Re: [time-nuts] Tbolt with Palisade?

2009-01-20 Thread Grant Hodgson
Robert

Thanks, looks like the hassle factor is greater than the fun factor on 
this one  :(

Guess I'll have to start a search for an HP58532A, VIC-100, Vaisala  or 
similar.  I don't think a cheapy £4 patch antenna will give the same 
performance.

regards

Grant


 Hi Grant,
 Keep the Palisade as it is. It's got a useful 1 PPS output. Also it's almost 
 impossible to open the case without destroying it. The two halves are epoxyed 
 together with a very good joint geometry! There is no obvious way to get to 
 the antenna output. If you want to hack something, have a look for one of the 
 Vaisalla GPS radiosondes. They have a nice Bi-Helix antenna, LNA and filter. 
 But even a simple patch on a ground plane will do.
 
 Robert G8RPI.
 
 


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[time-nuts] Tbolt with Palisade?

2009-01-18 Thread Grant Hodgson
Does anybody know how difficult it would be to use just the antenna + 
LNA part of a Trimble Palisade?  Have Tbolt but no antenna. I can get a 
Palisade for much less than a proper GPS antenna.  Coax length would be 
about 20 feet, connected to the output of the Palisade's LNA (or output 
filter if fitted).

Only possible problem I envisage is that the Palisade LNA will probably 
have less gain than say a 58532A.  However, the latter is designed for 
long cable runs; I'm guessing that this unusual arrangement might work 
with a fairly short cable run.  Powering the Palisade LNA shouldn't be 
too difficult me thinks.

regards

Grant

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Re: [time-nuts] Close-in phase noise question...

2008-12-17 Thread Grant Hodgson
Brian

Thanks for the details.

There are a number of problems with crystal filters.  A crystal filter 
will have a finite bandwidth, and at offsets less than half the 
bandwidth the filter won't have a significant effect on the phase noise. 
  For example the 40MHz xtal filter used in the 8662A has a bandwidth of 
6kHz (according to the service manual), so phase noise at less than 3kHz 
offset will not be affected.

For your application you would need a filter with a very narrow 
bandwidth indeed - maybe 50Hz or so.  Ignoring the manufacturing issues 
of such a device, there could be problems with temperature sensitivity 
and microphony.  These problems could of course be overcome, but I'm not 
convinced that a crystal filter would give an overall benefit in this 
application, given that the primary goal is to achieve leading-edge 
close in phase noise.

The MSA1105 has better phase noise than I thought, but I'd still be 
tempted to change one or both of the passive doubler/buffer stages to an 
active doubler, if the figures for the NIST active doubler are correct.

regards

Grant

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Re: [time-nuts] Close-in phase noise question...

2008-12-16 Thread Grant Hodgson

Brian

Could you give some more details?  I think alternative solutions to 
MMICs at 5 and 10MHz would give much lower phase noise.

Bruce's web pages have a number of designs that will get the 5MHz 
reference up to 20MHz in 2 stages :-

http://www.ko4bb.com/~bruce/FrequencyMultipliers.html

Another approach would be to use op-amps instead of MMICs, op-amps with 
a low flicker corner frequency should give lower close in noise than a 
MMIC, but probably won't be as good as a discrete solution.

regards

Grant

   
 
 Looking for comment here...
 
 The background:
 I'm working on a sub mm-wave LO chain for
 a ham radio application. While chasing issues
 of close-in phase (ie: within 1KHz of RF
 carrier) by peeling the layers of the onion,
 I'm starting to question the performance of
 the MMICs that are used as buffers and amps
 following my Wenzel reference OCXOs.
 
 Question(s):
 Should any MMIC be allowed to be driven
 close to compression or into compression
 when striving for best close-in noise?
 
 I know and have seen the NF of a MMIC
 degrade while in compression, but my
 target right now is close-in noise rather
 than broadband noise.
 
 My design, in summary, takes 5MHz up to 630GHz
 via several multipliers and PLL stages.
 
