Im a bit on the bad side with hittite right now, when i was working at the big M i didnt have any problems getting samples from them but now its not as easy , they want me to buy the samples but then they have a min order of 10ea which really is overkill financially !
The reason why you cant get past 10GHz is that as far as i know those YIGs use bipolar transistors and not GaAS, the phase noise performance seem to support this theory, getting anything out of a bipolar transistor past 10GHz is a tough job, i spend countless days and month testing simulating and building prototypes trying to get a 12GHz DRO going (to be used as one half of a push push design for 24GHz), there are a few good devices from infineon and a fairly new one from NXP that produce results but back when those endwave parts were conceived state of the art was about 10GHz !
Im really only interested in 8GHz which the device should do, im using a passive doubler to go to 16GHz and then a MIMIX Doubler to go to 32GHz, why a passive doubler for the first stage ? well the answer is simple, im getting about +14dBm from the YIG, active doublers usually take about -6 to 0dBm so i would have to kill almost 14dB, the conversion loss of the doubler is 12dB so im ending up with +2dBm, now run this signal trough a splitter, lose 6dB thats -4dBm , the active doubler i use produces +16dBm @ 0dBm input so im getting about +14dBm at the output which is perfect.
John Miles <jmiles@...> wrote:
I have tried running those YTOs past 10 GHz, and what happens is that they
just stop oscillating beyond a certain point (about 10.3 GHz as I recall).
If you bolt the oscillator to a good thermal sink and keep an eye on the
temperature it will probably be safe enough... but whether it will still
oscillate is another question.
I'd be interested in hearing how things go with the sampling phase detector.
Conversion loss at high harmonics, and the resulting need for lots of IF
gain, can really eat your lunch with those. From what I've seen there is no
longer much upside to using harmonic samplers over modern PFD chips. The
best of the Analog Devices parts (ADF4108, about $7/ea.) will work at Fin=8
GHz and Fcomp=100 MHz. You can't run either of them at N=32,000 and expect
miracles, obviously.
Obligatory HP content: I spent a lot of time trying to clean up my 8566B's
first LO synthesizer before I realized that the conversion loss of the YTO
sampler was never going to let me do better than about -105 to -110 dBc/Hz.
The low effective N factor rules out the ADF41xx series PLLs in that
application, but I think I could have gotten into the -120 dBc/Hz range with
a Hittite HMC363/HMC439 combination if my motivation hadn't run out.
-- john, KE5FX
toggle quoted message
Show quoted text
-----Original Message-----
From: hp_agilent_equipment@...
[mailto:hp_agilent_equipment@...]On Behalf Of lothar baier
Sent: Friday, November 16, 2007 4:30 PM
To: hp_agilent_equipment@...
Subject: RE: [hp_agilent_equipment] Stellex YIGs
thanks for the datasheet, unfortunatly it doesnt give a max
current for the coil, the part i have says 8.5-9.25GHz it tunes
to 8GHz @ 150mA however i dont know if this is acceptable for
long term operation.
I know about the phasenoise performance for the synthesizers
thats why im using a SPD rather than a PLL Chip along with a
100MHz low phasenoise reference.
Endwave actually swallowed Stellex as far as i know, stellex
used to be WJ components , then WJ became stellex and then
stellex got taken over by endwave.
--------------------------------- Never miss a thing. Make Yahoo your homepage.
|
I have tried running those YTOs past 10 GHz, and what happens is that they
just stop oscillating beyond a certain point (about 10.3 GHz as I recall).
If you bolt the oscillator to a good thermal sink and keep an eye on the
temperature it will probably be safe enough... but whether it will still
oscillate is another question.
I'd be interested in hearing how things go with the sampling phase detector.
Conversion loss at high harmonics, and the resulting need for lots of IF
gain, can really eat your lunch with those. From what I've seen there is no
longer much upside to using harmonic samplers over modern PFD chips. The
best of the Analog Devices parts (ADF4108, about $7/ea.) will work at Fin=8
GHz and Fcomp=100 MHz. You can't run either of them at N=32,000 and expect
miracles, obviously.
