Reply by ●April 15, 20192019-04-15
On Sunday, 14 April 2019 21:41:59 UTC+1, George Herold  wrote:

> On Friday, April 12, 2019 at 11:19:04 PM UTC-4, daku...@gmail.com wrote:



> > Could some electronics guru here shed some light on this Could a single stage common collector amplifier exhibit amplitude modulation ?
> > 
> > I have the SPICE model of a simple common collector amplifier
> > consisting of two base bias resistors, a collector resistor and an input and a output DC blocking capacitor, as well as a source and 
> > a load resistor of 50.0 Ohm. The BJT collector is connected to Vcc via a RFC coil. I have tried input signal frequencies from 100 MHz 
> > to 750 MHz, with SPICE transient analysis. Each time, I have seen a 
> > output signal envelope, at the same spot on the time axis. I have
> > tried several common RF|microwave transistors as BFR92A, BFS17, 
> > BFQ67W and HFA3134, but the bproblem is always there. 
> > 
> > All hints and suggestions are welcome - thanks in advance.
> 
> Hmm I'm thinking you need to down load LTspice and post *.asc
> schematics.  
> 
> George H.


or just a sketch


NT
Reply by George Herold ●April 14, 20192019-04-14
On Friday, April 12, 2019 at 11:19:04 PM UTC-4, daku...@gmail.com wrote:

> Could some electronics guru here shed some light on this Could a single stage common collector amplifier exhibit amplitude modulation ?
> 
> I have the SPICE model of a simple common collector amplifier
> consisting of two base bias resistors, a collector resistor and an input and a output DC blocking capacitor, as well as a source and 
> a load resistor of 50.0 Ohm. The BJT collector is connected to Vcc via a RFC coil. I have tried input signal frequencies from 100 MHz 
> to 750 MHz, with SPICE transient analysis. Each time, I have seen a 
> output signal envelope, at the same spot on the time axis. I have
> tried several common RF|microwave transistors as BFR92A, BFS17, 
> BFQ67W and HFA3134, but the bproblem is always there. 
> 
> All hints and suggestions are welcome - thanks in advance.


Hmm I'm thinking you need to down load LTspice and post *.asc
schematics.  

George H.
Reply by John Larkin ●April 14, 20192019-04-14
On Sat, 13 Apr 2019 00:07:50 -0700 (PDT), dakupoto@gmail.com wrote:


>On Saturday, April 13, 2019 at 12:16:05 PM UTC+5:30, Robert Baer wrote:
>> dakupoto@gmail.com wrote:
>> > Could some electronics guru here shed some light on this Could a single stage common collector amplifier exhibit amplitude modulation ?
>> > 
>> > I have the SPICE model of a simple common collector amplifier
>> > consisting of two base bias resistors, a collector resistor and an input and a output DC blocking capacitor, as well as a source and
>> > a load resistor of 50.0 Ohm. The BJT collector is connected to Vcc via a RFC coil. I have tried input signal frequencies from 100 MHz
>> > to 750 MHz, with SPICE transient analysis. Each time, I have seen a
>> > output signal envelope, at the same spot on the time axis. I have
>> > tried several common RF|microwave transistors as BFR92A, BFS17,
>> > BFQ67W and HFA3134, but the bproblem is always there.
>> > 
>> > All hints and suggestions are welcome - thanks in advance.
>> >   
>> > 
>>     Err... isn't a "common collector amplifier" an emitter follower?
>>     And....isn't the circuit you are talking about a common emitter 
>> amplifier (base in, collector out)?
>> 
>> 
>> ---
>> This email has been checked for viruses by Avast antivirus software.
>> https://www.avast.com/antivirus
>
>I do not have any collector resistor, and the output is taken (via a DC blocking capacitor) from the transistor emitter terminal. Please see my response to John Larkin's message.


We can't help you if you don't show us what you are doing.


-- 

John Larkin         Highland Technology, Inc

lunatic fringe electronics
Reply by Tauno Voipio ●April 14, 20192019-04-14
On 13.4.19 21:27, Piglet wrote:

