Re: #qcx class e #pa #lpf..... or hunting for the optimum #qcx #pa


Jim Allyn - N7JA
 

On Mon, May 11, 2020 at 07:12 AM, ajparent1/KB1GMX wrote:
Please start with a 13.8V power supply.
As  I stated above, I did start with 13.8 volts.

Then subtract out the series polarity protect diode.
As I stated above, I did subtract voltage drop across the series polarity protect diode, using the data from the manufacturer's data sheet.

Then subtract the voltage drop across Q6 during TX (if its saturated maybe a half volt).

As I stated above, I did subtract the voltage drop aross Q6, using the data from the manufacturer's data sheet.

I assure you the voltage applied to the collectors via L4 is NOT 13.8V and
likely closer to 12... ok, maybe 12.8ish

As I stated above, using the manufacturer's data for the drop across D3 and for the drop across Q6, I calculated 13.12 volts at the collector of Q6.  I had to interpolate these numbers off the graph, so they might be off a little.  In an earlier life, if this were my radio, and the numbers for voltage drop across D3 and Q6 were the numbers you gave instead of the numbers the manufacturer gave, I'd probably have looked for a different vendor for those parts, if this were a critical application.  (See my next paragraph.)  When I buy and build a QCX, I will probably measure those things and look for other ways to improve the performance of the QCX.  If I decide to use mine portable, I will probably replace IC11  with a well filtered and (if needed) well shielded switcher to improve battery life.

The 74ACt00, yes it also adds current when clocked and it would require
measuring that as well as the increased current from driving the gates of the
BS170s as that's about 180pf of total gate capacitance.

I didn't measure it.  Not having a QCX here, I calculated the current draw from the numbers on the manufacturer's datasheets, and the standard formula P = C X V^2 X F.  I summed up all of the capacitances that have to be driven when in transmit, including the internal capacitances of the three gates of IC3 that are being driven and neglected the microamps current draw of IC3D which is not being driven at MHz frequencies, the input capacitance of IC3B and IC3C that has to be driven by the Si5351, the input capacitance of IC3A which has to be driven by IC3B, and the input capacitances of the three BS170s which have to be driven by IC3A.  That total draws a lot more current than one might think.  (In the 1980s, I worked for a company that built alphanumeric display pagers.  Probably these days most people would have no clue what that is.  I like to say we invented texting, and really, we did.  Anyway,  in the process, I learned a HELL of a LOT about reducing power consumption.  When a new engineer at some point a few years later wrote a change order to use a bipolar transistor to turn on the receiver instead of the FET I had specified because the bipolar transistor was cheaper and he wanted to save money, I showed him my spreadsheet and told him exactly how much that would reduce the battery life of the pager.  Battery life was a big deal in those days before lithium batteries, and I had EVERYTHING in my spreadsheet.)

Also you do  need to know what at the drains but for all practical uses L4 is 
much less than 50 milliohms so the junction of  C34 and L4 will be extremely
close to the drain voltage applied [less than .04V error].

Which is why I left out the drop across L4.  I did consider calculating how much wire is in it and what the resistance of that wire would be, but decided it wouldn't be worth the trouble.


IN the end you have verified most of what I said and pointed outu a miss.
The voltages I used may not match yours but i did say go measure it.
As did I say go measure it.  My point was that though there are ways you can calculate things like that, there is no substitute for measuring it.  Or better yet, do both.  And in my earlier life, if the measurements and calculations didn't agree, I would absolutely go figure out why.

In the end the trivial way is likely good enough  but far from accurate.

And if Manuel is curious about the efficiency, he needs to learn how to measure it.  And I think he probably just learned a lot.  Manuel, I appreciate your IR photographs, and there is likely an IR camera in my near future.

Allison, I don't mean to be rude or insulting to you here, but it's just my nature to check things like this and add my two cents worth, and I know I can come across that way at times.  (Probably way too often.  I am not a "people person", and I'm old enough that that's not likely to change.)  No offense is intended, and I recognize and acknowledge that you are one of the more knowledgeable people here, and by a significant margin.  73

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