Pi-L Output Network Calculator

[K1JJ]

Does anyone know of a simple online  Pi-L  network calculator that is not Excel based?

I don't see anything on the web or in the AMfone archives.


TNX.

T

[Jim, W5JO]

Look up WA2WHV site.  I think he has an application there if the site is still there.

[K1JJ]

Thanks, Jim, but that site has just a pi network calculator, not a Pi-L.


In the meantime, my question is,  does a pi-L help reduce the C1 capacitance requirement vs: a standard pi network?  I have a tube for 10M that has a high plate shunt-C.  This internal shunt value is about what is needed for C1 already on 28.7 mhz.  If I add a C1 for tuning, this total capacitance will be too high.  I was hoping a Pi-L wud help reduce this problem...

T



  

[Jim, W5JO]

T if you have an Orr book, say the 21st edition, there is a chart that will take care of you.  Usual design impedance for the Pi portion is 300 ohms then the last inductor is enough to get to desired impedance, 50-75 ohms.  If you don't have the book I can scan the page for you and email.

What is the load impedance?  C1 values range from 56 pf @ 1 K down to 13 PF @ 4.5 Kohms for a Q of 10.  

[Steve - K4HX]

I think there is a calculator in this sw package.

http://www.cq-amateur-radio.com/cq_ham_calc/cq_ham_calc.html

[K5UJ]

why not bypass C1 on 10?   I think on 10 there is high circ. current through the plate blocking caps.   Avoid anything dinky.

[K1JJ]

Thanks  for the suggestions.

Well, after reading what Bill Orr says, the C1 cap will still remain the same value in either a pi or Pi-L. All other components change value, however.   I don't know how I got the impression C1 would be less. I've seen Pi-L's used by the good buddies on 11M so figgered this was a solution for the shunt C problem.  **  Update ** (However, my later post using a web calculator shows C1 requirement to be much lower with a Pi-L, thus a standard pi was used in the end)

Anyway, for a pi-L, L1 is usually 1.25 times it's pi-network counterpart.     C2 becomes 1/2 to 2/3 of the normal C2.  Also C2 must have its voltage increased by X3.

The well known Pi-L advantage is the extra 15db of second harmonic attenution.

Since I already wired it up as a pi-L, we'll see if I can get away with it as-is.  John, the reason for C1 is to have something to tune. If I eliminate it I wud have to tune L1, which may be the next alternative if the total C1 is too high and I need to disconnect it. However, the minimum value of my mini C1, a vac variable, is only about 5pf, so not so bad.


T

[K5UJ]

ah yes of course--the thing might be to parallel some cap with C1 that will bring its range way down to some low value so you can still vary it.

[Jim, W5JO]

Sounds like you will be ok.

[Opcom]

If you can stomach DOS programs, this might be useful or maybe entertaining. They are freeware and come with a money back guarantee.

http://www.montagar.com/~patj/rf_read.htm

Back in the day I wrote these programs in Turbo Pascal to calculate power supplies and Pi and Pi-L circuits. The UI is simple text entry, one line after another, and it prints a simple tabulation of answers on the DOS screen.

The PIout.exe program allows one to insert the conduction angle in degrees.

The source code might still exist if there is any interest (the horror of that!).

The calculations and conventions are derived from the ancient and weighty tomes of the Old Masters.

Pascal is responsible for my current dislike of programming.

[w3jn]

Pascal is responsible for my current dislike of programming.

 

It's also one reason (of many, I might add) I abandoned all thought of pursuing a computer science degree and went with electronics engineering instead.   With the strict syntax rules and structure you'd think the Germans invented Pascal.

[IN3IEX]

Hi K1:

Could you try this method:

http://amfone.net/Amforum/index.php?topic=29105.0  ?

If you match to Rmin it produces an L network.
Please let me know if it works for you.

TNX

Giorgio

[K1JJ]

Tnx for the info, Giorgio.   I have everything figured out at this point so can start testing and optimizing this amplifier now.


Funny comments about Pascal...  I first learned Basic in 1980 and then went on to Turbo Pascal.  I didn't know any better back in 1988 and wrote many programs using it, mainly for trading markets.  Later, "Easy Language" came out by Tradestation, which is also Pascal. That's all I've ever used and program using it every day..  I realize C and other languages have since dominated, but I speak Pascal here and that's all..      Thank God I never had to earn a living programming exclusively.

T

[W8VG]

Try K8KK...he wrote a nice article in ER while back and has a webpage/on line app--can google it up.  I used his program do design the Pi in my HB 813 rig--worked great.  He also has Pi-L program.