 -Brian

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Re: [time-nuts] DMTD mixer question

2008-12-04 Thread Grant Hodgson
Jim

Figures such as -200dBc/Hz probably relate to the phase noise figure of 
merit which some PLL suppliers like Nat. Semi, Hittite and AD use to 
compare various PLL offerings.  These figures are normalised to a 1Hz 
comparison frequency and unity division ratio; to get a prediction of 
PLL phase noise within the loop bandwidth you need to scale for both 
comparison frequency and division ratio.  This FOM is somewhat crude, as 
it doesn't take into account flicker noise, amongst other things, and 
loses accuracy with very high comparison frequencies.  Banerjee goes 
into more detail about this subject.

regards

Grant

--snip--

I seem to recall seeing a number like -190dBc/Hz or -200dBc/Hz for these 
hot stuff PFDs, but I can't recall where, maybe Banerjee's PLL book?

--snip--

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Re: [time-nuts] US Shipping Was huntron tracker advice

2008-11-27 Thread Grant Hodgson
There are companies that provide a 'real' USA mail address and then 
forward the items on, overseas.

Google 'US address' and 'USA address'.

regards

Grant

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[time-nuts] 53310A help

2008-10-30 Thread Grant Hodgson
Does anybody know how to use the signal source that comes with the HP 53310A
Modulation Domain Analyser?  The MDA is fine, but I don't have a manual for
the signal source, and there seems to be nothing coming out of it - and yes, I
checked the battery.  There's no mention of how to use the signal source in
the 53310A manual.

regards

Grant Hodgson



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Re: [time-nuts] Low phase noise digital divider (in 600MHz to10MHz area)

2008-01-25 Thread Grant Hodgson
Anders

One option is to use just the programmable divider part of a PLL IC, 
such as those from National Semiconductors or Analog Devices.  Or, use a 
Hittite HMC394 programmable counter preceded by a fast /2 flip flop. 
The PLLs will need serial programming via a micro-controller or other 
logic device; the HMC394 uses parallel programming so is easier to 
implement.

Neither the PLLs nor the HMC394 counter need external edge conditioning 
- they will work with sine wave inputs.

These solutions won't give you as good a phase noise performance as a 
regenerative divider, but if you want something that you can just plug 
together then they will work for relatively little effort.  And you 
don't need to worry about -ve supply voltages which some ECL devices need.

regards

Grant

 From: Anders Time [EMAIL PROTECTED]
 Subject: [time-nuts] Low phase noise digital divider (in 600MHz
 to10MHz area)
 To: time-nuts@febo.com
 Message-ID:
 [EMAIL PROTECTED]
 Content-Type: text/plain; charset=ISO-8859-1
 
 Have been locking around for a good article on how to design a good Low
 phase noise digital divider(in 600MHz to 10MHz area), but the have not found
 any good literature. Today most people talk about regenerative dividers, but
 are a rather complex subject.
 Does anyone have experience in what logic family that have the lowest noise
 TTL, AC, HC, F etc?
 What is the upper limit for ECL diviers? My first idea was to use ECL to
 divide down to 100MHz area and then to use lower noise TTL to go down to
 10MHz.
 What about edge-conditioning circuit at divider input? Have seen people talk
 about it, but no info what it does?
 Thanks
 Anders

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Re: [time-nuts] Spec An for phase noise measurements

2008-01-21 Thread Grant Hodgson
Matt

It depends on what you want to measure.  If all you want to do is 
measure the relatively close-in phase noise of (say) a single-loop PLL, 
then an 8560 is fine - I know, because that's what I used for some time. 
  But if you want to measure the noise floor of a VCO, PLL or other 
source then even the best spec. an. just does not have enough dynamic 
range, so other techniques have to be employed, such as the 
down-conversion techniques that have been discussed here recently.

There's a circuit on the Wenzel website for a suitable PLL/LNA that will 
do most of the downconversion, just add a suitable mixer and off you go. 
I was seriously looking at building one until an 11729B popped up for a 
price I couldn't refuse.  The only problem with building one is the time 
- your choice as to whether you want to build/buy.

And it also depends on how close to the carrier you want to get - most 
8590 series analysers go down to 9kHz, if you down-converted and want to 
get closer than that then you will indeed need another analyser.  There 
is an option on the 8560s that take the lower frequency limit down to 
30Hz, which is close enough for most applications.

