[time-nuts] Common-View GPS Network

[Jim Lux]

On 4/15/13 8:36 PM, Chris Albertson wrote:
> On Mon, Apr 15, 2013 at 8:23 PM, Tom Van Baak <tvb at leapsecond.com> wrote:
>
> I'd be curious what level of improvement is possible. It will depend on the
>> receiver and the antenna. I believe the NIST project uses fancy antennas
>> but normal M12 receivers. So there's hope for the amateur.
>>
>
> The M12 is certainly affordable, something like $60. but what is a "fancy
> antenna"?  How are they different from a normal timing antena?
>


Probably a choke ring? With small variation in phase center over viewing 
angles.  The "secret sauce" is in the design of the crossed dipole 
elements which are not flat, nor are they constant width.

http://facility.unavco.org/kb/questions/311/Choke+Ring+Antenna+Calibrations 
has dimensions

fins are 50-63 mm tall, 25 mm apart, etc.

I suspect that this is not a high precision sort of thing.. (that is, if 
your fin spacing isn't exactly 25.1 mm it doesn't make much difference)

L1 is 1575 MHz (approx) or a wavelength of 19 cm.  So the fins are 0.315 
to 0.26 lambda high and 0.13 lambda apart.  If you were making a fancy 
corrugated horn, you make the fins range from 1/2 lambda to 1/4 lambda 
so you get a nice transition from shorted to open, but that's not what 
they're doing here.