[time-nuts] Simple GPSDO Multiple Outputs - buffered line driver options?
Taka Kamiya
tkamiya9 at yahoo.com
Tue Jan 21 21:49:52 UTC 2020
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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