Your experience with function generators

[Antonio I0JX]

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]

Antonio I0JX wrote:

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
http://www.dougdeals.com/p-6037-hp-3312a-function-generator-operating-service-manual.aspx

There's a service manual if you think there is something wrong with it?

You don't say how bad of stability ? I wouldn't think it would be bad
enough to be noticeable in a hour or two use. You could have bad caps in
the power supply with intermitting leaks causing some voltage instabilities?

Jamie



Thanks Jamie.

I already have the service manual, but it is not of too much help (it is
very difficult to locate components on the boards, moreover components bear
a proprietary HP identification code which does not help).

Setting the generator at say 10 MHz and listening the produced carrier on an
SSB communications receiver, the tone sounds VERY rough (this indicating a
lot of phase noise).

However, more than phase noise, what worries me is frequency stability. Even
though I have not done precise measurements, I would say that the 10-MHz
carrier steadily shifts downwards in frequency at a rate of say a couple of
kHz per minute. Moreover it is a bit "jumpy", i.e. frequency does not vary
smoothly, though not to the extent of indicating some instability in
components. Knocking on the boards produces no discernible effect.

Waiting for the generator to get thermally stabilized, the situation
improves but not as much as I would have expected.

As that is the only function generator I ever possessed, I cannot be sure
whether instability is inherent in the principle by which carrier frequency
is produced (i.e. by charging a capacitor at constant current).

So, knowing the experience of other people would be of great help to me.

Regards

Tony

 

[Antonio I0JX]

Antonio I0JX wrote:

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

http://www.dougdeals.com/p-6037-hp-3312a-function-generator-operating-service-manual.aspx

There's a service manual if you think there is something wrong with it?

You don't say how bad of stability ? I wouldn't think it would be bad
enough to be noticeable in a hour or two use. You could have bad caps in
the power supply with intermitting leaks causing some voltage instabilities?

Jamie



Thanks Jamie.

I already have the service manual, but it is not of too much help (it is
very difficult to locate components on the boards, moreover components bear
a proprietary HP identification code which does not help).

Setting the generator at say 10 MHz and listening the produced carrier on an
SSB communications receiver, the tone sounds VERY rough (this indicating a
lot of phase noise).

However, more than phase noise, what worries me is frequency stability. Even
though I have not done precise measurements, I would say that the 10-MHz
carrier steadily shifts downwards in frequency at a rate of say a couple of
kHz per minute. Moreover it is a bit "jumpy", i.e. frequency does not vary
smoothly, though not to the extent of indicating some instability in
components. Knocking on the boards produces no discernible effect.

Waiting for the generator to get thermally stabilized, the situation
improves but not as much as I would have expected.

As that is the only function generator I ever possessed, I cannot be sure
whether instability is inherent in the principle by which carrier frequency
is produced (i.e. by charging a capacitor at constant current).

So, knowing the experience of other people would be of great help to me.

Regards

Tony

 

[Antonio I0JX]

"Jamie" ha scritto nel messaggio newsvt9r.13378$IQ1.11384@newsfe18.iad...

Antonio I0JX wrote:

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
http://www.dougdeals.com/p-6037-hp-3312a-function-generator-operating-service-manual.aspx

There's a service manual if you think there is something wrong with it?

You don't say how bad of stability ? I wouldn't think it would be bad
enough to be noticeable in a hour or two use. You could have bad caps in
the power supply with intermitting leaks causing some voltage instabilities?

Jamie

Thanks Jamie.

I already have the service manual, but it is not of too much help (it is
very difficult to locate components on the boards, moreover components bear
a proprietary HP identification code which does not help).

Setting the generator at say 10 MHz and listening the produced carrier on an
SSB communications receiver, the tone sounds VERY rough (this indicating a
lot of phase noise).

However, more than phase noise, what worries me is frequency stability. Even
though I have not done precise measurements, I would say that the 10-MHz
carrier steadily shifts downwards in frequency at a rate of say a couple of
kHz per minute. Moreover it is a bit "jumpy", i.e. frequency does not vary
smoothly, though not to the extent of indicating some instability in
components. Knocking on the boards produces no discernible effect.

Waiting for the generator to get thermally stabilized, the situation
improves but not as much as I would have expected.

As that is the only function generator I ever possessed, I cannot be sure
whether instability is inherent in the principle by which carrier frequency
is produced (i.e. by charging a capacitor at constant current).

So, knowing the experience of other people would be of great help to me.

Regards

Tony

 

[Jamie]

Antonio I0JX wrote:

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
http://www.dougdeals.com/p-6037-hp-3312a-function-generator-operating-service-manual.aspx

There's a service manual if you think there is something wrong with it?

You don't say how bad of stability ? I wouldn't think it would be bad
enough to be noticeable in a hour or two use. You could have bad caps in
the power supply with intermitting leaks causing some voltage instabilities?

