[time-nuts] Crude Survey Technique
johncroos at aol.com
johncroos at aol.com
Fri Nov 22 22:04:27 UTC 2013
Hello and thanks to all for the great ideas.
Re: [time-nuts] Crude Survey Technique
Some interim comments:
*agree with regard to using pole star. However it is below freezing here and so I won't be out in the dark with my camera. A good verification technique that must await warmer weather!!
*thanks for the suggestion re. the transit. Unfortunately the elevation measurement only goes to 30 degrees and I am at 38.7 degrees latitude. I should have bought the one with more elevation range and a built in precision compass. Still might do that.
*I have a Stocker and Yale Army compass - nice thing but 2 degrees is probabily beyond its capability except as a sanity check
*Forced my T-bolt to find itself 9 times in the last 24 hours:
Average Longitude : -94.70983
Extreme Spread :000090 degrees
Standard Devation : 2.58 e-5 degrees
At my latitude 1 degree is 285,402.9 Ft
So the error at 1 standard deviation is 7.4 ft.
Who ever guessed 10 ft has achieved GURU status.
So doing the ATAN at various ranges we get
200 ft 2.12 degrees
400 ft 1.06 degrees
600ft 0.71 degrees.
400 ft is easy and 600 is possible. However the sun shadow method seems an equally good approach.
Question - If I use 3 T-bolts on the same antenna, feedline, splitter etc. and run 3 instances of T-bolt mon - can the results be improved???
Thanks for all the help - john k6iql
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To: time-nuts <time-nuts at febo.com>
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Today's Topics:
1. Re: Crude Survey Technique (Robert Atkinson)
2. Re: DMTD: Mixer DC offset will result in time offset at
zero-crossing detector out? (Bruce Griffiths)
3. Re: Isolation achieved by opamp based isoamp? (Charles Steinmetz)
4. Re: Off-Topic Question -- German Composition Resistors
(Didier Juges)
5. Re: Thunderbolt Simulator (paul swed)
6. Re: Crude Survey Technique (Brian Lloyd)
----------------------------------------------------------------------
Message: 1
Date: Fri, 22 Nov 2013 17:06:51 +0000 (GMT)
From: Robert Atkinson <robert8rpi at yahoo.co.uk>
To: Discussion of precise time and frequency measurement
<time-nuts at febo.com>
Subject: Re: [time-nuts] Crude Survey Technique
Message-ID:
<1385140011.91089.YahooMailNeo at web171902.mail.ir2.yahoo.com>
Content-Type: text/plain; charset=iso-8859-1
Hi Jim,
I disagree, the Medium Landing Compass IS accurate to better than 30 minutes
(0.5deg). This is also the smallest graduation so it can be read to better than
15 minutes. The calibration chart is given to 10 minutes every 15 degrees. It
does of course indicate the orientation of the local magnetic field. To ensure
there is no local distortions you need to do a site survey. This can be acheived
by comparing bearings to a distant object along a baseline or taking reciprical
bearings. CAA CAP562 part 8 leaflet 1 http://www.helitavia.com/docs/CAP562_2007_08.pdf?
has lots of good info.
(full version here http://www.caa.co.uk/docs/33/CAP562RFS.pdf? large file over
10MB)
Robert G8RPI (CEng, licenced aircraft engineer for 30 years, I've done many
aircraft swings)?
________________________________
From: Jim Lux <jimlux at earthlink.net>
To: time-nuts at febo.com
Sent: Friday, 22 November 2013, 14:25
Subject: Re: [time-nuts] Crude Survey Technique
On 11/21/13 11:32 PM, Robert Atkinson wrote:
> I'd also go for a compass if you want magnetic north, but then I have a good
one, a "medium landing compass". Mine dates from WWII but they are still made
http://www.sirs.co.uk/ground/landing_compasses/patt2/landing_resource
> These are used to align the standbay and remote reading compasses on aircraft.
Good to half a degree. If you need better ther is the Watts Datum Compass.
>
> Robert G8RPI.
That compass is *precise* to 1/2 degree, but not *accurate* to 1/2
degree. It comes with a calibration card, and is presumably used in a
place with a uniform field (e.g. for calibrating an aircraft compass,
which is done in an open area with no known magnetic anomalies).? If
you're in a different environment, the card values may be incorrect.
It is essentially as "comparison standard".? You put it next to the
aircraft and move both in a systematic pattern and you use it to
"calibrate out" the variations in the plane's internal compass.
