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8568B YTO unlocked
开云体育Hi allI have a 8568B spectrum analyzer which has some strange flickering traces sometimes. I found out that the traces do not flicker if the frequency span is narrow, for instance 1 MHz. As soon as I use a wider span, the traces are kind of unstable.
I then opened the RF section and found following behaviour: with a large span, the YTO unlocked LED flashes sometimes, however, I get no YTO warning on the screen.
If I lower the span to 1 MHz or less, the YTO unlocked LED is off all the time and the traces on the screen are nice and stable.
Is it normal that, when larger spans are used, the YTO unlocks from time to time? If not, why don't I get the YTO unlock message on the screen?
Tobias, HB9FSX
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I don't know about the screen flickering, but I do think the YTO loop behavior is normal. At wider spans it is not constantly phase-locked - it is driven open-loop with fairly accurate sweep current, and I think possibly re-phase-locked just at the beginning of the sweep each time around. For wide spans, you can't resolve the small frequency error on-screen anyway, but for narrow ones, more stability is needed, so the LO is locked. It's also possible that the narrow spans instead fix the first LO and use the second LO for sweeping - I can't recall for sure, but it should be one of those two schemes.
Definitely get the manual if you haven't already. Ed |
开云体育On my 8566b, if the span is greater than certain MHz, the sweep source is operate in “Lock and Roll” mode - locks to the sweep start frequency then applies a ramp to roll.Calvin On Oct 15, 2017, at 11:34 AM, edbreya@... [hp_agilent_equipment] <hp_agilent_equipment@...> wrote:
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开云体育Hi,I have the manual, of course :-)
But I cannot find some info about when the YTO is allowed to be unlocked.
I also have not yet managed to fix the flickering trace. Actually, 'flickering' ist not quite the right expression; it is a bit more complicated: if there is a signal on the screen and the marker is moved along the trace, the trace is slightly 'pulled'
along the frequency axis towards the direction in which the marker is moved, which looks like an unstable, flickering display if the marker is moved fast (e.g. when turning the knob rapidly). As soon as marker movement is stopped, the trace bumps back at its
former position.
However, this absolutely strange behaviour can only be observed when the span is wider than 1 MHz; in this case also the YTO unlock LED is flashing (but no warning message on the screen).
I hope I have some time tomorrow to check the tant caps. I hope it is not the YTO or a mixer which went on the blink, but I guess as long as the YTO oscillates and signals can be viewed correctly (in principle) on the screen, then the RF path seems to
be all good.
Tobias
-------- Original message --------
From: "edbreya@... [hp_agilent_equipment]"
Date: 10/15/17 20:34 (GMT+01:00)
To: hp_agilent_equipment@...
Subject: [hp_agilent_equipment] Re: 8568B YTO unlocked
?
I don't know about the screen flickering, but I do think the YTO loop behavior is normal. At wider spans it is not constantly phase-locked - it is driven open-loop with fairly accurate sweep current, and I think possibly re-phase-locked just at the beginning
of the sweep each time around. For wide spans, you can't resolve the small frequency error on-screen anyway, but for narrow ones, more stability is needed, so the LO is locked. It's also possible that the narrow spans instead fix the first LO and use the second
LO for sweeping - I can't recall for sure, but it should be one of those two schemes. |
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-------- Original message --------
From: "Calvin Guan guancalvin@... [hp_agilent_equipment]"
Date: 10/16/17 00:20 (GMT+01:00)
To: hp_agilent_equipment@...
Subject: Re: [hp_agilent_equipment] Re: 8568B YTO unlocked
?
On my 8566b, if the span is greater than certain MHz, the sweep source is operate in “Lock and Roll” mode - locks to the sweep start frequency then applies a ramp to roll.
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开云体育Tobias,As?G?ran said, 8568 and 8566 are different design. I have no knowledge of 8568 so I can only speak for 8566. In 8566, if the frequency span is less than 5mhz, YTO is phase locked during the entire sweep?— the FM coil is driven by the loop’s LPF?so that the YTO is phase locked. Side note, HP called it?“integrator" which is not what my?professor and textbook say. Integrator(1/s) is not LPF(a/(s+a)) mathematically but oh well... For frequency span >5mhz, the YTO is?phase locked to the sweep start frequency during retrace(Lock), then the sample/hold circuit (between YTO’s second LPF and FM coil) is first in sample mode to store the tuning voltage from the LPF, then is placed in hold mode, which breaks the loop, the capacitor holds the constant voltage to the FM coil. Then the sweep ramp is fed to the YO mail coil to sweep(Roll). This Lock-and-Roll scheme is also used in 8340/41 too. Hope that helps! Calvin On Oct 18, 2017, at 12:53 PM, Tobias Pluess tobias.pluess@... [hp_agilent_equipment] <hp_agilent_equipment@...> wrote:
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G?ran Krusell