[time-nuts] Crude Survey Technique

johncroos at aol.com johncroos at aol.com
Fri Nov 22 16:16:33 UTC 2013


 Stephen -


 [time-nuts] Crude Survey Technique

 

 Thanks for describing your method. I am learning a lot. here is agovt web site that will give the compass correction for any long and lat. Here in KS the magnetic pole is about 2.3 degrees to the east.

Once all the ideas are in, I will put together a summary.

I have a number of the required tools, compass, several T-bolts, surveyor's transit, tall poles, laser level, and bulls-eye levels.
So with all of these good ideas I am sure I will get it right. It will be interesting to cross check the various methods.

It also occurred to me that I could buy a 3 ft length of hardened steel shafting, wrap a couple of dozen turns of # 6 around it and then connect it to a big lead acid battery via a 200 Amp fuse. Should result in a 3 ft long compass needle. You only get to use the fuse once though!

Thanks to all  -john

 

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Sent: Fri, Nov 22, 2013 6:29 am
Subject: time-nuts Digest, Vol 112, Issue 75


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Today's Topics:

   1. Re: Motorola M12+ (Azelio Boriani)
   2. Re: Isolation achieved by opamp based isoamp? (Bruce Griffiths)
   3. Re: DMTD: Mixer DC offset will result in time offset at
      zero-crossing detector out? (Bruce Griffiths)
   4. Re: Crude Survey Technique (Stephan Sandenbergh)
   5. Re: Strange 100ns jumps on Motorola M12+T (Bob Camp)
   6. Re: DMTD: Mixer DC offset will result in time offset at
      zero-crossing detector out? (Stephan Sandenbergh)


----------------------------------------------------------------------

Message: 1
Date: Fri, 22 Nov 2013 11:45:17 +0100
From: Azelio Boriani <azelio.boriani at screen.it>
To: Discussion of precise time and frequency measurement
	<time-nuts at febo.com>
Subject: Re: [time-nuts] Motorola M12+
Message-ID:
	<CAL8XPmPPU6e2g90veAFKzMDqVPMsE+qL+Uxr6+RcVHUueyd_Zg at mail.gmail.com>
Content-Type: text/plain; charset=ISO-8859-1

Strange item... it has an M12+ and a supporting board full of
components. Protocol translation from 12-channel to 8-channel? The
link to the PDF file returns a 404.

On Fri, Nov 22, 2013 at 9:32 AM, Pascual Arbona Lopez
<p.arbona at securimar.com> wrote:
> I am wondering if this is a sustitute of  the original oncore VP receiver for 
the Z3801 -Z3805. (E-pay 281161070304 )
> _______________________________________________
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------------------------------

Message: 2
Date: Sat, 23 Nov 2013 00:18:50 +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] Isolation achieved by opamp based isoamp?
Message-ID: <528F3D9A.5090903 at xtra.co.nz>
Content-Type: text/plain; charset=ISO-8859-1; format=flowed

Stephan Sandenbergh wrote:
> Something that would be interesting to know is if certain opamps are better
> suited toward S12 isolation than others. I guess at the expense of noise
> floor and 1/f corner one could cascade two opamps to improve the S12
> isolation further.
>
>    
The flicker noise corner of an opamp may be lower than you think.
Current feedback opamps may have higher flicker noise corners than volt 
feedback opamps
> As soon as you are looking at frequencies of 100MHz you are probably left
> with the discrete options in any way.
>    
There are 1GHz and 10GHz opamps available.

Bruce
>
> On 22 November 2013 11:45, Stephan Sandenbergh<ssandenbergh at gmail.com>wrote:
>
>    
>> Thanks for the spec. I suspected that it would be in that ball park.
>>
>> The discrete transistor type amplifiers achieve around 120dB or more at
>> 10MHz. But, they are a lot more effort to implement than the opamp designs.
>>
>> I believe the transformer in this case is for ground loop isolation rather
>> than S12 isolation.
>>
>>
>> On 21 November 2013 20:20, Charles Steinmetz<csteinmetz at yandex.com>wrote:
>>
>>      
>>> Corby wrote:
>>>
>>>   This opamp buffer has 80-90db isolation.
>>>        
>>>>          
>>> That is typical at 5 to 10 MHz *if* (i) all of the splitting is done on
>>> the input side (i.e., each output has its own op amp), and (ii) the
>>> splitter and all of the construction (grounds, shielding, etc.) is done
>>> correctly.
>>>
>>> If any splitting is done on the output side of the op amp(s), by using
>>> one op amp to drive more than one output through separate back terminating
>>> resistors, the outputs that share an op amp will only be isolated by 30 to
>>> maybe 40 dB (again, assuming that the op amp has been well chosen and all
>>> of the construction is done correctly).
>>>
>>> Best regards,
>>>
>>> Charles
>>>
>>>
>>>
>>>
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>>>        
>>
>>      
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>    