Jamie

 

[Ecnerwal]

In article <4f666f29$0$1375$4fafbaef@reader1.news.tin.it>,
"Antonio I0JX" <vernucci@tin.it> wrote:

However, more than phase noise, what worries me is frequency stability. Even
though I have not done precise measurements, I would say that the 10-MHz
carrier steadily shifts downwards in frequency at a rate of say a couple of
kHz per minute. Moreover it is a bit "jumpy", i.e. frequency does not vary
smoothly, though not to the extent of indicating some instability in
components. Knocking on the boards produces no discernible effect.

Waiting for the generator to get thermally stabilized, the situation
improves but not as much as I would have expected.

As that is the only function generator I ever possessed, I cannot be sure
whether instability is inherent in the principle by which carrier frequency
is produced (i.e. by charging a capacitor at constant current).

So, knowing the experience of other people would be of great help to me.

Well, I started to type something up and then went and looked at the
owners manual for what you have online, and realized that most of what I
was typing about was a moot point. Specifically, the FG I bought uses a
quartz crystal timebase - it could have a better one, and it can take an
external to allow use of as spiffy a timebase as you might like. Leaving
it on for a few hours greatly improves stability as the crystal warms &
stabilizes.

The FG you have, by contrast, uses a capacitor charged by a constant
current as its time base, and both "presumably" and also "from a quick
look at the manual" has a fair number of potentiometers (trimmer as well
as front panel) in the circuit (presumably, these affect what the
constant current is.) Those tend not to age well, IME. You can certainly
try a can of contact cleaner on the pots. I don't know what they'd use
for a timing capacitor, but I would assume it would be something (a
type) more stable than an electrolytic that would be prone to drying
out, so the pots is what I'd mostly suspect. They tend to corrode and
get weird with old age, so the moving contact does not make reliable
contact, and may be making some sort of contact but with a film of
corrosion that affects the contact value.

Then again, a dried out electrolytic elsewhere in the circuit could be
the culprit (the other standard old age issue) or something completely
else could be wrong.

Since there does not seem to be a method to feed the thing a different
timebase, the "simple in my case" diagnostic of putting a different
timebase into it does not appear to apply.

I had used some of the "similar in concept" Beckman FGs in the past,
which is one reason I went looking for a quartz-crystal based FG when
buying my own (HP3325A, a few years past yours but still quite retro
from these days.) I hated fiddling with the dial trying to get a precise
frequency. Contrariwise, some folks hate the 3325A precisely because it
does not have a dial....

Dial or no dial, I think stability and quartz crystal run together in
these things. An ovenized crystal is better, and with an external
reference input, you can get as precise as you can afford with
GPS-clocking, rubidium references or the like (or just one really good
ovenized crystal that you use for all your local reference inputs. At
least your counter will agree with your generator in that case.)

--
Cats, coffee, chocolate...vices to live by
Please don't feed the trolls. Killfile and ignore them so they will go away.

 

[Jamie]

Antonio I0JX wrote:

Antonio I0JX wrote:

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

http://www.dougdeals.com/p-6037-hp-3312a-function-generator-operating-service-manual.aspx


There's a service manual if you think there is something wrong with it?

You don't say how bad of stability ? I wouldn't think it would be bad
enough to be noticeable in a hour or two use. You could have bad caps in
the power supply with intermitting leaks causing some voltage
instabilities?

Jamie



Thanks Jamie.

I already have the service manual, but it is not of too much help (it is
very difficult to locate components on the boards, moreover components
bear a proprietary HP identification code which does not help).

Setting the generator at say 10 MHz and listening the produced carrier
on an SSB communications receiver, the tone sounds VERY rough (this
indicating a lot of phase noise).

However, more than phase noise, what worries me is frequency stability.
Even though I have not done precise measurements, I would say that the
10-MHz carrier steadily shifts downwards in frequency at a rate of say a
couple of kHz per minute. Moreover it is a bit "jumpy", i.e. frequency
does not vary smoothly, though not to the extent of indicating some
instability in components. Knocking on the boards produces no
discernible effect.

Waiting for the generator to get thermally stabilized, the situation
improves but not as much as I would have expected.

As that is the only function generator I ever possessed, I cannot be
sure whether instability is inherent in the principle by which carrier
frequency is produced (i.e. by charging a capacitor at constant current).

So, knowing the experience of other people would be of great help to me.

Regards

Tony


I think you better do a check on the electrolytic in that unit. It

sounds like you have bad power supply caps. Bad caps can cause a lot of
instabilities because they clean the power rails, keep the DC smooth,
which could the source of your noise you're hearing and the fact that
it's drifting that bad tells me you may have leaky caps that are sitting
on voltage references.. These caps are going through the forming cycle
and changing the references.. They're most likely to old to reform and
should be replaced.

