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

Bob Camp lists at rtty.us
Wed Oct 10 23:06:01 UTC 2012


On Oct 10, 2012, at 7:03 PM, Magnus Danielson <magnus at rubidium.dyndns.org> wrote:

> On 10/11/2012 12:03 AM, Bob Camp wrote:
>> 
>> 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...
> 
> True.
> 
> But we are talking about wise design for GPS antenna use.

…. unless we suddenly need much steeper skirts due to a change in band allocations.

> 
>>>> 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.
> 
> Indeed it is, which is why it may contribute significantly unless done with care. I do know those that temperature stabilizes both the concrete pillar and cable conduct.
> 
> Cheers,
> Magnus
> 
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