Beware the options on the 8560 - option 103 replaces the nice OCXO with 
a cheaper TCXO; the stability and accuracy with opt 103 should be fine 
for most uses, but due to the poorer stability of the TCXO, you lose the 
1Hz Resolution bandwidth which may or may not be a problem.  Just check 
exactly what options you are getting in advance.  However,  option 103 
was  cheaper, which tipped the balance for me; I can use an external 
10MHz reference if I want greater stability and accuracy, but I still 
can't get the 1Hz RBW !

Also check the frequency range if you want to go above 22GHz - the 8563E 
will definitely go to 26.5GHz; some, but not all, 8653As stop at 22GHz.

I love the 8560s, they are an order of magnitude better than the 8590s 
for serious RF work.

regards

Grant

Matt wrote :-

 Message: 1
 Date: Mon, 21 Jan 2008 11:20:03 -0800
 From: Matt Ettus [EMAIL PROTECTED]
 Subject: [time-nuts] Spec An for phase noise measurements
 To: Discussion of precise time and frequency measurement
   time-nuts@febo.com
 Message-ID:
   [EMAIL PROTECTED]
 Content-Type: text/plain; charset=ISO-8859-1
 
 I am considering getting a new spectrum analyzer so I can make better
 phase noise measurements than with my 8596E.  I've looked at the 8566B
 and the 8562 and 8563 since I need coverage to at least 6 GHz.  The
 8566 is huge and ancient, though, so I think I'm leaning away from
 that one.  Anybody have other suggestions?  Some of the Advantest
 units seem to be reasonably priced on ebay, but it is hard to figure
 out what their phase noise performance is.
 
 Also, what is the difference between the A, B, and E models on the
 8560 series?  The A models are much cheaper on ebay.
 
 Thanks,
 Matt

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Re: [time-nuts] xtal oscillator phase noise

2008-01-02 Thread Grant Hodgson
Henk ten Pierick wrote:
--snip--
 
 It showed to be very difficult to come lower than what I have now. If 
 can be the crystal. How can I decide?

As an absolute minimum, you need to know the crystal dynamic (or 
motional) parameters - the crystal supplier should be able to provide 
these.  If not, you can measure them on a network analyser whilst you 
look for another crystal supplier.

Then you should be able to simulate the phase noise of the oscillator 
using a harmonic balance or similar method as used in Microwave Office, 
Genesys, ADS, Ansoft Desginer, QUCS etc.  Failing that, a small-signal 
(linear) open-loop analysis would at least give an estimate of the 
loaded Q, which can be used to predict phase noise - but ignoring 
flicker noise.  Some SPICE-based simulators might be able to help.

--snip--
 
 I used the BC375 for the low Rbb' and assume that the noise corner must 
 be low as a result of that. Is this not true?

There are many different types of noise - the base bulk resistance of a 
transistor contributes to shot noise, which is close to being 'white' - 
i.e. equal magnitude /Hz at all frequencies.  This does not have a 
significant effect on phase noise at offsets close to the carrier, and 
at 30Hz offset the flicker noise dominates.  Flicker noise is not 
'white' noise - flicker noise increases at a rate of 1/f, or 10dB/decade 
as the offset frequency is reduced, and simply choosing a transistor 
with low Rbb' is not sufficient - the noise mechanisms are different.

For an 11MHz oscillator I would use 2N5179s as advocated by Rick for 
both the sustaining amplifier and the limiter - this is a very popular 
transistor for oscillators in this frequency range.  I'd be surprised if 
the BC375 generated less noise than the 2N5179.  This would mean 
changing the circuit topology to use an NPN transistor instead of the 
BF450 which is PNP.


 At 11MHz, most crystal oscillators use parallel resonant crystals,
 although some are series resonant, such as the excellent Driscoll
 oscillator which is capable of the performance you desire with a
 suitable crystal.
 
 I was aware that most lower frequency circuits are parallel resonant. I 
 used series in class A because I thought is was better, it is easier to 
 use the current though the xtal. Is there a fundamental difference 
 between parallel ore series w.r.t performance?

