[time-nuts] high rev isolation amps

Rob Sherwood. rob at nc0b.com
Sat Mar 26 20:47:43 EDT 2016


I forgot to add, after the step attenuators at the output of the combiner, there is a 10 dB pad right at the back of the radio to provide a better return loss to the combiner. 

Rob, NC0B

Sent from my iPad

> On Mar 26, 2016, at 6:34 PM, "Rob Sherwood." <rob at nc0b.com> wrote:
> 
> I use two ZHL-32A buffer amps, the appropriate Mini-Circuits LPFs, and 20 dB pads into a 4-way Mini-Circuits combiner. I believe it is ports 2&3 that have even better isolation than a 2-way combiner.  These buffer amps run on 24 volts, where the ZFL-500LN doesn't have the output capability to test 100+ dB radios.  Some tests need a third signal source and complimentary buffer amp and associated items. 
> 
> To test a K3S or an IC-7851, it also requires HP 8642A generators that have lower phase noise than these top of the line rigs.  Even my 8662A generators are not good enough, though they were 5 years ago.  Now add the Flex 6700 and the ANAN-200D, the RMDR performance of a hand full of rigs is amazing. 
> 
> Unfortunately transmitter performance has not kept pace with receiver improvement. 
> 
> It will be interesting to test the new IC-7300 DSR with knobs (and lots of menus). 
> 
> Rob
> NC0B
> 
> Sent from my iPad
> 
>> On Mar 26, 2016, at 6:00 PM, "jimlux" <jimlux at earthlink.net> wrote:
>> 
>> 
>> 
>>> On 3/26/16 2:30 PM, Rob Sherwood. wrote:
>>> You cannot add the directivity and gain.  Doesn't work that way.  Rob, NC0B.
>> 
>> Yeah, I kind of figured that after getting the S parameters from minicircuits.
>> 
>>> Sent from my iPad
>>> 
>>>> On Mar 26, 2016, at 2:00 PM, "jimlux" <jimlux at earthlink.net> wrote:
>>>> 
>>>> 
>>>> 
>>>> Consulting the time-nuts hive mind here..
>>>> 
>>>> I'm looking for off the shelf connectorized amplifiers with very good reverse isolation for doing things like intermod measurements (e.g. 2 signal generators followed by amps/pads into a combiner) and phase noise measurements for a digital receiver.
>>>> 
>>>> 1-100 MHz kind of frequency range..
>>>> 
>>>> I've used ZFL-500LN (30dB gain, 27 dB directivity in the data sheet, which I interpret as 57dB reverse) , ZX60-4016 (really more of a microwave amp, and not so hot reverse wise.. 25 dB)
>>>> 
>>>> I'm not particularly cost constrained, so a higher power amp (which also reduces distortion products from the amp) followed by pads is always an alternative.
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