Obligatory HP content: I spent a lot of time trying to clean up my 8566B's
first LO synthesizer before I realized that the conversion loss of the YTO
sampler was never going to let me do better than about -105 to -110 dBc/Hz.
The low effective N factor rules out the ADF41xx series PLLs in that
application, but I think I could have gotten into the -120 dBc/Hz range with
a Hittite HMC363/HMC439 combination if my motivation hadn't run out.
-- john, KE5FX
toggle quoted message
Show quoted text
-----Original Message-----
From: hp_agilent_equipment@...
[mailto:hp_agilent_equipment@...]On Behalf Of lothar baier
Sent: Friday, November 16, 2007 4:30 PM
To: hp_agilent_equipment@...
Subject: RE: [hp_agilent_equipment] Stellex YIGs
thanks for the datasheet, unfortunatly it doesnt give a max
current for the coil, the part i have says 8.5-9.25GHz it tunes
to 8GHz @ 150mA however i dont know if this is acceptable for
long term operation.
I know about the phasenoise performance for the synthesizers
thats why im using a SPD rather than a PLL Chip along with a
100MHz low phasenoise reference.
Endwave actually swallowed Stellex as far as i know, stellex
used to be WJ components , then WJ became stellex and then
stellex got taken over by endwave.
|
thanks for the datasheet, unfortunatly it doesnt give a max current for the coil, the part i have says 8.5-9.25GHz it tunes to 8GHz @ 150mA however i dont know if this is acceptable for long term operation. I know about the phasenoise performance for the synthesizers thats why im using a SPD rather than a PLL Chip along with a 100MHz low phasenoise reference. Endwave actually swallowed Stellex as far as i know, stellex used to be WJ components , then WJ became stellex and then stellex got taken over by endwave. John Miles <jmiles@...> wrote: They're equivalent to these Endwave parts, as far as I can tell: The YTOs themselves are nice parts, but the popular synthesizer boards that use them are noisy. The comparison frequency is relatively low (250 kHz), causing a 90-dB in-band PN penalty. With a higher Fcomp you can do quite a bit better. -- john, KE5FX Does anyone has a detailed datasheet of the stellex permanent magnet
YTOs that are commonly offered on ebay ? im especially interested in
the max current the coil can take without frying.
Im in the process of building a 32GHz Synthesizer and want to use one
of those YIGs to generate a 8GHz Signal that then will be multiplied to
16GHz and then to 32GHz ,im planing on using a SPD from metelics for
this task driven by a 100MHz Crystal oscillator, i know theres better
stuff around but im trying to utilize stuff in got in my drawer.
Anyway i need a datasheet for the YTO to be able to properly design the
loop filter and driver circuitry.
--------------------------------- Never miss a thing. Make Yahoo your homepage.
|
They're equivalent to these Endwave parts, as far as I can tell:
The YTOs themselves are nice parts, but the popular synthesizer boards that
use them are noisy. The comparison frequency is relatively low (250 kHz),
causing a 90-dB in-band PN penalty. With a higher Fcomp you can do quite a
bit better.
-- john, KE5FX
toggle quoted message
Show quoted text
Does anyone has a detailed datasheet of the stellex permanent magnet
YTOs that are commonly offered on ebay ? im especially interested in
the max current the coil can take without frying.
Im in the process of building a 32GHz Synthesizer and want to use one
of those YIGs to generate a 8GHz Signal that then will be multiplied to
16GHz and then to 32GHz ,im planing on using a SPD from metelics for
this task driven by a 100MHz Crystal oscillator, i know theres better
stuff around but im trying to utilize stuff in got in my drawer.
Anyway i need a datasheet for the YTO to be able to properly design the
loop filter and driver circuitry.
|
Does anyone has a detailed datasheet of the stellex permanent magnet
YTOs that are commonly offered on ebay ? im especially interested in
the max current the coil can take without frying.
Im in the process of building a 32GHz Synthesizer and want to use one
of those YIGs to generate a 8GHz Signal that then will be multiplied to
16GHz and then to 32GHz ,im planing on using a SPD from metelics for
this task driven by a 100MHz Crystal oscillator, i know theres better
stuff around but im trying to utilize stuff in got in my drawer.
