[time-nuts] Advanced 5 to 10 MHz doubler
paul swed
paulswedb at gmail.com
Tue Jun 14 18:22:06 UTC 2011
Lets see feb to june. Time to restart this thread.
I found this a very interesting thread and finally ordered the transformers
from mini circuits. Needed some other parts and had enough of an order to
make sense.
I do plan to build the circuit and try some of the comments suggested to see
what happens.
Though this may take a bit of time. Lots of other things to work on.
Regards
Paul
WB8TSL
On Wed, Feb 16, 2011 at 9:11 AM, paul swed <paulswedb at gmail.com> wrote:
> This has been a great read.
> Though I don't have a need at the moment. I may assemble this with the
> various comments just to try it out. Dead bug style.
> Regards
>
>
> On Wed, Feb 16, 2011 at 8:46 AM, Paramithiotti, Luciano Paolo S <
> luciano.paramithiotti at hp.com> wrote:
>
>>
>> Bruce,
>> I have collected yours comments, I hope they will be usefull for my next
>> doubler version.
>> A question: do you have ever made a physical doubler like this? if so, can
>> you show us the schematic, photos and results of measurements made?
>>
>> Luciano
>>
>> Luciano P. S. Paramithiotti
>>
>>
>>
>> -----Original Message-----
>> From: time-nuts-bounces at febo.com [mailto:time-nuts-bounces at febo.com] On
>> Behalf Of Bruce Griffiths
>> Sent: martedì 15 febbraio 2011 22.19
>> To: Discussion of precise time and frequency measurement
>> Subject: Re: [time-nuts] Advanced 5 to 10 MHz doubler
>>
>> Simulation using LTSpice confirms that the 2N3904's actually saturate in
>> this circuit.
>> The phase noise performance will be poor.
>> The transistor conduction angle is also poorly defined and significant
>> conduction overlap due to saturation may render the circuit ineffective at
>> high frequencies.
>>
>> The attached circuit schematic using a 1:4 (impedance ratio) input
>> transformer will work much better and has a relatively well defined large
>> signal input impedance.
>> The output filter can be elaborated by replacing the 80pF caps with a
>> combination of series tuned LC traps and a smaller shunt capacitance to
>> reduce the level unwanted components.
>> Suitable 100uH inductors (with SRF > 20MHz) are readily available from
>> Farnell/element14.
>> The output impedance is relatively low and a better match to 50 ohms may
>> be achieved by adding a suitable low phase noise output buffer amp stage.
>> Alternatively a 4:1 impedance ratio transformer can be used at the
>> collector node with its primary shunted by a 200 ohm resistor.
>>
>> Any balancing circuitry (should this be necessary) should be implemented
>> at the BJT emitters as any attempt to do this at the collectors will be
>> ineffective.
>>
>> Bruce
>>
>> Bruce Griffiths wrote:
>> > Paramithiotti, Luciano Paolo S wrote:
>> >> http://www.timeok.it/files/5_to10_mhz_advanced_doubler.pdf
>> >>
>> >>> This design appears to have gone somewhat astray.
>> >>> high impedance unless of course the transistors enter saturation in
>> >>> which case the phase noise performance will be severely degraded.
>> >>> The best place for a balance adjustment circuit is actually in the
>> >>> emitter circuit.
>> >> *The collector balancing work correctly and is more simple to
>> implement.
>> >>
>> > I contend that the collector balancing technique you use only works
>> > because the doubler isn't operating correctly.
>> > With a high impedance collector output it would be relatively
>> > ineffective unless the balancing resistance is increased to a level
>> > that degrades the phase noise performance or saturation occurs.
>> >>> The description of the biasing is misleading in that the actual bias
>> >>> level that sets the crossover current is determined by the signal
>> >>> dependent voltage>across the two 0.1uF capacitors in the emitter.
>> >>> With a 1:1 input transformer the quoted figure of 35 ohms for the
>> >>> input impedance seems excessive for large signal operation of the CB
>> >>> stages unless of>course they saturate.
>> >> *the input impedance is 35 Ohms @ 0dBm as measured with network
>> >> vector analyzer. It can be upgraded to 50 ohms adding resistance on
>> >> emitters, with some gain reduction and probably less phase noise. I
>> >> will do some modification in the next future, including an input 6
>> >> Mhz low pass filter. As you know, the input signal have to be pure
>> >> sinewave to avoid unsymmetrical positive and negative half wave and
>> >> obvious unbalaced output and high harmonics contens. I will test also
>> >> the common emitter configuration to better isolate the doubler from
>> >> the input impedance and level variations. Regarding the input level I
>> >> have setup it's range, as my personal standard,from +7 to +13 dBm.
>> >>
>> > I thought as much, the large signal input impedance (this is far more
>> > important than the small signal value) will be much lower.
>> > Since the bias shifts with input signal level the small signal input
>> > impedance that you measured is of little value.
>> >
>> >>> It would also appear that the 20MHz tank 5.6uH + 12pF as drawn is
>> >>> inappropriate in that it inevitably leads to saturated operation.
>> >>> A series resonant 20MHz tank from the collector node to ground would
>> >>> be a better choice.
>> >> * The LC on collector is to adapt the impedance between the doubler
>> >> and the filter and to cut the higher harmonics. The filter itself
>> >> contain trap for 15 20 and 30 Mhz.
>> >>
>> > Maybe so, but the filter input topology adopted is inappropriate for
>> > low phase noise and avoiding saturation.
>> > Attempting to match the (poorly predictable and varying - with
>> > temperature and input signal level) collector output impedance to the
>> > filter input impedance is misguided, just treat the output as a high
>> > impedance source. The 4:1 (impedance ratio) output transformer should
>> > suffice, if necessary you can add a 200 ohm resistor in shunt from the
>> > collector node to Vcc if you need a 50 ohm output impedance. In
>> > practice it may be better to buffer the output with a series
>> > transformer feedback stage with well defined output impedance. Series
>> > resonant LC traps from the doubler collector node to ground should be
>> > more effective than parallel resonant series traps in that the high
>> > frequency component amplitudes at the doubler collector will be
>> > significantly reduced rather than enhanced by the filter.
>> >
>> >>> A snapshot or even a sketch of the collector voltage waveforms would
>> >>> be useful in showing that the transistors saturate or not.
>> >> *Actually the prototype is gone to friend's home and I cannot do any
>> >> more measure on it. My next prototype's pubblication will be complete
>> >> of collector voltage waveform to better understand the working
>> >> condition of the doubler stage. I think the 2N3904 is not the best
>> >> solution, i will test some more devices and bias point.
>> >>
>> > At 10MHz you will find that most wideband transistors will be noisier.
>> > However using transistors with a lower base spreading resistance than
>> > the 2N3904 may be useful.
>> >> Thank you
>> >> Luciano
>> >>
>> >> note: I'm not a genius, I just try to enjoy myself. If someone follow
>> >> me, is at his own risk.
>> >>
>> >>
>> >>
>> >> Luciano P. S. Paramithiotti
>> >>
>> >>
>> > Bruce
>> >
>> >
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>>
>>
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