Re: [time-nuts] Tale of Two GPStars...

[Bob kb8tq]

Hi

Ok, let’s put some numbers on this.

What goes into your typical “Rb GPSDO” gizmo is a telecom Rb. They normally 
start off around 2x10^-11at 1 second. They drop by the square root of tau as 
you 
go on out. Indeed the PRS-10 has an odd bump in the 1 to 10 second range, there
is an exception to every rule :).

So:

At 100 sec the Rb is at 2x10^-12. A good OCXO can indeed beat this number.

At 1,000 sec the Rb is at 6x10^-13. It is better at that point than 99.99% of 
the OCXO’s out there.

At 10,000 sec the Rb is trying to hit 2x10^-13 ….

The first gotcha is that the loop adds noise to all these numbers. Your typical 
telecom GPSDO
box struggles to stay below 1x10^-11 at 10 to 100 seconds. 

The second issue is that these all are impacted by temperature. If your lab 
moves a couple degrees 
C with a 30 to 90 minute cycle, that’s pretty normal. Temperature sensitivity 
coefficients 
of 1x10^-11 to 1x10^-12 / C are not unheard of ( 1x10^-11 x 50 = 5x10^-10). 
That’s going to impact
both the OCXO and the Rb as you go from 1K to 10K seconds…..

The good news (I guess) is that most control loops turn things over to the GPS 
past a few hundred
seconds. How well the OCXO does past that is sort of irrelevant. There’s not 
enough data on the
Rb versions to really know what they do. 

Some numbers on Rb vs OCXO in a GPSDO can be found  in the SRS 740 spec sheets. 
If somebody 
wants to send me an Rb based one I’d be happy to run some numbers. I already 
have the data on the 
OCXO version. 

https://www.thinksrs.com/downloads/pdfs/catalog/FS740c.pdf 


The unit is aimed at a lab bench rather than telecom environment. It does 
indeed do a bit better
than the typical $70 telecom GPSDO. The data sheet shows an Rb to OCXO 
“crossover” in the
vicinity of 60 seconds.  At least on the OCXO version the data shown should be 
interpreted as 
“typical” rather than a spec limit …. That may impact the real world crossover 
point.

Bob

> On Jun 5, 2020, at 12:50 AM, Charles Steinmetz  wrote:
> 
> Bruce wrote:
> 
>> And I'm still amazed I lucked out with the rubidium module.
> 
> Actually, the unit's PN and ADEV performance would almost certainly be 
> considerably better with a good OCXO instead of the Rb.
> 
> At low tau, the PN and ADEV performance of a GPSDO is determined by the local 
> oscillator (generally, an OCXO or Rb).  The OCXO is better with respect to PN 
> and ADEV than a Rb out to tau >~1000 seconds, so in the very important area 
> of tau <1000 seconds, the Rb unit loses to the OCXO unit.  Above tau >~1000, 
> the averaged GPS signal governs PN and ADEV performance, so you never really 
> benefit from the Rb oscillator.
> 
> Unless holdover performance is the most important criterion (which it almost 
> certainly will *not* be for a time nut), a GPSDO with a good OCXO is superior 
> at all tau to one with a Rb.
> 
> Best regards,
> 
> Charles
> 
> 
> 
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Re: [time-nuts] Tale of Two GPStars...

[Steve - Home]

I have a GPStar that hadn’t been used in a few years. I’ve misplaced the wall 
wart power supply. Could someone pass along the output voltage and current 
numbers of the wall wart, please? I think I can figure out the DIN connector 
pin numbers but that would be helpful, too. My manual is pretty sparse in that 
area. If I recall it says “plug in the AC adapter”...

Thanks!

Steve K. 
WB0DBS



> On Jun 4, 2020, at 10:00 PM, paul swed  wrote:
> 
> Somebody else actually has a GPStar (Odetics) and working?
> My units stopped working about 4 months ago. They are circa 1994 as I
> recall. Had 2 neither would work. Have one now as I used the case and rack
> mounts for another project.
> These are much older then what you have as the GPS receiver is actually
> discreet components.
> Regards
> Paul
> WB8TSL
> 
>> On Thu, Jun 4, 2020 at 8:59 PM Bruce Lane 
>> wrote:
>> 
>>After many moons, my trusty GPStar 365 (updated to a 565 through
>> firmware and a receiver change) finally bit the dust. Symptom: It kept
>> flipping between 'Coasting' and 'Recovering,' never quite reaching
>> 'Locked.' The DAC value either ended up maxed (65534) or min'd (0).
>> 
>>Contacted Tim Gavin at Zyfer-FEI for advice. Strongest possibility:
>> OCXO went south. Tried manually setting the DAC for mid-point (32768)
>> and manually tweaking the coarse tuning on said OCXO against a
>> known-good 10MHz source of equal precision (translation: Another GPSDO).
>> 
>>Didn't work. Tried replacing the OCXO itself, and doing the
>> alignment
>> trick. Still no joy.
>> 
>>Considering the lack of schematics: Emit large sigh, put unit
>> aside,
>> start searching Ebay for replacement.
>> 
>>Found a late-model (black case) 565-310 for a reasonable price,
>> bought
>> it. Arrived a week later (yesterday at work). Opened it up, delighted to
>> find I got a better deal than I thought in that the thing's got a
>> rubidium module (FE-5650A to be exact).
>> 
>>Did initial power-up/burn-in test with a local GPS antenna; Unit
>> went
>> to TFOM 4 and 'Locked' within a half-hour and stayed that way all day,
>> DAC number just slightly above mid-point.
>> 
>>However -- Date way off due to outdated Motorola UT+ receiver
>> module.
>> Replaced said UT+ with the M12M drop-in module from Synergy GPS. Fired
>> up -- and got NO satellite tracking ID's!
>> 
>>Mutter something vulgar. Do more poking around. Suddenly realize
>> the
>> firmware in the replacement 565 is at 1.06, while my original unit was
>> at 1.08. "I wonder if..."
>> 
>>Swap 1.08 firmware chip into replacement 565. Power on. Goes
>> through
>> factory reset -- and comes up perfectly normal! Sat numbers appearing on
>> tracking report. Just checked it a moment ago (about 15 minutes after
>> initial re-power) and it's at TFOM 4 / Locked! And it stayed that way
>> through a 24-hour burn-in check.
>> 
>>Conclusion: In the 565 series, you need version 1.08 firmware to
>> support Motorola's M12, or similar replacements.
>> 
>>And I'm still amazed I lucked out with the rubidium module. ;-)
>> 
>>Keep on tickin'...
>> 
>> --
>> ---
>> Bruce Lane, ARS KC7GR
>> http://www.bluefeathertech.com
>> kyrrin (at) bluefeathertech dot com
>> "Quando Omni Flunkus Moritati" (Red Green)
>> 
>> ___
>> time-nuts mailing list -- time-nuts@lists.febo.com
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>> http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com
>> and follow the instructions there.
>> 
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Re: [time-nuts] Tale of Two GPStars...

