[time-nuts] buffer amp transformers...

[Bruce Griffiths]

For this application you'll need a bandwidth of somewhat more than 10MHz 
to preserve the clock slew rate.
Those transformers are better suited to sinewave operation at 5 or 10MHz.

If one uses a pair of transformers (one for the feedback and one to 
isolate the output) then wider bandwidth 1:1 transformers can be used.
Or one could just elect to capacitively couple the load.

Alternatively one can just wind one's own trifilar transformer using a 
suitable binocular ferrite core.

Bruce

Henry Hallam wrote:
> The spec sheet lists them as being good to 10MHz; would they be ok at
> 16MHz with a little more loss, or should I worry about resonances with
> parasitic capacitance?
>
> 73 de Henry M0HMH in Santa Cruz
>
> On Wed, Aug 4, 2010 at 9:14 PM,<k6rtm at comcast.net>  wrote:
>    
>> I think I'm a time-nut; as symptoms I include (1) a lot of Mini-Circuits parts on my bench, (2) searches on eBay for Mini-Circuits goodies, and (3) the desire to know how my LPRO, 10811, and Thunderbolt are different, and how much better a Thunderbolt would be with a 10811 double-oven in it...
>>
>> Anyway, here's an eBay auction for 25 T-626 1:1:1 transformers -- item number: 220544907085
>> http://cgi.ebay.com/25-Mini-Circuits-T-626-RF-Transformers-0-01-10-MHz-/220544907085?cmd=ViewItem&pt=LH_DefaultDomain_0&hash=item335980374d
>>
>> which look like just the thing for this amp...
>>
>> 73 de bob k6rtm in silicon valley
>>
>>
>> -------------------------
>> Message: 4
>> Date: Thu, 05 Aug 2010 10:05:39 +1200
>> From: Bruce Griffiths<bruce.griffiths at xtra.co.nz>
>> Subject: Re: [time-nuts] Buffer / distribution amplifier for TCXO
>> To: Discussion of precise time and frequency measurement
>> <time-nuts at febo.com>
>> Message-ID:<4C59E433.6000202 at xtra.co.nz>
>> Content-Type: text/plain; charset="iso-8859-1"; Format="flowed"
>>
>> Bruce Griffiths wrote:
>>      
>>> In which case a linear distribution amplifier is probably required.
>>>
>>> With only a ~3V supply available, options for the distribution
>>> amplifier topology are somewhat limited.
>>> In principle you could use an emitter follower driving 4 other emitter
>>> followers with a resistor in series with the emitters of the output
>>> devices and the AC coupled loads to match the source to the
>>> interconnecting cable impedance to minimise reflections without
>>> requiring excessive dissipation in the emitter followers.
>>> With the low voltage supply available, using an RF choke is series
>>> with the emitter follower's emitter to ground resistor will also be
>>> useful in achieving the required dynamic range.
>>>
>>> Bruce
>>>        
>> A more efficient buffer amplifier circuit schematic is attached.
>>
>> The series transformer feedback stage has high input impedance and an
>> output impedance matched to the transmission line (yes it works well
>> with long transmission lines as well).
>> However a trifilar wound RF transformer is required.
>>
>> In principle the various GPS receivers could be connected to taps along
>> an end terminated transmission line using feedthrough connections with
>> compensation for the tap shunt capacitance if necessary.
>>
>> A lower impedance line (eg 50 ohms) could also be driven at the expense
>> of a higher collector current.
>> In this case the value of R3 would need to be reduced to around 100 ohms
>> or so.
>>
>> Bruce
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>
>
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