Actually the same applies to the
Deviation, at the fundamental Icom output it should be 4 times less
"wide" than the output deviation. In this particular case.
Wade
-----
Original Message -----
Sent: Sunday, December 19, 2004 2:47 PM
Subject: Re: [Repeater-Builder] GE Mastr II PLL vs.
Multiplier (crystal) exciter in duplex service.
I stand corrected, in part
anyway. In this GE radio the deviation is indeed at a divide by 12
from the output. This is why I said "usually", I am not familiar with
the intricate details of all radios. Especially GE's, I was a Motorola
tech for quite a few years. I will leave the GE's to others like you
who are more familiar with their inner workings.
However, even in this
particular radio, I noticed the PLL circuit uses a X3 from the original
ICOM freq as the PLL reference. This is made obvious by the divide by
4 fed back from the output of the VCO. So even though the PLL circuit
here is not more stable by a factor of 12, as I initially stated, it
theoretically should be more stable by a factor of 4. This does not
appy to deviation in this case but it will most definately apply to
frequency drift.
My 2 and a half cents worth.
Wade - KR7K
-----
Original Message -----
Sent: Sunday, December 19, 2004 11:04 AM
Subject: Re: [Repeater-Builder] GE Mastr II PLL vs.
Multiplier (crystal) exciter in duplex service.
Hi Wade,
I'm sorry, but I have to disagree with your stability theory on the GE
Mastr II PLL high-band exciter. If you refer to the PDF manual for the
PLL exciter:
<http://www.repeater-builder.com/ge/lbi-library/lbi-30398n.pdf>
You will see under the "Description" the exciter utilizes the 12th
multiple of the FM ICOM to lock the VCO on frequency. It goes into
more detail about this in the "Circuit Analysis" section of the same
manual. So, the FM ICOM's multiplication certainly does factor into
the stability of the PLL exciter, and one can generalize it has the
same frequency stability as its multiplier counterpart. In addition,
the modulation of the PLL exciter is produced in the crystal reference
(FM ICOM) as well, and is also multiplied up to the desired deviation.
Since the time constant of the Lead/Lag filter allows for near
instantaneous correction of the VCO, changes in frequency at the audio
rate are superimposed onto the output frequency.
Hope this helps...
Kevin Custer
Wade Lake wrote:
Kevin Custer wrote:
The advantage here is the same frequency stability is achieved by the use of the quartz reference
Actually, a PLL oscillator is much more stable than a multiplied crystal oscillator. because with a multiplied quartz oscillator, frequency drift and frequency error (usually deviation as well) is multiplied by 12, at least in the case of the High band GE MASTR II.
Not to dissagree with you Kevin, your answer is good, I think you nailed it. I just wanted to point out that stability is a very strong point of the PLL. Since it operates on the desired frequency, no frequency error/drift is multiplied.
Wade - KR7K
