[time-nuts] buffer amp transformers...

[k6rtm at comcast.net]

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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End of time-nuts Digest, Vol 73, Issue 12 
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