------------------------------

Message: 3
Date: Sat, 23 Nov 2013 00:15:15 +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: <528F3CC3.9010802 at xtra.co.nz>
Content-Type: text/plain; charset=UTF-8; format=flowed

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?
>    
>
>
> _______________________________________________
> time-nuts mailing list -- time-nuts at febo.com
> To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
> and follow the instructions there.
One can always add AC coupling to eliminate this effect as in 
http://www.wriley.com/A%20Small%20DMTD%20System.pdf

Bruce


------------------------------

Message: 4
Date: Fri, 22 Nov 2013 13:31:04 +0200
From: Stephan Sandenbergh <ssandenbergh at gmail.com>
To: Discussion of precise time and frequency measurement
	<time-nuts at febo.com>
Subject: Re: [time-nuts] Crude Survey Technique
Message-ID:
	<CADbj3vY8unLvjeE77Kh=T3pO5bGyUK=REjXeLEoRM-P+=425mw at mail.gmail.com>
Content-Type: text/plain; charset=UTF-8

John,

We had a similar problem when we're trying to setup various antennas at
various locations pointing at different true North bearings. It turned out
quite hard to find true North.

We found single carrier GPS surveyed points to be inaccurate to produce
good bearings across such a short base line. Also, you'll end up with two
points with some bearing w.r.t. North. Now the problem is that of finding a
third point to give you your N-S base line.

In the end we used a tripod, calibrated gun sight and a turn table with
degrees markings (those that the photonics people use). If you'd like to
use this method, you survey a single point on your property (preferably on
the base line your interested in). Also survey a land mark, like a radio
mast a few km's away. The further away (the longer the base line) the less
accurate your surveyed points need to be. Now calculate the North
bearing of this base line using these two points. Now back at your property
at the surveyed point, point your cross hair at the radio mast and set the
number of degrees on the turn table to that you have calculated. Fix the
turn table. 0 degrees should now be true North, and you could now use the
cross hair to survey the other point.

The tripod should be levelled very carefully, since errors here will put
you in a different plane and you will end up calculating vector components
in that plane.



On 21 November 2013 20:52, <johncroos at aol.com> wrote:

>  I wish to establish a north south line on my property to an accuracy of
> +/- 2 degrees.
> Could this be done by loading a T-bolt, Antenna, Power source, and laptop
> into my
> little red wagon? The idea being to find two positions several hundred ft
> apart where either LH or T-bolt Mon report the same latitude? Will either
> of these programs report to sufficient accuracy? The base line would be 300
> ft, though more is possible.I realizes that the T-bolt is not a survey
> device, but I can spend several hours fixing each position if required.
>
> All comments appreciated.?? -73 john k6iql
>
>
>
>
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------------------------------

Message: 5
Date: Fri, 22 Nov 2013 07:06:28 -0500
From: Bob Camp <lists at rtty.us>
To: Discussion of precise time and frequency measurement
	<time-nuts at febo.com>
Subject: Re: [time-nuts] Strange 100ns jumps on Motorola M12+T
Message-ID: <01D166A8-D93A-4B4D-B195-606A6A0DE906 at rtty.us>
Content-Type: text/plain; charset=windows-1252

Hi

Something is going wrong somewhere. The question is where.  Three ideas / 
targets here:

The counter is a 100 ns (10 MHz input) beast, so it *might* be the issue. 

The offset source or the GPS might also be the issue (thus avoiding 1/10.24 
MHz).

The idea with the larger offset is that there is no significant accuracy 
degradation with a modest increase in the offset. The exact value isn?t the 
issue there, just making it larger. That way you will still properly capture 
stuff in the 100 (or more) ns range. 

