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

Dr. David Kirkby (Kirkby Microwave Ltd) drkirkby at kirkbymicrowave.co.uk
Sun Jul 19 09:27:32 EDT 2015

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.
>>      *   *   *
>>      *   *   *
>> 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.

> Best regards,
> Charles


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