[time-nuts] what is acceptable harmonic content & level for a 10Mhz standard?

[walter shawlee 2]

I have been working on a compact portable 10Mhz bench standard
using both an FE FE5680A Rb oscillator and an Oscilloquartz ovenized
crystal oscillator.  I was curious to see how their short and long term 
stability
would work out, and I needed something to drive my 6502 amp to pipe the signal 
to some bench instruments which could benefit from better master references.  
all of these were inexpensive ebay acquisitions, so the total cost to make the 
package is maybe $250 plus a few weekends work and a left-over but nice looking 
tilt-bail case & Condor 65W switching power supply.

I drove everything from some independently, heavily post-filtered +15VDC power.

to try and keep any unexpected interaction to a minimum, the outputs exit though 
floating BNCs, so they don't have an unwanted ground loop at the case.  only the 
FE5680A is physically grounded to the case for heatsinking, so the connection is 
a single point.


while looking at the outputs of the two sources, I saw some surprising 20Mhz 
harmonic content on my spectrum analyzer.  I expected a bit from the 5680A, but 
it was actually much bigger on the OCXO, which had a chinese add-on dual buffer 
board attached.  I had thought there might be some, so I also scored some little 
10Mhz BP filters at the same time and did some before/after tests.


here's what I got:

FE5680A 10Mhz (+5dBm), 20Mhz (-55dBm)  (with filter)

OCXO   10Mhz (-2dBm), 20Mhz (-35dBm) as received
OCXO   10Mhz (-5dBm), 20Mhz (-60dBm) with filter

I hate to distribute any spurious RF around the lab, so I thought less harmonic 
content was the better plan, although I realize that as a counter time base 
source, it is probably irrelevant, but might play a role in my 8656B RF 
generator as added unwanted spurs.  I was a bit disturbed by the low level and 
harmonics from the OCXO assembly, so I thought some external comments about 
norms were needed at this point before I go further.


what kind of harmonic content does everyone else see in their 10Mhz standards?  
the -5dBm level seems too low to me, I am used to 0 to +5-7dBm from sources, but 
I have not tried to run it through the distribution amp yet, so possibly that's 
enough.  I can try and dig into the totally undocumented surface mounted chinese 
add-on board to improve things, and increase the level, but hard to say what 
will happen there.


all comments and data welcome.
all the best,
walter



--
Walter Shawlee 2, President
Sphere Research Corporation
3394 Sunnyside Rd.,  West Kelowna,  BC
V1Z 2V4  CANADA  Phone: (250) 769-1834
walt...@sphere.bc.ca
WS2: We're all in one boat, no matter how it looks to you.
Love is all you need. (John Lennon)
But, that doesn't mean other things don't come in handy. (WS2)

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Re: [time-nuts] what is acceptable harmonic content & level for a 10Mhz standard?

[paul swed]

Walter that OCXO sure looks odd I would expect unfiltered to be a lot
better then that. I would guess that several possibilities exist.
The actual crystal is a 5 MHz and it feeds a doubler.
The chain has something thats gone non-linear. -5dbm seems low to me.
Oscilloquartz have a very fine reputation on time-nuts. I do not own one
nor most likely never will.
So you are right to ask and suspect.
Regards
Paul
WB8TSL

On Tue, Jan 26, 2016 at 2:52 PM, walter shawlee 2 
wrote:

> I have been working on a compact portable 10Mhz bench standard
> using both an FE FE5680A Rb oscillator and an Oscilloquartz ovenized
> crystal oscillator.  I was curious to see how their short and long term
> stability
> would work out, and I needed something to drive my 6502 amp to pipe the
> signal to some bench instruments which could benefit from better master
> references.  all of these were inexpensive ebay acquisitions, so the total
> cost to make the package is maybe $250 plus a few weekends work and a
> left-over but nice looking tilt-bail case & Condor 65W switching power
> supply.
> I drove everything from some independently, heavily post-filtered +15VDC
> power.
>
> to try and keep any unexpected interaction to a minimum, the outputs exit
> though floating BNCs, so they don't have an unwanted ground loop at the
> case.  only the FE5680A is physically grounded to the case for heatsinking,
> so the connection is a single point.
>
> while looking at the outputs of the two sources, I saw some surprising
> 20Mhz harmonic content on my spectrum analyzer.  I expected a bit from the
> 5680A, but it was actually much bigger on the OCXO, which had a chinese
> add-on dual buffer board attached.  I had thought there might be some, so I
> also scored some little 10Mhz BP filters at the same time and did some
> before/after tests.
>
> here's what I got:
>
> FE5680A 10Mhz (+5dBm), 20Mhz (-55dBm)  (with filter)
>
> OCXO   10Mhz (-2dBm), 20Mhz (-35dBm) as received
> OCXO   10Mhz (-5dBm), 20Mhz (-60dBm) with filter
>
> I hate to distribute any spurious RF around the lab, so I thought less
> harmonic content was the better plan, although I realize that as a counter
> time base source, it is probably irrelevant, but might play a role in my
> 8656B RF generator as added unwanted spurs.  I was a bit disturbed by the
> low level and harmonics from the OCXO assembly, so I thought some external
> comments about norms were needed at this point before I go further.
>
> what kind of harmonic content does everyone else see in their 10Mhz
> standards?  the -5dBm level seems too low to me, I am used to 0 to +5-7dBm
> from sources, but I have not tried to run it through the distribution amp
> yet, so possibly that's enough.  I can try and dig into the totally
> undocumented surface mounted chinese add-on board to improve things, and
> increase the level, but hard to say what will happen there.
>
> all comments and data welcome.
> all the best,
> walter
>
>
>
> --
> Walter Shawlee 2, President
> Sphere Research Corporation
> 3394 Sunnyside Rd.,  West Kelowna,  BC
> V1Z 2V4  CANADA  Phone: (250) 769-1834
> walt...@sphere.bc.ca
> WS2: We're all in one boat, no matter how it looks to you.
> Love is all you need. (John Lennon)
> But, that doesn't mean other things don't come in handy. (WS2)
>
> ___
> time-nuts mailing list -- time-nuts@febo.com
> To unsubscribe, go to
> https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
> and follow the instructions there.
>
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Re: [time-nuts] what is acceptable harmonic content & level for a 10Mhz standard?