Bob

On Nov 22, 2013, at 4:38 AM, Stephan Sandenbergh <ssandenbergh at gmail.com> wrote:

> Hi,
> 
> Ok, the 53131A trigger settings: I've turned auto trigger off and set it to
> trigger at 2V (I think this is right, but I'll have to go and double check
> the exact threshold setting) threshold. Sensitivity is set to high.
> 
> Location is GPS surveyed and all M12+'s are set to position hold mode.
> 
> I did record the time stamped GPS data as well so will go have a look at
> what happened to the constellation at the time of the jumps. Will post when
> I have results.
> 
> Sorry if I'm a little slow here, but why is it better to use larger
> offsets? Also I get that 100ns is exactly one cycle of 10MHz, but why would
> the 53131A have trouble with this? Surely it uses linear interpolators
> along with digital counters to calculate the result. Also, I assume the
> counting doesn't happen at 10MHz, but at a much higher multiple. Had it
> been done at 10MHz I'd understand that skipping a beat would result in
> 100ns offset. Granted I don't know much about the innards of the 53131A.
> 
> 
> 
> 
> On 22 November 2013 02:25, Bob Camp <lists at rtty.us> wrote:
> 
>> Hi
>> 
>> To be clear - the idea of going to a non-100 ns multiple is a good one.
>> You probably should avoid multiples of 1/10.24 MHz as well.
>> 
>> Bob
>> 
>> On Nov 21, 2013, at 8:00 AM, Azelio Boriani <azelio.boriani at screen.it>
>> wrote:
>> 
>>> Yes, do not use tiny offsets, go to 1us: I use microseconds offsets to
>>> take PPSes measurements .
>>> 
>>> On Thu, Nov 21, 2013 at 1:34 PM, Bob Camp <lists at rtty.us> wrote:
>>>> Hi
>>>> 
>>>> The counter and offset generator both should be quite accurate at a 1
>> us offset. That?s large enough that you are outside the range of most GPS
>> jumps. If you are going to move things around, you might as well move out
>> to that vicinity.
>>>> 
>>>> Bob
>>>> 
>>>> On Nov 21, 2013, at 6:20 AM, Tom Van Baak <tvb at LeapSecond.com> wrote:
>>>> 
>>>>>> Below is a plot so you could see exactly what I measured. What is
>> peculiar
>>>>>> is that the time jumps by exactly 100ns to 200ns. Almost as if the GPS
>>>>>> receiver decides to offset the time by twice the amount I set it to.
>> Which
>>>>>> is why I initially thought it might be a firmware thing. I suppose
>>>>>> multipath is a good explanation, it is just odd that the time error is
>>>>>> exactly 100ns.
>>>>> 
>>>>> Hi Stephan,
>>>>> 
>>>>> A quick test you could perform is set the offset to 125 ns instead of
>> 100 ns and see if the jumps still occur, still occur at 100 ns, or now
>> occur at 125 ns.
>>>>> 
>>>>> Since you have three M12's offset the third one by 150 ns and see if
>> it experiences jumps too.
>>>>> 
>>>>> Question -- are you using the external 10 MHz reference input or
>> output for any of your 53131A counters?
>>>>> 
>>>>> /tvb
>>>>> 
>>>>> _______________________________________________
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------------------------------

Message: 6
Date: Fri, 22 Nov 2013 14:19:26 +0200
From: Stephan Sandenbergh <ssandenbergh at gmail.com>
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:
	<CADbj3vbCUL=MGnsLQadyjmcmpjnEN1JzT=KA=anvnSuJNwNo+g at mail.gmail.com>
Content-Type: text/plain; charset=UTF-8

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)?

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?
>>
>>
>> _______________________________________________
>> time-nuts mailing list -- time-nuts at febo.com
>> To unsubscribe, go to https://www.febo.com/cgi-bin/
>> mailman/listinfo/time-nuts
>> and follow the instructions there.
>>
> One can always add AC coupling to eliminate this effect as in
> http://www.wriley.com/A%20Small%20DMTD%20System.pdf
>
> Bruce
> _______________________________________________
> time-nuts mailing list -- time-nuts at 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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