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

Bob Camp kb8tq at n1k.org
Sun Jul 19 11:25:21 EDT 2015


Hi


> On Jul 19, 2015, at 9:27 AM, Dr. David Kirkby (Kirkby Microwave Ltd) <drkirkby at kirkbymicrowave.co.uk> wrote:
> 
> On 19 July 2015 at 10:56, 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.
>> 
> 
> Minicircuits don't say "best" or "worst" but the data sheet does say
> "adjacent" and "opposite". But I'm not disputing there are 4 different
> isolation figures, but I could only measure 3.
> 
> 
>> 
>> 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?
>> 
> 
> I wont say I have decided for sure, but an obvious candidate is a
> Minicircuits ZHL-2-8, since I have one here sitting around doing nothing.
> The specs on that are:
> 
> Gain min 31 dB, typical 36 dB
> 1 dB compression point minimum +29 dBm.
> 
> That has plenty of gain, and in fact would need an attenuator around 24 dB
> if the typical gain is realized. It would also be running it a few dB below
> the 1 dB compression point. But someone (perhaps even yourself) mentioned
> phase noise increases as you get near the 1 dB compression point. That
> amplifier does not have a great deal of headroom - just 3 dB.
> 
> I was also considering the possibility of using a discrete transistor,
> where it could be run well below the 1 dB compression point, rather than 3
> dB below it.
> 
> All I need to find is a 24 V linear power supply of 600 mA or more. I
> suspect I have one of them lying around too.
> 

Be very careful about some of the packaged amplifiers. Many of the designs 
do *not* hold their noise performance when driven to within 20 db of the compression
point. Phase noise dégradation of > 20 db is not at all uncommon with some 
of the designs out there.

Bob


> 
> 
>> Best regards,
>> 
>> Charles
>> 
> 
> Dave
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