However you're going to be subject to the local magnetic field anomalies
(and they're surprisingly large).
http://minerals.usgs.gov/news/newsletter/v1n2/3aeromag.html
On the 1km scale maps in the USGS reports, you can see magnetic
anomalies of 500 nT.? Earth's field is about 30-60 microTesla, so these
anomalies are in the "one part in 100" kind of range.? It is true that
the gradient is fairly small: It is unlikely you have an anomaly of 500
nT and your neighbor has -200 nT. But it's obvious that the magnetic
variation (angle between true and indicated magnetic north) isn't the
nice smooth surface implied by the map of variation you get with the
compass.
http://dspace.sunyconnect.suny.edu/bitstream/handle/1951/47859/Winslow_MS.pdf;jsessionid=7D7A116045A54816C9DCF963AF3D2580?sequence=1
is a short paper that talks about gradients in a small scale anomaly of
0.22 nT/meter? (and I get the impression that that is big).
There's also other locally produced magnetic fields you'd have to worry
about.
I gave an E&M class a problem to figure out if you could tell whether
you could use a hand compass to tell if the Pacific Intertie 1MV HVDC
link (3000 A) was operating bipolar or unipolar. (at 50 meters, the
field from one wire is about 6 microTesla, so yes, you can detect it)
http://msi.nga.mil/MSISiteContent/StaticFiles/HoMCA.pdf
is all about calibrating a ship's compass
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Message: 2
Date: Sat, 23 Nov 2013 06:29:01 +1300
From: Bruce Griffiths <bruce.griffiths at xtra.co.nz>
To: Discussion of precise time and frequency measurement
<time-nuts at febo.com>
Subject: Re: [time-nuts] DMTD: Mixer DC offset will result in time
offset at zero-crossing detector out?
Message-ID: <528F945D.80902 at xtra.co.nz>
Content-Type: text/plain; charset=ISO-8859-1; format=flowed
Stephan Sandenbergh wrote:
> Hi,
>
> Thanks - mystery solved. This is one of the systems that I looked at,
> and missed the DC block in the second amplification stage. I guess it is
> possibly a large Ceramic 10uF. My bad.
>
> Thank you for putting up those web pages I find them to be very good
> references. I spent quite a lot of time reading through them.
>
> Something that puzzles me though is your mixer termination (
> http://www.ko4bb.com/~bruce/LowNoiseMixerPreamp.html). What is the logic in
> having the second balun (and connected in that way)?
>
>
1st section is common mode low pass filter, 2nd section is differential
common mode low pass filter.
Bruce
> Regards,
>
> Stephan.
>
>
> On 22 November 2013 13:15, Bruce Griffiths<bruce.griffiths at xtra.co.nz>wrote:
>
>
>> Stephan Sandenbergh wrote:
>>
>>
>>> Hi,
>>>
>>> I'm playing with dual-mixer time difference stuff again. And, came across
>>> this and I find it somewhat puzzling since no one else seems to have
>>> encountered it. Possibly because I'm missing something?
>>>
>>> The doubly balanced mixers (of the type known to be used in DMTDs and
>>> phase
>>> noise measurement systems) are known to have DC offsets. So much so that
>>> the guys doing phase noise measurements employ elaborate DC removal
>>> circuits in their preamps to combat this.
>>>
>>> Here's my question: why isn't this DC offset removed in any DMTD circuits
>>> I've seen? It seems standard practice to attach the filtered mixer output
>>> directly to the zero crossing detector.
>>>
>>> I did a quick simulation (see attached):
>>>
>>> The mixer beat is a 10Hz sine 0.7Vpp. If you then use a Collins style zero
>>> crossing detector the first stage will have a small gain (I chose a gain
>>> of
>>> 2.83 from Bruce Griffiths pages (
>>> http://www.ko4bb.com/~bruce/ZeroCrossingDetectors.html)). I then compare
>>> this ideal signal to that of a similar one that is offset by 40mV. Notice
>>> the asymmetry in the signal due to offset.
>>>
>>> 40mV result in 1.8ms offset
>>> 4mV result in 180us offset
>>>
>>> Obviously, once the time offset is there no amount of subsequent slope
>>> amplification will remove it.
>>>
>>> I've tested this in practice and bingo, I now have a very accurate way of
>>> plotting relative mixer DC offset over time.
>>>
>>> Any comments?
>>>
>>>
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>>>
>> One can always add AC coupling to eliminate this effect as in
>> http://www.wriley.com/A%20Small%20DMTD%20System.pdf
>>
>> Bruce
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>>
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------------------------------
Message: 3
Date: Fri, 22 Nov 2013 12:33:43 -0500
From: Charles Steinmetz <csteinmetz at yandex.com>
To: Discussion of precise time and frequency measurement
<time-nuts at febo.com>
Subject: Re: [time-nuts] Isolation achieved by opamp based isoamp?
Message-ID: <20131122214450.in9mIASU at smtp14.mail.yandex.net>
Content-Type: text/plain; charset="us-ascii"; format=flowed
Stephan wrote:
>The discrete transistor type amplifiers achieve around 120dB or more
>at 10MHz.
Well, SOME discrete transistor amplifiers CAN achieve 120dB or more
of reverse isolation, if everything is done properly. But 120dB or
more takes careful attention to detail at every step -- it is very
far from automatic.