Anyway i need a datasheet for the YTO to be able to properly design the
loop filter and driver circuitry.
|
Re: DIY: Repair of HP Step Attenuators
Thanks John! Best George --- In hp_agilent_equipment@..., J Forster <jfor@...> wrote:
FWIW, do it over a tray w/ turned up edges. I just spent over an
hour chasing small bits of an assembly because I ignored that precaution.
Best,
-John
g47g wrote:
Thanks. I'll try to disassemble the unit, then I hope I'll see the
reason of the failure. [snip]
|
Re: Hp-8443A Tracking Generator Problems
They are very likely Sealectro or MicroDot. If you email me a (small ) pic of
both M and F, off list, I'll see if I can ID them.
If they are gold plated with Teflon insulation between center and outer
conductors, Sealectro is the most likely choice.
-John
David C. Hallam wrote:
toggle quoted message
Show quoted text
I did call them GOOFY because that is what they are. They are goofy because
I think the only place in the whole world they were used was the jacks and
plugs for the cables of the connections between modules of the 8443A. They
are not SMA, SMB, or SMC. I have looked at drawing of each of these types
are the are not same as what HP used. I have no idea what they are or
where to obtain them. I would certainly appreciate it if anyone could
identify them along with a source of supply. As far as I am concerned their
official description is "unobtainiun".
David
KC2JD/4
|
Re: Hp-8443A Tracking Generator Problems
If you can email me photographs, I'll compare them to
what's in my 8443A.
But it doesn't really matter. The only important one
for your present purpose is A6W1, the one from the RF amp to
the counter's INT input. All you have to do is scope
it long enough to verify that there's RF there; this
can be accomplished without an adaptor.
Dave Wise
toggle quoted message
Show quoted text
-----Original Message-----
From: hp_agilent_equipment@...
[mailto:hp_agilent_equipment@...]On Behalf Of David C.
Hallam
Sent: Friday, November 16, 2007 3:19 PM
To: hp_agilent_equipment@...
Subject: RE: [hp_agilent_equipment] Hp-8443A Tracking
Generator Problems
I did call them GOOFY because that is what they are. They
are goofy because
I think the only place in the whole world they were used was
the jacks and
plugs for the cables of the connections between modules of
the 8443A. They
are not SMA, SMB, or SMC. I have looked at drawing of each
of these types
are the are not same as what HP used. I have no idea what
they are or
where to obtain them. I would certainly appreciate it if anyone could
identify them along with a source of supply. As far as I am
concerned their
official description is "unobtainiun".
David
KC2JD/4
-----Original Message-----
From: hp_agilent_equipment@...
[mailto:hp_agilent_equipment@...]On Behalf Of David Wise
Sent: Friday, November 16, 2007 5:03 PM
To: hp_agilent_equipment@...
Subject: RE: [hp_agilent_equipment] Hp-8443A Tracking
Generator Problems
I didn't call them goofy, David Hallam (the OP) did.
You and I are referring to what's more commonly called
"Hybrid-D" connectors. (From context,
I judge that David Hallam is thinking of the SMB (SMC?)
plugs on the inter-assembly cables inside the instrument.
The hybrid-D of interest in this thread actually has no
standard D contacts at all, it's all coaxes. Which by the
way are called "Size 8". Not to inundate you with 8's,
but the connector pin layout is called "8W8", which
predictably means 8 contacts 8 of which are coax.
Regards,
Dave Wise
> -----Original Message-----
> From: hp_agilent_equipment@...
> [mailto:hp_agilent_equipment@...]On Behalf Of
J Forster
> Sent: Friday, November 16, 2007 2:02 PM
> To: hp_agilent_equipment@...
> Subject: Re: [hp_agilent_equipment] Hp-8443A Tracking
> Generator Problems
>
>
> Sealectro is a brand. They made SMA, SMB, SMC, and a number
> of other miniature
> coax connectors. They ALSO made a number of proprietary types
> in addition to the
> standards.
>
> As to 'goofy', do you mean the D connectors w/ the mix of
> coax and ordinary
> pins?
