[time-nuts] tracking position & orientation

[Bob kb8tq]

Hi

The “cheap” approach these days is to use a uBlox ZED-F9P 

https://www.digikey.com/products/en/rf-if-and-rfid/rf-evaluation-and-development-kits-boards/859?k=F9P <https://www.digikey.com/products/en/rf-if-and-rfid/rf-evaluation-and-development-kits-boards/859?k=F9P>

along with one (or more) the <$100 eBay antennas. You take 24 hour data 
runs and ship them off to any of several free analysis outfits. One is NRCan.
There are a lot of others. They all do a fine job.

Bob



> On Nov 21, 2019, at 3:13 PM, Eric Scace <eric at scace.org> wrote:
> 
>   I need another project like a hole in the head — but curiosity continues to nag me.
> 
>   I moved to Boulder CO a few months ago. The “curiosity” is to determine the position of two antennas at either end of my house and monitor it over time, with the idea that one could see plate movement in 3 dimensions plus rotation around the axes.
> 
>   What hardware/software would be suitable for a TimeNuts (PositionNuts?) project like this?
> 
> — Eric K3NA
> 
> 
>> On 11/21/19 8:00 AM, Bob kb8tq wrote:
>> Hi
>> 
>> Way back in time, the first gear out there to use what we now look at as “normal” antennas 
>> was survey gear. For various reasons they decided on a 12V power supply and 40 to 50 db
>> of gain in the preamp mounted in the antenna. They also got into L1 / L2 pretty quickly. 
>> 
>> A bit later the cell phone (and later broadcast) guys got into this. In a location with a lot of 
>> RF (like a cell site) having a lot of gain at the antenna didn’t work all that well. IMD issues 
>> got into the act pretty quickly. In addition, front end filtering was required to reduce overload
>> issues. The focus was on L1 only so filtering was relatively easy.
>> 
>> There is a whole separate set of antennas that put a big chunk of the RF portion of the radio
>> in the antenna. Those still survive here and there. I have one of them and probably a couple
>> of dozen of the more “normal” antennas. 
>> 
>> As time marched on, supplying 12V to antennas became a bit less popular. Most of the cell 
>> guys went over to a 5V antenna supply. The net result was 12V 50 db survey antennas that did 
>> L1/L2 and much smaller 5V 25 db antennas for “timing”. The timing antennas didn’t do L1/L2 so
>> not going to work for survey. The survey antennas had way to much gain and no filtering so 
>> not going to work for a cell site. 
>> 
>> Indeed things did and do get crossed up in various pro and basement systems. With care and
>> the right set of circumstances things may work. In other cases the result can be an ongoing set
>> of systems issues over an entire network of stations. 
>> 
>> Prices for a good new survey antenna are up in the many thousands of dollars range. They have
>> very stable phase centers and (usually) test results to allow correction of any residual phase 
>> issues. This is part of what lets you get into the “couple of mm” range on a survey. 
>> 
>> For timing, you have to dig a bit and answer a few questions. Is your concern how close you
>> are to BIH? If so you will need to know all the delays in your system. This includes the delays
>> in the antenna filters and the preamp. Is your concern (or measure) the ADEV at 1 second?
>> If so the delays are not a concern. Your antenna choice may be a bit different depending on
>> this focus.
>> 
>> Bob
> 
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