Anyone got any mileage, manuals, rumors, etc. of the Wavetek 273 signal generator? A customer is testing a PLL that I designed. The PLL is designed to go into the far sub-Hz bandwidths, and they're having trouble getting it to lock onto the 15kHz signal from a Wavetek 273. I've got it running off of a crystal oscillator divided down and made into a sine wave, and it's perking along quite happily at a bandwidth of 1/50th Hz. They can't run it at a bandwidth below about 5Hz. All I can find for that signal generator are places selling manuals, and a picture of the front panel. It has a digital readout and appears to be synthesized -- yet it's actual performance doesn't seem to jibe with the performance my customer is seeing. So I'm wondering if its broken, or if it's just a multivibrator oscillator behind a dolled-up digital panel, or what. -- www.wescottdesign.com
Wavetek 273
Started by ●November 21, 2011
Reply by ●November 21, 20112011-11-21
On Mon, 21 Nov 2011 17:43:28 -0600, Tim Wescott <tim@seemywebsite.com> wrote:>Anyone got any mileage, manuals, rumors, etc. of the Wavetek 273 signal >generator? > >A customer is testing a PLL that I designed. The PLL is designed to go >into the far sub-Hz bandwidths, and they're having trouble getting it to >lock onto the 15kHz signal from a Wavetek 273. I've got it running off >of a crystal oscillator divided down and made into a sine wave, and it's >perking along quite happily at a bandwidth of 1/50th Hz. > >They can't run it at a bandwidth below about 5Hz. > >All I can find for that signal generator are places selling manuals, and >a picture of the front panel. It has a digital readout and appears to be >synthesized -- yet it's actual performance doesn't seem to jibe with the >performance my customer is seeing. > >So I'm wondering if its broken, or if it's just a multivibrator >oscillator behind a dolled-up digital panel, or what.Maybe it has so much jitter that your loop can't lock to it? Sometimes you have to have a wider acquisition BW, then ease into narrow. ...Jim Thompson -- | James E.Thompson, CTO | mens | | Analog Innovations, Inc. | et | | Analog/Mixed-Signal ASIC's and Discrete Systems | manus | | Phoenix, Arizona 85048 Skype: Contacts Only | | | Voice:(480)460-2350 Fax: Available upon request | Brass Rat | | E-mail Icon at http://www.analog-innovations.com | 1962 | I love to cook with wine. Sometimes I even put it in the food.
Reply by ●November 21, 20112011-11-21
On Mon, 21 Nov 2011 16:47:01 -0700, Jim Thompson wrote:> On Mon, 21 Nov 2011 17:43:28 -0600, Tim Wescott <tim@seemywebsite.com> > wrote: > >>Anyone got any mileage, manuals, rumors, etc. of the Wavetek 273 signal >>generator? >> >>A customer is testing a PLL that I designed. The PLL is designed to go >>into the far sub-Hz bandwidths, and they're having trouble getting it to >>lock onto the 15kHz signal from a Wavetek 273. I've got it running off >>of a crystal oscillator divided down and made into a sine wave, and it's >>perking along quite happily at a bandwidth of 1/50th Hz. >> >>They can't run it at a bandwidth below about 5Hz. >> >>All I can find for that signal generator are places selling manuals, and >>a picture of the front panel. It has a digital readout and appears to >>be synthesized -- yet it's actual performance doesn't seem to jibe with >>the performance my customer is seeing. >> >>So I'm wondering if its broken, or if it's just a multivibrator >>oscillator behind a dolled-up digital panel, or what. > > Maybe it has so much jitter that your loop can't lock to it? Sometimes > you have to have a wider acquisition BW, then ease into narrow.It has so much low-frequency jitter (wander? -- call it what you will) that the loop locks, then after a while unlocks. The signal that they'll be locking onto is going to be very stable, so one would like to test the loop with a test source whose stability matches the ultimate one. They're waiting to cut me a PO for more work until they've verified that it works, which is reasonable. I know darn well it works just fine, so I want to help them achieve their test goals! -- www.wescottdesign.com
