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Old 20th Nov 2022, 8:02 pm   #21
dmowziz
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Default Re: Common Emitter Amplifier Design S Parameters

Quote:
Originally Posted by G0HZU_JMR View Post
It looks like the gain has now increased to be closer to the simulation.

Your input inductor doesn't look to be very friendly in terms of adjustability. Can you rewind it using thinner wire such that you can easily stretch the windings to alter the inductance? The Q will go down a bit but I'm not sure that matters st the moment. Adjusting this inductance may help here.
Alright I'll change the coil... If same thing, I'll try and use ugly style..
Thanksss


Lol nice, COD!
It might be nice to get a controller rather than use keyboard and mouse.
Although if you do this, we might rarely see you here

I meant controller

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Old 20th Nov 2022, 8:02 pm   #22
paulsherwin
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Default Re: Common Emitter Amplifier Design S Parameters

Let's stay on topic please. This isn't a gaming forum.
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Old 20th Nov 2022, 9:29 pm   #23
G0HZU_JMR
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Default Re: Common Emitter Amplifier Design S Parameters

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Alright I'll change the coil... If same thing, I'll try and use ugly style..
Thanksss
I tried tacking together your circuit in ugly style although I used thinner wire to make it easier to adjust. I think you are using one of my old s-parameter data files for the 2N3904 at 7Vce and 10mA.

I tried using the same file data and compared it to the measurements of the ugly built version.

I got good agreement as below. I didn't try modelling the inductance of the short ugly interconnecting wires between components. The agreement might have been even closer if I did this.

Note that I spotted that the design isn't unconditionally stable for out of band frequencies so you would have to be careful how you terminated it in a real application.
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Old 20th Nov 2022, 10:11 pm   #24
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Default Re: Common Emitter Amplifier Design S Parameters

I used 0.4mm enamelled copper wire for the output inductor. This is quite fine and easy to adjust. I used 24SWG tinned copper wire for the input inductor and this is about 0.56mm diameter. This was a bit stiffer to adjust but you can see I achieved the 18dB gain your initial simulation predicted. My simulation used a very basic inductor model, but it still agreed quite well with your simulation and my ugly built version.

The s2p model I gave you for the 2N3904 should be really good provided that you have a 2n3904 made by the same manufacturer as me. I've posted up the image below before, but these are the 2N3904 parts I used to create the s2p data model. These were purchased from Farnell. Ideally you should be using the same if you want to get good agreement.

Most radio tinkerers will never attempt what you are trying to do even when they have been playing radio for decades. So, my advice would be to keep at it and keep refining your simulation and modelling skills
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Old 20th Nov 2022, 10:56 pm   #25
dmowziz
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Default Re: Common Emitter Amplifier Design S Parameters

Quote:
Originally Posted by G0HZU_JMR View Post
I used 0.4mm enamelled copper wire for the output inductor. This is quite fine and easy to adjust. I used 24SWG tinned copper wire for the input inductor and this is about 0.56mm diameter. This was a bit stiffer to adjust but you can see I achieved the 18dB gain your initial simulation predicted. My simulation used a very basic inductor model, but it still agreed quite well with your simulation and my ugly built version.

The s2p model I gave you for the 2N3904 should be really good provided that you have a 2n3904 made by the same manufacturer as me. I've posted up the image below before, but these are the 2N3904 parts I used to create the s2p data model. These were purchased from Farnell. Ideally you should be using the same if you want to get good agreement.

Most radio tinkerers will never attempt what you are trying to do even when they have been playing radio for decades. So, my advice would be to keep at it and keep refining your simulation and modelling skills

Yeah my 2N3904BU is the same I think because I finally did the oscillator in this thread. #28. I attach measurement (it's not perfect)

https://www.vintage-radio.net/forum/...=191460&page=2

One key thing I learned here was to keep the transistor flat down (you did not mention it but you kept yours that way too)... So looking at the board, how you do it helps too.



Using ugly construction now...I changed the input inductor to one using 24AWG (The s11 improved abit : I'm still on this inductor).


Thankss... I'm on this tonight till I make progress
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Old 21st Nov 2022, 1:46 am   #26
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Default Re: Common Emitter Amplifier Design S Parameters

Didn't add an important part of the oscillator plot (the phase)


I see the "trick" in the amplifier design... Your board reveals it

I followed accordingly and got the image... s21, s11 not perfect with simulation.. But the S11 is alot better to what I had before (minimum -12dB)

I want to make a change to see better improvement then return to my pcb..