> On 13/04/2019 18:41, Tauno Voipio wrote:
>> On 13.4.19 19:12, John Larkin wrote:
>>> On Sat, 13 Apr 2019 00:03:37 -0700 (PDT), dakupoto@gmail.com wrote:
>>>
>>>> On Saturday, April 13, 2019 at 10:46:07 AM UTC+5:30, John Larkin wrote:
>>>>> On Fri, 12 Apr 2019 20:19:00 -0700 (PDT), dakupoto@gmail.com wrote:
>>>>>
>>>>>> Could some electronics guru here shed some light on this Could a
>>>>>> single stage common collector amplifier exhibit amplitude 
>>>>>> modulation ?
>>>>>>
>>>>>> I have the SPICE model of a simple common collector amplifier
>>>>>> consisting of two base bias resistors, a collector resistor and an
>>>>>> input and a output DC blocking capacitor, as well as a source and
>>>>>> a load resistor of 50.0 Ohm. The BJT collector is connected to Vcc
>>>>>> via a RFC coil. I have tried input signal frequencies from 100 MHz
>>>>>> to 750 MHz, with SPICE transient analysis. Each time, I have seen a
>>>>>> output signal envelope, at the same spot on the time axis. I have
>>>>>> tried several common RF|microwave transistors as BFR92A, BFS17,
>>>>>> BFQ67W and HFA3134, but the bproblem is always there.
>>>>>>
>>>>>> All hints and suggestions are welcome - thanks in advance.
>>>>>>
>>>>>
>>>>> Post the Spice sim? .asc for LT Spice.
>>>>>
>>>>>
>>>>>
>>>>>
>>>>> -- 
>>>>>
>>>>> John Larkin         Highland Technology, Inc
>>>>>
>>>>> lunatic fringe electronics
>>>>
>>>> I use HSpice and Ngspice, both of which allow text netlists,
>>>> but the circuit is so simple that I have given a description below:
>>>> Vcc 15 Volt
>>>> VCC -> Collector terminal 1.0uH
>>>> Emitter terminal ->  ground - RE -375 Ohm
>>>> Vcc -> intermediate node - RB1 - 3750 Ohm
>>>> Intermediate node -< ground - RB2 - 595 Ohm
>>>> Intermediate node -> base terminal - RFC coil 1.0uH
>>>> Both DC blocking capacitor(input, output) are 10 uF
>>>> Input signal amplitude is 1.5 Volt, the frequency has been
>>>> varied between 100 MHz and 750 MHz, mostly around 250 MHz
>>>
>>> Too many words! How about a screen shot or a sketch?
>>
>> I hope that I understood his description right:
>>
> 
> You got the input signal going to the base with L in the bias feed, I 
> read the OP description as having the L in series with the base so 
> signal input also went via the L.
> 
> I agree it unclear which is the right interpretation?
> 
> piglet
> 


There is no description where the feed capacitor connects near
the base. I tried to pick the less bad interpretation.

A 1uH series inductor strangles the signal pretty well.

-- 

-TV
Reply by Piglet ●April 13, 20192019-04-13
On 13/04/2019 18:41, Tauno Voipio wrote:

> On 13.4.19 19:12, John Larkin wrote:
>> On Sat, 13 Apr 2019 00:03:37 -0700 (PDT), dakupoto@gmail.com wrote:
>>
>>> On Saturday, April 13, 2019 at 10:46:07 AM UTC+5:30, John Larkin wrote:
>>>> On Fri, 12 Apr 2019 20:19:00 -0700 (PDT), dakupoto@gmail.com wrote:
>>>>
>>>>> Could some electronics guru here shed some light on this Could a
>>>>> single stage common collector amplifier exhibit amplitude modulation ?
>>>>>
>>>>> I have the SPICE model of a simple common collector amplifier
>>>>> consisting of two base bias resistors, a collector resistor and an
>>>>> input and a output DC blocking capacitor, as well as a source and
>>>>> a load resistor of 50.0 Ohm. The BJT collector is connected to Vcc
>>>>> via a RFC coil. I have tried input signal frequencies from 100 MHz
>>>>> to 750 MHz, with SPICE transient analysis. Each time, I have seen a
>>>>> output signal envelope, at the same spot on the time axis. I have
>>>>> tried several common RF|microwave transistors as BFR92A, BFS17,
>>>>> BFQ67W and HFA3134, but the bproblem is always there.
>>>>>
>>>>> All hints and suggestions are welcome - thanks in advance.
>>>>>
>>>>
>>>> Post the Spice sim? .asc for LT Spice.
>>>>
>>>>
>>>>
>>>>
>>>> --
>>>>
>>>> John Larkin         Highland Technology, Inc
>>>>
>>>> lunatic fringe electronics
>>>
>>> I use HSpice and Ngspice, both of which allow text netlists,
>>> but the circuit is so simple that I have given a description below:
>>> Vcc 15 Volt
>>> VCC -> Collector terminal 1.0uH
>>> Emitter terminal ->  ground - RE -375 Ohm
>>> Vcc -> intermediate node - RB1 - 3750 Ohm
>>> Intermediate node -< ground - RB2 - 595 Ohm
>>> Intermediate node -> base terminal - RFC coil 1.0uH
>>> Both DC blocking capacitor(input, output) are 10 uF
>>> Input signal amplitude is 1.5 Volt, the frequency has been
>>> varied between 100 MHz and 750 MHz, mostly around 250 MHz
>>
>> Too many words! How about a screen shot or a sketch?
>
> I hope that I understood his description right:
>


You got the input signal going to the base with L in the bias feed, I 
read the OP description as having the L in series with the base so 
signal input also went via the L.