Reply by ●November 21, 20112011-11-21
On Mon, 21 Nov 2011 17:52:12 -0600, Tim Wescott <tim@seemywebsite.com> wrote:>On Mon, 21 Nov 2011 16:47:01 -0700, Jim Thompson wrote: > >> On Mon, 21 Nov 2011 17:43:28 -0600, Tim Wescott <tim@seemywebsite.com> >> wrote: >> >>>Anyone got any mileage, manuals, rumors, etc. of the Wavetek 273 signal >>>generator? >>> >>>A customer is testing a PLL that I designed. The PLL is designed to go >>>into the far sub-Hz bandwidths, and they're having trouble getting it to >>>lock onto the 15kHz signal from a Wavetek 273. I've got it running off >>>of a crystal oscillator divided down and made into a sine wave, and it's >>>perking along quite happily at a bandwidth of 1/50th Hz. >>> >>>They can't run it at a bandwidth below about 5Hz. >>> >>>All I can find for that signal generator are places selling manuals, and >>>a picture of the front panel. It has a digital readout and appears to >>>be synthesized -- yet it's actual performance doesn't seem to jibe with >>>the performance my customer is seeing. >>> >>>So I'm wondering if its broken, or if it's just a multivibrator >>>oscillator behind a dolled-up digital panel, or what. >> >> Maybe it has so much jitter that your loop can't lock to it? Sometimes >> you have to have a wider acquisition BW, then ease into narrow. > >It has so much low-frequency jitter (wander? -- call it what you will) >that the loop locks, then after a while unlocks. The signal that they'll >be locking onto is going to be very stable, so one would like to test the >loop with a test source whose stability matches the ultimate one. > >They're waiting to cut me a PO for more work until they've verified that >it works, which is reasonable. I know darn well it works just fine, so I >want to help them achieve their test goals!What is the point of an extremely narrow bandwidth? What you need is a very high-Q VCO but with a bandwidth adequate to not lose the source. ...Jim Thompson -- | James E.Thompson, CTO | mens | | Analog Innovations, Inc. | et | | Analog/Mixed-Signal ASIC's and Discrete Systems | manus | | Phoenix, Arizona 85048 Skype: Contacts Only | | | Voice:(480)460-2350 Fax: Available upon request | Brass Rat | | E-mail Icon at http://www.analog-innovations.com | 1962 | I love to cook with wine. Sometimes I even put it in the food.
Reply by ●November 21, 20112011-11-21
On Mon, 21 Nov 2011 17:12:32 -0700, Jim Thompson wrote:> On Mon, 21 Nov 2011 17:52:12 -0600, Tim Wescott <tim@seemywebsite.com> > wrote: > >>On Mon, 21 Nov 2011 16:47:01 -0700, Jim Thompson wrote: >> >>> On Mon, 21 Nov 2011 17:43:28 -0600, Tim Wescott <tim@seemywebsite.com> >>> wrote: >>> >>>>Anyone got any mileage, manuals, rumors, etc. of the Wavetek 273 >>>>signal generator? >>>> >>>>A customer is testing a PLL that I designed. The PLL is designed to >>>>go into the far sub-Hz bandwidths, and they're having trouble getting >>>>it to lock onto the 15kHz signal from a Wavetek 273. I've got it >>>>running off of a crystal oscillator divided down and made into a sine >>>>wave, and it's perking along quite happily at a bandwidth of 1/50th >>>>Hz. >>>> >>>>They can't run it at a bandwidth below about 5Hz. >>>> >>>>All I can find for that signal generator are places selling manuals, >>>>and a picture of the front panel. It has a digital readout and >>>>appears to be synthesized -- yet it's actual performance doesn't seem >>>>to jibe with the performance my customer is seeing. >>>> >>>>So I'm wondering if its broken, or if it's just a multivibrator >>>>oscillator behind a dolled-up digital panel, or what. >>> >>> Maybe it has so much jitter that your loop can't lock to it? Sometimes >>> you have to have