Re: [time-nuts] time-nuts Digest, Vol 159, Issue 14 SDR hacking

[Andre]

> On Oct 9, 2017, at 10:20 AM, jimlux  wrote:
>
> I'm trying to come up with a relatively simple scheme to calibrate an HF 
> antenna array - I've got a bunch of RTL-SDRs operating as a distributed array 
> spread over a few 10s of meters.
>
> In terms of frequency, I think it should work fairly well - I tune the
> RTL's front end, look for my calibration combs that are "in band" and fit
> an appropriate function to the signal (there should be a well defined phase
> relationship between the harmonics)
>
> So
**

Also have SDR here. Interestingly the issue I found is you do need a good fast 
PC or packets will get lost.  I use a quad core Phenom with 8GB and it still 
loses data as it's highest sample rate  resoldering USB helped somewhat.  

I have a Tektronix 015-040 5mV/mA CT if someone has a use with pigtail lead and 
screw end. Has non standard fitting 

Andre
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Re: [time-nuts] precision frequency/time/amplitude reference

[jimlux]

On 10/9/17 8:02 AM, Bob kb8tq wrote:

Hi

Pick a couple of local broadcast stations and record them. That will give you a 
baseline
for each of the parameters you are after in real time. They *will* drift.

Past that, I’d go with a sweep of each node before installation. That will give 
you the
frequency response and (to some degree) a guess for noise and spurs.



The RTL-SDR has only about 2 MHz BW, so you'd have to be lucky to have a 
broadcast station in the band (and if I'm looking at trying to image 
Jupiter with an interferometer, at 20.1 MHz, I'm not sure that the SW 
broadcast bands cover within 2MHz - and you'd be subject to the vagaries 
of propagation.. low sunspots = low critical frequency = not much 
skywave propagation for WWV).


So a local reference would be nice.  Originally, I thought about just 
radiating a CW tone (perhaps modulated with timecode), but then, I 
realized I'd also like to calibrate the RF chain in the receiver, so 
feeding a calibrated pulse that has spurs (hey, a "marker beacon" in old 
school radios with a analog dial)



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Re: [time-nuts] precision frequency/time/amplitude reference

[jimlux]

On 10/9/17 8:00 AM, Mattia Rizzi wrote:

Hi,
I did something similar when I had to deliver synchronization over IEEE
802.15.4-CSS (Chirp spread spectrum).
If you have SDR on both ends (TX & RX), you can use complex chirp signals
and then cross-correlation at RX. Just be sure that the multi-path is not
killing you (i.e. the cross-correlation peak has a width smaller than
multi-path echoes delay).
If you use up & down chirps, you can compensate the time-shift introduced
by carrier frequency offset (due to RF front-end).
To estimate clock frequency offset, well, just send a repetitive pattern.
Amplitude is easy as well.

My application is more like an HF interferometer/radio telescope, so I 
don't have any control over the transmitted signal.


I am willing to transmit a "pilot tone" of some sort to allow me to do 
the interelement cal, but I'd like it to be "real simple". An RTL-SDR is 
receive only, but the beaglebone microcontroller next to it can generate 
pulse trains, for instance.




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Re: [time-nuts] precision frequency/time/amplitude reference

[jimlux]

On 10/9/17 9:58 AM, David Witten wrote:

Jim,

If I understand what you are attempting (I may well not), you might
consider the approach taken here:

https://github.com/tejeez/rtl_coherent


that is where you have a common clock distributed to the RTLs
"A single 28.8 MHz reference clock is distributed to all dongles. "

What I want to do is have the dongles completely independent running 
with their own computer off a battery.  Capture the data to a SDcard 
and then post process it to do the interferometry



And do this with a self contained calibration approach (i.e. not depend 
on there being a convenient radio station which has a signal in band, etc.)


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Re: [time-nuts] Novatel Dual frequency GNSS receivers on ebay

[Bob kb8tq]

Hi

One would *guess* that since it has the 702 antenna on it, it does have L1/L2 
firmware enabled
in the receiver ( 701 = single L1 band, 702 = L1 / L2, 703 = L1,L2.L5 ). Indeed 
the hardware 
spans a wide range of “things” depending on the exact license keys you shoot 
into it. Buying 
those keys “after the fact” never seemed to be very cost effective ….

