The frequency stability of my HP3312A function generator is poor, very annoying for any practical use. I am trying to determine whether that behavior is fairly normal for function generators, or my particular unit has got a problem.
What is your experience on function generators frequency stability?
Thanks & 73
Tony Rome, Italy
"Antonio I0JX" wrote in news:4f665080$0$1388$ snipped-for-privacy@reader2.news.tin.it:
it depends on the clock source; some generators use better,ovenized crystal timebases. The HP synthesizers had an option for high stability timebases,ISTR. or you can feed in an external timebase. At TEK,I used to feed a HP3336 with the output from my WWVB receiver.
-- Jim Yanik jyanik at localnet dot com
"Jim Yanik" ha scritto nel messaggio news:XnsA01AB1050DA2Ajyaniklocalnetcom@216.168.3.44...
"Antonio I0JX" wrote in news:4f665080$0$1388$ snipped-for-privacy@reader2.news.tin.it:
it depends on the clock source; some generators use better,ovenized crystal timebases. The HP synthesizers had an option for high stability timebases,ISTR. or you can feed in an external timebase. At TEK,I used to feed a HP3336 with the output from my WWVB receiver.
-- Jim Yanik jyanik at localnet dot com Thanks Jim. the oscillator of my HP function generator utilizes a circuit whereby a capacitor is charged at constant current, and frequency is adjusted by a front-panel potentiometer. One may not expect much from that, but frequency stability is really bad. I should find someone having a generator working on the same principle, if not just the same HP model. Regards. Tony
"Antonio I0JX"
** Normally, frequency stability relates to the internal temperature of a generator - so frequency stability = temperature stability. If the frequency varies independently of temperature, then there is something wrong like a faulty frequency control pot.In any case, the tempco of a carbon track pot ( as used in the 3312a) is way higher than metal film resistors and film capacitors.
How bad is your unit's stability ?
If ( after a 1 hour warm up ) you set the gene at 10kHz and waited 30 minutes - what would the new frequency be?
.... Phil
"Jim Yanik"
** It's an analogue function generator.Stability depends on the tempcos of Rs, Cs and pots.
.... Phil
"Antonio I0JX" wrote in news:4f667089$0$1385$ snipped-for-privacy@reader1.news.tin.it:
Thanks Jim.
the oscillator of my HP function generator utilizes a circuit whereby a capacitor is charged at constant current, and frequency is adjusted by a front-panel potentiometer. One may not expect much from that, but frequency stability is really bad. I should find someone having a generator working on the same principle, if not just the same HP model.
Regards.
Tony
my apologies,I had thought that the HP33xx series were all digital synthesizers. you're not going to get "good" freq stability from an analog generator.
does the freq. stability meet the specs? if so,are the specs good enough for what you want?
maybe your potentiometer is dirty or noisy,or some capacitor in the current source has gone bad.
maybe I'll go look at the schematics and specs,if I can find the manual and it's not a huge file.
-- Jim Yanik jyanik at localnet dot com
How good stability were you expecting? Are you asking about temperature stability, or just drift?
The HP3312A was not intended to be the ultimate stable frequency standard. Just because it goes up to RF frequencies doesn't mean it can substitute for a proper RF generator. If you look at the specifications:
you'll see that the frequency stability is not specified. That should be a clue. Dial accuracy is only 5%, whatever that means.
If you want accuracy and stability, I suggest a synthesized function generator.
If you want to do it yourself with a PLL, build an external phase comparitor, with the output going to the FM sweep input, and the inputs from the sync output, and a suitable frequency reference. A
1KHz reference frequency, will give a frequency output locked at 1KHz intervals.-- Jeff Liebermann jeffl@cruzio.com 150 Felker St #D http://www.LearnByDestroying.com Santa Cruz CA 95060 http://802.11junk.com Skype: JeffLiebermann AE6KS 831-336-2558
Statements like "frequency stability is bad or poor will get you nowhere. What are your requirements for stability? Under what conditions? Temperature variability, time variability, noise??? At what frequency? What is the stability you are MEASURING? What is the stability spec of the generator? Stability is a NUMBER, not a vague statement of dissatisfaction.
HP equipment of that vintage was typically near the better end of performance for equipment of that vintage. But even HP equipment breaks. Performance is usually better near the top end of the dial. Just 'cause you can get 1000:1 range on the knob doesn't mean you should.
OK, I looked up the spec. I can't find any reference in the spec to frequency stability, other than it takes an hour for the frequency to get within 5% of the dial setting. That oughta tell you something.
In general, if your requirements contain the word "stability", a function generator is a poor choice.
or. get one of those DDS AF from Rigol like I did.
Now there's a thing of beauty for the price. I got it when it was on sale and paid less.
Jamie
does the freq. stability meet the specs?
The HP manual does not tell anything on frequency stability. No useful info found on the web either.
if so,are the specs good enough for what you want?
Not at all. The instrument is nearly unusable for my purposes.