[paul swed]

Steve and yet another GPStar.
My units are older and just GPStar by Odetics and use ocxo.
These old units actually had external down converters that are quite
complicated but nicely done.
The din plug was +5 and +12. 2 pins for each plus grounds.
Yours may be different if newer. But as you guessed really easy to figure
out.
Regards
Paul
WB8TSL

On Fri, Jun 5, 2020 at 10:03 AM Steve - Home  wrote:

> I have a GPStar that hadn’t been used in a few years. I’ve misplaced the
> wall wart power supply. Could someone pass along the output voltage and
> current numbers of the wall wart, please? I think I can figure out the DIN
> connector pin numbers but that would be helpful, too. My manual is pretty
> sparse in that area. If I recall it says “plug in the AC adapter”...
>
> Thanks!
>
> Steve K.
> WB0DBS
>
>
>
> > On Jun 4, 2020, at 10:00 PM, paul swed  wrote:
> >
> > Somebody else actually has a GPStar (Odetics) and working?
> > My units stopped working about 4 months ago. They are circa 1994 as I
> > recall. Had 2 neither would work. Have one now as I used the case and
> rack
> > mounts for another project.
> > These are much older then what you have as the GPS receiver is actually
> > discreet components.
> > Regards
> > Paul
> > WB8TSL
> >
> >> On Thu, Jun 4, 2020 at 8:59 PM Bruce Lane 
> >> wrote:
> >>
> >>After many moons, my trusty GPStar 365 (updated to a 565 through
> >> firmware and a receiver change) finally bit the dust. Symptom: It kept
> >> flipping between 'Coasting' and 'Recovering,' never quite reaching
> >> 'Locked.' The DAC value either ended up maxed (65534) or min'd (0).
> >>
> >>Contacted Tim Gavin at Zyfer-FEI for advice. Strongest
> possibility:
> >> OCXO went south. Tried manually setting the DAC for mid-point (32768)
> >> and manually tweaking the coarse tuning on said OCXO against a
> >> known-good 10MHz source of equal precision (translation: Another GPSDO).
> >>
> >>Didn't work. Tried replacing the OCXO itself, and doing the
> >> alignment
> >> trick. Still no joy.
> >>
> >>Considering the lack of schematics: Emit large sigh, put unit
> >> aside,
> >> start searching Ebay for replacement.
> >>
> >>Found a late-model (black case) 565-310 for a reasonable price,
> >> bought
> >> it. Arrived a week later (yesterday at work). Opened it up, delighted to
> >> find I got a better deal than I thought in that the thing's got a
> >> rubidium module (FE-5650A to be exact).
> >>
> >>Did initial power-up/burn-in test with a local GPS antenna; Unit
> >> went
> >> to TFOM 4 and 'Locked' within a half-hour and stayed that way all day,
> >> DAC number just slightly above mid-point.
> >>
> >>However -- Date way off due to outdated Motorola UT+ receiver
> >> module.
> >> Replaced said UT+ with the M12M drop-in module from Synergy GPS. Fired
> >> up -- and got NO satellite tracking ID's!
> >>
> >>Mutter something vulgar. Do more poking around. Suddenly realize
> >> the
> >> firmware in the replacement 565 is at 1.06, while my original unit was
> >> at 1.08. "I wonder if..."
> >>
> >>Swap 1.08 firmware chip into replacement 565. Power on. Goes
> >> through
> >> factory reset -- and comes up perfectly normal! Sat numbers appearing on
> >> tracking report. Just checked it a moment ago (about 15 minutes after
> >> initial re-power) and it's at TFOM 4 / Locked! And it stayed that way
> >> through a 24-hour burn-in check.
> >>
> >>Conclusion: In the 565 series, you need version 1.08 firmware to
> >> support Motorola's M12, or similar replacements.
> >>
> >>And I'm still amazed I lucked out with the rubidium module. ;-)
> >>
> >>Keep on tickin'...
> >>
> >> --
> >> ---
> >> Bruce Lane, ARS KC7GR
> >> http://www.bluefeathertech.com
> >> kyrrin (at) bluefeathertech dot com
> >> "Quando Omni Flunkus Moritati" (Red Green)
> >>
> >> ___
> >> time-nuts mailing list -- time-nuts@lists.febo.com
> >> To unsubscribe, go to
> >> http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com
> >> and follow the instructions there.
> >>
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> > and follow the instructions there.
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>
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Re: [time-nuts] Tale of Two GPStars...

