[time-nuts] Spectrum Analyzer Specifications --> phase noise test set

Alexander Pummer alexpcs at ieee.org
Fri Mar 25 19:42:29 EDT 2016


Use TNC, which is free of the problem and it fits into the same hole...
73
KJ6UHN
Alex

On 3/25/2016 3:46 PM, Bob Camp wrote:
> Hi
>
> The sensitivity of BNC connectors goes up quite a bit as they wear out. Both sides of
> the connection are subject to wear. Replacing both sides is often the only solution when
> they get noisy. That said, “screw down” connectors are a better way to go.
>
> The “capacitive loading” termination of the mixer is something that a number of us
> tried to reproduce when the paper came out. Even after fairly extensive conversations
> with the authors, the effect seems be quite difficult to reproduce. It certainly is not a
> “general solution” to the problem.
>
> Bob
>
>
>> On Mar 25, 2016, at 5:55 PM, Bruce Griffiths <bruce.griffiths at xtra.co.nz> wrote:
>>
>> As long as BNC connectors are avoided as their phase shift isnt that stable.. A small mechanical disturbance will change it significantly. Actually low noise PN measurement systems can be very sensitive to cable movement. Bolting modules to a metal baseplate helps a lot as does using intermodule connections comprising SMA(m)-SMA(m) barrels rather than cables.
>> There's also the question of mixer port termination.The nist paper by Walls and Stein indicates that capacitive termination of the IF port may be effective in reducing noise whilst maintaining a flat response fro dc to around 50KHz.Small value resistors in series with the RF and LO ports are then useful in reducing the VSWR.
>> Bruce
>>
>>
>>     On Saturday, 26 March 2016 10:10 AM, Bob Camp <kb8tq at n1k.org> wrote:
>>
>>
>>
>> Hi
>>
>>> On Mar 25, 2016, at 1:55 PM, jimlux <jimlux at earthlink.net> wrote:
>>>
>>> On 3/25/16 5:07 AM, Bob Camp wrote:
>>>> Hi
>>>>
>>>> The reverse isolation issue is indeed one of the weaknesses of this setup. For testing
>>>> OCXO’s isolation is not a big deal. A normal OCOX has very good output buffering
>>>> to give it the stability you are after. If you are running (maybe) a VCO with no buffering, that
>>>> assumption falls apart. The VCO will  / can injection lock through the mixer. In that
>>>> case you *do* need an amp to provide enough isolation to prevent the injection lock.
>>>>
>>>
>>> But if someone were building a little module for a cheap and cheerful noise analyzer, then the buffer amp would be a separate module.
>> That’s how I have always done it in the past. The need for the bufferer is rare enough that including it in the
>> basic analyzer module is not cost effective. The HP 3048 has the same basic issue (isolation) and they made
>> the same decision there.
>>
>> Bob
>>
>>
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