Bob

> On Oct 9, 2017, at 4:02 PM, Tom Van Baak  wrote:
> 
> Christopher,
> 
> Thanks for that additional information. Can you (or Gregory) also comment on 
> the external frequency input / output and the 1PPS output of this receiver?
> 
> A quick look at the om-2128.pdf and om-2129.pdf documents has words 
> like "better than 250 ns accuracy" and "50 ns increments" but I didn't see 
> mention of 1PPS quantization, sawtooth correction, or other words commonly 
> used in GPS timing receiver specifications. I'm guessing this product is 
> mostly designed for the PN part of PNT (Positioning, Navigation, Timing)?
> 
> /tvb
> 
> - Original Message - 
> From: "Christopher Hoover" 
> To: "Discussion of precise time and frequency measurement" 
> 
> Sent: Monday, October 09, 2017 12:35 PM
> Subject: Re: [time-nuts] Novatel Dual frequency GNSS receivers on ebay
> 
> 
>> I have quite a bit of experience with Novatel hardware include OEM6, CPT
>> and SPAN.
>> 
>> CPT is an IMU made by KVH and relabeled by Novatel.The accelerometers
>> are MEMs and the roll rate sensors are FOGs.   Pretty old design.
>> Performance is decent (but not auto alignment good).
>> 
>> http://www.kvh.com/Military-and-Government/Gyros-and-Inertial-Systems-and-Compasses/Gyros-and-IMUs-and-INS/IMUs/CG-5100.aspx
>> 
>> SPAN is the "solution."SPAN-CPT puts the CPT IMU and the receiver in a
>> single box.   You could also get just the CPT in a box.
>> 
>> The feature set enabled depends on the software keys that are loaded.
>> Caveat emptor.
>> 
>> Dual receiver (even if you have the hardware) and ALIGN feature are extra
>> features.
>> 
>> Also worth noting is that the circular connectors used on some of the
>> hardware are pricey.  Some are impossible to assemble without specialty
>> tools.
>> 
>> -- Christopher.
>> 73 de AI6KG
>> 
>> 
>> On Sat, Oct 7, 2017 at 2:36 PM, J. L. Trantham  wrote:
>> 
>>> Any idea what they are selling for at this time?
>>> 
>>> I see that some sold for the BIN price of $349.99 up until June 20.  After
>>> that, 'Offer Accepted' occurred up through October 5, with a BIN price now
>>> of $649.99, all plus $40 shipping.
>>> 
>>> Joe
>>> 
>>> -Original Message-
>>> From: time-nuts [mailto:time-nuts-boun...@febo.com] On Behalf Of Gregory
>>> Maxwell
>>> Sent: Saturday, October 07, 2017 2:17 PM
>>> To: Discussion of precise time and frequency measurement
>>> Subject: [time-nuts] Novatel Dual frequency GNSS receivers on ebay
>>> 
>>> There is an ebay listing for "Novatel GPS-702-GG with SPAN-CPT Single
>>> Enclosure GNSS/INS Receiver + Cable" with a fairly large number available.
>>> 
>>> This is a Novatel OEM628 dual frequency receiver (supports GPS, Glonass,
>>> SBAS, apparently including L1C and L2C), plus a three fiber ring gyros
>>> (with bias performance that blows away any mems gyro I've ever used) and an
>>> 3-axis mems acceletrometer in an aluminum case, plus a decent dual
>>> frequency antenna.  This is a generation-ish old kit.
>>> The industrial casing conspires to make it look somewhat less modern than
>>> it actually is.
>>> 
>>> The receivers have external clock input (though not plumbed to the outside
>>> of the case) which appears to work though I didn't try much with it yet.
>>> Mine came with 2013-ish firmware but easily upgraded to current (2016)
>>> firmware. There is a windows based firmware update tool which talks to it
>>> over serial and is very straight forward (The firmware update OEM6631.zip
>>> can be found via google).
>>> 
>>> You can communicate with them over serial in ascii, there is extensive
>>> firmware documentation that goes over every command
>>> https://www.novatel.com/assets/Documents/Manuals/om-2129.pdf  some of
>>> which are specific to other modules. There is also a separate manual for
>>> the inertial navigation specific features (NovAtel SPAN-CPT Users
>>> manual.pdf)
>>> 
>>> The external clock should allow you to hang it off a more stable
>>> oscillator which will improve the stability of the GNSS results, and _I
>>> presume_ improve the quality of the PPS output-- the firmware manual and
>>> operating manual are thin on details, and mostly just go into telling you
>>> how to adjust the kalman filter constants for different clock types.
>>> 
>>> These also appear to support the novatel 'align' mode where you serial
>>> connect two receivers separated by a short baseline and get really accurate
>>> absolute headings; I'm planning on trying that that but haven't set it up
>>> yet.
>>> 
>>> Looks like uber (last 