[Steve - Home]

I just proved my memory isn’t what it used to be. My unit is a GPStat Frequency 
Measurement System, Model 345-200. Not a GPStar as I thought. I just dug it out 
and the label on the bottom says input +5, +12V 3W. I’ll dig into it later as I 
have another dig to do - 35’ trench 6” wide, 18” deep for power to a utility 
building. 

Steve




> On Jun 5, 2020, at 9:10 AM, paul swed  wrote:
> 
> Steve and yet another GPStar.
> My units are older and just GPStar by Odetics and use ocxo.
> These old units actually had external down converters that are quite
> complicated but nicely done.
> The din plug was +5 and +12. 2 pins for each plus grounds.
> Yours may be different if newer. But as you guessed really easy to figure
> out.
> Regards
> Paul
> WB8TSL
> 
>> On Fri, Jun 5, 2020 at 10:03 AM Steve - Home  wrote:
>> 
>> I have a GPStar that hadn’t been used in a few years. I’ve misplaced the
>> wall wart power supply. Could someone pass along the output voltage and
>> current numbers of the wall wart, please? I think I can figure out the DIN
>> connector pin numbers but that would be helpful, too. My manual is pretty
>> sparse in that area. If I recall it says “plug in the AC adapter”...
>> 
>> Thanks!
>> 
>> Steve K.
>> WB0DBS
>> 
>> 
>> 
 On Jun 4, 2020, at 10:00 PM, paul swed  wrote:
>>> 
>>> Somebody else actually has a GPStar (Odetics) and working?
>>> My units stopped working about 4 months ago. They are circa 1994 as I
>>> recall. Had 2 neither would work. Have one now as I used the case and
>> rack
>>> mounts for another project.
>>> These are much older then what you have as the GPS receiver is actually
>>> discreet components.
>>> Regards
>>> Paul
>>> WB8TSL
>>> 
 On Thu, Jun 4, 2020 at 8:59 PM Bruce Lane 
 wrote:
 
   After many moons, my trusty GPStar 365 (updated to a 565 through
 firmware and a receiver change) finally bit the dust. Symptom: It kept
 flipping between 'Coasting' and 'Recovering,' never quite reaching
 'Locked.' The DAC value either ended up maxed (65534) or min'd (0).
 
   Contacted Tim Gavin at Zyfer-FEI for advice. Strongest
>> possibility:
 OCXO went south. Tried manually setting the DAC for mid-point (32768)
 and manually tweaking the coarse tuning on said OCXO against a
 known-good 10MHz source of equal precision (translation: Another GPSDO).
 
   Didn't work. Tried replacing the OCXO itself, and doing the
 alignment
 trick. Still no joy.
 
   Considering the lack of schematics: Emit large sigh, put unit
 aside,
 start searching Ebay for replacement.
 
   Found a late-model (black case) 565-310 for a reasonable price,
 bought
 it. Arrived a week later (yesterday at work). Opened it up, delighted to
 find I got a better deal than I thought in that the thing's got a
 rubidium module (FE-5650A to be exact).
 
   Did initial power-up/burn-in test with a local GPS antenna; Unit
 went
 to TFOM 4 and 'Locked' within a half-hour and stayed that way all day,
 DAC number just slightly above mid-point.
 
   However -- Date way off due to outdated Motorola UT+ receiver
 module.
 Replaced said UT+ with the M12M drop-in module from Synergy GPS. Fired
 up -- and got NO satellite tracking ID's!
 
   Mutter something vulgar. Do more poking around. Suddenly realize
 the
 firmware in the replacement 565 is at 1.06, while my original unit was
 at 1.08. "I wonder if..."
 
   Swap 1.08 firmware chip into replacement 565. Power on. Goes
 through
 factory reset -- and comes up perfectly normal! Sat numbers appearing on
 tracking report. Just checked it a moment ago (about 15 minutes after
 initial re-power) and it's at TFOM 4 / Locked! And it stayed that way
 through a 24-hour burn-in check.
 
   Conclusion: In the 565 series, you need version 1.08 firmware to
 support Motorola's M12, or similar replacements.
 
   And I'm still amazed I lucked out with the rubidium module. ;-)
 
   Keep on tickin'...
 
 --
 ---
 Bruce Lane, ARS KC7GR
 http://www.bluefeathertech.com
 kyrrin (at) bluefeathertech dot com
 "Quando Omni Flunkus Moritati" (Red Green)
 
 ___
 time-nuts mailing list -- time-nuts@lists.febo.com
 To unsubscribe, go to
 http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com
 and follow the instructions there.
 
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>> 
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Re: [time-nuts] Tale of Two GPStars...

[paul swed]

OK GPStat is yet some version of GPStar from odetics.

On Fri, Jun 5, 2020 at 10:41 AM Steve - Home  wrote:

