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

Bob Camp lists at rtty.us
Wed Oct 10 18:03:35 EDT 2012


On Oct 10, 2012, at 5:05 PM, Magnus Danielson <magnus at rubidium.dyndns.org> wrote:

> On 10/10/2012 01:09 PM, Bob Camp wrote:
>> Hi
>> 
>> …. and if we have to go to something more exotic than simple two pole filters the group delay (and it's variation) has got to go up.
> 
> Yes and no.
> 
> As you add pole-pairs, their group delay contributions adds up. However, as you add pole-pairs you also get a pair of zeros for the slopes (typically located in 0 and infinity for band-pass response) and you can back off considerably in Q values, and aim for maximum flat group delay in the pass-band. See the difference between the amplifiers in the article.
> 

Unless you need to go to something with sharp skirts. Then you are likely to start from a fairly high Q lowpass prototype and add a delay equalizer. Starts to add up pretty fast...

>> At least some of the HP splitters have RF filters in them. The same is true of GPS receivers. A receiver or splitter in the attic will have many of the same group delay issues as an antenna. I know, who would put one in the attic. Just how warm does that rack get as the air-conditioning cycles and the vents clog up?
> 
> The filters do add up, true. But then one should also recall the cable in the total, as covered by others.

indeed, but it's a bit tough to keep the cable all indoors.
> 
> Cheers,
> Magnus
> 
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