Re: [time-nuts] Novatel Dual frequency GNSS receivers on ebay

[Poul-Henning Kamp]

In message <6C47315934DF482EB10A679D10C09093@pc52>, "Tom Van Baak" writes:

>I'm guessing this product is
>mostly designed for the PN part of PNT (Positioning, Navigation, Timing)?

At least with the firmwares I have had a chance to test, that is clearly
the case.  I don't know if they have firmware revs focused on timing,
but even if they do, the hardware for the PPS output doesn't seem particularly
well geared towards real-time uses, but more for post-factum correction.

-- 
Poul-Henning Kamp   | UNIX since Zilog Zeus 3.20
p...@freebsd.org | TCP/IP since RFC 956
FreeBSD committer   | BSD since 4.3-tahoe
Never attribute to malice what can adequately be explained by incompetence.
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Re: [time-nuts] Novatel Dual frequency GNSS receivers on ebay

[Tom Van Baak]

Christopher,

Thanks for that additional information. Can you (or Gregory) also comment on 
the external frequency input / output and the 1PPS output of this receiver?

A quick look at the om-2128.pdf and om-2129.pdf documents has words 
like "better than 250 ns accuracy" and "50 ns increments" but I didn't see 
mention of 1PPS quantization, sawtooth correction, or other words commonly used 
in GPS timing receiver specifications. I'm guessing this product is mostly 
designed for the PN part of PNT (Positioning, Navigation, Timing)?

/tvb

- Original Message - 
From: "Christopher Hoover" 
To: "Discussion of precise time and frequency measurement" 
Sent: Monday, October 09, 2017 12:35 PM
Subject: Re: [time-nuts] Novatel Dual frequency GNSS receivers on ebay


>I have quite a bit of experience with Novatel hardware include OEM6, CPT
> and SPAN.
> 
> CPT is an IMU made by KVH and relabeled by Novatel.The accelerometers
> are MEMs and the roll rate sensors are FOGs.   Pretty old design.
> Performance is decent (but not auto alignment good).
> 
> http://www.kvh.com/Military-and-Government/Gyros-and-Inertial-Systems-and-Compasses/Gyros-and-IMUs-and-INS/IMUs/CG-5100.aspx
> 
> SPAN is the "solution."SPAN-CPT puts the CPT IMU and the receiver in a
> single box.   You could also get just the CPT in a box.
> 
> The feature set enabled depends on the software keys that are loaded.
> Caveat emptor.
> 
> Dual receiver (even if you have the hardware) and ALIGN feature are extra
> features.
> 
> Also worth noting is that the circular connectors used on some of the
> hardware are pricey.  Some are impossible to assemble without specialty
> tools.
> 
> -- Christopher.
> 73 de AI6KG
> 
> 
> On Sat, Oct 7, 2017 at 2:36 PM, J. L. Trantham  wrote:
> 
>> Any idea what they are selling for at this time?
>>
>> I see that some sold for the BIN price of $349.99 up until June 20.  After
>> that, 'Offer Accepted' occurred up through October 5, with a BIN price now
>> of $649.99, all plus $40 shipping.
>>
>> Joe
>>
>> -Original Message-
>> From: time-nuts [mailto:time-nuts-boun...@febo.com] On Behalf Of Gregory
>> Maxwell
>> Sent: Saturday, October 07, 2017 2:17 PM
>> To: Discussion of precise time and frequency measurement
>> Subject: [time-nuts] Novatel Dual frequency GNSS receivers on ebay
>>
>> There is an ebay listing for "Novatel GPS-702-GG with SPAN-CPT Single
>> Enclosure GNSS/INS Receiver + Cable" with a fairly large number available.
>>
>> This is a Novatel OEM628 dual frequency receiver (supports GPS, Glonass,
>> SBAS, apparently including L1C and L2C), plus a three fiber ring gyros
>> (with bias performance that blows away any mems gyro I've ever used) and an
>> 3-axis mems acceletrometer in an aluminum case, plus a decent dual
>> frequency antenna.  This is a generation-ish old kit.
>> The industrial casing conspires to make it look somewhat less modern than
>> it actually is.
>>
>> The receivers have external clock input (though not plumbed to the outside
>> of the case) which appears to work though I didn't try much with it yet.
>> Mine came with 2013-ish firmware but easily upgraded to current (2016)
>> firmware. There is a windows based firmware update tool which talks to it
>> over serial and is very straight forward (The firmware update OEM6631.zip
>> can be found via google).
>>
>> You can communicate with them over serial in ascii, there is extensive
>> firmware documentation that goes over every command
>> https://www.novatel.com/assets/Documents/Manuals/om-2129.pdf  some of
>> which are specific to other modules. There is also a separate manual for
>> the inertial navigation specific features (NovAtel SPAN-CPT Users
>> manual.pdf)
>>
>> The external clock should allow you to hang it off a more stable
>> oscillator which will improve the stability of the GNSS results, and _I
>> presume_ improve the quality of the PPS output-- the firmware manual and
>> operating manual are thin on details, and mostly just go into telling you
>> how to adjust the kalman filter constants for different clock types.
>>
>> These also appear to support the novatel 'align' mode where you serial
>> connect two receivers separated by a short baseline and get really accurate
>> absolute headings; I'm planning on trying that that but haven't set it up
>> yet.
>>
>> Looks like uber (last position was ubers offices in denver) had a fleet of
>> these things. The couple I got run great, including the IMU, the antennas
>> obviously spent a long time outside, but work fine. The cable they come
>> with is weird, but I had no problem chopping one end off and figuring out
>> the pinout (see bottom).
>>
>> The novatel OEM6 is well supported by rtklib and I was able to get
>> post-processed positions very easily.
>>
>> Seller takes best offers a fair amount below the $649 asking price.
>> Looks like they may have another 30 or so of them.
>>
>> May be useful 