I agree it unclear which is the right interpretation?

piglet
Reply by Tauno Voipio ●April 13, 20192019-04-13
On 13.4.19 19:12, John Larkin wrote:

> On Sat, 13 Apr 2019 00:03:37 -0700 (PDT), dakupoto@gmail.com wrote:
> 
>> On Saturday, April 13, 2019 at 10:46:07 AM UTC+5:30, John Larkin wrote:
>>> On Fri, 12 Apr 2019 20:19:00 -0700 (PDT), dakupoto@gmail.com wrote:
>>>
>>>> Could some electronics guru here shed some light on this Could a single stage common collector amplifier exhibit amplitude modulation ?
>>>>
>>>> I have the SPICE model of a simple common collector amplifier
>>>> consisting of two base bias resistors, a collector resistor and an input and a output DC blocking capacitor, as well as a source and
>>>> a load resistor of 50.0 Ohm. The BJT collector is connected to Vcc via a RFC coil. I have tried input signal frequencies from 100 MHz
>>>> to 750 MHz, with SPICE transient analysis. Each time, I have seen a
>>>> output signal envelope, at the same spot on the time axis. I have
>>>> tried several common RF|microwave transistors as BFR92A, BFS17,
>>>> BFQ67W and HFA3134, but the bproblem is always there.
>>>>
>>>> All hints and suggestions are welcome - thanks in advance.
>>>>
>>>
>>> Post the Spice sim? .asc for LT Spice.
>>>
>>>
>>>
>>>
>>> -- 
>>>
>>> John Larkin         Highland Technology, Inc
>>>
>>> lunatic fringe electronics
>>
>> I use HSpice and Ngspice, both of which allow text netlists,
>> but the circuit is so simple that I have given a description below:
>> Vcc 15 Volt
>> VCC -> Collector terminal 1.0uH
>> Emitter terminal ->  ground - RE -375 Ohm
>> Vcc -> intermediate node - RB1 - 3750 Ohm
>> Intermediate node -< ground - RB2 - 595 Ohm
>> Intermediate node -> base terminal - RFC coil 1.0uH
>> Both DC blocking capacitor(input, output) are 10 uF
>> Input signal amplitude is 1.5 Volt, the frequency has been
>> varied between 100 MHz and 750 MHz, mostly around 250 MHz
> 
> Too many words! How about a screen shot or a sketch?


I hope that I understood his description right:

-- 

-TV


Version 4
SHEET 1 880 688
WIRE 176 96 16 96
WIRE 448 96 176 96
WIRE 16 144 16 96
WIRE 176 144 176 96
WIRE 448 192 448 96
WIRE 16 256 16 224
WIRE 176 256 176 224
WIRE 288 256 176 256
WIRE 288 272 288 256
WIRE 448 336 448 272
WIRE -80 384 -96 384
WIRE 64 384 -80 384
WIRE 288 384 288 352
WIRE 288 384 128 384
WIRE 384 384 288 384
WIRE -80 432 -80 384
WIRE 448 448 448 432
WIRE 544 448 448 448
WIRE 688 448 608 448
WIRE 176 464 176 256
WIRE 448 464 448 448
WIRE -80 576 -80 512
WIRE 176 576 176 544
WIRE 448 576 448 544
FLAG 176 576 0
FLAG 448 576 0
FLAG 16 256 0
FLAG -96 384 In
IOPIN -96 384 In
FLAG 688 448 Out
IOPIN 688 448 Out
FLAG -80 576 0
SYMBOL npn 384 336 R0
SYMATTR InstName Q1
SYMBOL ind 272 256 R0
SYMATTR InstName L1
SYMATTR Value 1&micro;
SYMBOL ind 432 176 R0
SYMATTR InstName L2
SYMATTR Value 1&micro;
SYMBOL res 160 448 R0
SYMATTR InstName R1
SYMATTR Value 595
SYMBOL res 160 128 R0
SYMATTR InstName R2
SYMATTR Value 3750
SYMBOL res 432 448 R0
SYMATTR InstName R3
SYMATTR Value 375
SYMBOL voltage 16 128 R0
SYMATTR InstName V1
SYMATTR Value 15V
SYMBOL cap 128 368 R90
WINDOW 0 0 32 VBottom 2
WINDOW 3 32 32 VTop 2
SYMATTR InstName C1
SYMATTR Value 10&micro;
SYMBOL cap 608 432 R90
WINDOW 0 0 32 VBottom 2
WINDOW 3 32 32 VTop 2
SYMATTR InstName C2
SYMATTR Value 10&micro;
SYMBOL voltage -80 416 R0
SYMATTR InstName V2
SYMATTR Value SINE(0 1 100e6)
SYMATTR Value2 AC 1
TEXT -56 632 Left 2 !.ac oct 8 100Meg 1000Meg
TEXT -48 672 Left 2 !;.tran 0 0.1m 0
Reply by John Larkin ●April 13, 20192019-04-13
On Sat, 13 Apr 2019 00:03:37 -0700 (PDT), dakupoto@gmail.com wrote:


>On Saturday, April 13, 2019 at 10:46:07 AM UTC+5:30, John Larkin wrote:
>> On Fri, 12 Apr 2019 20:19:00 -0700 (PDT), dakupoto@gmail.com wrote:
>> 
>> >Could some electronics guru here shed some light on this Could a single stage common collector amplifier exhibit amplitude modulation ?
>> >
>> >I have the SPICE model of a simple common collector amplifier
>> >consisting of two base bias resistors, a collector resistor and an input and a output DC blocking capacitor, as well as a source and 
>> >a load resistor of 50.0 Ohm. The BJT collector is connected to Vcc via a RFC coil. I have tried input signal frequencies from 100 MHz 
>> >to 750 MHz, with SPICE transient analysis. Each time, I have seen a 
>> >output signal envelope, at the same spot on the time axis. I have
>> >tried several common RF|microwave transistors as BFR92A, BFS17, 
>> >BFQ67W and HFA3134, but the bproblem is always there. 
>> >
>> >All hints and suggestions are welcome - thanks in advance.
>> > 
>> 
>> Post the Spice sim? .asc for LT Spice.
>> 
>> 
>> 
>> 
>> -- 
>> 
>> John Larkin         Highland Technology, Inc
>> 
>> lunatic fringe electronics
>
>I use HSpice and Ngspice, both of which allow text netlists, 
>but the circuit is so simple that I have given a description below:
>Vcc 15 Volt
>VCC -> Collector terminal 1.0uH
>Emitter terminal ->  ground - RE -375 Ohm 
>Vcc -> intermediate node - RB1 - 3750 Ohm
>Intermediate node -< ground - RB2 - 595 Ohm
>Intermediate node -> base terminal - RFC coil 1.0uH
>Both DC blocking capacitor(input, output) are 10 uF
>Input signal amplitude is 1.5 Volt, the frequency has been 
>varied between 100 MHz and 750 MHz, mostly around 250 MHz


Too many words! How about a screen shot or a sketch?


-- 

John Larkin         Highland Technology, Inc

lunatic fringe electronics
Reply by Johann Klammer ●April 13, 20192019-04-13
On 04/13/2019 10:40 AM, tabbypurr@gmail.com wrote:

> On Saturday, 13 April 2019 08:07:54 UTC+1, daku...@gmail.com  wrote:
>> On Saturday, April 13, 2019 at 12:16:05 PM UTC+5:30, Robert Baer wrote:
>>> dakupoto@gmail.com wrote:
>>>> Could some electronics guru here shed some light on this Could a single stage common collector amplifier exhibit amplitude modulation ?
>>>>
>>>> I have the SPICE model of a simple common collector amplifier
>>>> consisting of two base bias resistors, a collector resistor and an input and a output DC blocking capacitor, as well as a source and
>>>> a load resistor of 50.0 Ohm. The BJT collector is connected to Vcc via a RFC coil. I have tried input signal frequencies from 100 MHz
>>>> to 750 MHz, with SPICE transient analysis. Each time, I have seen a
>>>> output signal envelope, at the same spot on the time axis. I have
>>>> tried several common RF|microwave transistors as BFR92A, BFS17,
>>>> BFQ67W and HFA3134, but the bproblem is always there.
>>>>
>>>> All hints and suggestions are welcome - thanks in advance.
>>>>   
>>>>
>>>     Err... isn't a "common collector amplifier" an emitter follower?
>>>     And....isn't the circuit you are talking about a common emitter 
>>> amplifier (base in, collector out)?
> 
>> I do not have any collector resistor, and the output is taken (via a DC blocking capacitor) from the transistor emitter terminal. Please see my response to John Larkin's message.
> 
> Your RFC makes it no longer a common emitter amp.
> You fail to say what you actually mean by 'exhibit amplitude modulation'.
> 
> 
> NT
> 

He hasn't posted his spice deck, but I suspect the turn on transient through one 
of his chokes will cause a slow oscillation, quenching the Ic
to zero periodically and thus modulate his output with a low frequency sine.

