[time-nuts] 10MHz dist amps

[John Ackermann N8UR]

Thanks, Bruce.  That's pretty much it -- while the layout/lack of
shielded enclosure might have a bit to do with it, the opamps used
(MAX477) aren't super-duper low noise at the floor.  The AD8055 we've
used in the lasts few batches since the MAX477 went unobtainium seems to
be a little quieter.

Re the frequency range, the opamps are rated to I think something like
275 MHz but there is some roll-off built into the design to reduce a
tendency toward oscillation; no real attempt was made to keep it flat
across frequency.

There's some difference in frequency response depending on the input
level and gain setting, but in general the gain is around unity at 5 and
10 MHz, then rises about 5 dB to peak at about 40 MHz, then it falls off
to abotu -9 dB at 100 MHz.

At the time I designed the unit, I was young and foolish* and thought a
5 or 10 MHz bandpass filter might be a good idea.  I soon learned and
now strongly discourage including the filter unless you have a very good
reason.

73,
John

* I just looked at the original design files and good Lord, they date
back to August, 2005.  That thing is going on 15 years old without a
significant change, other than the opamp substitution (which was a
direct drop-in replacement).
----

On 10/23/19 7:38 PM, Bruce Griffiths wrote:
> Its measured noise floor is consistent with that expected from the noise specifications for the opamps employed.
> 
> Bruce
> 
>> On 24 October 2019 at 08:46 Tom Knox <actast at hotmail.com> wrote:
>>
>>
>> Hi John;
>> Amazing product, I did not realize you could use the TADD-1 for 100MHz distribution.
>> I do have a question, as someone who has tested most of the commercially available distribution amps on the market TADD-1's -140dB @ 1Hz is among the very very best best in the industry, (nothing is close for the price) but compared to the very best the noise floor is a bit higher. Is this simply a result of a raw board instead of a shielded enclosure?
>> Thanks;
>>
>> Tom Knox
>>
>> 303-554-0307
>>
>> actast at hotmail.com
>>
>> "Peace is not the absence of violence, but the presence of Justice" Both MLK and Albert Einstein
>>
>> ________________________________
>> From: time-nuts <time-nuts-bounces at lists.febo.com> on behalf of John Ackermann. N8UR <jra at febo.com>
>> Sent: Wednesday, October 23, 2019 11:54 AM
>> To: ew via time-nuts <time-nuts at lists.febo.com>
>> Subject: Re: [time-nuts] 10MHz dist amps
>>
>> FWIW, I designed the TADD-1 to have equal length signal paths for all six channels.
>>
>> 73,
>> John
>>
>> On Oct 23, 2019, 1:01 PM, at 1:01 PM, "Bill Dailey, MD, MSEng, MSMI" <docdailey at gmail.com> wrote:
>>> I am working in a project that requires me to have very similarly
>>> phased
>>> 10mhz references (beamforming).
>>>
>>> Previously I just used splitters for 10MHz but now I am graduating to a
>>> distribution amplifier.  Looking for suggestions/recommendations and
>>> what I
>>> should consider.  Distributing a Fury or a manually set 1111a (May have
>>> the
>>> numbers wrong on this) oscillator.
>>>
>>> 1. TADD-1 x 2
>>> 2. 5087A
>>> 3. 58502A
>>>
>>> 2&3 are from the usual auction site and may have problems now or in the
>>> future.
>>> --
>>> Doc
>>>
>>> Bill Dailey
>>> KXØO
>>> _______________________________________________
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