[time-nuts] 5065A Rb Cavity RX - Varactor repair?

[Gerhard Hoffmann]

Am 22.10.20 um 23:54 schrieb Richard (Rick) Karlquist:
> I suspect that the stock 5065 chain has better
> phase noise than this chip.  I know for sure
> that you can get much better phase noise than
> this chip by using conventional architectures.
> Of course they are more complicated, etc.  Just
> wanted to put this chip in perspective.
>
> Rick N6RK
>
>
> On 10/22/2020 12:12 PM, Gerhard Hoffmann wrote:
>>
>> This is a ADF5356 with 2 LT3042 to clean up the supply voltage.
>> I measured the successor to this board yesterday on 10 GHz out
>> with my new 1/8 prescaler and the SR620 counter and some

As long as you can measure the noise with a 89441A vector signal

analyzer instead of a signal source analyzer, it cannot be leading edge.

Close-in, it seems quite ok. Enough to guide a 5 MHz crystal oscillator, 
and

also to guide a (in my case) 10 GHz dielectric osc with a Q of 20 to 30K.

Sorry, I must stay diffuse at this point.


My question for the phase noise in the Engineer Zone was also kinda 
"scheinheilig",

German word, (hypocritical, falsely innocent, ...lost in translation). I 
know that I could

go to a phase detector frequency of 150 MHz with this chip (instead of 
20*2), and it

would help for sure.  But I'm still struggling to make a connection between

the Windows evaluation software results and the data sheet.  My software 
driver is

1200 lines of C code (but including lots of comments.) ~400 bits to be 
set up.


And the 100th harmonic of 60 MHz won't be a phase noise wonder either, with

or without a SRD. You can see the effect in the well-known pictures of 
the old

HP spectrum analyzers that display a staircase with many a step, 
depending on

the LO harmonic.


Sky and MA/COM still make step recovery diodes, whether they fit is a 
different

question. But I cannot think of a special SRD failure mode. If you can 
do that,

solder it out and measure it with a normal Ohm meter. If it still 
behaves diode-ish,

it is very probably a working SRD. Maybe without the soldering, 
depending on the circuit.

Repairing will always be cheaper than transplanting a completely new heart.


Cheers, Gerhard