Re: [time-nuts] Novatel Dual frequency GNSS receivers on ebay

[Christopher Hoover]

I have quite a bit of experience with Novatel hardware include OEM6, CPT
and SPAN.

CPT is an IMU made by KVH and relabeled by Novatel.The accelerometers
are MEMs and the roll rate sensors are FOGs.   Pretty old design.
Performance is decent (but not auto alignment good).

http://www.kvh.com/Military-and-Government/Gyros-and-Inertial-Systems-and-Compasses/Gyros-and-IMUs-and-INS/IMUs/CG-5100.aspx

SPAN is the "solution."SPAN-CPT puts the CPT IMU and the receiver in a
single box.   You could also get just the CPT in a box.

The feature set enabled depends on the software keys that are loaded.
Caveat emptor.

Dual receiver (even if you have the hardware) and ALIGN feature are extra
features.

Also worth noting is that the circular connectors used on some of the
hardware are pricey.  Some are impossible to assemble without specialty
tools.

-- Christopher.
73 de AI6KG


On Sat, Oct 7, 2017 at 2:36 PM, J. L. Trantham  wrote:

> Any idea what they are selling for at this time?
>
> I see that some sold for the BIN price of $349.99 up until June 20.  After
> that, 'Offer Accepted' occurred up through October 5, with a BIN price now
> of $649.99, all plus $40 shipping.
>
> Joe
>
> -Original Message-
> From: time-nuts [mailto:time-nuts-boun...@febo.com] On Behalf Of Gregory
> Maxwell
> Sent: Saturday, October 07, 2017 2:17 PM
> To: Discussion of precise time and frequency measurement
> Subject: [time-nuts] Novatel Dual frequency GNSS receivers on ebay
>
> There is an ebay listing for "Novatel GPS-702-GG with SPAN-CPT Single
> Enclosure GNSS/INS Receiver + Cable" with a fairly large number available.
>
> This is a Novatel OEM628 dual frequency receiver (supports GPS, Glonass,
> SBAS, apparently including L1C and L2C), plus a three fiber ring gyros
> (with bias performance that blows away any mems gyro I've ever used) and an
> 3-axis mems acceletrometer in an aluminum case, plus a decent dual
> frequency antenna.  This is a generation-ish old kit.
> The industrial casing conspires to make it look somewhat less modern than
> it actually is.
>
> The receivers have external clock input (though not plumbed to the outside
> of the case) which appears to work though I didn't try much with it yet.
> Mine came with 2013-ish firmware but easily upgraded to current (2016)
> firmware. There is a windows based firmware update tool which talks to it
> over serial and is very straight forward (The firmware update OEM6631.zip
> can be found via google).
>
> You can communicate with them over serial in ascii, there is extensive
> firmware documentation that goes over every command
> https://www.novatel.com/assets/Documents/Manuals/om-2129.pdf  some of
> which are specific to other modules. There is also a separate manual for
> the inertial navigation specific features (NovAtel SPAN-CPT Users
> manual.pdf)
>
> The external clock should allow you to hang it off a more stable
> oscillator which will improve the stability of the GNSS results, and _I
> presume_ improve the quality of the PPS output-- the firmware manual and