> I just proved my memory isn’t what it used to be. My unit is a GPStat
> Frequency Measurement System, Model 345-200. Not a GPStar as I thought. I
> just dug it out and the label on the bottom says input +5, +12V 3W. I’ll
> dig into it later as I have another dig to do - 35’ trench 6” wide, 18”
> deep for power to a utility building.
>
> Steve
>
>
>
>
> > On Jun 5, 2020, at 9:10 AM, paul swed  wrote:
> >
> > Steve and yet another GPStar.
> > My units are older and just GPStar by Odetics and use ocxo.
> > These old units actually had external down converters that are quite
> > complicated but nicely done.
> > The din plug was +5 and +12. 2 pins for each plus grounds.
> > Yours may be different if newer. But as you guessed really easy to figure
> > out.
> > Regards
> > Paul
> > WB8TSL
> >
> >> On Fri, Jun 5, 2020 at 10:03 AM Steve - Home 
> wrote:
> >>
> >> I have a GPStar that hadn’t been used in a few years. I’ve misplaced the
> >> wall wart power supply. Could someone pass along the output voltage and
> >> current numbers of the wall wart, please? I think I can figure out the
> DIN
> >> connector pin numbers but that would be helpful, too. My manual is
> pretty
> >> sparse in that area. If I recall it says “plug in the AC adapter”...
> >>
> >> Thanks!
> >>
> >> Steve K.
> >> WB0DBS
> >>
> >>
> >>
>  On Jun 4, 2020, at 10:00 PM, paul swed  wrote:
> >>>
> >>> Somebody else actually has a GPStar (Odetics) and working?
> >>> My units stopped working about 4 months ago. They are circa 1994 as I
> >>> recall. Had 2 neither would work. Have one now as I used the case and
> >> rack
> >>> mounts for another project.
> >>> These are much older then what you have as the GPS receiver is actually
> >>> discreet components.
> >>> Regards
> >>> Paul
> >>> WB8TSL
> >>>
>  On Thu, Jun 4, 2020 at 8:59 PM Bruce Lane  >
>  wrote:
> 
>    After many moons, my trusty GPStar 365 (updated to a 565 through
>  firmware and a receiver change) finally bit the dust. Symptom: It kept
>  flipping between 'Coasting' and 'Recovering,' never quite reaching
>  'Locked.' The DAC value either ended up maxed (65534) or min'd
> (0).
> 
>    Contacted Tim Gavin at Zyfer-FEI for advice. Strongest
> >> possibility:
>  OCXO went south. Tried manually setting the DAC for mid-point (32768)
>  and manually tweaking the coarse tuning on said OCXO against a
>  known-good 10MHz source of equal precision (translation: Another
> GPSDO).
> 
>    Didn't work. Tried replacing the OCXO itself, and doing the
>  alignment
>  trick. Still no joy.
> 
>    Considering the lack of schematics: Emit large sigh, put unit
>  aside,
>  start searching Ebay for replacement.
> 
>    Found a late-model (black case) 565-310 for a reasonable price,
>  bought
>  it. Arrived a week later (yesterday at work). Opened it up, delighted
> to
>  find I got a better deal than I thought in that the thing's got a
>  rubidium module (FE-5650A to be exact).
> 
>    Did initial power-up/burn-in test with a local GPS antenna; Unit
>  went
>  to TFOM 4 and 'Locked' within a half-hour and stayed that way all day,
>  DAC number just slightly above mid-point.
> 
>    However -- Date way off due to outdated Motorola UT+ receiver
>  module.
>  Replaced said UT+ with the M12M drop-in module from Synergy GPS. Fired
>  up -- and got NO satellite tracking ID's!
> 
>    Mutter something vulgar. Do more poking around. Suddenly realize
>  the
>  firmware in the replacement 565 is at 1.06, while my original unit was
>  at 1.08. "I wonder if..."
> 
>    Swap 1.08 firmware chip into replacement 565. Power on. Goes
>  through
>  factory reset -- and comes up perfectly normal! Sat numbers appearing
> on
>  tracking report. Just checked it a moment ago (about 15 minutes after
>  initial re-power) and it's at TFOM 4 / Locked! And it stayed that way
>  through a 24-hour burn-in check.
> 
>    Conclusion: In the 565 series, you need version 1.08 firmware to
>  support Motorola's M12, or similar replacements.
> 
>    And I'm still amazed I lucked out with the rubidium module. ;-)
> 
>    Keep on tickin'...
> 
>  --
>  ---
>  Bruce Lane, ARS KC7GR
>  http://www.bluefeathertech.com
>  kyrrin (at) bluefeathertech dot com
>  "Quando Omni Flunkus Moritati" (Red Green)
> 
>  ___
>  time-nuts mailing list -- time-nuts@lists.febo.com
>  To unsubscribe, go to
>  http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com
>  and follow the instructions there.
> 
> >>> ___
> >>> time-nuts mailing 

Re: [time-nuts] A simple sampling DMTD

[Joseph Gwinn]

On Sat, 30 May 2020 12:00:01 -0400, time-nuts-requ...@lists.febo.com 
wrote:
Re: time-nuts Digest, Vol 190, Issue 40
[snip]
> Message: 3
> Date: Sat, 30 May 2020 11:43:40 +0200
> From: Jan-Derk Bakker 
> To: Discussion of precise time and frequency measurement
>   
> Subject: Re: [time-nuts] A simple sampling DMTD
> Message-ID:
>   
> Content-Type: text/plain; charset="utf-8"
> 
> Dear Joe,
> 
> Thank you for your mail; always happy with the dialogue.
> 
> In a way we have come full circle; the Sherman/Jordens NIST paper was one
> of my primary references for the design I made last summer. (It would have
> been helpful had I linked to it upthread; I could have sworn I had done so,
> but I cannot find the post.)

I don't recall seeing it either.

 
> The arctan-based approach in the NIST paper is computationally infeasible
> on an 8-bit processor. Even so, back in November I have dumped raw samples
> over USB to a PC to see how much improvement can be seen over a simple
> least squares linear ZCD. As was discussed before, bandpass filtering and
> more advanced phase estimation are complementary in their results: with
> ideal band pass filtering, the phase detection becomes much less critical
> (and vice versa). The best balance I could find at the time was a tracking
> loop which runs a 501-point BPF FIR kernel on three points of the period of
> both channels (expected on-time, ~1/6th period early, ~1/6th period late)
> and then uses the arctangens to determine the phase. This produced ADEV
> results about 1dB worse than running the FIR+arctan on all samples, and
> about 1dB better than the simple ZCD with cascaded
> differentiators/integrators as computationally inexpensive filters. This
> gave me a workable baseline for the DMTD with reduced sampling rate and
> reduced computational effort.