73's
Geo W8VG/6
Rancho Palos Verdes CA 

[K5UJ]

if you think pascal is rigid and inflexible try Fortran.  i have not used either since college. everything is Perl, Python, database and shell scripts now.

[W1FVB]

a web based one, that might be useful:
http://home.sandiego.edu/~ekim/e194rfs01/jwmatcher/matcher2.html

[K1JJ]

a web based one, that might be useful:
http://home.sandiego.edu/~ekim/e194rfs01/jwmatcher/matcher2.html

Yes!   Just what I was looking for.  That link has calculations for both the Pi-L and the Pi, in addition to 14 more networks.  They are all figured out at the same time... cool.

This should be added to the AMfone website archives. Best I've seen.

It shows that the standard pi-network is best for a tube with big plate shunt C.   For similar conditions, it showed C1 needing 56pf for the Pi and only 9pf for the Pi-L.   In testing, I found this to be true and the Pi was superior to matching this tube with big shunt C.   Total C1, (tube plate shunt + variable capacitor) network requirement needs to be as large as possible to give adjustment range.

I'm all set now.

Thanks for posting that, OM.

T

[KC2ZFA]

It shows that the standard pi-network is best for a tube with big plate shunt C...

...and low impedance, yes ?

Peter

[W4AMV]

Note that the source and load required inputs are all series form. If your tube design parameters are in parallel form (typical for semiconductors), you will need to convert those impedance sets from parallel to series before using the applet.

Alan

[K1JJ]

Note that the source and load required inputs are all series form. If your tube design parameters are in parallel form (typical for semiconductors), you will need to convert those impedance sets from parallel to series before using the applet.

Alan

  I don't understand, Alan.  Please explain.

In the link, let's take a look at the third picture down on the right. This shows a standard pi-network.  For a standard linear amplifier tube stage at 29 mhz, (29e6) using 1200 ohms source+ J0,  50 ohms output+ J0, Q=12, it gives the  following approx values:

C1= 55pf
L1= .64uh
C2= 246 pf

How would this differ according to your thoughts?

Tnx.

T

[W4AMV]

You are correct T. However, you chose the case where the load and source are REAL. Not complex. If their is reactance present or you wish to handle any stray C, or in fact the device has an associated C or L, then the load is COMPLEX. Now, the applet wants the entry to be in SERIES form.  Usually for power devices ahe load line (device output) is expressed as some RL//CP... and if that is the case, just need to convert to its series equivalent. I wrote an applet like this some time ago. The first entry point was....

IS YOUR LOAD COMPLEX?
IS YOUR LOAD SERIES FORM or PARALLEL FORM?

And then I would make the appropriate conversion dependent on the topology of the matching network.

Hope that is clear. Again what you did is on the money, it only gets sticky if the termination is complex.

[K1JJ]

Tnx for the explanation Alan.  I guess it's close enuff for now...

At this point the amplifier appears to tune with the network parameters given, at least according to the MFJ-259B going into the 50 ohm pi-network backwards. The real fire test may be tmw.  I may post some pics and results.  Might even get it on 10M by the weekend with some luck.

Right now got the tube's fil on for 24 hours to burn out the gas.

T

[WA1GFZ]

Tom,
Let me know if you want to do any on air tests. I'll be around all weekend.

[K1JJ]

Tom,
Let me know if you want to do any on air tests. I'll be around all weekend.

Sounds good, Frank.

Then I'll make it a goal to have it running on 10M this weekend.  I'd like to have you look at it on your HPSDR and check the bandwidth and cleanliness, etc.   If it works out and the band is good, maybe we can hold some court SW or NE.  With the 10M corntest this weekend, shud be some big activity on ssb too.

I'll let ya know the results.


T

[Gito]

Hi T

A pi net work consist of C1 for resonance an L and  a C2 loading coil.

So we always thought that the resonance must be made by C1,actually if We have a fix C1 (not variable,in this case the tube internal C) but close to the C needed for resonance,with the right value of L ,we can dip it by C2 ( the loading  Capacitor),if the current of the tube is to high after we find a dip,
change the value of the L make it longer(more turns} dip it again with C2 ,than the current will be smaller than before,by changing the value of  L and C2 setting we can have the current expected by the Tube.of course the Q factor will also change ,but not to great.

But this condition ,the C1 must have the value close to the Tube capacitance.needed for the Pi network(after calculating it).


Gito.N