> operating manual are thin on details, and mostly just go into telling you
> how to adjust the kalman filter constants for different clock types.
>
> These also appear to support the novatel 'align' mode where you serial
> connect two receivers separated by a short baseline and get really accurate
> absolute headings; I'm planning on trying that that but haven't set it up
> yet.
>
> Looks like uber (last position was ubers offices in denver) had a fleet of
> these things. The couple I got run great, including the IMU, the antennas
> obviously spent a long time outside, but work fine. The cable they come
> with is weird, but I had no problem chopping one end off and figuring out
> the pinout (see bottom).
>
> The novatel OEM6 is well supported by rtklib and I was able to get
> post-processed positions very easily.
>
> Seller takes best offers a fair amount below the $649 asking price.
> Looks like they may have another 30 or so of them.
>
> May be useful for doing time transfer especially with the clock input.
> Just using it to get nice dual band observations to precisely survey an
> antenna location for a traditional GPSDO may improve GPSDO performance by a
> fair amount.
>
> Here is the signals and wire colors on the cables mine came with.
> YMMV, I'd suggest not blindly trusting that colors match on other
> units.These cables don't plumb out many of the signals from the
> module (in particular, they don't carrying COM2, which is why I haven't
> tried multi-receiver headings yet, since I'd need to figure out how to talk
> to it over USB if com1 is in use for that), I'm unsure if they're wired
> through the to external connector.
>
> 01 white  power return (-)
> 02 brown  9-18 VDC power input (+)
> 03 yellowCOM1 RS232 TX
> 05 pink   COM1 RS232 RX
> 09 green  COM1 GND
> 10 black  USB D+
> 11 purple USB D-
> 12 yellow 

Re: [time-nuts] precision frequency/time/amplitude reference

[David Witten]

Jim,

If I understand what you are attempting (I may well not), you might
consider the approach taken here:

https://github.com/tejeez/rtl_coherent

and here:

https://github.com/tejeez/rtl_coherent/blob/master/hardware/simple/README.md

or order a noise-source and antenna switches from here:

http://coherent-receiver.com/products/rtl-sdr-extension-card/noise-source

http://coherent-receiver.com/products/rtl-sdr-extension-card/antenna-switch

(disclaimer: no personal connection to above links)

Dave
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Re: [time-nuts] precision frequency/time/amplitude reference

[Mattia Rizzi]

Hi,
I did something similar when I had to deliver synchronization over IEEE
802.15.4-CSS (Chirp spread spectrum).
If you have SDR on both ends (TX & RX), you can use complex chirp signals
and then cross-correlation at RX. Just be sure that the multi-path is not
killing you (i.e. the cross-correlation peak has a width smaller than
multi-path echoes delay).
If you use up & down chirps, you can compensate the time-shift introduced
by carrier frequency offset (due to RF front-end).
To estimate clock frequency offset, well, just send a repetitive pattern.
Amplitude is easy as well.


cheers,
Mattia



2017-10-09 16:20 GMT+02:00 jimlux :