Not really, it's the circuit topology determines whether a parallel or 
series resonant crystal is used.  Your circuit appears to be a variant 
of the Driscoll oscillator, which usually uses a series resonant crystal 
and is capable of exceptionally high performance, however there are a 
number of differences in your circuit, which I've never seen before, 
although I can't claim to be an expert oscillator designer.  Circuit 
simulation is a good (no - essential) starting point, and would give you 
a good idea of the relative merits of the features of your circuit.

--snip--
 
 I do normally not have access to a FSUP but borrowed the instrument for 
 two weeks. To my luck it has the B60 option and I used this of coarse. 
 There must be a reason for my employer to buy this fantastic tool.
 
 Henk
 

OK, but given that the noise level is currently way above the noise 
floor of the FSUP, using cross-correlation doesn't add anything - it 
just slows down the measurement.  Cross-correlation would only be of 
benefit to reduce the noise floor of the instrument if/when the phase 
noise of the oscillator has been reduced enough to justify it - it can 
seriously slow down the measurement.

regards

Grant
 


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Re: [time-nuts] xtal oscillator phase noise

2007-12-30 Thread Grant Hodgson
Henk

Two things will dominate if you want such a low phase noise spec.:- the 
  loaded Q of the oscillator circuit, and the flicker corner frequency 
of the sustaining amplifier transistor.  To get a high loaded Q you need 
a crystal with a high unloaded Q - maybe 100 000 or more - this isn't 
difficult to achieve from a good crystal manufacturer, but you can't 
expect any old crystal to work.  And the rest of the oscillator circuit 
should not load the crystal too much, otherwise the loaded Q, and thus 
phase noise, will suffer.  Good crystal manufacturers will provide the 
necessary measurements of series resistance, motional inductance (or 
capacitance, or unloaded Q - doesn't matter which) and static 
capacitance.  Lesser crystal manufacturers - don't.

Also the flicker corner frequency of the transistor needs to be as low 
as possible.  Generally speaking, at offsets below the flicker corner 
frequency you will get 30dB/decade, above the flicker corner frequency 
you should get 20dB/decade, or flat, depending on the level of the phase 
noise floor.  If you can find a transistor with a lower corner 
frequency, the flicker noise will be reduced.  In fact, this is one of 
the dominant parameters when choosing a transistor as an oscillator - 
any old transistor can be made to oscillate, but to do so with a low 
flicker corner frequency is not so easy, and the corner frequency is 
usually a function of bias current.

At 11MHz, most crystal oscillators use parallel resonant crystals, 
although some are series resonant, such as the excellent Driscoll 
oscillator which is capable of the performance you desire with a 
suitable crystal.

Then you have the added problem of the FSUP.  It's a superb instrument, 
but it has it's limitations.  The FSUP data sheet states a phase noise 
spec. of -130dBc at 10Hz offset for a 10MHz signal, which gives a 
resulting sensitivity of -127dBc - 3dB worse than what you are trying to 
achieve.  You would need option B60 (cross correlation) to significantly 
reduce the effect of the internal source by (say) 15db or so.

regards

Grant

Henk wrote :-
Hello,

Some questions on xtal oscillator phase noise. Attached the
measurement result of my series resonant xtal oscillator.
It is a class A, ibias 5 mA, Ixtal 1 mArms. Transistor selected for
low Rbb' 20 Ohm, Ft 100MHz. Reference voltage 5V from an ADR445,
filtered with 10uF folie cap. Phase noise target -130dBc at 10Hz.

1. Is series resonant better or easier to engineer than parallel
resonant?

2. Where should I have 20 dB/decade and where 30 B/decade?

3. Some suggestions for the next 25dB?

4. Is there more to learn from the attached picture?

regards,

Henk

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Re: [time-nuts] Super Regulator links

2007-12-14 Thread Grant Hodgson
Torex make some very nice low noise regulators; the XC6204 series has 
been around for some years now and appears to offer much lower noise 
levels than the 723 :-

http://www.torex-europe.com/products/range/125

Click on 'Technical Diagrams' to see the noise plot of the 3V part - sub 
1uV /rtHz at all frequencies above 100Hz.  One has to assume that the 
noise specification for the uA723 is per rtHz, in which case the Torex 
part has lower noise.  The uA723 has higher ripple rejection though.

