[time-nuts] To use or not to use transmission line splitters for GPS receivers

Magnus Danielson magnus at rubidium.dyndns.org
Wed Oct 10 08:11:54 UTC 2012


Hi!

I forgot to mention, but the peak group delay of a pole pair is d_peak = 
2*Q/w0 = Q / (pi * f0)

Hence, the group delay increases linearly with increasing Q values. 
Shift the Q, and your delay vary, shift the center-frequency, and you 
dip off the peak.

Cheers,
Magnus

On 10/09/2012 10:55 PM, Magnus Danielson wrote:
> On 10/09/2012 09:27 PM, John Ackermann N8UR wrote:
>> Here's a link to a USNO paper that measured the tempco of three GPS
>> amplifiers: http://www.dtic.mil/cgi-bin/GetTRDoc?AD=ADA490830
>>
>> They found that amplifier filtering was the prime cause of tempco, and
>> the narrowest bandpass amplifier they looked at had a group delay range
>> of 4 nanoseconds over the range of -15 to +45 degrees C.
>
> This is a good paper. I've read it before. It presents three strategies
> for GPS amplifiers:
>
> 1) Wide-band amplifier, represented by the AOA Wideband amplifier
> 2) Narrow-band amplifier with peaks, represented by the AOA narrow band
> amplifier
> 3) Narrow-band amplifier with no peaks, represented by the KW microwave
> phase-stable narrow band amplifier.
>
> The wide-band amplifier has around 4 ns group delay, and it is fairly
> flat and stable. Since there isn't much delay to start with, it doesn't
> change a whole lot either. Since the amplifier isn't very flat, it also
> has some variations in group delay. It's fairly natural. The downside is
> that it has no suppression of interference, so we should do some damping.
>
> The second case tries to achieve just that, but in order to create steep
> slopes around the pass-band, they have used two resonances, one on each
> side of the pass-band. You see the peaking effect on the gain curve of
> figure 1, but oh... they show up clearly in the group delay measurement
> of figure 2 too. This is expected from the theory, as these two
> pole-pairs has fairly high Q, their group delay will show this property
> in the direct vicinity of their respective resonances, just as their
> contribution to gain will do. So, nice steep slopes and good
> suppression, but lots of group delay, and by that higher sensitivity to
> environmental effects, i.e. temperature.
>
> The third example shows wider but much flatter amplitude response, and
> essentially flat group delay. This is what you expect from maximum flat
> group delay filters such as Bessel/Thompson. No wonders those are
> specified as measuring filters for digital transmission. Lesser delay,
> and lesser sensitivity. The downside is that the cost of steep slopes
> comes from a higher number of needed poles/zeros.
>
> Just as I expect from traditional signal theory.
> Again, you get what you pay for.
>
> Now you know why I want a network analyzer reaching this area at home.
>
> Cheers,
> Magnus
>
> _______________________________________________
> 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.





More information about the Time-nuts_lists.febo.com mailing list