What I don't understand is why everything must be done in that 8-bit 
processor.  The traditional solution / architecture is to use the 8-bit 
processor only for data collection and forwarding, and do the big math 
in the commodity X86 computer which is controlling the data collection 
head.  Then, ArcTan et al are easy.

 
> (One of the limiting factors with the arctan-approach was that the quality
> of the amplitude estimator plays a large role in the accuracy of the end
> result. With arctan2 on I/Q data this is less of an issue; a FPGA can
> efficiently do both in one go with a CORDIC)

Yes, full I+Q is the way to go.  I recall Sam Stein commenting an an 
article regarding the development of the 5120 instrument that a major 
cause of noise floor was the noise as the beatnote signals passed 
through zero.  His solution was precisely I+Q, because the total power 
delivered is constant.

Also, the Sherman/Jordens NIST paper specifically uses batch processing 
and curve-fitting, and not a FFT, for computational simplicity and to 
avoid the need for window taper functions.  Nor are FFTs as precise and 
a batch fit.

Joe Gwinn

 
> Inspired by the NIST paper my sampling DMTD was designed to take an FPGA
> daughterboard (the two rows of headers visible on
> http://www.lartmaker.nl/time-nuts/dmtd-proto.jpg ). Last February I have
> designed such a daughterboard (see attached image). Sadly, due to the
> COVID-19 crisis my lab has closed for the foreseeable future; as I don't
> have facilities to reliably populate 0402 parts and QFN packages at home,
> this will have to wait for now.
> 
> (@Luciano: Yes, having this available as a solution accessible to amateurs
> has always been one of my goals)
> 
> Sincerely,
> 
> JDB.
> [I've been working on other mildly time-nutty things that *can* be soldered
> at home lately; hope to have a post in a week or two]
> 
[snip]
> 
> On Fri, May 29, 2020 at 6:07 PM Joseph Gwinn  wrote:
> 
[snip]
>> 
>> "Oscillator metrology with software defined radio, Jeff A. Sherman and
>> Robert Jordens (of NIST),  Review of Scientific Instruments 87, 054711
>> (2016); https://doi.org/10.1063/1.4950898.  (Open version:
>> )

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[time-nuts] ThunderBolt question

[Robert DiRosario]

I have a Trimble ThunderBolt GPSDO that I just received. It has an F 
connector for the antenna input, and BNC connectors for the 1 pps and 10 
MHz outputs. Is the receiver input impedance really 75 Ohms, or is it 50 
Ohms and they just used the F connector to distinguish it from the 
others? What do people do, just use a 50 Ohm antenna?


Thanks

Robert DiRosario

KA3ZYX

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Re: [time-nuts] ThunderBolt question

[Tim Shoppa]

Many of us use F connectors and 75 ohm CATV RG-6 coax for GPS antennas when
both antenna and receiver are specified for 50 ohms.

Don't sweat the difference between 75 and 50 ohms.

Tim N3QE

On Fri, Jun 5, 2020 at 7:22 PM Robert DiRosario  wrote:

> I have a Trimble ThunderBolt GPSDO that I just received. It has an F
> connector for the antenna input, and BNC connectors for the 1 pps and 10
> MHz outputs. Is the receiver input impedance really 75 Ohms, or is it 50
> Ohms and they just used the F connector to distinguish it from the
> others? What do people do, just use a 50 Ohm antenna?
>
> Thanks
>
> Robert DiRosario
>
> KA3ZYX
>
> ___
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Re: [time-nuts] ThunderBolt question

[Dana Whitlow]

Robert,

One does not know what the RF input impedance of the unit is unless one
measures it (very carefully at low levels) with a VNA or similar instrument.

Just 'cause some manufacturer says that it's 50 ohms does not mean very
much- it's not uncommon to see actual impedances off by a factor of 1,5:1 or
even 2:1.  I've heard of people using 75 ohm line with F connectors at both
ends to connect an antenna to a GPS receiver and claim that it causes no
problems.  The nice thing about 75 ohm line with F connectors is that it's
readily available in various lengths at your friendly local brick and mortar
stores.

I'd just try it and see how it works.  Then look deeper only if you come to
suspect that the GPS unit's performance is not up to snuff.

Dana (K8YUM)


On Fri, Jun 5, 2020 at 6:22 PM Robert DiRosario  wrote:

> I have a Trimble ThunderBolt GPSDO that I just received. It has an F
> connector for the antenna input, and BNC connectors for the 1 pps and 10
> MHz outputs. Is the receiver input impedance really 75 Ohms, or is it 50
> Ohms and they just used the F connector to distinguish it from the
> others? What do people do, just use a 50 Ohm antenna?
>
> Thanks
>
> Robert DiRosario
>
> KA3ZYX
>
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> http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com
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Re: [time-nuts] ThunderBolt question

[DON MURRAY via time-nuts]

Robert...

Try to find QUAD SHIELD RG-6.


73
Don
W4WJ

On Friday, June 5, 2020 Dana Whitlow  wrote:
Robert,

One does not know what the RF input impedance of the unit is unless one
measures it (very carefully at low levels) with a VNA or similar instrument.

Just 'cause some manufacturer says that it's 50 ohms does not mean very
much- it's not uncommon to see actual impedances off by a factor of 1,5:1 or
even 2:1.  I've heard of people using 75 ohm line with F connectors at both
ends to connect an antenna to a GPS receiver and claim that it causes no
problems.  The nice thing about 75 ohm line with F connectors is that it's
readily available in various lengths at your friendly local brick and mortar
stores.

I'd just try it and see how it works.  Then look deeper only if you come to
suspect that the GPS unit's performance is not up to snuff.

