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

Magnus Danielson magnus at rubidium.dyndns.org
Wed Oct 10 23:03:06 UTC 2012


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.

>>> 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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