[time-nuts] Simple GPSDO Multiple Outputs - buffered line driver options?

Tue Jan 21 22:16:57 UTC 2020

Hi

If you are doing direct measurements on a 10 MHz signal *and* counting on the expanded
frequency resolution of a 53131, that’s not going to work. There is an HP app note somewhere
that explains why in great detail. The quick read version is that the sampling process falls apart.

Bob

> On Jan 21, 2020, at 4:49 PM, Taka Kamiya via time-nuts <time-nuts at lists.febo.com> wrote:
> 
> I'm not the OP but I was just throwing some ideas about cheap way to distribute.
> But the responses were very timely.  I am, indeed, using HP53132A, RG58, and were doing ADEV measurement of a 10MHz signal.  I have my answers already so I won't go into details but I was seeing some explainable indications.  It might very likely be leak from or into the reference/input.  I will use double shielded and phase stable cables and see if I can eliminate the issue.
> 
> Thanks a-bunch!
> --------------------------------------- 
> (Mr.) Taka Kamiya
> KB4EMF / ex JF2DKG
> 
> 
>    On Tuesday, January 21, 2020, 4:27:26 PM EST, Bob kb8tq <kb8tq at n1k.org> wrote:  
> 
> Hi
> 
> If all you are doing is driving a 5335 and running at 1 second gate times, then there’s not
> a lot to worry about. If indeed you are multiplying this or that up to X band for various purposes
> then  ….. that’s different. Both are in the “hobbyist” range.
> 
> Spurs matter for some things and don’t matter much for others. A spur at -120 at 10 MHz 
> may be up around -60 db at 10 GHz. It might matter there … it might not. A -60 db spur 
> at 10 MHz gets into the “yikes” range if directly multiplied. 
> 
> How big is your bench? How long are your feed cables? You are getting into a significant 
> fraction of a wavelength at 10’ of cable. If unterminated (and / or poorly shielded) it will spray
> a bit of RF. 
> 
> Lots of details and no single answer without digging deeper into what you are trying to do.
> 
> Bob
> 
>> On Jan 21, 2020, at 4:06 PM, Bryan _ <bpl521 at outlook.com> wrote:
>> 
>> On the point of using a MDA-3V at the hobbyist bench level, any issues that one needs to be concerned about. A few modification projects online, but none really comment on any issues or performance.
>> 
>> -=Bryan=-
>> 
>> ________________________________
>> From: time-nuts <time-nuts-bounces at lists.febo.com> on behalf of Bob kb8tq <kb8tq at n1k.org>
>> Sent: January 21, 2020 7:57 AM
>> To: Taka Kamiya <tkamiya9 at yahoo.com>; Discussion of precise time and frequency measurement <time-nuts at lists.febo.com>
>> Subject: Re: [time-nuts] Simple GPSDO Multiple Outputs - buffered line driver options?
>> 
>> Hi
>> 
>> Cross talk between the reference in and the measured signal on the 53131 series can be an
>> issue . The counter drops resolution in the vicinity of 10 MHz as a result. There is also an  issue
>> with  the sampling process rather than direct feedthrough.
>> 
>> If you are measuring things like phase noise, having a lot of 10 MHz running around the lab will put a
>> spur in the phase noise plot. It may be close enough in that you don’t notice it every time. The same
>> sort of spur will play nasties with things like ADEV measurements. Getting a 10V RMS signal down
>> 120 db is tough …
>> 
>> Finally if you happen to be playing with radios, WWV is at 10 MHz. It does not take a lot of reference
>> signal to get back into the typical receiving antenna.
>> 
>> ======
>> 
>> If you are daisy chaining counters, there are several ways to do it:
>> 
>> 1) Drive the “ext ref in” and daisy chain off of “ext ref out”. This way the signal is buffered at each device.
>> It may add a bit of noise, but you can go a long way doing this.
>> 
>> 2) Put a coax Tee connector at each instrument. If the device is high Z in, this can do ok. If it is a 50 ohm
>> termination all the time … not so much. Even with the high Z input it’s better for short runs than long ones.
>> 
>> 3) Mix the two approaches. If you have a variety of gear, use the ones with ref in / ref out as buffers. String
>> the other gear in-between those boxes.
>> 
>> Bob
>> 
>>> On Jan 21, 2020, at 10:27 AM, Taka Kamiya via time-nuts <time-nuts at lists.febo.com> wrote:
>>> 
>>> I've tried daisy chaining 4 HP5335A.  By the time signal got to the 4th box, it was too weak to reliably drive the 1 pps.  I had a terminator at the last tee with short length of RG58s between boxes.  I guess some box puts relatively heavy load on the signal?
>>> 
>>> I'd like to know why 10V is a bad idea.  (besides too close to the upper limit)  Cross talk between what/where?
>>> 
>>> To OP:I have video amplifiers Extron MDA-3V successfully used for this.  1 port in, 3 ports out ones by Extron are very inexpensive at 10 dollars+/-.  I never did formal testing but reading on all counters matched exactly.  They are 75 ohms but it didn't matter in my use case.  You can change/adjust internal resisters if you are concerned.
>>> 
>>> ---------------------------------------
>>> (Mr.) Taka Kamiya
>>> KB4EMF / ex JF2DKG
>>> 
>>> 
>>>   On Tuesday, January 21, 2020, 7:45:22 AM EST, Bob kb8tq <kb8tq at n1k.org> wrote:
>>> 
>>> Hi
>>> 
>>> What are you driving?
>>> 
>>> Most “normal” gear is pretty happy with a fairly wide range of input levels. Obviously things
>>> like termination and long lengths of coax can get into the act. For 4 outputs, a passive splitter
>>> with 6 db of loss should do just fine. You have only taken the output voltage down by 2:1 ….
>>> 
>>> Just for reference:
>>> 
>>> https://www.avionteq.com/Document/53131A-specification-sheet.pdf <https://www.avionteq.com/Document/53131A-specification-sheet.pdf>
>>> 
>>> Calls out a 200 mv to 10V RMS input level as acceptable For a variety of reasons, 10V RMS
>>> is a really bad idea (cross talk ….). Lower is better in this case.
>>> 
>>> Bob
>>> 
>>>> On Jan 21, 2020, at 4:19 AM, skipp isaham via time-nuts <time-nuts at lists.febo.com> wrote:
>>>> 
>>>> Hello once again to the Group,
>>>> 
>>>> May I ask what the current relatively simple options are for
>>>> expanding a Thunderbolt or equivalent... output for distribution
>>>> to multiple devices?
>>>> 
>>>> Although I expect only two or three isolated / buffered outputs
>>>> will be required in my example. I'm worried about signal level
>>>> if a passive system (Mini Circuits divider or equivalent type)
>>>> is used.
>>>> 
>>>> Would appreciate a few quick opinions on what is practical and
>>>> seems to work well.
>>>> 
>>>> thank you in advance
>>>> 
>>>> regards,
>>>> 
>>>> skipp
>>>> 
>>>> skipp025 at yahoo dot com
>>>> 
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>> 
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> 
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