Dana    (K8YUM)


On Fri, Jun 5, 2020 at 6:22 PM Robert DiRosario  wrote:

> I have a Trimble ThunderBolt GPSDO that I just received. It has an F
> connector for the antenna input, and BNC connectors for the 1 pps and 10
> MHz outputs. Is the receiver input impedance really 75 Ohms, or is it 50
> Ohms and they just used the F connector to distinguish it from the
> others? What do people do, just use a 50 Ohm antenna?
>
> Thanks
>
> Robert DiRosario
>
> KA3ZYX
>
> ___
> time-nuts mailing list -- time-nuts@lists.febo.com
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> http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com
> and follow the instructions there.
>
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Re: [time-nuts] ThunderBolt question

[Taka Kamiya via time-nuts]

50 ohm / 75 ohm question is really irrelevant in this kind of thing.  Trmble 
itself says in manual, not to be concerned with this apparent mismatch.
In my particular case, I have a home lab standard and existing system.  I have 
an antenna and network of distribution amplifiers.  They are all 50 ohms and N 
connectors.  Some ports have BNC adapters attached.  I have pretty much 
standardized everything to SMA, N, or BNC.

I boxed a power supply, T-bolt, and buffer amp in a metal case.  I bought a 
short cable (RG58) that goes from F to BNC.  On back of the case, I have BNC to 
N adapter.  I also have a few adapters that goes from F to BNC for the test 
bench.  It really doesn't matter what you use, as long as it makes a solid 
connection. 

Advantage of F connectors and RG6 are, cheap, abundant, and low loss for the 
size.  Advantage of having house standard is, less adapters and less 
headache.

--- 
(Mr.) Taka Kamiya
KB4EMF / ex JF2DKG
 

On Friday, June 5, 2020, 7:22:33 PM EDT, Robert DiRosario 
 wrote:  
 
 I have a Trimble ThunderBolt GPSDO that I just received. It has an F 
connector for the antenna input, and BNC connectors for the 1 pps and 10 
MHz outputs. Is the receiver input impedance really 75 Ohms, or is it 50 
Ohms and they just used the F connector to distinguish it from the 
others? What do people do, just use a 50 Ohm antenna?

Thanks

Robert DiRosario

KA3ZYX

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Re: [time-nuts] ThunderBolt question

[Dana Whitlow]

I'd like to point out that mismatches at the ends of an antenna cable *can*
cause trouble.  When both ends are mismatched, each bit of detail in the
signal
gets partially reflected back and forth, each time delayed by the round
trip propagation
delay in the cable, and so you have something like multipath going on.
Fortunately the
successive reflections get weaker with time, generally quite rapidly.
Since many
GPS users seem very concerned about multipath resulting from poor antenna
placement,
I think this factor should be considered as well and not just get swept
under the rug.

The amplitude of the "multipath" resulting from cable mismatches depends on
the product
of the voltage reflection coefficients at the two ends of the cable.  If
either end is perfectly
matched, then the quality of the match at the other end is not significant
vis-a-vis apparent
multipath problems and only affects transmission loss.

But when there is a mismatch on both ends, then the length of the cable
comes into play
as well.  A longer cable means more delay between successive reflections,
which is just
like multipath involving longer delays between the direct and the reflected
signals.

Cheers,

Dana  (K8YUM)

On Fri, Jun 5, 2020 at 7:13 PM Taka Kamiya via time-nuts <
time-nuts@lists.febo.com> wrote:

> 50 ohm / 75 ohm question is really irrelevant in this kind of thing.
> Trmble itself says in manual, not to be concerned with this apparent
> mismatch.
> In my particular case, I have a home lab standard and existing system.  I
> have an antenna and network of distribution amplifiers.  They are all 50
> ohms and N connectors.  Some ports have BNC adapters attached.  I have
> pretty much standardized everything to SMA, N, or BNC.
>
> I boxed a power supply, T-bolt, and buffer amp in a metal case.  I bought
> a short cable (RG58) that goes from F to BNC.  On back of the case, I have
> BNC to N adapter.  I also have a few adapters that goes from F to BNC for
> the test bench.  It really doesn't matter what you use, as long as it makes
> a solid connection.
>
> Advantage of F connectors and RG6 are, cheap, abundant, and low loss for
> the size.  Advantage of having house standard is, less adapters and less
> headache.
>
> ---
> (Mr.) Taka Kamiya
> KB4EMF / ex JF2DKG
>
>
> On Friday, June 5, 2020, 7:22:33 PM EDT, Robert DiRosario <
> ka3...@comcast.net> wrote:
>
>  I have a Trimble ThunderBolt GPSDO that I just received. It has an F
> connector for the antenna input, and BNC connectors for the 1 pps and 10
> MHz outputs. Is the receiver input impedance really 75 Ohms, or is it 50
> Ohms and they just used the F connector to distinguish it from the
> others? What do people do, just use a 50 Ohm antenna?
>
> Thanks
>
> Robert DiRosario
>
> KA3ZYX
>
> ___
> time-nuts mailing list -- time-nuts@lists.febo.com
> To unsubscribe, go to
> http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com
> and follow the instructions there.
>
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>
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Re: [time-nuts] ThunderBolt question

[Didier Juges]

Even more so when the cable is long, as it is likely to be with a GPS
receiver. The cable attenuation does wonders attenuating the effects of
VSWR...

