[time-nuts] Distribution amp - Use a video amp unit ?

[Randy D. Hunt]

On 3/26/2012 8:15 AM, Charles P. Steinmetz wrote:
> Bruce wrote:
>
>> A circuit schematic for a current feedback triple with reasonably low 
>> noise and distortion is attached.
>
> Quite a good performer for such a simple circuit.  I found, both in 
> modeling and on the bench, that there is the usual noise bump at 
> 200-300 MHz and non-monotonic behavior out in the 900 MHz region.  The 
> latter can be solved by using an MPSH10 for Q1, which also brings the 
> in-band noise and phase noise down a little.  The former can be 
> addressed by adding 8-10 pF across R2, at the expense of lowering the 
> 3 dB point from around 150 MHz to around 80 MHz.  For use as a 5 or 10 
> MHz distribution amp, I'd include the cap.
>
> The input impedance stays decently high everywhere the amp has useful 
> gain -- there should be no problem paralleling 10 of them on a 50 ohm 
> source.  You can raise R2 just a tad to get back to unity gain, if 
> needed.  The reverse isolation is about 35 dB.  This can be improved 
> to around 50 dB by adding an emitter follower at the input, adjusting 
> R7 and R8 to maintain Q1's base voltage.  The noise increase is 
> negligible.
>
> It is fairly sensitive to power supply noise, so you want a nice quiet 
> supply.  I used a regulator built with an LM399 and LT1028.
>
> Since the transformer is 1:1, one might be tempted to omit it.  For a 
> distribution amp that will be connected to a number of different 
> instruments, however, one is well advised to include it to isolate the 
> various returns.  6 bifilar turns on a T43-37 toroid core and 14 
> bifilar turns on a T61-37 both worked fine for me.  If you have 1:1 
> transformers from a spare Ethernet card, those should, too.
>
> For a Q&D distribution amp, this would be a pretty good candidate.
>
> Best regards,
>
> Charles
>
>
>
>
>
>
>
> _______________________________________________
> time-nuts mailing list -- time-nuts at febo.com
> To unsubscribe, go to 
> https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
> and follow the instructions there.
>
if one is distributing 10 Mhz, does it really matter what the circuit 
does at 300 and 900 Mhz??

73's,
Randy, KI6WAS