Frequency measurement results:
- Just turned on. Frequency = 5.000 MHz Delta F = 0
- 15 minutes after. Delta F = -98 kHz
- 30 minutes after. Delta F = - 116 kHz
- 45 minutes after. Delta F = -132 kHz
- 60 minutes after. Delta F = -141 kHz
- 75 minutes after. Delta F = -147 kHz
maybe your potentiometer is dirty or noisy,or some capacitor in the current source has gone bad.
I lubricated switches and potentiometers. A capacitor may well be, but it is difficult to locate components on the board.
maybe I'll go look at the schematics and specs,if I can find the manual and it's not a huge file.
Thanks. Anyway again my question is: is my generator faulty or all instruments based on the same (analog) frequency generation principle (charging a capacitor at constant current) behave more or less the same?
-3% drift is pretty horrible, even for Wun Hung Lo. Something's busted.
Cheers
Phil Hobbs
-- Dr Philip C D Hobbs Principal Consultant ElectroOptical Innovations LLC Optics, Electro-optics, Photonics, Analog Electronics 160 North State Road #203 Briarcliff Manor NY 10510 845-480-2058 hobbs at electrooptical dot net http://electrooptical.net
Statements like "frequency stability is bad or poor will get you nowhere. What are your requirements for stability? Under what conditions? Temperature variability, time variability, noise??? At what frequency?
My requirements are fairly modest. Just to tune HF receivers and their IF chains. Say from 200 kHz to 10 MHz. Noise and temperature is not an issue for my case.
What is the stability you are MEASURING?
Frequency measurement results:
- Just turned on. Frequency = 5.000 MHz Delta F = 0
- 15 minutes after. Delta F = -98 kHz (drift = 6.5 kHz per minute)
- 30 minutes after. Delta F = - 116 kHz (drift = 3.7 kHz per minute)
- 45 minutes after. Delta F = -132 kHz (drift = 2.9 kHz per minute)
- 60 minutes after. Delta F = -141 kHz (drift = 2.3 kHz per minute)
- 75 minutes after. Delta F = -147 kHz (drift = 2.0 kHz per minute)
Drift is too high for any practical use.
What is the stability spec of the generator? Stability is a NUMBER, not a vague statement of dissatisfaction.
Tell HP. They do not mention frequency stability in the manual and no useful information can be found on the web.
HP equipment of that vintage was typically near the better end of performance for equipment of that vintage. But even HP equipment breaks. Performance is usually better near the top end of the dial. Just 'cause you can get 1000:1 range on the knob doesn't mean you should.
This is just I what I would to like to know: which is people experience with non-HP generators using an analog frequency-generation circuit.
OK, I looked up the spec. I can't find any reference in the spec to frequency stability, other than it takes an hour for the frequency to get within 5% of the dial setting. That oughta tell you something.
Well, that figure is also related to dial accuracy, but can serve to broadly figure out frequency stability.
In general, if your requirements contain the word "stability", a function generator is a poor choice.
I know, but if they produce them, they evidently serve to do something. In my case there is nothing I can do with such a poor generator. And that is HP! Again my question is: is my generator faulty or all instruments based on the same (analog) frequency generation principle (charging a capacitor at constant current) behave more or less the same?
Regards.
Tony
In any case, the tempco of a carbon track pot ( as used in the 3312a) is way higher than metal film resistors and film capacitors.
How bad is your unit's stability ?
If ( after a 1 hour warm up ) you set the gene at 10kHz and waited 30 minutes - what would the new frequency be?
Frequency measurement results:
- Just turned on. Frequency = 5.000 MHz Delta F = 0
- 15 minutes after. Delta F = -98 kHz (drift = 6.5 kHz per minute)
- 30 minutes after. Delta F = - 116 kHz (drift = 3.7 kHz per minute)
- 45 minutes after. Delta F = -132 kHz (drift = 2.9 kHz per minute)
- 60 minutes after. Delta F = -141 kHz (drift = 2.3 kHz per minute)
- 75 minutes after. Delta F = -147 kHz (drift = 2.0 kHz per minute)
Drift is too high for any practical use.
Tried to lubricate potentiometers and switches with no success.
Again my question is: is my generator faulty or all instruments based on the same (analog) frequency generation principle (charging a capacitor at constant current) behave more or less the same?
Regards.
Tony
How good stability were you expecting? Are you asking about temperature stability, or just drift?
The HP3312A was not intended to be the ultimate stable frequency standard. Just because it goes up to RF frequencies doesn't mean it can substitute for a proper RF generator. If you look at the specifications:
you'll see that the frequency stability is not specified. That should be a clue. Dial accuracy is only 5%, whatever that means.
If you want accuracy and stability, I suggest a synthesized function generator.