a wider acquisition BW, then ease into narrow. >> >>It has so much low-frequency jitter (wander? -- call it what you will) >>that the loop locks, then after a while unlocks. The signal that >>they'll be locking onto is going to be very stable, so one would like to >>test the loop with a test source whose stability matches the ultimate >>one. >> >>They're waiting to cut me a PO for more work until they've verified that >>it works, which is reasonable. I know darn well it works just fine, so >>I want to help them achieve their test goals! > > What is the point of an extremely narrow bandwidth?To reject measurement noise.> What you need is a > very high-Q VCO but with a bandwidth adequate to not lose the source.Well, depending on how much things are corrupted by noise I suppose you're right. I may, indeed, be gilding the lily on this particular part of the system. But their test source is still miles less stable than their ultimate source, and it's causing me grief! -- www.wescottdesign.com
Reply by ●November 21, 20112011-11-21
On Mon, 21 Nov 2011 18:18:18 -0600, Tim Wescott <tim@seemywebsite.com> wrote:>On Mon, 21 Nov 2011 17:12:32 -0700, Jim Thompson wrote: > >> On Mon, 21 Nov 2011 17:52:12 -0600, Tim Wescott <tim@seemywebsite.com> >> wrote: >> >>>On Mon, 21 Nov 2011 16:47:01 -0700, Jim Thompson wrote: >>> >>>> On Mon, 21 Nov 2011 17:43:28 -0600, Tim Wescott <tim@seemywebsite.com> >>>> wrote: >>>> >>>>>Anyone got any mileage, manuals, rumors, etc. of the Wavetek 273 >>>>>signal generator? >>>>> >>>>>A customer is testing a PLL that I designed. The PLL is designed to >>>>>go into the far sub-Hz bandwidths, and they're having trouble getting >>>>>it to lock onto the 15kHz signal from a Wavetek 273. I've got it >>>>>running off of a crystal oscillator divided down and made into a sine >>>>>wave, and it's perking along quite happily at a bandwidth of 1/50th >>>>>Hz. >>>>> >>>>>They can't run it at a bandwidth below about 5Hz. >>>>> >>>>>All I can find for that signal generator are places selling manuals, >>>>>and a picture of the front panel. It has a digital readout and >>>>>appears to be synthesized -- yet it's actual performance doesn't seem >>>>>to jibe with the performance my customer is seeing. >>>>> >>>>>So I'm wondering if its broken, or if it's just a multivibrator >>>>>oscillator behind a dolled-up digital panel, or what. >>>> >>>> Maybe it has so much jitter that your loop can't lock to it? Sometimes >>>> you have to have a wider acquisition BW, then ease into narrow. >>> >>>It has so much low-frequency jitter (wander? -- call it what you will) >>>that the loop locks, then after a while unlocks. The signal that >>>they'll be locking onto is going to be very stable, so one would like to >>>test the loop with a test source whose stability matches the ultimate >>>one. >>> >>>They're waiting to cut me a PO for more work until they've verified that >>>it works, which is reasonable. I know darn well it works just fine, so >>>I want to help them achieve their test goals! >> >> What is the point of an extremely narrow bandwidth? > >To reject measurement noise. > >> What you need is a >> very high-Q VCO but with a bandwidth adequate to not lose the source. > >Well, depending on how much things are corrupted by noise I suppose >you're right. I may, indeed, be gilding the lily on this particular part >of the system. But their test source is still miles less stable than >their ultimate source, and it's causing me grief!What are you using for a phase detector? ...Jim Thompson -- | James E.Thompson, CTO | mens | | Analog Innovations, Inc. | et | | Analog/Mixed-Signal ASIC's and Discrete Systems | manus | | Phoenix, Arizona 85048 Skype: Contacts Only | | | Voice:(480)460-2350 Fax: Available upon request | Brass Rat | | E-mail Icon at http://www.analog-innovations.com | 1962 | I love to cook with wine. Sometimes I even put it in the food.