[Richard (Rick) Karlquist]

On 1/26/2016 11:52 AM, walter shawlee 2 wrote:

I have been working on a compact portable 10Mhz bench standard
using both an FE FE5680A Rb oscillator and an Oscilloquartz ovenized


It is important for a 10 MHz source to launch a pure sine wave
and also to have an accurate 50 ohm impedance at 10 MHz and its
harmonics.  This is because a sine wave is the only waveform
having the property that it is immune from distortion due to
reflections from poorly matched loads.  IE, sine wave with
multipath resolves again to a sine wave.  It is important to
have a broadband 50 ohm output impedance to absorb reflections
from loads, especially load-generated harmonics.  You didn't
ask, but you also want a lot of reverse isolation to avoid
pulling the OCXO.  All of these were addressed in the design
of the output section of the 5071A cesium standard.  It was
really quite non-trivial.  Specifically, the harmonics are
down over 80 dB.

Rick Karlquist N6RK
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Re: [time-nuts] what is acceptable harmonic content & level for a 10Mhz standard?

[Bob Camp]

Hi

If your OCXO is putting out less than 0 dbm, it’s broke. Given the way these 
parts are treated
in the salvage loop, damage is not unusual. There are a *lot* of examples of 
surplus OCXO’s
with low output. Normally it’s a damaged output cap or something like it.  I’ve 
seen roughly half the units
in some lots come in that way ….

Bob

> On Jan 26, 2016, at 2:52 PM, walter shawlee 2  wrote:
> 
> I have been working on a compact portable 10Mhz bench standard
> using both an FE FE5680A Rb oscillator and an Oscilloquartz ovenized
> crystal oscillator.  I was curious to see how their short and long term 
> stability
> would work out, and I needed something to drive my 6502 amp to pipe the 
> signal to some bench instruments which could benefit from better master 
> references.  all of these were inexpensive ebay acquisitions, so the total 
> cost to make the package is maybe $250 plus a few weekends work and a 
> left-over but nice looking tilt-bail case & Condor 65W switching power supply.
> I drove everything from some independently, heavily post-filtered +15VDC 
> power.
> 
> to try and keep any unexpected interaction to a minimum, the outputs exit 
> though floating BNCs, so they don't have an unwanted ground loop at the case. 
>  only the FE5680A is physically grounded to the case for heatsinking, so the 
> connection is a single point.
> 
> while looking at the outputs of the two sources, I saw some surprising 20Mhz 
> harmonic content on my spectrum analyzer.  I expected a bit from the 5680A, 
> but it was actually much bigger on the OCXO, which had a chinese add-on dual 
> buffer board attached.  I had thought there might be some, so I also scored 
> some little 10Mhz BP filters at the same time and did some before/after tests.
> 
> here's what I got:
> 
> FE5680A 10Mhz (+5dBm), 20Mhz (-55dBm)  (with filter)
> 
> OCXO   10Mhz (-2dBm), 20Mhz (-35dBm) as received
> OCXO   10Mhz (-5dBm), 20Mhz (-60dBm) with filter
> 
> I hate to distribute any spurious RF around the lab, so I thought less 
> harmonic content was the better plan, although I realize that as a counter 
> time base source, it is probably irrelevant, but might play a role in my 
> 8656B RF generator as added unwanted spurs.  I was a bit disturbed by the low 
> level and harmonics from the OCXO assembly, so I thought some external 
> comments about norms were needed at this point before I go further.
> 
> what kind of harmonic content does everyone else see in their 10Mhz 
> standards?  the -5dBm level seems too low to me, I am used to 0 to +5-7dBm 
> from sources, but I have not tried to run it through the distribution amp 
> yet, so possibly that's enough.  I can try and dig into the totally 
> undocumented surface mounted chinese add-on board to improve things, and 
> increase the level, but hard to say what will happen there.
> 
> all comments and data welcome.
> all the best,
> walter
> 
> 
> 
> -- 
> Walter Shawlee 2, President
> Sphere Research Corporation
> 3394 Sunnyside Rd.,  West Kelowna,  BC
> V1Z 2V4  CANADA  Phone: (250) 769-1834
> walt...@sphere.bc.ca
> WS2: We're all in one boat, no matter how it looks to you.
> Love is all you need. (John Lennon)
> But, that doesn't mean other things don't come in handy. (WS2)
> 
> ___
> time-nuts mailing list -- time-nuts@febo.com
> To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
> and follow the instructions there.

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