>
> -John
>
>
>
> David Wise wrote:
>
> > They did call them by an obsolete name, "selectro" (or was
> it "sealectro"?).
> >
>
>
>
>
> Yahoo! Groups Links
>
>
>
>
[Non-text portions of this message have been removed]
Yahoo! Groups Links
|
Re: Hp-8443A Tracking Generator Problems
I did call them GOOFY because that is what they are. They are goofy because
I think the only place in the whole world they were used was the jacks and
plugs for the cables of the connections between modules of the 8443A. They
are not SMA, SMB, or SMC. I have looked at drawing of each of these types
are the are not same as what HP used. I have no idea what they are or
where to obtain them. I would certainly appreciate it if anyone could
identify them along with a source of supply. As far as I am concerned their
official description is "unobtainiun".
David
KC2JD/4
toggle quoted message
Show quoted text
-----Original Message-----
From: hp_agilent_equipment@...
[mailto:hp_agilent_equipment@...]On Behalf Of David Wise
Sent: Friday, November 16, 2007 5:03 PM
To: hp_agilent_equipment@...
Subject: RE: [hp_agilent_equipment] Hp-8443A Tracking Generator Problems
I didn't call them goofy, David Hallam (the OP) did.
You and I are referring to what's more commonly called
"Hybrid-D" connectors. (From context,
I judge that David Hallam is thinking of the SMB (SMC?)
plugs on the inter-assembly cables inside the instrument.
The hybrid-D of interest in this thread actually has no
standard D contacts at all, it's all coaxes. Which by the
way are called "Size 8". Not to inundate you with 8's,
but the connector pin layout is called "8W8", which
predictably means 8 contacts 8 of which are coax.
Regards,
Dave Wise
> -----Original Message-----
> From: hp_agilent_equipment@...
> [mailto:hp_agilent_equipment@...]On Behalf Of J Forster
> Sent: Friday, November 16, 2007 2:02 PM
> To: hp_agilent_equipment@...
> Subject: Re: [hp_agilent_equipment] Hp-8443A Tracking
> Generator Problems
>
>
> Sealectro is a brand. They made SMA, SMB, SMC, and a number
> of other miniature
> coax connectors. They ALSO made a number of proprietary types
> in addition to the
> standards.
>
> As to 'goofy', do you mean the D connectors w/ the mix of
> coax and ordinary
> pins?
>
> -John
>
>
>
> David Wise wrote:
>
> > They did call them by an obsolete name, "selectro" (or was
> it "sealectro"?).
> >
>
>
>
>
> Yahoo! Groups Links
>
>
>
>
|
Re: Hp-8443A Tracking Generator Problems
I didn't call them goofy, David Hallam (the OP) did.
You and I are referring to what's more commonly called
"Hybrid-D" connectors. (From context,
I judge that David Hallam is thinking of the SMB (SMC?)
plugs on the inter-assembly cables inside the instrument.
The hybrid-D of interest in this thread actually has no
standard D contacts at all, it's all coaxes. Which by the
way are called "Size 8". Not to inundate you with 8's,
but the connector pin layout is called "8W8", which
predictably means 8 contacts 8 of which are coax.
Regards,
Dave Wise
toggle quoted message
Show quoted text
-----Original Message-----
From: hp_agilent_equipment@...
[mailto:hp_agilent_equipment@...]On Behalf Of J Forster
Sent: Friday, November 16, 2007 2:02 PM
To: hp_agilent_equipment@...
Subject: Re: [hp_agilent_equipment] Hp-8443A Tracking
Generator Problems
Sealectro is a brand. They made SMA, SMB, SMC, and a number
of other miniature
coax connectors. They ALSO made a number of proprietary types
in addition to the
standards.
As to 'goofy', do you mean the D connectors w/ the mix of
coax and ordinary
pins?
-John
David Wise wrote:
They did call them by an obsolete name, "selectro" (or was it "sealectro"?).
Yahoo! Groups Links
|
Re: Hp-8443A Tracking Generator Problems
Sealectro is a brand. They made SMA, SMB, SMC, and a number of other miniature
coax connectors. They ALSO made a number of proprietary types in addition to the
standards.