Reply by ●November 21, 20112011-11-21
On Mon, 21 Nov 2011 17:43:28 -0600, Tim Wescott <tim@seemywebsite.com> wrote:>Anyone got any mileage, manuals, rumors, etc. of the Wavetek 273 signal >generator? > >A customer is testing a PLL that I designed. The PLL is designed to go >into the far sub-Hz bandwidths, and they're having trouble getting it to >lock onto the 15kHz signal from a Wavetek 273. I've got it running off >of a crystal oscillator divided down and made into a sine wave, and it's >perking along quite happily at a bandwidth of 1/50th Hz. > >They can't run it at a bandwidth below about 5Hz. > >All I can find for that signal generator are places selling manuals, and >a picture of the front panel. It has a digital readout and appears to be >synthesized -- yet it's actual performance doesn't seem to jibe with the >performance my customer is seeing. > >So I'm wondering if its broken, or if it's just a multivibrator >oscillator behind a dolled-up digital panel, or what.If the jitter/FM is on the order of 5 Hz out of 15 KHz, you should be able to see that on an oscilloscope, analog or digital. Decent analog scopes had timebase jitter of a part in 30,000 or so. You could also zoom up the zero crossings and look for uglies there. An old Wavetek could easily have that sort of jitter. Even a modern DDS generator can have period jitter in the ballpark of 1 part in 10,000 at low frequencies, where the output lowpass filter doesn't affect the DAC quantization much. Worse if the DAC doesn't have a lot of bits. We do interpolation in our DDS signal generators, which helps some, but not everybody does that. John
Reply by ●November 21, 20112011-11-21
Tim, if you are doing the phase comparison ON the output frequency, i.e. there is no division, then the "Dynamic range" of phase jitter that the loop can tolerate without cycle slip is the same as the linear range of the phase detector itself which is typicaly 180 to 360 deg. If the jitter execeeds this value, the loop will cycle slip and no longer be "phase locked" The way to improve this is to divide the variable and ref frequency before they are phase compared. For example if you divide both by 10, then you still have a loop operating on the same frequency but the loop can tolerate 10 times the amount of phase jitter without cycle slipping. (Of course you have to modify the loop filter accordingly as well) I came across this problem first a long time ago when designing a PLL FM transmitter. We wanted the VCO to be FM'd with the audio but want the PLL to keep the average frequency correct. In order to get this to work correctly, we had to divide the comparison frequency down to so that at the max freq deviation at the lowest audio freq, the phase change at the phase detector was within it's dymaic range. This is an interesitng problem.. Mark K
Reply by ●November 22, 20112011-11-22
Tim Wescott wrote:> Anyone got any mileage, manuals, rumors, etc. of the Wavetek 273 signal > generator? > > A customer is testing a PLL that I designed. The PLL is designed to go > into the far sub-Hz bandwidths, and they're having trouble getting it to > lock onto the 15kHz signal from a Wavetek 273. I've got it running off > of a crystal oscillator divided down and made into a sine wave, and it's > perking along quite happily at a bandwidth of 1/50th Hz. > They can't run it at a bandwidth below about 5Hz.What is your PLL acquisition bandwidth?> All I can find for that signal generator are places selling manuals, and > a picture of the front panel. It has a digital readout and appears to be > synthesized -- yet it's actual performance doesn't seem to jibe with the > performance my customer is seeing.The 1e-5 is too much of accuracy expectation for the off-the-shelf MCU grade crystal; not mentionning 1e-6. You can reliably count on 1e-4.> So I'm wondering if its broken, or if it's just a multivibrator > oscillator behind a dolled-up digital panel, or what.Add a discriminator to your PLL or use a frequency-phase detector to assist the initial pull-in. Vladimir Vassilevsky DSP and Mixed Signal Design Consultant http://www.abvolt.com
Reply by ●November 22, 20112011-11-22
On Mon, 21 Nov 2011 22:36:33 -0600, Vladimir Vassilevsky <nospam@nowhere.com> wrote:> > >Tim Wescott wrote: > >> Anyone got any mileage, manuals, rumors, etc. of the Wavetek 273 signal >> generator? >> >> A customer is testing a PLL that I designed. The PLL is designed to go >> into the far sub-Hz bandwidths, and they're having trouble getting it to >> lock onto the 15kHz signal from a Wavetek 273. I've got it running off >> of a crystal oscillator divided down and made into a sine wave, and it's >> perking along quite happily at a bandwidth of 1/50th Hz. >> They can't run it at a bandwidth below about 5Hz. > >What is your PLL acquisition bandwidth? > >> All I can find for that signal generator are places selling manuals, and >> a picture of the front panel. It has a digital readout and appears to be >> synthesized -- yet it's actual performance doesn't seem to jibe with the >> performance my customer is seeing. > >The 1e-5 is too much of accuracy expectation for the off-the-shelf MCU >grade crystal; not mentionning 1e-6. You can reliably count on 1e-4.$3 Digikey packaged crystal oscillators have typical jitters of a few ns per second... parts in 1e9, or 1e8 for a really bad one. Tempcos are usually a fraction of a PPM per degree C. They are usually within 10 PPM of advertised frequency, at least initially. A decent SC-cut OCXO has one-second jitter of a few parts in 1e12. John