Didier KO4BB

On Fri, Jun 5, 2020 at 6:30 PM Tim Shoppa  wrote:

> Many of us use F connectors and 75 ohm CATV RG-6 coax for GPS antennas when
> both antenna and receiver are specified for 50 ohms.
>
> Don't sweat the difference between 75 and 50 ohms.
>
> Tim N3QE
>
> On Fri, Jun 5, 2020 at 7:22 PM Robert DiRosario 
> wrote:
>
> > I have a Trimble ThunderBolt GPSDO that I just received. It has an F
> > connector for the antenna input, and BNC connectors for the 1 pps and 10
> > MHz outputs. Is the receiver input impedance really 75 Ohms, or is it 50
> > Ohms and they just used the F connector to distinguish it from the
> > others? What do people do, just use a 50 Ohm antenna?
> >
> > Thanks
> >
> > Robert DiRosario
> >
> > KA3ZYX
> >
> > ___
> > time-nuts mailing list -- time-nuts@lists.febo.com
> > To unsubscribe, go to
> > http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com
> > and follow the instructions there.
> >
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Re: [time-nuts] ThunderBolt question

[Tom Holmes]

Dana...

I think that you are neglecting two important mitigating factors.

1. the cable loss at 1575MHz, even for a 25' run of RG-6, reduces those
reflections quite a lot from one end to the other. It amounts to 2 - 3
dB in 25', depending on cable quality.

2. a 1.5:1 SWR is not a very big reflection to begin with, on the order of
20% of the incident power, about  7 dB. I am rounding a lot here just to
keep the math easy...for me. 

By the time a reflection has made the round trip from the receiver back to
the antenna and them back to the receiver, which is how the delay would have
to manifest itself, it will be down at least 15 dB from its original self,
and probably more. Given the coding of GPS signals which allows several
satellites to share a common frequency band, that is not going to be much of
a problem. And if only one end of the path actually is 75 ohms, then there
won't be a delayed signal.

Tom Holmes, N8ZM

-Original Message-
From: time-nuts  On Behalf Of Dana Whitlow
Sent: Friday, June 05, 2020 9:01 PM
To: Taka Kamiya ; Discussion of precise time and
frequency measurement 
Subject: Re: [time-nuts] ThunderBolt question

I'd like to point out that mismatches at the ends of an antenna cable *can*
cause trouble.  When both ends are mismatched, each bit of detail in the
signal
gets partially reflected back and forth, each time delayed by the round
trip propagation
delay in the cable, and so you have something like multipath going on.
Fortunately the
successive reflections get weaker with time, generally quite rapidly.
Since many
GPS users seem very concerned about multipath resulting from poor antenna
placement,
I think this factor should be considered as well and not just get swept
under the rug.

The amplitude of the "multipath" resulting from cable mismatches depends on
the product
of the voltage reflection coefficients at the two ends of the cable.  If
either end is perfectly
matched, then the quality of the match at the other end is not significant
vis-a-vis apparent
multipath problems and only affects transmission loss.

But when there is a mismatch on both ends, then the length of the cable
comes into play
as well.  A longer cable means more delay between successive reflections,
which is just
like multipath involving longer delays between the direct and the reflected
signals.

Cheers,

Dana  (K8YUM)

On Fri, Jun 5, 2020 at 7:13 PM Taka Kamiya via time-nuts <
time-nuts@lists.febo.com> wrote:

> 50 ohm / 75 ohm question is really irrelevant in this kind of thing.
> Trmble itself says in manual, not to be concerned with this apparent
> mismatch.
> In my particular case, I have a home lab standard and existing system.  I
> have an antenna and network of distribution amplifiers.  They are all 50
> ohms and N connectors.  Some ports have BNC adapters attached.  I have
> pretty much standardized everything to SMA, N, or BNC.
>
> I boxed a power supply, T-bolt, and buffer amp in a metal case.  I bought
> a short cable (RG58) that goes from F to BNC.  On back of the case, I have
> BNC to N adapter.  I also have a few adapters that goes from F to BNC for
> the test bench.  It really doesn't matter what you use, as long as it
makes
> a solid connection.
>
> Advantage of F connectors and RG6 are, cheap, abundant, and low loss for
> the size.  Advantage of having house standard is, less adapters and less
> headache.
>
> ---
> (Mr.) Taka Kamiya
> KB4EMF / ex JF2DKG
>
>
> On Friday, June 5, 2020, 7:22:33 PM EDT, Robert DiRosario <
> ka3...@comcast.net> wrote:
>
>  I have a Trimble ThunderBolt GPSDO that I just received. It has an F
> connector for the antenna input, and BNC connectors for the 1 pps and 10
> MHz outputs. Is the receiver input impedance really 75 Ohms, or is it 50
> Ohms and they just used the F connector to distinguish it from the
> others? What do people do, just use a 50 Ohm antenna?
>
> Thanks
>
> Robert DiRosario
>
> KA3ZYX
>
> ___
> time-nuts mailing list -- time-nuts@lists.febo.com
> To unsubscribe, go to
> http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com
> and follow the instructions there.
>
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>
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Re: [time-nuts] ThunderBolt question

[Wes]

A 1.5:1 SWR = ~14 dB return loss.


On 6/5/2020 6:42 PM, Tom Holmes wrote:

Dana...

I think that you are neglecting two important mitigating factors.

1. the cable loss at 1575MHz, even for a 25' run of RG-6, reduces those
reflections quite a lot from one end to the other. It amounts to 2 - 3
dB in 25', depending on cable quality.

2. a 1.5:1 SWR is not a very big reflection to begin with, on the order of
20% of the incident power, about  7 dB. I am rounding a lot here just to
keep the math easy...for me.

By the time a reflection has made the round trip from the receiver back to
the antenna and them back to the receiver, which is how the delay would have
to manifest itself, it will be down at least 15 dB from its original self,
and probably more. Given the coding of GPS signals which allows several
satellites to share a common frequency band, that is not going to be much of
a problem. And if only one end of the path actually is 75 ohms, then there
won't be a delayed signal.

Tom Holmes, N8ZM



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Re: [time-nuts] ThunderBolt question

[Richard Solomon]

I have used these "Hockey Puck" GPS
antennas with 100' (thats feet) of RG-174.

