I found that on the FRS-C and the X72 the frequency output was not at
all linear with respect to EFC, which made things worse with large
dacgains. After _MANY_ hours of watching and playing with different
settings, I came to the conclusion that you just need to be patient when
using Fury+Rb, don't expect it to converge like an OCXO, but it will
over a few hours and give you a good result as long as you have stable
power and shield it from air streams. High dacgain and efcs give you
the false hope that it will converge fast, but as the unit settles the
loop will fail, and it will start fighting with itself.
The SYNC:IMME can be useful when trying different loop settings.
I found some of my notes for various things I ran with the Fury.
LPRO-101 currently running
COARSE DAC: 55
DAC GAIN: 1000
EFC SCALE: 1.30
OCXO SLOPE: POSITIVE
temp co: 0.00
aging co: -0.00558
phase co: 35
lpro orig
lpro cd 92
dac gain 1000
efc scale 1.30
efc damping 2
efc slope pos
phase co 30
lpro 2
coarse dac 95
dac gain 1300
efcs 1.30
efcdamping 5
ocxo slope pos
agin comp 0.05333
phaseco 35
datum ocxo #1 (From RFG-XO)
coarse dac 64
dac gain 80
efcs 4
efcdamping 10
ocxo slope pos
agin comp 0.27086
phaseco 35
datum ocxo #2
coarse dac 64
dac gain 100
efcs 2.8
efcdamping 10
ocxo slope pos
agin comp 0.14901
phaseco 35
datum ocxo #2 from RFG-XO In an RFG chassis
cd 69
dg 30.00
efcs 12.00
efcd 5
ocxo slope pos
aging comp -0.06559
phaseco 40
tempco was a major issue with the datum ocxo
keeping it in the RFG-XO chassis helped
Efratom FRS-A
DAC GAIN: 5000.00
EFC SCALE: 0.50
EFC DAMPING: 25
OCXO SLOPE: POSITIVE
PHASE CORRECTION: 0.500000
TTL output, pad to below +13dBm, FRS-A needs to settle, open bench
air current problems.
FRS-A #2
dac gain: 4000
efcs: 1.2
efcdamping: 25
phaseco: 15
hard time recovering, from coarsedac bumps
X72
dac gain: 2000
efcs 1.2
efcdamping 25
phaseco: 15
jumps, tempco issues.
Scott
On 07/27/2010 09:16 PM, [email protected] wrote:
Hi John, Brian,
actually we set D to 0, and use P and I gains.
Yes, the DACGAIN is an overall gain of the loop output - to normalize for
different oscillator voltage/frequency sensitivities.
I forgot that the DACGAIN is limited to 10,000, so instead of setting it to
20,000 one can set it to 10,000 and multiply the P and I parts both by 2x,
that gives pretty much the same effect as setting DACGAIN to 20,000.
Please note that aging and tempco compensation may then take a couple of
days to fully settle again.
I have not tried such high gains since we don't have any oscillators here
with such small F/V range, please advise what you find out.
bye,
Said
In a message dated 7/27/2010 19:04:36 Pacific Daylight Time, [email protected]
writes:
That part I understand (your drawing), its a basic phase lock loop.
What I am having trouble with is the Fury's commands relationship.
OK. Sorry for the BW.
Basically you tune a loop by starting with the P, I, and D set to zero.
You slowly crank up the P until it starts to become unstable. (Put in a
small step perturbation and look at the response for ringing) Then crank
up the D until it stabilizes, then crank up the P again. When you have got
a stable fairly well performing loop, you introduce some I. You may have
to tweek P and D to keep stability.
It looks like your system has an overall gain (DACG) and a P and D
controller gain. This is not uncommon to avoid switching a bunch of caps.
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