[time-nuts] Distribution amp - Use a video amp unit ?
pete at petelancashire.com
Sun Mar 25 19:28:56 UTC 2012
Sounds like Paul and I have similar DA's or will soon when a Leitch gets to the
front porch next week. Its bandwidth is spec'd at 30 MHz.
The only question I have on using DA's is the effect of them being designed to
work in a 75 ohm environment.
One thing to watch out for is what cards they have in them.
On Sun, Mar 25, 2012 at 11:39 AM, paul swed <paulswedb at gmail.com> wrote:
> Well the easy answer.
> The older 1984 video amps would roll off above 6 MC or so.
> However as the IC technology took over they easily could do 30 Mhz.
> I have used Grass valley 8500 series for at least 10-15 years and the work
> very well.
> I also have sets of Leitch DAs that are fine.
> Picked up the whole tray for some silly amount of $ 20 I think.
> I prefer the simple 8601 DAs but have 8604 delay days and they can all be
> made into simple DAs with a few jumpers that are on the boards.
> I have also used a rgb da 6 output for each channel. No issue at all.
> One comment you would want to insure the amps are ac coupled and clamping
> turned off since there is no sync signal to establish the clamp level.
> On Sun, Mar 25, 2012 at 2:14 PM, Bruce Griffiths <bruce.griffiths at xtra.co.nz
>> cfo wrote:
>>> I need a distribution amp for my Tbolt , with 6..8+ outputs
>>> The TAPR-1 is NA , and the successor status is ???.
>>> I need it for distributing 10Mhz ref-clock to Counters
>>> (HP,Racal,Phillips), a Rigol Sig-gen& maybe Oscilloscopes etc.
>>> It's for "better than ocxo/hobby use" , and not Tnut (ps accuracy).
>>> I have seen suggestions for using a video distributiution unit.
>>> But in my part of the world (EU) , there isn't a lot on "eby".
>>> I have seen some RGB amps , and was wondering if i could use those ?
>>> Could i use a 1:6 RGB unit for : Tbolt on R , FEI-5680A on G - and ?? on
>>> B ?
>>> I'm not experienced (yet) in the analog domain.
>>> If i go (simple diy) Would this one work (also wo. the trafo's) ?
>>> I do have some trafo's on an old 10Mhz 8-chan Hub , that i might be able
>>> to salvage if needed.
>>> Thanx for any input/hints
>>> CFo - T-Nut beginner Denmark.
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>> Winding your own transformers isnt particularly difficult if you have
>> suitable (binocular) cores.
>> The discrete amplifier shown has a class AB output stage, lower distortion
>> is possible if a class A output stage is used (requires an extra resistor
>> between the output stage emitters and an additional diode in series with
>> the LED).
>> With a Class A output stage the 39 ohm resistors should be replaced by a a
>> pair of 100 ohm resistors to match the load.
>> Significantly lower distortion is possible if feedback from the output to
>> the input stage is used.
>> If the feedback gain is unity (or less) at dc higher AC gains won't
>> significantly degrade the close in phase noise.
>> A different amplifier topology using the same number of transistors will
>> allow a higher reverse isolation to be achieved.
>> One problem with video distribution units (aside from the relatively high
>> phase noise floor) is the limited output drive available. For some purposes
>> 16-20dBm outputs are desirable.
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