[time-nuts] Tbolt altitude error

Bruce Griffiths bruce.griffiths at xtra.co.nz
Thu Jan 14 22:06:04 UTC 2010


Eventually the flicker noise of most amplifiers (apart from chopper 
stabilised and related amplifiers) will exceed the noise of a resistor.
The internal zener noise will in most cases be much larger than 
amplifier noise.

The output noise (due to the filter components) of an RC low pass filter 
is SQRT(kT/C) where C is the filter capacitance.
For C ~ 1uF the noise is ~3.7 nV rms.
Such noise will add about 3.7E-17 additional FM noise to an HP10811A if 
applied directly to the EFC input.
This additional noise several orders of magnitude less than the effect 
of other noise sources, so the filter noise is unlikely to be a 
significant issue.
However the noise due to the resistor used to add a zero to the filter 
response is not filtered by the loop filter capacitor.
Only the low pass filter at the amplifier output and that within the EFC 
circuit affects this.

Bob Camp wrote:
> Hi
>
> Back when the Z3801 was new, some GPS's would let you pick a specific geoid
> model to use for altitude. Apparently it's a receiver side choice of what
> model to use.
>
> Bob
>
> -----Original Message-----
> From: time-nuts-bounces at febo.com [mailto:time-nuts-bounces at febo.com] On
> Behalf Of John Green
> Sent: Thursday, January 14, 2010 4:36 PM
> To: time-nuts at febo.com
> Subject: Re: [time-nuts] Tbolt altitude error
>
> I had a Tbolt and a Z3801 both fed from the same antenna and they indicated
> 26 meters differenence in altitude. The 3801 seemed closer to right. If
> geoid error were the cause, it seems that both would indicate about the
> same.
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