RE: [linrad] ATF33143 and K.

[Leif Asbrink <leif.asbrink@xxxxxxxxxxxxxxxxxxxx]

Hi Jim,

I have never played around with simulation software, I can
not judge how useful it might be. Stray inductances can
be extremely important, I do not know how to model things
properly.

At the moment I am busy with lower frequency things;)


Does the simulation say how much the NF is degraded by the series 
resistor ? Probably very little, but if there is a NF evaluation
it would be interesting to know.

73

Leif

> I have learned much experimenting with the simulated ATF33143 amp 
> in Serenade SV.
> The referance amp from Lionel uses 3.2nh inductance on each 
> source lead. I did a simulated
> output impedance measurement and found it to be 15 ohms. The 
> overall results are much
> better when using 14.5nh on each source lead. In that case, the 
> output impedance is 55 ohms.
> I find that I still must throw away some power in resistors, so I 
> add 10 ohm in series. This 
> makes 65 ohms, so I use 65 ohm resistors in a diplexor. A 220 ohm 
> load resistor makes
> S22 look like 50 ohm at all frequencies. Odd thing. For the most 
> part, the drain needs series
> resistance for a good K rather then some loss by adding a load. 
> In this case when I remove
> the 220 ohm load resistor, K drops from 1.13 to .99 near 144 Mhz.
> 
> I did try using less source inductance to lower the impedance. 
> This created a moving target.
> I could never get K back over 1. Even more resistance had to be 
> used in series with the drain.
> K was never really very good at any source inductance setting.  I 
> had to use a feedback
> network to turn it into a VHF transistor. Then K is very high 
> except at 144 where it can be
> just over one as long as some series resistance is used.
> I think conventional circuits throw away a lot of gain and power. 
> The lossless feedback
> circuit throws away a similar amount of gain, but perhaps throws 
> away less power.
> I was able to bring the impedance down to 50 ohms, but K is 
> dangerously close to 1 then.
> 
> I am anxious to make some p1 measurements.
> 
> K is a funny animal. I am still trying to figure it out. It is 
> some sort of a gain limit.
> I have out of band K under control. It is impossible to have 
> large amounts of gain
> and a good 144 Mhz K at the same time.
> The preamps that I have modeled (designed by others) all have a K 
> below 1 at some
> frequency or another. Usually it is poor near 2M and above 5 gig. 
> My preamp has a 
> K in the thousands above 1Ghz.
> 
> 73, Jim.
> 



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