> I'm trying to come up with a relatively simple scheme to calibrate an HF
> antenna array - I've got a bunch of RTL-SDRs operating as a distributed
> array spread over a few 10s of meters.
>
> The things I want to do are:
> a) determine the phase/time offset between stations relative to other nodes
> b) determine the sample rate (clock rate) variation relative to other nodes
> c) determine the amplitude calibration (of each node).
>
> One of the schemes I cam up with was to take the output from the sample
> clock oscillator, divide it down to around 500 kHz or 1 MHz, and then use
> that to generate short pulses by switching a precision voltage reference.
>
> That pulse train (the spectrum of which is a comb with lots of harmonics)
> would be connected to the antenna of the node.
>
> So, I get a precise amplitude pulse train into my own node receiver - so I
> can calibrate my receiver gain.  And, I radiate a low power pulse train to
> the other nodes.  By looking at the digitized signal on the other nodes, I
> can figure out relative clock rate (and, to a lesser extent, whether the
> antenna has changed)
>
> This scheme seems to hang together, but a lot depends on that switch that
> turns my internal clock derived pulse train into a precise amplitude and
> edges.
>
> Off hand, it seems that almost any sort of transistor (BJT or FET) would
> work as long as the rise/fall time is fast enough to get the harmonic comb
> up high enough (I'm only interested up to, say, 50 MHz - yeah, the RTL-SDR
> will tune higher, but for this project I'm not so worried about that).
>
> I suppose too, that I could do a "bench calibration" of each unit the
> first time (to take out component/component variations in the switch), as
> long as the switch properties are stable, or at least vary in a known way.
>
> In terms of amplitude, the amplitude of the fundamental should be pretty
> stable, but I can see the relative amplitude of the high harmonics falling
> in precision - small changes in switch rise/fall time will affect that more.
>
> In terms of frequency, I think it should work fairly well - I tune the
> RTL's front end, look for my calibration combs that are "in band" and fit
> an appropriate function to the signal (there should be a well defined phase
> relationship between the harmonics)
>
> So, one remaining issue is how to get "time" out of this. Since the
> individual nodes are battery powered and not connected to a network in real
> time, I would assume that their internal clock is good to maybe 1 second.
> I was thinking I could try and encode a standard time code (Irig) on the
> pulses from my comb generator, either by changing the pulse rate, or by
> changing the pulse width?
>
> Any other clever ideas?
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> ailman/listinfo/time-nuts
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Re: [time-nuts] precision frequency/time/amplitude reference

[Bob kb8tq]

Hi

Pick a couple of local broadcast stations and record them. That will give you a 
baseline 
for each of the parameters you are after in real time. They *will* drift. 

Past that, I’d go with a sweep of each node before installation. That will give 
you the 
frequency response and (to some degree) a guess for noise and spurs. 

Bob



> On Oct 9, 2017, at 10:20 AM, jimlux  wrote:
> 
> I'm trying to come up with a relatively simple scheme to calibrate an HF 
> antenna array - I've got a bunch of RTL-SDRs operating as a distributed array 
> spread over a few 10s of meters.
> 
> The things I want to do are:
> a) determine the phase/time offset between stations relative to other nodes
> b) determine the sample rate (clock rate) variation relative to other nodes
> c) determine the amplitude calibration (of each node).
> 
> One of the schemes I cam up with was to take the output from the sample clock 
> oscillator, divide it down to around 500 kHz or 1 MHz, and then use that to 
> generate short pulses by switching a precision voltage reference.
> 
> That pulse train (the spectrum of which is a comb with lots of harmonics) 
> would be connected to the antenna of the node.
> 
> So, I get a precise amplitude pulse train into my own node receiver - so I 
> can calibrate my receiver gain.  And, I radiate a low power pulse train to 
> the other nodes.  By looking at the digitized signal on the other nodes, I 
> can figure out relative clock rate (and, to a lesser extent, whether the 
> antenna has changed)
> 
> This scheme seems to hang together, but a lot depends on that switch that 
> turns my internal clock derived pulse train into a precise amplitude and 
> edges.
> 
> Off hand, it seems that almost any sort of transistor (BJT or FET) would work 
> as long as the rise/fall time is fast enough to get the harmonic comb up high 
> enough (I'm only interested up to, say, 50 MHz - yeah, the RTL-SDR will tune 
> higher, but for this project I'm not so worried about that).
> 
> I suppose too, that I could do a "bench calibration" of each unit the first 
> time (to take out component/component variations in the switch), as long as 
> the switch properties are stable, or at least vary in a known way.
> 
> In terms of amplitude, the amplitude of the fundamental should be pretty 
> stable, but I can see the relative amplitude of the high harmonics falling in 
> precision - small changes in switch rise/fall time will affect that more.
> 
> In terms of frequency, I think it should work fairly well - I tune the RTL's 
> front end, look for my calibration combs that are "in band" and fit an 
> appropriate function to the signal (there should be a well defined phase 
> relationship between the harmonics)
> 
> So, one remaining issue is how to get "time" out of this. Since the 
> individual nodes are battery powered and not connected to a network in real 
> time, I would assume that their internal clock is good to maybe 1 second.  I 
> was thinking I could try and encode a standard time code (Irig) on the pulses 
> from my comb generator, either by changing the pulse rate, or by changing the 
> pulse width?
> 
> Any other clever ideas?
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[time-nuts] precision frequency/time/amplitude reference