As to 'goofy', do you mean the D connectors w/ the mix of coax and ordinary
pins?
-John
David Wise wrote:
toggle quoted message
Show quoted text
They did call them by an obsolete name, "selectro" (or was it "sealectro"?).
|
Re: HP-8443A Tracking Generator Problems
I said that two sentences later:
"At narrow
RBW settings, you have to fine-tune the TG to be exactly
on frequency, that's the screwdriver adjustment on the front
panel. Since you don't know that it's spot-on, start with
a wide RBW then narrow it down."
Said screwdriver adjustment trims the 3MHz LO which mimics the
final I.F. of the 8552. Late versions of the 8443A have a
"Restore Signal" mode which uses the actual IF signal from
the 8552. In that mode, as long as it's within the SA's RBW,
the TG puts out exactly the frequency presented to the SA's RF input.
Note: This doesn't work with early 8552's, they don't bring
their final IF out to the bulkhead. While the mod is conceptually
simple, it's physically difficult due to the location of
the contacts, so I haven't done it to my 8552A.
And another note: When the 8553B is in FULL scan mode, it
puts out its own marker in addition to the one from the
8443A. Fortunately they are recognisably different:
the former is a dip in trace height while the latter
is a change in trace intensity. And a note about that.
How much brighter it gets depends on the Marker Intensity
control, which adjusts the time the scan is paused at
the marker position.
Regards,
Dave Wise
toggle quoted message
Show quoted text
-----Original Message-----
From: hp_agilent_equipment@...
[mailto:hp_agilent_equipment@...]On Behalf Of J Forster
Sent: Friday, November 16, 2007 1:54 PM
To: hp_agilent_equipment@...
Subject: Re: [hp_agilent_equipment] Re: HP-8443A Tracking Generator
Problems
ONLY, if the TG is actually putting out the same frequency as
the SA is
tuned to. I have an AIL 757 and TG. If the tracking control
is not tuned
right, the YIG in the SA's front end will be tuned to a
different frequency
than the TG and you see little to nothing on the SA.
-John
David Wise wrote:
You don't even have to select zero span. The function and
purpose of a TG is to output, at all times, whatever frequency
the SA is listening to. As the SA scans, so does the TG.
In all scan modes, the SA should show a horizontal line
at a height determined by the TG's output amplitude. [snip]
|
Re: HP-8443A Tracking Generator Problems
ONLY, if the TG is actually putting out the same frequency as the SA is
tuned to. I have an AIL 757 and TG. If the tracking control is not tuned
right, the YIG in the SA's front end will be tuned to a different frequency
than the TG and you see little to nothing on the SA.
-John
David Wise wrote:
toggle quoted message
Show quoted text
You don't even have to select zero span. The function and
purpose of a TG is to output, at all times, whatever frequency
the SA is listening to. As the SA scans, so does the TG.
In all scan modes, the SA should show a horizontal line
at a height determined by the TG's output amplitude. [snip]
|
Re: HP-8443A Tracking Generator Problems
Take a look at the Wiltrons. The advantage is that the marker accuracy is independent of the GHz/Volt calibrations. In fact, I have a little home brew unit in a Tek TM-500 PI that does just that... mixer, LPF, detector, comparator.
-John
lothar baier wrote:
toggle quoted message
Show quoted text
this is another way but i havent seen anyone using this in centuries, the last time i saw it was on a old jerrold sweeper, everything i had ever since was using the approach i described, problem with the RF method is that its quite expensive to realize, a directional coupler, sampling mixer and the oscillator and frequency counter costs money and space and also takes away from the RF power, another factor is that whenever you use a comb generator you run the risk of finding your peaks "everywhere" even in places you dont want them :)
DC or LF stuff is cheap and doesnt take up much space so i think thats why most companies opted for this approach
J Forster <jfor@...> wrote:
lothar baier wrote:
ok there are two basic ways to create a marker in a swept system, one is called RF blanking the other one is called intensity modulation, ok usually you have a control voltage thats proportional to your RF frequency, if the analyzer sweeps its basically a ramp, each point of the ramp corresponds to a certain frequency, you feed this signal to a comparator and compare it to a DC voltage thats adjustable (coming from your marker pot) anytime the ramp "hits" this threshold you get a pulse on your comparator output, you route this pulse back into your display and use it to crank up the intensity just a bit at this point and there you have a marker blip on your screen :) There is another way. You sample the RF, mix it with a (frequency settable) oscillator, run the output through a LPF, detector, and comparator and use this output for intensity markers.