No problem locking up. Granted, the antenna
needs an unobstructed view, but the antennas
today work a lot better.

I have a Laptop in the shack, near an inner
wall, with one of these GPS/GLONASS USB
units. I consistently see 8 or more satellites
and get a 3D fix. That's on my desktop with
an SB-220 looming over the antenna.

Try it, you will be surprised.

73, Dick, W1KSZ

On Fri, Jun 5, 2020 at 6:43 PM Tom Holmes  wrote:

> Dana...
>
> I think that you are neglecting two important mitigating factors.
>
> 1. the cable loss at 1575MHz, even for a 25' run of RG-6, reduces those
> reflections quite a lot from one end to the other. It amounts to 2 - 3
> dB in 25', depending on cable quality.
>
> 2. a 1.5:1 SWR is not a very big reflection to begin with, on the order of
> 20% of the incident power, about  7 dB. I am rounding a lot here just to
> keep the math easy...for me.
>
> By the time a reflection has made the round trip from the receiver back to
> the antenna and them back to the receiver, which is how the delay would
> have
> to manifest itself, it will be down at least 15 dB from its original self,
> and probably more. Given the coding of GPS signals which allows several
> satellites to share a common frequency band, that is not going to be much
> of
> a problem. And if only one end of the path actually is 75 ohms, then there
> won't be a delayed signal.
>
> Tom Holmes, N8ZM
>
> -Original Message-
> From: time-nuts  On Behalf Of Dana
> Whitlow
> Sent: Friday, June 05, 2020 9:01 PM
> To: Taka Kamiya ; Discussion of precise time and
> frequency measurement 
> Subject: Re: [time-nuts] ThunderBolt question
>
> I'd like to point out that mismatches at the ends of an antenna cable *can*
> cause trouble.  When both ends are mismatched, each bit of detail in the
> signal
> gets partially reflected back and forth, each time delayed by the round
> trip propagation
> delay in the cable, and so you have something like multipath going on.
> Fortunately the
> successive reflections get weaker with time, generally quite rapidly.
> Since many
> GPS users seem very concerned about multipath resulting from poor antenna
> placement,
> I think this factor should be considered as well and not just get swept
> under the rug.
>
> The amplitude of the "multipath" resulting from cable mismatches depends on
> the product
> of the voltage reflection coefficients at the two ends of the cable.  If
> either end is perfectly
> matched, then the quality of the match at the other end is not significant
> vis-a-vis apparent
> multipath problems and only affects transmission loss.
>
> But when there is a mismatch on both ends, then the length of the cable
> comes into play
> as well.  A longer cable means more delay between successive reflections,
> which is just
> like multipath involving longer delays between the direct and the reflected
> signals.
>
> Cheers,
>
> Dana  (K8YUM)
>
> On Fri, Jun 5, 2020 at 7:13 PM Taka Kamiya via time-nuts <
> time-nuts@lists.febo.com> wrote:
>
> > 50 ohm / 75 ohm question is really irrelevant in this kind of thing.
> > Trmble itself says in manual, not to be concerned with this apparent
> > mismatch.
> > In my particular case, I have a home lab standard and existing system.  I
> > have an antenna and network of distribution amplifiers.  They are all 50
> > ohms and N connectors.  Some ports have BNC adapters attached.  I have
> > pretty much standardized everything to SMA, N, or BNC.
> >
> > I boxed a power supply, T-bolt, and buffer amp in a metal case.  I bought
> > a short cable (RG58) that goes from F to BNC.  On back of the case, I
> have
> > BNC to N adapter.  I also have a few adapters that goes from F to BNC for
> > the test bench.  It really doesn't matter what you use, as long as it
> makes
> > a solid connection.
> >
> > Advantage of F connectors and RG6 are, cheap, abundant, and low loss for
> > the size.  Advantage of having house standard is, less adapters and less
> > headache.
> >
> > ---
> > (Mr.) Taka Kamiya
> > KB4EMF / ex JF2DKG
> >
> >
> > On Friday, June 5, 2020, 7:22:33 PM EDT, Robert DiRosario <
> > ka3...@comcast.net> wrote:
> >
> >  I have a Trimble ThunderBolt GPSDO that I just received. It has an F
> > connector for the antenna input, and BNC connectors for the 1 pps and 10
> > MHz outputs. Is the receiver input impedance really 75 Ohms, or is it 50
> > Ohms and they just used the F connector to distinguish it from the
> > others? What do people do, just use a 50 Ohm antenna?
> >
> > Thanks
> >
> > Robert DiRosario
> >
> > KA3ZYX
> >
> > ___
> > time-nuts mailing list -- time-nuts@lists.febo.com
> > To unsubscribe, go to
> > http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com
> > and follow the instructions there.
> >
> > ___
> > time-nuts 

Re: [time-nuts] ThunderBolt question

[Kevin Rowett]

You will need a “GPS antenna” with an LNA in it for decent (perhaps at all) 
reception.

F connector is/was common for GPS antenna connections.  I doubt the receiver is 
anything close to 50 ohms, or 75 ohms

73, K6TD


> On Jun 5, 2020, at 4:24 PM, Robert DiRosario  wrote:
> 
> I have a Trimble ThunderBolt GPSDO that I just received. It has an F 
> connector for the antenna input, and BNC connectors for the 1 pps and 10 MHz 
> outputs. Is the receiver input impedance really 75 Ohms, or is it 50 Ohms and 
> they just used the F connector to distinguish it from the others? What do 
> people do, just use a 50 Ohm antenna?
> 
> Thanks
> 
> Robert DiRosario
> 
> KA3ZYX
> 
> ___
> time-nuts mailing list -- time-nuts@lists.febo.com
> To unsubscribe, go to 
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