[jimlux]

I'm trying to come up with a relatively simple scheme to calibrate an HF 
antenna array - I've got a bunch of RTL-SDRs operating as a distributed 
array spread over a few 10s of meters.


The things I want to do are:
a) determine the phase/time offset between stations relative to other nodes
b) determine the sample rate (clock rate) variation relative to other nodes
c) determine the amplitude calibration (of each node).

One of the schemes I cam up with was to take the output from the sample 
clock oscillator, divide it down to around 500 kHz or 1 MHz, and then 
use that to generate short pulses by switching a precision voltage 
reference.


That pulse train (the spectrum of which is a comb with lots of 
harmonics) would be connected to the antenna of the node.


So, I get a precise amplitude pulse train into my own node receiver - so 
I can calibrate my receiver gain.  And, I radiate a low power pulse 
train to the other nodes.  By looking at the digitized signal on the 
other nodes, I can figure out relative clock rate (and, to a lesser 
extent, whether the antenna has changed)


This scheme seems to hang together, but a lot depends on that switch 
that turns my internal clock derived pulse train into a precise 
amplitude and edges.


Off hand, it seems that almost any sort of transistor (BJT or FET) would 
work as long as the rise/fall time is fast enough to get the harmonic 
comb up high enough (I'm only interested up to, say, 50 MHz - yeah, the 
RTL-SDR will tune higher, but for this project I'm not so worried about 
that).


I suppose too, that I could do a "bench calibration" of each unit the 
first time (to take out component/component variations in the switch), 
as long as the switch properties are stable, or at least vary in a known 
way.


In terms of amplitude, the amplitude of the fundamental should be pretty 
stable, but I can see the relative amplitude of the high harmonics 
falling in precision - small changes in switch rise/fall time will 
affect that more.


In terms of frequency, I think it should work fairly well - I tune the 
RTL's front end, look for my calibration combs that are "in band" and 
fit an appropriate function to the signal (there should be a well 
defined phase relationship between the harmonics)


So, one remaining issue is how to get "time" out of this. Since the 
individual nodes are battery powered and not connected to a network in 
real time, I would assume that their internal clock is good to maybe 1 
second.  I was thinking I could try and encode a standard time code 
(Irig) on the pulses from my comb generator, either by changing the 
pulse rate, or by changing the pulse width?


Any other clever ideas?
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Re: [time-nuts] PRS10 PRBB Shematics

[Li Ang]

Hi Guys
   I have just bought 2 kinds of PRS10 connectors on taobao.com. (PCB type and 
cable type, refer to the attached photo). It is about 8$ each(the D-SUB + 
center RF part). If you are looking for it, I can send you the link off the 
list. 




Yours


Li Ang / BI7LNQ


-- Original --
From:  "Jacques Tiete";;
Date:  Mon, Oct 9, 2017 11:37 AM
To:  "TimeNuts";

Subject:  Re: [time-nuts] PRS10 PRBB Shematics



Thanks for the prompt reactions, in the mean time I understood Cannon 
connectors can be a real pain in the xxx :-) to figure out the right one. 

Jacques




Op 6 okt. 2017, om 23:19 heeft Jacques Tiete  het volgende 
geschreven:

Fellow timenuts,

I’d like to find some more info about the SRS “PRBB” breakout board for the 
PRS10, schematic diagram, parts list (eg. the cannon pcb connector used) and 
all relevant info.
An internet/timenuts research did not turn up anything relevant.


thanks & 73’s,

Jacques


Jacques Tiete
jacq...@tiete.org
GSM: 32(0)499 99 83 78




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