I would get a cap meter and start checking the electro's and any
tantalum units..

Also, get a can of spray coolant for components and let it warm up and
then start spraying some resistors and even caps to find a sudden jump
in activity.

Jamie

 

[Antonio I0JX]

Well, I started to type something up and then went and looked at the
owners manual for what you have online, and realized that most of what I
was typing about was a moot point. Specifically, the FG I bought uses a
quartz crystal timebase - it could have a better one, and it can take an
external to allow use of as spiffy a timebase as you might like. Leaving
it on for a few hours greatly improves stability as the crystal warms &
stabilizes.

The FG you have, by contrast, uses a capacitor charged by a constant
current as its time base, and both "presumably" and also "from a quick
look at the manual" has a fair number of potentiometers (trimmer as well
as front panel) in the circuit (presumably, these affect what the
constant current is.) Those tend not to age well, IME. You can certainly
try a can of contact cleaner on the pots. I don't know what they'd use
for a timing capacitor, but I would assume it would be something (a
type) more stable than an electrolytic that would be prone to drying
out, so the pots is what I'd mostly suspect. They tend to corrode and
get weird with old age, so the moving contact does not make reliable
contact, and may be making some sort of contact but with a film of
corrosion that affects the contact value.

Then again, a dried out electrolytic elsewhere in the circuit could be
the culprit (the other standard old age issue) or something completely
else could be wrong.

Since there does not seem to be a method to feed the thing a different
timebase, the "simple in my case" diagnostic of putting a different
timebase into it does not appear to apply.

I had used some of the "similar in concept" Beckman FGs in the past,
which is one reason I went looking for a quartz-crystal based FG when
buying my own (HP3325A, a few years past yours but still quite retro
from these days.) I hated fiddling with the dial trying to get a precise
frequency. Contrariwise, some folks hate the 3325A precisely because it
does not have a dial....

Dial or no dial, I think stability and quartz crystal run together in
these things. An ovenized crystal is better, and with an external
reference input, you can get as precise as you can afford with
GPS-clocking, rubidium references or the like (or just one really good
ovenized crystal that you use for all your local reference inputs. At
least your counter will agree with your generator in that case.)

------------------------------------
I tried to lubricate all contacts and potentiometer with no success. A
capacitor? It could well be, but it is very difficult to locate the
components on the board. Also, the schematic diagram drawing is of poor
quality.

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

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?

73
Tony I0JX

 

[Ecnerwal]

In article <4f67a085$0$1389$4fafbaef@reader1.news.tin.it>,
"Antonio I0JX" <vernucci@tin.it> wrote:

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

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?

Looked at as change per 15 minutes (rather than total change in total
time, which I believe is what you've reported above) this suggests that
a 1 hour warmup makes the drift 10 times better, and a 2 hour warmup
might be plenty for many purposes. If not enough for your purposes, shop
for a newer unit.

15m 98 kHz (1.9%)
30m 18 kHz (0.36%)
45m 16 kHz (0.32%)
60m 9 kHz (0.18%)
75m 6 kHz (0.12%)

I doubt that yours can be expected to do better - my general
understanding for capacitor-timebase performance is that 0.10% is about
as good as you might expect, so I'd extrapolate from what you report
that at 90-120 minutes of warmup time, it would be doing as well as it
can, and you should certainly avoid doing anything that you wish to
remain stable in the first 30-45 minutes it's on. Whether it was any
faster to warm up when it was new is best left to anyone that happens by
and used one when it was new, but I doubt it was greatly better.

Might be interesting to leave it on overnight, tune it in the morning,
and see how well it sits at that point. That's assuming it's neither too
noisy nor too much of a power drain to leave on all night.

If you desire more stability in less time, a newer unit is probably in
order, and if you desire considerably more stability (parts per million
is not hard to get) make that a quartz-crystal based unit.

--
Cats, coffee, chocolate...vices to live by
Please don't feed the trolls. Killfile and ignore them so they will go away.

 

[Michael A. Terrell]

Antonio I0JX wrote:

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?

The manual is copyright 1974, and equipment of that era had to stay
on 24/7 for any stability. Check the ripple of the two power rails, and
for open zeners in the power supply. If you simply need something to be
on frequency, check out a DDS signal generator.
http://www.ebay.com/itm/220949184582 is a 0Hz to 50 MHz signal source
with simple pushbutton setup. It isn't as fancy as the HP3325, but it
works well for <$50 US. Add an attenuator, and if needed, and opamp to
allow for DC offset. You can buy just the DDS chip & crystal on a PC
boardfor under $10 US and use the demo software from Analog Devices to
set the frequency & level from a PC, through the parallel port.


--
You can't have a sense of humor, if you have no sense.