On 3/27/16 4:40 AM, Dr. David Kirkby (Kirkby Microwave Ltd) wrote:
On 27 Mar 2016 03:00, "jimlux" <[email protected]> wrote:
On 3/26/16 3:25 PM, Bruce Griffiths wrote:
On Saturday, March 26, 2016 09:30:30 PM Rob Sherwood. wrote:
You cannot add the directivity and gain. Doesn't work that way. Rob,
NC0B.
Sent from my iPad
Minicircuits would disagree with that and its their amplifier.
Bruce
Well, it's a bit inconsistent between gain, directivity and S parameters.
at 5.4 MHz the ZFL-500LN has the following S parameters @ 15 V in the
.s2p file (there's two units' measurements in the files)
S11 -35.5, -32.1
S21 29.7, 29.5
S12 -47.5,- 47.2
S22 -39.5, -28.3
On the other hand, the data sheet "typical data" says: at 5.4MHz 27.9 dB
gain, 26.5 dB directivity, which Minicircuits defines as isolation-gain
(implying isolation is 54.4)
http://www.minicircuits.com/pdfs/ZFL-500LN.pdf
I think you are wrong there. From the Touchstone .s2p data you give above:
Isolation (dB) = - |S12|=+47.5 dB.
Gain (dB) = |S21|=+29.7 dB.
Yes, that's what I would think: roughly 29 dB gain, roughly 47 dB
reverse isolation... BUT, that's nothing like what the data sheet says.
Directivity, a term I can't say that I have seen much applied to amplifiers
other than by Minicircuits, is according to the Minicircuits definition,
the difference between isolation and gain. But I don't see a note of
whether its gain - isolation or isolation-gain.
I just assumed it's whichever has the positive sign, since the published
numbers are positive: so isolation-gain..
Assuming the latter, the
directivity would be
47.5-28.7=18.8 dB.
That doesn't agree with your result, nor does it agree with the
Minicircuits typical value of 26.5 dB.
I was using the data sheet numbers for gain/directivity and working
backwards to a reverse isolation.
But the Minicircuits typical gain in the data sheet is 27.94 dB.
I learned from a Minicrcuits sales rep that the "typical" data in their
data sheets is the result of one device taken randomly from the production
line. It is not any sort of average. I find that very odd, and so did the
sales rep, but I was told that was true.
I'm not surprised at all. And it's obvious that the data sheet number
doesn't happen to match either of the two devices they provide as
S-parameter data.
I think it is time to confirm these numbers with Minicircuits, but I would
not rely on "typical" data if you want a guaranteed isolation.
Maybe there's some sort of assumption about source/load impedance (e.g.
not necessarily perfect 50 ohms)
I doubt that is so. S-parameters by definition assume that all other ports
are terminated in devices which reflect no power at the system impedance.
In the case of most devices that's 50 Ohm loads, but in the case of mixed
waveguide/coaxial devices waveguide loads would be used.
Yes about the S parameters.. I was wondering if the "gain" and
"isolation" numbers made some other assumptions..
Minicircuits do a range of high isolation amplifiers. I assume that they
guarantee figures for those although I have not checked.
The ZFL-500LN is one of the high isolation amps (I searched for
isolation>40dB to get the list.
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