The Torex XC6204 is specifically intended for noise-critical 
applications such as oscillators, PLLs and the like - it's not really a 
general purpose regulator like the 723.

Torex parts are available in the UK (and maybe elsewhere) from Farnell, 
other distributors also stock them.

I suspect that lower noise regulators are now available.

regards

Grant


John Miles wrotre :-

What are some of your favorite low-noise regulators?  When I made the 
remark about the uA723, I was specifically thinking of its performance 
compared to the LT1762.  With Cref=5 uF, the uA723's output noise 
voltage is rated at 2.5 uV from 100 Hz to 10 kHz.  The LT1762, which 
seems to be among Linear's quietest parts, is rated at 20 uV from 100 Hz 
to 100 kHz, with external bypassing that places most of the noise at 
lower frequencies.  Snake oil or not, that's 18 dB less noise from the 723.

There are various hacks like Wenzel's that can clean up after a noisy
regulator, but if there are quieter fully-integrated solutions out there 
I'd like to hear about them.  Posted back to the list in case there are 
other views on the subject...

-- john, KE5FX

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Re: [time-nuts] Prologix 3478A

2007-11-30 Thread Grant Hodgson
Chuck et al

I connected my Prologx 3.12 to the 3478A, ran 7470.exe and the 3478A's 
TLK icon came on straight away, with the RMT icon coming on a few 
seconds later.  Repeated it for good measure with the same result.

7470.exe reported an error saying that it was talking to unsupported 
device '0.43700E.00' or something similar so the Prologix was getting 
some data from the 3478A.

Looks like the Prologix adapter is OK.

regards

Grant


 Hi Grant,
 
 It is an axiom of the GPIB world that if a device gets addressed, it
 will sit up at attention and wait for commands.  The 3478A shows that
 it is waiting by lighting up a couple of annunciators on the bottom
 row of the LCD that you never see otherwise.
 
 All you have to do to test whether the Prologix can work with your
 3478A is address it.  So, if you change the 3478A's address to match your
 HP analyzer's, and then run John's program, you should see these 
 annunciators
 light up.
 
 The 3478A won't do anything useful that way, but it will prove that
 it hears the Prologix, something mine can't do.
 
 -Chuck Harris
 
 Grant Hodgson wrote:
 Chuck

 I've got a Prologix 3.12 and a 3478A; I've only ever used the former 
 with John Ms. s/w and HP analysers.  I'll happily test it with the 
 3478A if you give me some simple instructions for a simple XP user.

 regards

 Grant
 
 


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Re: [time-nuts] Osc. Phase Noise Article

2007-09-25 Thread Grant Hodgson
); SAEximRunCond expanded to false
Errors-To: [EMAIL PROTECTED] RETRY

But watch out for the mistakes in some of the equations - e.g. the right 
hand side of eqn 2 is wrong, but eqn 3 is correct, and eqn  9 is wrong.

Don't know if there are any other mistakes, but it's a good article so 
far - haven't finished reading it yet, I can only take so much trig. in 
one day.

regards

Grant

 Message: 3
 Date: Tue, 25 Sep 2007 08:30:49 -0700
 From: Had [EMAIL PROTECTED]
 Subject: [time-nuts] Osc. Phase Noise Article
 To: time-nuts-febo.com time-nuts@febo.com
 Message-ID: [EMAIL PROTECTED]
 Content-Type: text/plain; charset=us-ascii; format=flowed
 
 
 In the current (September) issue of the Microwave Journal there is a 
 pretty comprehensive article Oscillator Phase Noise: Theory and 
 Prediction. It may viewed on the Microwave Journal Web site 
 at  www.mwjournal.com.  Page 178 for the print version.
 
 Best to all,
 Had
 

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Re: [time-nuts] Neat toys on eBay for PN measurement

2007-07-10 Thread Grant Hodgson
); SAEximRunCond expanded to false
Errors-To: [EMAIL PROTECTED]

John

Don't know if you got an answer, but this is my understanding :-

The 11729B needs to have an external 640MHz reference input for 
measurements above 1280MHz.  The 11729C has a SAW-based 640MHz 
oscillator built-in, but it can take an external 640MHz reference signal 
if one is available, such as from the 8662A.