Best regards,
Charles
------------------------------
Message: 4
Date: Fri, 22 Nov 2013 13:34:00 -0600
From: Didier Juges <shalimr9 at gmail.com>
To: Robert Atkinson <robert8rpi at yahoo.co.uk>, Discussion of precise
time and frequency measurement <time-nuts at febo.com>
Subject: Re: [time-nuts] Off-Topic Question -- German Composition
Resistors
Message-ID:
<CAMQqFu=TcLbDGD5t8WgPEUiyRfjVOG6-TCSd5pdPsx+-VT-7bg at mail.gmail.com>
Content-Type: text/plain; charset=ISO-8859-1
Must have been Allen Bradley :)
Same problem here with military equipment!
On Thu, Nov 21, 2013 at 4:17 PM, Robert Atkinson <robert8rpi at yahoo.co.uk>wrote:
> May be a bit of drift and reading back to front. Some years ago we bought
> a quantity of moulded carbon compostion resistors from a top US
> manufacturer. A sample check showed that none of them met the 10%
> tolerance. The maufacturer said "bake them for a day two"! The resistors
> then passed. Why not replace them with modert types you ask? Type approved
> equipment with the original designers long gone and the current type
> certificate holder unwilling or unable to approve the change. Welcome to
> the world of aviation where we are still supporting equipment designed 50
> or more years ago.
>
> Robert G8RPI.
>
>
>
>
> ________________________________
> From: Adrian <rfnuts at arcor.de>
> To: Discussion of precise time and frequency measurement <
> time-nuts at febo.com>
> Sent: Thursday, 21 November 2013, 20:53
> Subject: Re: [time-nuts] Off-Topic Question -- German Composition Resistors
>
>
> Hi Bruce,
> no. Same color code here.
> However, certain carbon composition resistors from the 60's/70's are
> notoriously unreliable. The common effect is drift to significantly
> higher values. Besides that, they can get pretty noisy.
> Adrian
>
> Brucekareen at aol.com schrieb:
> > While tracing out a PC board from an instrument manufactured in Germany,
> I
> > quickly discovered the color code on 1/4-watt composition resistors is
> not
> > the same as that commonly used in the US For example, I would measure
> > about 10,000-ohms across a presumably good resistor that appeared to be
> marked
> > 2700-ohms. Has/does Germany used a different code for such parts?
> >
> > Bruce, KG6OJI
> > _______________________________________________
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> >
>
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------------------------------
Message: 5
Date: Fri, 22 Nov 2013 14:28:04 -0500
From: paul swed <paulswedb at gmail.com>
To: Discussion of precise time and frequency measurement
<time-nuts at febo.com>
Subject: Re: [time-nuts] Thunderbolt Simulator
Message-ID:
<CAD2JfAgrHU_XpT2W=TSvmFTF6D_gRTejEA47+yLfu-YXwG26tA at mail.gmail.com>
Content-Type: text/plain; charset=ISO-8859-1
Link is good
Thanks again
On Fri, Oct 25, 2013 at 3:32 PM, Didier Juges <shalimr9 at gmail.com> wrote:
> In order to test my upcoming Thunderbolt Monitor, I developed a small piece
> of software to allow me to generate controlled Primary and Supplemental
> timing packets per the Trimble spec.
> I think the result may be useful to those who own Trimble Tunderbolt
> monitoring tools, so I decided to make it available.
> It is very much beta at this point, but during my testing, I could not make
> it fail when talking to the Trimble Thunderbolt Monitor software.
> You can download it from
> http://www.ko4bb.com/Timing/GPSMonitor/TBoltSim.php
>
> Let me know how it goes via direct message, no need to bog the list down
> with this.
>
> Didier KO4BB
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------------------------------
Message: 6
Date: Fri, 22 Nov 2013 11:19:51 -0600
From: Brian Lloyd <brian at lloyd.com>
To: "jfor at quikus.com" <jfor at quikus.com>, Discussion of precise time
and frequency measurement <time-nuts at febo.com>
Subject: Re: [time-nuts] Crude Survey Technique
Message-ID:
<CAE3hgTdk3+g-hjik8EkgSf6TuXxtVqHxUF3zKzGrNZ_HFi=vfA at mail.gmail.com>
Content-Type: text/plain; charset=ISO-8859-1
On Friday, November 22, 2013, J. Forster wrote:
> If the telescope on your transit can go to your lattitude, sight Polaris
> and you're done after a simple calculation.
This is the simplest high-accuracy solution. Celestial navigation is your
friend.
A magnetic compass is the simplest solution. Magnetic variation is found on
all VFR aviation navigation charts.
2 degrees is an interesting number. It seems either too accurate or not
accurate enough for most applications I can think of.
<https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts>
--
Brian Lloyd, WB6RQN/J79BPL
706 Flightline Drive
Spring Branch, TX 78070
brian at lloyd.com
+1.916.877.5067
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