On 10/11/2012 12:03 AM, Bob Camp wrote:
On Oct 10, 2012, at 5:05 PM, Magnus Danielson<[email protected]>
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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