The spec. for the 11729C internal 640MHz osc is not as good as that of 
the 8662A at offsets of up to about 20kHz or so, but at offsets above 
50kHz the 11729C SAW is better than the 8662A's xtal osc.

AFAIK, there is no physical difference between an 8662A with and without 
option 03.  All this option does is mean that somebody has done an extra 
set of measurements on the 640MHz reference output to confirm that it 
did indeed meet the spec.  There was also an option H40 which had an 
even lower noise 10MHz reference which reduced the phase noise at 
offsets up to about 100Hz by 8dB for both the main output and the 640MHz 
reference output.

Also, the 640MHz reference input to the 11729 does not have to be phase 
locked - as long as it does not drift at a rate outside the 11729's PLL 
hold-in range then it will work.  The 11729's PLL will pull the signal 
generator to compensate for drift in either of the two reference inputs 
(640MHz and/or external signal generator).

I've got an 11729B, but no 8662A, so I've started working on the design 
of a very-low phase noise 640MHz source based on an 80MHz crystal osc. 
But until that's ready, I've still been able to make measurements below 
1280MHz without the external reference input.  The Racal 9087 is a 
suitable reference signal generator up to 1.3GHz, which can be phase 
locked, and at offsets greater than about 1kHz it actually has lower 
phase noise than the 8662A.  Other low-noise generators are also 
avaialble...

And for those that can't resist tinkering with the fine offerings from 
the HP labs, I've been wondering if it would be possible or practical to 
replace the internal Step-Recovery Diode comb generator in the 11729B/C 
with one of the Non-Linear Transmission Line comb generators from 
Picosecond Pulse Labs.  PsPL are quoting a 15-20dB reduction in phase 
noise for their NTL comb generator compared to an SRD.  Seems almost too 
good to be true; don't know how much they cost for one-offs but it would 
be interesting to see if it could be used to reduce the residual phase 
noise of the 11729.

regards

Grant

 John Miles wrote :-
 
 That's something I meant to ask you about, Rick, as a follow-up to an old
 Usenet post of yours from 1995.  From looking over the block diagram in the
 11729B-1 app note, it appears that there is no reason why you couldn't feed
 any sufficiently-clean 640 MHz signal in.  Obviously, you want to drive it
 with the cleanest source you can find, but I don't see any other
 constraints.
 
 But some of the 8662As did not have the optional (003) specified SSB phase
 noise for rear-panel output feature, including mine.  They all seem to 
 have
 provided a 640 MHz output at an unused internal SMB jack, though.  Is there
 something special about the reference multiplier section in an option-3
 8662A that actually improves the noise level available at this jack?
 
 I'd already added a BNC jack to the rear panel to bring the 640 MHz clock
 out in anticipation of buying or building a downconverter, and I expect it
 will work OK with this 11729C, but I am not sure whether I should expect 
 the
 fully-characterized option-3 noise performance, or something worse.  Any
 thoughts on that?
 
  From your Usenet post I understand that there is supposed to be a feature
 that lets you turn the built-in 640 MHz SAW filter into an oscillator in
 case an 8662A isn't available, but I also understand that this is really
 only a utility/test function.  If there's no way to phase-lock the 
 resulting
 SAW oscillator, I can see why.
 
 -- john, KE5FX
 
 


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Re: [time-nuts] Neat toys on eBay for PN measurement

2007-07-10 Thread Grant Hodgson
); SAEximRunCond expanded to false
Errors-To: [EMAIL PROTECTED]

The 8662A derrives it's 640MHz o/p from a (very) good 10MHz crystal osc. 
which is then doubled 6 times and filtered at the 40MHz and 160MHz 
stages with crystal filters.  The problem with using so many multipliers 
is that the noise floor increases at every doubler stage, which is why 
the filters are necessary to reduce the the noise floor down to 
something close to thermal.

