Jean-Daniel HB9AKQ wrote:
On 22 mar, 16:17, Leon wrote:
On Mar 22, 9:49 am, Jean-Daniel HB9AKQ wrote:
Hello,
I am in the process of choosing a technology for a crystal filter in
that frequency range. I am facing the choice of buying a filter and
paying the price, or to build a filter myself.
The questions I am facing are these:
1) Do the MQF (Monolytic Crystal Filter) withstand high level signals,
like 1 mW or more, and what is their shape on the frequency domain (do
they go steeply down and do they have parasitic responses) ?
2) I am actually ready to try one of the lattice crystal filters as
described by Rhode in his may 1981 article (I can send you a copy for
the asking), where there are 4 crystals in 2 pairs separated in
frequency by about the 2 thirds of the desired passband. I would find
the crystals by sorting out batches of crystals on the frequency
meter. One can put 2 of these filters in series separated by a 1-dB
resistive pad (8 crystals total). Any experience to report on these
filters?
3) How good are ladder filters with overtone crystals? I do know that
ladder filters with such crystals are excellent on their fundamental
(3rd overtone crystals), but can you have them filter on the overtone,
with a tuned circuit up front ?
It's quite easy to buy 40 MHz fundamental crystals, which could be
used for a ladder filter.- Masquer le texte des messages précédents -
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Oh, I'll check that out, the highest I saw was around 24MHz at 1mW,
but I also quite a few at Digikey's going to 50MHz,but I do not know
if they are overtone or not. In any case they withstand only 50 or 200
uW, which is not enough for an up-conversion roofing filter that gets
dBm galore
The power ratings on crystals are their allowable _dissipation_, not the
amount that can be going _through_ them. So you want to look at the
amount of power being lost in the filter to estimate capabilities, not
the amount of power being dissipated at your load.
--
Tim Wescott
Wescott Design Services
http://www.wescottdesign.com
Do you need to implement control loops in software?
"Applied Control Theory for Embedded Systems" gives you just what it says.
See details at
http://www.wescottdesign.com/actfes/actfes.html