If you want to do it yourself with a PLL, build an external phase comparitor, with the output going to the FM sweep input, and the inputs from the sync output, and a suitable frequency reference. A
1KHz reference frequency, will give a frequency output locked at 1KHz intervals.Hi Jeff
Frequency measurement results are:
- Just turned on. Frequency = 5.000 MHz Delta F = 0
- 15 minutes after. Delta F = -98 kHz (drift = 6.5 kHz per minute)
- 30 minutes after. Delta F = - 116 kHz (drift = 3.7 kHz per minute)
- 45 minutes after. Delta F = -132 kHz (drift = 2.9 kHz per minute)
- 60 minutes after. Delta F = -141 kHz (drift = 2.3 kHz per minute)
- 75 minutes after. Delta F = -147 kHz (drift = 2.0 kHz per minute)
Drift is too high for any practical use.
But before throwing it in the waste basket (as I'll probably do in the end), I would be curious to know the experience of other people having that generator or a similar one using the same (analog) frequency generation principle (charging a capacitor at constant current). Do all of them behave more or less the same? Is my unit faulty?
Regards.
Tony
150KHz of 5000KHz is 3% drift. That's within the specified 5%.
Really? I used a 3312A in the 1970's to do type certification on various radios. It was perfectly suited for running as an audio sweep generator, or for making manual plots of various devices frequency response. The only time I ran into trouble was when I had to generate a specific frequency tone, such as the Bell system test frequency of
1004Hz. I just connected a frequency counter and reset the dial every time it tried to move.Whether it's practical depends on what you are doing with it. What is your application? If it's generating a 5MHz RF signal to radio receiver, forget it. Not only is it not stable enough, but the AM and FM noise produced by the function generator is truly awful.
I think you'll find that it's a rather useful piece of equipment for audio, not RF. I suggest you keep it (or sell it). Checking eBay completed listings, they were recently sold from $70 to $150.
It's not faulty and all such analog instruments drift and are noisy. Please disclose your application and I can offer a class of suitable instruments, or a specific device that I like.
My (messy) bench:
I count 7 different signal sources on the bench. There are about 10 more scattered in different corners. One signal source just can't do everything.
-- # Jeff Liebermann 150 Felker St #D Santa Cruz CA 95060 # 831-336-2558 # http://802.11junk.com jeffl@cruzio.com # http://www.LearnByDestroying.com AE6KS
"Antonio I0JX"
** A function generator is ** NOT ** an RF generator !!!The drift you are seeing is completely normal - for a function generator.
Bloody stupid radio ham.
.... Phil
Your requirements are not modest. You are asking the device to perform a function it was never intended to do.
If you expect to tune receiver IF chains with a function generator, you need to be willing to wait for everything to warm up, use a secondary frequency measurement device and do the job quickly. It does sweep, so you could sweep the IF and use a marker.
I don't understand your numbers at all. I see 6 kHz in 15 minutes. By my math, that's ~400 Hz. / minute
Drift is just fine for the INTENDED uses.
TEK CFG280 11MHz sweep function generator. Started at 5MHz. Drifted up to 5.077 in 3 minutes, then started down. After 52minutes it was back down to 5.022 and drifting down at about 300Hz/minute. Pretty similar to yours after initial warmup. I made no attempt to factor out the startup drift of the internal frequency counter.
Remember, that's 5% of full scale. So with a 1000:1 frequency range, that can be up to 5000% off.
A function generator is a very nice general purpose instrument. You're using it for the wrong purpose.
Back in the day, I managed a function generator design group. I don't remember a single discussion about frequency stability. It was all about triangle linearity, square-wave transient response, sine-wave distortion and amplitude flatness with frequency.
There's nothing inherently unstable about the topology. But the devil is in the details. A crystal is stable because you can't change the frequency. A function generator is designed for a 1000:1 frequency range. That makes it exceedingly sensitive to parameter variations.
The HP is more vulnerable because it does include sweep functions designed to change the frequency. I'm stating the obvious here, but make sure the modulation functions are set to something other than FM. And the inputs are grounded, including the VCO input on the back.
I'm too lazy to study the schematic, but anything connected to the frequency path can inject drift. You might be able to cut loose some of the sweep functions.
Power supply voltage is critical. Direct measurements are difficult because of the small variations involved. Load the output with 50 ohms and vary the amplitude from 0 to max. If the frequency changes, you might want to check out the power supply. The reverse is not true. If the frequency does not change, that doesn't rule out temperature variations in the power supply voltages.
You can poke around inside with a tiny heat source. I use a catalytic butane hot-air gun from Portasol. Freeze mist works too if you can still find it. But, since there's a lot of temperature compensation going on in the loop, heating one component in the loop may lead you astray.
Bottom line, I think your generator is working fine. You're using it for an unintended purpose outside it's performance ability.
That's an emotional reaction. Would you be upset with your plow horse because it didn't win the Kentucky Derby? It's all about matching the tool to the task.
Don't throw it in the trash. I know a dozen people who'd love to have it.
** In each case, the radio ham idiot has divided Dekta F by the elapsed time.
How utterly clueless.
.... Phil
The guy came here for help. He has been courteous. Derision is inappropriate.
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