An alternative is to use a higher frequency crystal osc., such as 80MHz. 
  I guess that this is what Wenzel would do for a 640MHz osc, as 160MHz 
crystals would probably be 7th overtone which have lower Q and therefore 
higher phase noise than 80MHz 5th OT xtals.  That's the route that I'm 
exploring at the moment, and I think it should be possible to get close 
to the performance that Wenzer quote.  A crystal filter at 160MHz would 
be a bounus, an inverted MESA xtal filter at 320MHz or a SAW filter at 
either 320MHz or 640MHz would be better still, but I think this would 
start to add serious $$$ for small quantities.

An 80MHz crystal osc. would probably have worse phase noise very 
close-in (100Hz or less) but better far out and with a lower noise 
floor, compared to a 10MHz osc.  But as I'm not testing radars, I'm not 
after the ultimate close-in performance, I'm more interested in the 
performance at 3kHz-1MHz.

regards

Grant

John Miles wrote:
 Picosecond Pulse Labs quoted me $1,000 for one of the NLTL comb generators a
 couple of years ago.  They are nice parts, no question about it, and
 substantially better than SRD multipliers.
 
 In quantity, they would be cheaper, since I was just asking them for a
 one-off price to some random guy with a credit card.
 
 However, the residual noise floor of the 11729x is still lower than its
 absolute spec when driven by an 8662A's 640 MHz output (see page 42 of
 11729B-1).  So unless you plan to use a quieter 640-MHz driver than an
 option-3 8662A, there seems little benefit in improving its comb generator.
 Likewise, the noise at the 8662A's main output still limits the floor of at
 least some microwave measurements with the 11729.
 
 That said, I am trying to get a price quote out of Wenzel for a 640 MHz ULN
 OCXO:
 http://www.wenzel.com/pdffiles1/Oscillators/ULN_130_to_650.pdf
 
 This is the only OTS source I can find that's substantially cleaner than the
 'typical' figures quoted for the 8662A's 640-MHz output.  It would sure be
 nice to install one of these as an an internal source in the 11729, and
 drive its electrical tuning line from the quadrature PLL.
 
 -- john, KE5FX

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Re: [time-nuts] Low noise frequency multiplication

2007-03-01 Thread Grant Hodgson
Stephen

 It seems there are indeed many ways to kill a cat.

More ways than you could imagine...

IMHO, a 100MHz PLL is likely to give the best results, and is very easy 
to implement.  A 100MHz crystal oscillator should give very low phase 
noise and spur levels; crystals are readily available and there are 
quite a few circuits around.

Crystal oscillators running at 100MHz or so are widely used by radio 
hams for multiplication up to microwave frequencies so the phase noise 
and spur levels has to be low to start with, which a VCXO can achieve. 
Crystal oscillators can easily be disciplined with a varactor diode. 
Various PLL configuations exist to do this and the loop bandwidth is 
very narrow so the phase noise will not be degraded significantly by the 
PLL.

There are other ways as well, but my vote would be for the VCXO as above.

regards

Grant

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Re: [time-nuts] time-nuts Digest, Vol 29, Issue 86

2006-12-29 Thread Grant Hodgson
Stephan

--snip--

 
 I prefer phase detectors which is more continous such as mixers, XOR or
 S-R style phase detectors.
 
 In this case the phase detector is purely digital so I guess the loop filter
 could also be a purely digital IIR filter (or something?) I guess the only
 limitation is the frequency at which the digital system could run.
 

Going back through this thread, it seems you want to lock a 100MHz OCXO 
to a 10MHz reference, which is itself disciplined to PPS.  By far the 
easiest solution would be to discipline the 100MHz OCXO directly to the 
PPS - this will have negligible impact on the OCXO's phase noise and is 
a simple, reliable method - the Luis Cupido design will work very well 
for example, and there are other designs.

regards

Grant

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Re: [time-nuts] Wikipedia Dual-modulus Prescaler item

2006-12-22 Thread Grant Hodgson
Dunno if it's still relevant, but the Wikipedia article on dual-mode 
prescalers is confusing, to say the least.

Here's a much better description, written by a master of explaining the 
complicated to the uninitiated in simple terms - Dean Banerjee :-

http://www.national.com/AU/files/PLL_Building_Blocks.pdf

regards

Grant Hodgson

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