[time-nuts] Isolation and insertion loss of Minicircuits splitters

Bob Camp kb8tq at n1k.org
Sun Jul 19 12:39:59 UTC 2015


Hi

One thing worth checking:

The impedance at the “sum” port may or may not be 50 ohms. It’s worth checking before you 
go to extreme lengths to come up with a “perfect” 50 ohm amp. 

======

Since part of the world likes 75 ohms, it’s also worth taking a look at the isolation numbers 
with the sum port terminated in 75 (or 75 / 4) ohms. There are a number of high power / low
noise amps out there (apparently) designed for cable distribution systems. 

Bob

> On Jul 19, 2015, at 5:56 AM, Charles Steinmetz <csteinmetz at yandex.com> wrote:
> 
> Dave wrote:
> 
>> Some time ago I mentioned I'd bought a couple of Minicircuits 16-way power
>> splitters with the intention of making a 10 MHz distribution amplifier
>>     *   *   *
>> Here are the ISOLATION results.
>>     *   *   *
>> CONCLUSIONS
>>     *   *   *
>> 6) Despite the Minicircuits data sheets imply there are two isolation
>> figures for "adjacent" and "opposite", I measure 3 different values for
>> each splitter, not 2.
> 
> As I posted on January 8, there are actually four different cases in a 16-way splitter.  You have found that the port-to-port isolation of two of the four cases are indistinguishable in practice in the MCL splitters.
> 
> The datasheets do not imply that there are only the two cases.  MCL simply specified the best ("adjacent") and worst ("opposite") cases, without specifying the intermediate cases.
> 
> Good luck with your DA system.  For simple distribution of a frequency standard, it should work very well.  I use a similar system with a suitable ULN/HDR preamp to feed antennas to multiple receivers, and it performs superbly.
> 
> For an output at the typical instrumentation level of 1Vrms (13dBm), you will need an amplifier with a 50 ohm output impedance that puts out ~26dBm (=400mW, =4.5Vrms, =6.3Vpk, =12.6Vp-p).  The peak output current is >125mA.  If you are going to realize the 50 ohm output impedance with a low impedance amplifier and a 50 ohm buildout resistor for back-termination, the amplifier will need to put out over 25Vp-p into 100 ohms.  If you want the outputs at the same level as the original source, the amplifier will need to have a bit more than 12dB of gain.  Have you decided what you are going to use?
> 
> Best regards,
> 
> Charles
> 
> 
> 
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