[time-nuts] buffer amp transformers...

[Henry Hallam]

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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-- 
Henry Hallam

Sent from my Laptop