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Free Micro-Cap Simulation

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peterscott
(@peterscott)
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Antiqueradios.com/forums/Free Micro-Cap Simulation

www.nostalgiatech.co.uk

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Topic starter Posted : 09/01/2020 1:05 pm
peterscott
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After a few silly mistakes I did get it to work on this very complex circuit..

Clipboard06

It is because the company has closed that it has now been offered free. So no updates or support.

Peter

www.nostalgiatech.co.uk

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Topic starter Posted : 09/01/2020 6:37 pm
Nuvistor
(@nuvistor)
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It appears Windows only, not cross platform, pity but it’s  free so mustn’t complain, good that they thought to release it.

Frank

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Posted : 09/01/2020 8:41 pm
peterscott
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My last plot used the wrong transistor model and the wrong source.

Peter

Clipboard06

www.nostalgiatech.co.uk

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Topic starter Posted : 09/01/2020 11:04 pm
peterscott
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I thought I'd try it on a little frequency changer that I designed 40 years ago to convert the 405 line transmissions from Kirk o' Shotts (Channel 3 v. 56.75HMz) down to 45MHz for input to my HMV901.

The transfer function shows something but I'm not convinced that it recognises that the oscillator is oscillating and the mixer mixing!

Clipboard06

Peter

www.nostalgiatech.co.uk

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Topic starter Posted : 10/01/2020 8:37 am
Nuvistor
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Hi Peter,

The single transistor amp, second version, is the top graph frequency response and bottom graph the phase change at different frequencies?

Appreciate a bit of help with that circuit of the frequency  changer.

Presuming V1 and V2 are + and - supply rails and V3 is the Ch3 input. Q13 common base for matching to Q15 Mixer /Osc.

Not worked out what Q16 is doing though, I can see L4 is this the 45Mhz output?

That’s what I think could be occurring but probably very wrong, corrections appreciated.

Frank

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Posted : 10/01/2020 4:02 pm
peterscott
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@nuvistor

Hi Frank,

Thanks for your interest.

Yes, the single transistor plots are amplitude and phase.

The frequency changer plots are all voltages at various nodes. As you say V1 and V2 are just +5v and -5v rails.

Yes, Q15 is the mixer and Q13 is an efficient impedance conversion. Q16 is the oscillator but you can be forgiven for not realising that because for reasons beyond my understanding the simulation totally refuses to make it oscillate. It's a Colpitts that should be running at 11.75MHz. In the real circuit there is an extra tuning capacitor in parallel with C6 but I didn't see it as important for trying out the simulation. Unfortunately it's not the only thing that isn't simulating. I tried disconnecting the Colpitts and adding a simulated 12MHz source but the mixer just doesn't work and the 12MHz mysteriously disappears.

I should say the real circuit works very well. It even survived 30 years unused in my loft.

Ch 3to1

 I forgot to draw the decoupling cap at R4/L3 but I did add it to simulation without improvement.

The d.c. conditions in the simulation all look right but I'm beginning to wonder if I've discovered why Micro-cap stopped trading!

Kind regards,

Peter

www.nostalgiatech.co.uk

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Topic starter Posted : 10/01/2020 5:25 pm
Nuvistor
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Thanks for the update, your hand drawn circuit makes more sense to me than the digital one, I can see the Colpitts osc in that circuit. Just what you get used to looking at.

Frank

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Posted : 10/01/2020 6:00 pm
peterscott
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@nuvistor

The package does offer what looks like a good range of transistor models including my favourite 2N5179 but the model for that turned out to have an Ft of 30MHz instead of the 900MHz I was expecting but I found another model in their list ZTX5179_TX and that is what is in the single transistor simulation as well.

Peter

www.nostalgiatech.co.uk

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Topic starter Posted : 10/01/2020 6:04 pm
Cathovisor
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Posted by: @peterscott

The d.c. conditions in the simulation all look right but I'm beginning to wonder if I've discovered why Micro-cap stopped trading!

Have you tried simulating it in LTSpice, assuming you can find a suitable transistor in their library?

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Posted : 10/01/2020 6:32 pm
peterscott
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Hi Mike,

I spent quite a bit of time today trying to learn how to drive LTSpice with a very simple one transistor circuit. Am currently failing to understand "Failed to find DC operating point for AC analysis."

I've seen 2N5179 in model lists on the web I copied one into lib. There's a file "standard.bjt" in lib/cmp but despite me trying to change the read-only properties up the directory chain it refuses to let me add to the model list.

Peter

www.nostalgiatech.co.uk

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Topic starter Posted : 10/01/2020 7:00 pm
peterscott
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Clipboard07

This is my current mess.

www.nostalgiatech.co.uk

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Topic starter Posted : 10/01/2020 7:27 pm
Cathovisor
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Dud you set a DC voltage for V1 and a series resistance? I just tried copying your circuit and hit the wrong button, thus losing my work... oh, and add a ground reference to the circuit.

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Posted : 10/01/2020 7:45 pm
peterscott
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@cathovisor

I think I tried to connect the source to the circuit via a capacitor and not understanding the dc reference error I replaced it with the 5k resistor. I can't remember when I gave the source a 75 ohm series resistance.

It doesn't like capacitor coupling.

Clipboard07

.and starts a stepping routine that I don't understand but gives an incrementing message bottom left.

Peter

www.nostalgiatech.co.uk

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Topic starter Posted : 10/01/2020 7:56 pm
Cathovisor
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@peterscott

I did a few tweaks of your circuit, as illustrated below:

source edit1
source edit2

And this was the result measured at the collector of Q1.

peterscott cct

I'm off to bed now, but HTH...

Mike.

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Posted : 10/01/2020 9:50 pm
peterscott
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@cathovisor

Thanks Mike, That was kind of you to re-enter my circuit and put it a working state. I see my mistake was not including a ground connection to the circuit.

Peter ?

www.nostalgiatech.co.uk

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Topic starter Posted : 10/01/2020 10:07 pm
Cathovisor
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Yes, it really doesn't like you omitting that ground reference.

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Posted : 10/01/2020 10:14 pm
peterscott
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@cathovisor

I just tried simulating the frequency changer and the Colpitts oscillator was running but the frequency changer wasn't working very well. Anyway, after a few runs the schematic was looking rather small and on pressing a wrong magnifier symbol I appear to have totally deleted the simulation! ?

www.nostalgiatech.co.uk

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Topic starter Posted : 10/01/2020 11:58 pm
peterscott
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Well I decided to uninstall Micro-cap simulation and learn a bit more about LTSpice.

I'm not totally sure of my ground here but the AC analysis is not selective and the actual output of my real frequency changer does still have Channel 3 (56.75 MHz) larger than Channel 1 (45 MHz) by about 6dB. The spectrum analyser picture is taking CH 3 from an Aurora and includes the sound carrier.

P1020834 (Medium)

So I thought I would look into running an FFT on the unselective output of the LTSpice simulation. I have plotted it on a linear frequency axis. I only have the vision carriers in the simulation.

Clipboard08

Although the relative amplitudes are rather different I think the simulation is beginning to look quite attractive.

Peter

www.nostalgiatech.co.uk

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Topic starter Posted : 11/01/2020 3:36 pm
peterscott
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This looks better..

Clipboard09

www.nostalgiatech.co.uk

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Topic starter Posted : 11/01/2020 4:01 pm
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