John,
On 2021-08-19 05:19, John Miles wrote:
So, with a 5 MHz source, a RF generator that is doing DCFM lock of PLL
and then analyse spectrum of that, that fails to lock this PLL loop, and
I fail to get a monitored beat note that makes sense. So, I was hoping
someone had done this and could help me with the teething problems. Once
that is done I intended to redo this at 180 MHz and 1440 MHz just for fun.
Thus, 3047, 3048 and E5052 becomes off topic, and not part of this exercise.
If your 5 MHz source is a crystal oscillator, it's probably injection locking.
The phase detector has relatively poor port isolation, maybe 30 dB or so. You
almost always have to use isolation amps (note the plural) for crystal
oscillator measurement with these boxes.
The 5 MHz source I had on reach is an active hydrogen maser. The BVA in
it is already in lock. Isolation amps laying around here, so applying
those would be a good cause.
Another thing to check is the VCO gain parameter. This doesn't have to be
spot-on, but if you enter a value that's too far off, the initial beat note
lockup process may not work properly.
That seem to calculate out fine from the parameters I gave it.
If you are using an optional frequency counter as part of the setup, try
disabling it and letting the FFT analyzer measure the DUT properties.
OK, I can try that.
It's worth getting the E5500 working IMHO, as it's capable of doing everything
the 3048A system could without taking up a whole equipment rack. Rick's right
in that these instruments are sort of a pain in the neck to work with, but I
wouldn't say that they're primarily meant for residual tests. They are very
much suitable for general purpose AM/PM noise measurements as long as you have
the necessary peripherals and patience.
Well, pain in the neck or not, I want to get it working. I do have a bit
of peripherals and now I decided to make a more serious attempt at
getting it going. I have done residual tests and that works fine. The
hydrogen maser was measuring at around -177 dBc/Hz while the E4420B was
far above, which is expected. Still want that absolute measurement to
work, as I want to unlock more and more of the instrument.
The TimePod straight of the bat gives me 30 MHz, and with this thing I
go do 1.6 GHz, which expands to a lot of other sources. Yes, I know I
can go higher using external sources and mixers with the TimePod, but
being able to use another approach helps to verify what I see. There
will be more tests performed eventually.
Cheers,
Magnus
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