Noisy Fluke 6060A/AN signal generator
da...@drumheller.org
generator that appears to be a source of noise. For example, if I set
it to 1 Mhz and tune an AM radio to this frequency, I hear a light
crashing noise and an occasional pop/click. If I put a scope across
the radio's speaker, I can see the pops/clicks. Some other facts:
(1) I've poked around the power supply with my scope and find nothing
unusual.
(2) The magnitude of this noise is independent of the generator's RF
output level.
(3) When I switch-off the generator's output, but keep it powered and
running, the noise and clicks goes away.
(4) The RF output of the generator is clean. No noise or pops/clicks
are "floating" on the signal.
(5) The noise and pops/clicks only appears after, say, a 10-minute
warm-up.
Other than this, the signal generator work fine. I still suspect the
power supply--bad capacitors? Or perhaps some other noise source in
the house is getting a free ride at the generator's expense.
Any suggestions?
-Dave
Jamie
I would start monitoring the AC line it's plugged into.
it's noise that is just getting a free ride..
also, you should check the PS on the AC side of the
Diodes/rectifiers. Bridges/Rectifilers have a happen
of causing intermitting noise like this one they warm
up and are getting ready to go bad.
Also, even though you may not see any signal pops on the
PS cap leads, that does not mean the cap is good. I've seen
caps arc internally due to bad dielectric but not short.
They would at some time how ever. Bad contact switches will
also do this.
What i do to find problems like this is to use a R.F. sniffer
with a small loop so that you can tightly close in the area of
detection.
I have a grid meter i use for things like this. it works like a
charm.. I have found a good many bad components that exhibit this
behavior.
--
"I'm never wrong, once i thought i was, but was mistaken"
Real Programmers Do things like this.
http://webpages.charter.net/jamie_5
Charles Schuler
<da...@drumheller.org> wrote in message
news:1173631893.7...@c51g2000cwc.googlegroups.com...
The AM broadcast band is noisy. Have you tried running the amplitude of the
generator all the way up and loop coupling to the AM receiver? This would
tend to swamp out external sources of noise.
If it's still noisy, then the generator is indeed acting up. A phase-locked
loop is not the easiest thing to troubleshoot.
Ancient_Hacker
> I own a Fluke 6060A/AM (10 kHz to 520 MHz) synthesized signal
> generator that appears to be a source of noise.
Yipes. The Fluke 60xx generators are very complex and touchy. There
are very complex delay-line phase-noise-reduction loops, with about a
dozen delicate adjustments, plus a handful that are "factory adjust
only". Plus a few adjustments that are burned into a EPROM.
I'd take it to the top of a tall building and play "how loud is the
crash".
da...@drumheller.org
>
> Yipes. The Fluke 60xx generators are very complex and touchy. There
> are very complex delay-line phase-noise-reduction loops, with about a
> dozen delicate adjustments, plus a handful that are "factory adjust
> only". Plus a few adjustments that are burned into a EPROM.
>
> I'd take it to the top of a tall building and play "how loud is the
> crash".
I'm fairly sure phase noise is not significantly contributing to what
I'm hearing.
Using my amateur radio transceiver interfaced to my home computer
running a spectral analysis program, I've looked at the unmodulated
signals from the Fluke signal generator and found them to be narrower
than the carriers of the local AM broadcast stations. These AM
stations provide "full quieting," having no noticeable noise similar
in character to what I hear on the signal generator.
Even if the phase-noise reduction loop is the source of the problem,
it's no going to matter much because I principally use the generator
for receiver alignment. It's the pops and click that I'm looking to
eliminate.
-Dave
Charles Schuler
> I'm fairly sure phase noise is not significantly contributing to what
> I'm hearing.
>
> Using my amateur radio transceiver interfaced to my home computer
> running a spectral analysis program, I've looked at the unmodulated
> signals from the Fluke signal generator and found them to be narrower
> than the carriers of the local AM broadcast stations. These AM
> stations provide "full quieting," having no noticeable noise similar
> in character to what I hear on the signal generator.
>
> Even if the phase-noise reduction loop is the source of the problem,
> it's no going to matter much because I principally use the generator
> for receiver alignment. It's the pops and click that I'm looking to
> eliminate.
Dave ... since the noise starts after 10 minutes, it might be temperature
related. Have you tried cold spray?
da...@drumheller.org
wrote:
>
> Dave ... since the noise starts after 10 minutes, it might be temperature
> related. Have you tried cold spray?
Yes, I did.
I sprayed the circuit boards containing the output amp/modulator,
controller, attenuator and power supply--no change. I made sure I
sprayed the master oscillator--no change. I also made sure I sprayed
the power supply capacitors--also no change. However, they are large
and covered in plastic, so I doubt the spray had much internal effect
on these insulated thermal masses. The only thing I don't recall
spraying is the display circuit board.
In any case, I plan to replace the power supply capacitors anyway.
They're probably 25 years old and one of them is "bulging."
-Dave
Charles Schuler
<da...@drumheller.org> wrote in message
news:1173729082.9...@t69g2000cwt.googlegroups.com...
Ah bulging! Yes, change those for sure.
Good luck. By the way, I have worked on several RF generators and have been
able to fix them. It is worth the effort, since the good ones are costly to
replace.
Homer J Simpson
"Ancient_Hacker" <gr...@comcast.net> wrote in message
news:1173703404.4...@q40g2000cwq.googlegroups.com...
> Yipes. The Fluke 60xx generators are very complex and touchy. There
> are very complex delay-line phase-noise-reduction loops, with about a
> dozen delicate adjustments, plus a handful that are "factory adjust
> only". Plus a few adjustments that are burned into a EPROM.
Yeah, that sounds like a robust, field proof design.
da...@drumheller.org
wrote:
>
> Ah bulging! Yes, change those for sure.
>
> Good luck. By the way, I have worked on several RF generators and have been
> able to fix them. It is worth the effort, since the good ones are costly to
> replace.
I finally fixed it, taking more time to find the problem than I'll
ever care to admit.
The problem was a surface mount capacitor that's in parallel with the
varactor diodes in the voltage controlled oscillator (VCO).
Specifically, it was capacitor C3, a 1.5 picofarad (pF) capacitor
that's in series with R1, a 180 Ohm resistor. I removed this
capacitor and in its place I've temporarily soldered in a 1 pF ceramic
disc, zero-temperature coefficient capacitor.
Incidentally, I took Charles Schuler's advice and replaced the power
supply capacitors, both electrolytic and tantalum. Although none of
these proved to be the problem, the supply voltages are now cleaner.
-Dave, K3WQ