This system has the advantage that you can count the oscillator and have accurate digital markers, and, if you replace the oscillator w/ a comb generator, you get nice, calibrated pips.
Best,
-John
you could also use this pulse to turn the RF of your TG off for just a moment but then you would end up with a dark spot as a marker for a short time instead of beein brighter.
Your statement about you seein a bright blip on your screen as a marker along with the statement about you seen the marker even with the calibator connected to your RF section input makes me certain that your markers are intensity modulated !
|
Re: DIY: Repair of HP Step Attenuators
FWIW, do it over a tray w/ turned up edges. I just spent over an hour chasing
small bits of an assembly because I ignored that precaution.
Best,
-John
g47g wrote:
toggle quoted message
Show quoted text
Thanks. I'll try to disassemble the unit, then I hope I'll see the
reason of the failure. [snip]
|
Re: Hp-8443A Tracking Generator Problems
They did call them by an obsolete name, "selectro" (or was it "sealectro"?).
toggle quoted message
Show quoted text
-----Original Message-----
From: hp_agilent_equipment@...
[mailto:hp_agilent_equipment@...]On Behalf Of lothar baier
Sent: Friday, November 16, 2007 1:26 PM
To: hp_agilent_equipment@...
Subject: Re: [hp_agilent_equipment] Hp-8443A Tracking
Generator Problems
usually HP used SMC and SMB on the inside of most instrument,
i havent seen anything special in any of the HP Gear
|
Re: Hp-8443A Tracking Generator Problems
usually HP used SMC and SMB on the inside of most instrument, i havent seen anything special in any of the HP Gear Dan Rae <danrae@...> wrote: David C. Hallam wrote: I
believe it might be more expeditious to find another 8443A I can purchase,
only after verification that it is working properly, than to attempt the
repair of mine.
David if you do look for another one, try to find a later one with LED displays rather than nixie tubes, they are a little bit more reliable. But they are pretty easy to work on, all in all, given a modicum of test gear. I'd bet it is probably something very minor wrong with yours. And it's probably ten years since I had the lid off mine, but I don't remember anything odd about the coax connectors inside, SMC I think. Good luck, Dan --------------------------------- Be a better pen pal. Text or chat with friends inside Yahoo! Mail. See how.
|
Re: Hp-8443A Tracking Generator Problems
David C. Hallam wrote: I
believe it might be more expeditious to find another 8443A I can purchase,
only after verification that it is working properly, than to attempt the
repair of mine.
David if you do look for another one, try to find a later one with LED displays rather than nixie tubes, they are a little bit more reliable. But they are pretty easy to work on, all in all, given a modicum of test gear. I'd bet it is probably something very minor wrong with yours. And it's probably ten years since I had the lid off mine, but I don't remember anything odd about the coax connectors inside, SMC I think. Good luck, Dan
|
Hp-8443A Tracking Generator Problems
Thank you to all who replied to my request for help. I now understand more
about the operation of this piece of test gear and also believe the solution
to my problem is more complex than I originally thought.
Given the investment in time, money, and effort it will take to acquire
and/or fabricate things like circuit board extenders and jumper cables with
those goofy (Yes I still think HP used "goofy" connectors, they aren't SMA,
SMB, SMC, or SM* anything) connectors on one end and BNC on the other, I
believe it might be more expeditious to find another 8443A I can purchase,
only after verification that it is working properly, than to attempt the
repair of mine.
I will do what trouble shooting I can without those items before writing
this one off.