Thank you so much Jeremy
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Old 21st Nov 2022, 2:58 am   #27
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Default Re: Common Emitter Amplifier Design S Parameters

Jeremy's mentioned a couple of points which don't seem important at first glance, but which hide subtleties. Things you need to know because they can trip you up.

He mentioned out of band stability. OK, what frequencies do you want your circuit to not oscillate at?

As it's an amplifier and spurious oscillation at any frequency is likely to spoil the performance on your wanted signals, you want to know it will be stable at ALL frequencies. 'All' is a big ask. but making sure stability is OK in your circuit across the frequency range your device has enough gain to be able to oscillate in any circuit will do. Now, if you pursue modern high performance devices, you'll find many are strongly focused on a specific application with a specific band. You'll find the manufacturers s-parameer data covers the band and a bit around it, but they don't bother with any more.

The rats! That's useless for stability checking, and you'll have to measure and extract your own full frequency range anyway.

Look deeper and you'll find some (not many) of those devices with truncated s-parameter stacks have stability issues in the unpublished frequency ranges? And the only way you'll ever know is if you get and measure/try actual physical devices. Did the manufacturer know? Perhaps they never looked, having their cellphone-coloured goggles firmly on. Was t deliberately concealed? We'll never know.

The other subtlety is in the suggestion that you'll need to get the same make of transistor as Jeremy measured if you want to use his results.

Not all transistors of a given type number are the same. There are variations manufacturer to manufacturer, mask revision ditto, wafer ditto and individual ditto.

If you are pushing for optimum performance, you may be designing around parameters more tightly grouped than the type number spec (if it even has them) You measure parts and use the results. From time to time tha manufacturer revises or moves things and the shift in behaviour drops your design in the xxxx.

The other method of design is to design areond the guaranteed parameters with limit bounds of the type number. Good luck! there will usually be important parameters not tied down. Even if you get an s stack they'll be typicals without indications of variance.

So you have to do the best you can between these extremes. Wily RF designers have built up an idea of what (and who) they can trust.

Even with full band s-data there are beasties with stings in their tails. The AH312 is an elderly (now) HEMT transistor with on-chip bias controller. Manufacture has passed through several organisations as take-overs etc occurred. It goes to around 2GHz and can output a watt or so. It's an attractive little thing to drive bigger beasties when you need to make the airwaves sing.

It's trouble comes at much lower frequencies. If you're using it in the onesy-twosy gig part of the spectrum, a match to its input impedance looks like 2.2pf series, 2.2pf shunt and finally a few mm of transmission line into its input. That line also makes things easy, gobbling up the pads for the twin input pins. Handy!

Look at the s parameters and the forwards gain S21 climbs rapidly at lower frequencies to very worrying values. Look at the other s parameters and you really really want to make the network feeding it look lossy at low frequencies.. Ah, but you need to perform a match in the wanted band, and that forces values which look open circuit down at a dozen MHz. If you try to engineer a network to pull off this stunt, you run into spurious resonances in it. It can be done, but you're skating on a knife edge.

Come down in frequency and the MRF1513 looks like an affordable bargain for a few watts at VHF and 12v supplies. Now read the datasheet carefully and notice that parameters were measured with an RC network interposed in the gate connection. Oooo-er! Should you be worried? YES. They tell you in a couple of places in the data sheet, but not everywhere the taming network is used. In practice, this part is a right so and so to use to its full capabilities.

Be aware that the simulation approach to design is good, but it's limited by the quality of the data available. Dodgy stability tricks and the lack of bounds are the worst aspects.

You only find out about these things when you trip over them.

David
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Old 21st Nov 2022, 7:08 pm   #28
dmowziz
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Default Re: Common Emitter Amplifier Design S Parameters

Hi David..Thanks

From my understanding so far, since k>1 from 42 MHz to 300 MHz and if there's no other AC equivalent component except the matching elements then it can't oscillate in that range



In the MRF1513 datasheet, do you mean R1 and C5? Please what does it do?
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Old 21st Nov 2022, 7:32 pm   #29
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Default Re: Common Emitter Amplifier Design S Parameters

Don't have the MRF1513 datasheet in my head, but if those designators mean the ones I think, they are a lossy dampener to prevent the thing oscillating almost however you use it. They also serve to modify the s-data so it isn't glaringly obvious how unstable the raw device is.

Be aware that k factors assume you have a good wideband Z0 attached to the input matching network. Antennae are only good narrowband.

David
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