(I happened to play with sthg similar earlier)
Reply by Piglet ●April 13, 20192019-04-13
On 13/04/2019 07:48, dakupoto@gmail.com wrote:

> On Saturday, April 13, 2019 at 9:42:06 AM UTC+5:30, bitrex wrote:
>> On 4/12/19 11:19 PM, dakupoto@gmail.com wrote:
>>> Could some electronics guru here shed some light on this Could a single stage common collector amplifier exhibit amplitude modulation ?
>>>
>>> I have the SPICE model of a simple common collector amplifier
>>> consisting of two base bias resistors, a collector resistor and an input and a output DC blocking capacitor, as well as a source and
>>> a load resistor of 50.0 Ohm. The BJT collector is connected to Vcc via a RFC coil. I have tried input signal frequencies from 100 MHz
>>> to 750 MHz, with SPICE transient analysis. Each time, I have seen a
>>> output signal envelope, at the same spot on the time axis. I have
>>> tried several common RF|microwave transistors as BFR92A, BFS17,
>>> BFQ67W and HFA3134, but the bproblem is always there.
>>>
>>> All hints and suggestions are welcome - thanks in advance.
>>>
>>>
>>
>> Constant-voltage base biasing is fine at audio or low RF frequencies but
>> it's a lousy way to bias a high-frequency RF single-transistor amp.
>>
>> Please see e.g.
>> <https://www.qsl.net/va3iul/Bias/Bias_Circuits_for_RF_Devices.pdf>
>>
>> for how to bias RF amps at those frequencies, properly...
>
> I have seen this paper in the past, and in fact I do have a copy on a CD. The main issue is there is no indication as to how the
> the passive device component values(in particular resistors) are
> computed. I remember in the section on current mirror based biasing the author writes something like "..with appropriate
> choice of R1, R2...". So how are values of R1, R2 calculated anyway ?
>



Choose R1 and R2 to put the base voltage (and hence the emitter voltage 
plus Vbe drop) at the quiescent bias point you want for the signal 
handling you want.

In your example 3750 and 595 ohms from 15V puts the base at 2.05V and 
emitter about 0.7V lower. That means it will be incapable of handling 
the low going part of your 1.5V ac input as the transistor will be cut 
off before the low going peak and output will be clipped.

Better is to raise the bias so transistor remains conducting for all 
expected inputs. The usual rule of thumb is mid-point. i.e. emitter at 
7.5V thus base at 8.2V so one could use 680 and 820 ohms.

piglet
Reply by Tauno Voipio ●April 13, 20192019-04-13
On 13.4.19 10:07, dakupoto@gmail.com wrote:

> On Saturday, April 13, 2019 at 12:16:05 PM UTC+5:30, Robert Baer wrote:
>> dakupoto@gmail.com wrote:
>>> Could some electronics guru here shed some light on this Could a single stage common collector amplifier exhibit amplitude modulation ?
>>>
>>> I have the SPICE model of a simple common collector amplifier
>>> consisting of two base bias resistors, a collector resistor and an input and a output DC blocking capacitor, as well as a source and
>>> a load resistor of 50.0 Ohm. The BJT collector is connected to Vcc via a RFC coil. I have tried input signal frequencies from 100 MHz
>>> to 750 MHz, with SPICE transient analysis. Each time, I have seen a
>>> output signal envelope, at the same spot on the time axis. I have
>>> tried several common RF|microwave transistors as BFR92A, BFS17,
>>> BFQ67W and HFA3134, but the bproblem is always there.
>>>
>>> All hints and suggestions are welcome - thanks in advance.
>>>    
>>>
>>      Err... isn't a "common collector amplifier" an emitter follower?
>>      And....isn't the circuit you are talking about a common emitter
>> amplifier (base in, collector out)?
>>
>>
>> ---
>> This email has been checked for viruses by Avast antivirus software.
>> https://www.avast.com/antivirus
> 
> I do not have any collector resistor, and the output is taken (via a DC blocking capacitor) from the transistor emitter terminal. Please see my response to John Larkin's message.



To make it work as a common collector amplifier, you need to provide
a direct RF path to ground from the collector with a by-pass capacitor.
The RF choke spoils the ampifier.

-- 

-TV