David
KC2JD/4
|
Re: DIY: Repair of HP Step Attenuators
Thanks. I'll try to disassemble the unit, then I hope I'll see the reason of the failure. --- In hp_agilent_equipment@..., lothar baier <microwaveengineer1968@...> wrote:
most likely the cam is worn out or the little ball that locks the
cam in place is missing
g47g <g47g@...> wrote: Hi Lothar,
I have a 8495A manual step attenuator, and though it has the correct
attenuations on every step(?), but it needs force to switch the
attenuator in different positions, and also the well known "click"
cannot be heard, when turning (with some force) the knob.
Could you help me with some idea and procedure, as you did with the
electronic controlled equivalent ?
Thanks
George Galambos
--- In hp_agilent_equipment@..., "microwaveengineer1968"
<microwaveengineer1968@> wrote:
Since Agilent continiously ups the spare part prices and discontinues
parts it has become more and more important to go past normal repair
practices.
Step Attenuators for example can be repaired without any special
tools or cleanroom enviroment !
Lets take a look at the failure modes first, there are a few:
1.) Blown pads
Usually common with spectrum analyzers if a level past the damage
level of the attenuator was applied
2.) Cracked pads, pad has developed a hairline crack due to
mechanical stress !
3.) Improper contact, the contact in between the attenuator and
contact fingers is disturbed.
4.) Stuck solenoid
Quite common if attenuator hasnt been used in awhile
After we remove the attenuator from the instrument the first step is
to obtain the pinout and build us a little test bench consisting of a
powermeter and a signal generator, the good old 8481D or 8484A will
do nicely, if you dont have a sig gen use the 50MHz calibrator output
of the 435 or 436 or similar model, connect the cal output to the
30dB pad connect the sensor and zero and calibrate meter, the meter
will read -30dBm.
Disconnect the sensor from the attenuator and insert the Step
Attenuator, set step attenuator to 0dB, note the level on the
powermeter, now switch in the attenuator sections one by one measure
and note the level, 70dB attenuators are comprised of a 10 20 and
40dB Pad while 110dB Attenuators normally comprise of a 10 20 and two
40dB pads !
check every section individually, you should hear a click as you
enable each section, if you find a bad section note the value it
should have if all sections appear to be good repeat the test at a
higher frequency using a sig gen, if everything appears to be ok at
low frequency then most likely you have attenuator that just needs
cleaning.
Now lets take the attenuator apart, looking at the top you will see a
nut on each SMA connector, remove this nut this will allow for you to
remove the nameplate, under the plate you will see a wealth of allen
screws, remove those but note that the screws close to the SMA
connector are shorter than the other ones.
Now look at the small sideplate, not the one with the ribbon cable
but the other side - there are 4 small allen screws, remove those and
then remove the sideplate, careful not to lose the little wire mesh
here ! now slide out the u shaped cover and remove the top side.
You now have two parts, one beein the bottom side containing the
solenoids and the other one beein the top part containing the
attenuator pads.
First lets inspect the pads, you can measure them with a ohm meter,
they should measure in the vicinity of 50ohms , except of the 10dB
pad which can measure up to 70ohms or more.
Inspect the pads visually, are there any burned or cracked pads ? if
all pads look ok and check out at DC take a surgical swab and
isopropilic alcohol and carefully clean the contacts pads on the
attenuators.
Next look at the contacts, enable all solenoids and observe the
position of the contact tongues, they should be slightly above the
surface of the block, carefully clean the contact tongues with
alcohol, be careful not to bend them.
next put the solenoids back into the 0 position and look at the top
of the solenoids, you will see two little white plastic rods where
those meet the solenoid you should see little rubber rings , there
are 4 of those on each segment, usually over the years they go
briddle and then disappear, with those rings gone the attenuator wont
make contact anymore, you can buy the rings from watchmakers supply
stores as they are beein used for sprocket gaskets !
Now if your gaskets are there put the attenuator back together after
you cleaned everything and it should work now.
If you have a broken or burned pad dont stress over it the pads are
used in all HP attenuators so just find a attenuator on ebay and take
the pad you need out of it, you can also buy pads from agilent
however be prepared to pay $100-150 per
piece
---------------------------------
Get easy, one-click access to your favorites. Make Yahoo! your
homepage.
|
