45-70MHz crystal filters, MQF,lattice,ladder?
 

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 ?

Thanks for the comments
Jean-Daniel HB9AKQ

45-70MHz crystal filters, MQF,lattice,ladder?
 

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.

45-70MHz crystal filters, MQF,lattice,ladder?
 

Jean-Daniel HB9AKQ ) writes:
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.

Are you hoping/expecting to get a narrow filter out of this, or will
it be a roofing filter, with the real selectivity at a different frequency?

I thought there were limitations on selectivity at those frequencies.
I can't recall ever seeing a narrow filter up there (and while it's been a
long time since I read that QST article, which is the only article in
the ham magazines that I've seen about making crystal filters that high
up, I thought it addressed that issue).

If it's just a roofing filter you need, you can pull one out of an older
cellphone. The big clunky kind have parts that are recognizable.

Michael VE2BVW

45-70MHz crystal filters, MQF,lattice,ladder?
 

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 -

- Afficher le texte des messages précédents -

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

45-70MHz crystal filters, MQF,lattice,ladder?
 

On 22 mar, 16:50, (Michael Black) wrote:
Jean-Daniel HB9AKQ ) writes:
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.

Are you hoping/expecting to get a narrow filter out of this, or will
it be a roofing filter, with the real selectivity at a different frequency?

I thought there were limitations on selectivity at those frequencies.
I can't recall ever seeing a narrow filter up there (and while it's been a
long time since I read that QST article, which is the only article in
the ham magazines that I've seen about making crystal filters that high
up, I thought it addressed that issue).

If it's just a roofing filter you need, you can pull one out of an older
cellphone. *The big clunky kind have parts that are recognizable.

* *Michael *VE2BVW

Hello, I need a roofing filter with a few kHz wide that can withstand
1dBm or a little more.
I am not sure that the MQF you find on the market or in older
cellphones can do that. The frequency should be between 45 and 80 MHz
and the price should be right. What is your experience on this?

Thanks
Jean-Daniel HB9AKQ

45-70MHz crystal filters, MQF,lattice,ladder?
 

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 -

- Afficher le texte des messages précédents -

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

45-70MHz crystal filters, MQF,lattice,ladder?
 

Jean-Daniel HB9AKQ ) writes:
On 22 mar, 16:50, (Michael Black) wrote:
Jean-Daniel HB9AKQ ) writes:
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.

Are you hoping/expecting to get a narrow filter out of this, or will
it be a roofing filter, with the real selectivity at a different frequency=
?

I thought there were limitations on selectivity at those frequencies.
I can't recall ever seeing a narrow filter up there (and while it's been a=

long time since I read that QST article, which is the only article in
the ham magazines that I've seen about making crystal filters that high
up, I thought it addressed that issue).

If it's just a roofing filter you need, you can pull one out of an older
cellphone. =A0The big clunky kind have parts that are recognizable.

=A0 =A0Michael =A0VE2BVW



Hello, I need a roofing filter with a few kHz wide that can withstand
1dBm or a little more.
I am not sure that the MQF you find on the market or in older
cellphones can do that. The frequency should be between 45 and 80 MHz
and the price should be right. What is your experience on this?

But then it's not really a roofing filter.

That term applies to a filter used after the first mixer to limit
the passband but which doesn't provide ultimate selectivity.

My point was that I wonder if you can get a few KHz of selectivity
up there. Otherwise, we'd surely see it in commercial equipment
and even home made. All the design books decades ago would say the
best design is to put the ultimate selectivity right after the first
mixer of a receiver, yet as receiver design changed to put the first
IF in the 45 to 70MHz range, I've never seen an instance of a narrow
filter right after the first mixer.

I don't know whether it can be done, but the fact that it isn't done
suggests there are limitations.

The filters in a cellphone would be wide enough for FM, and given that
all the cellphones I've seen convert to a lower frequency where there
is another filter, they probably are relatively loose filters up at
45MHz or so.

MIchael VE2BVW

45-70MHz crystal filters, MQF,lattice,ladder?
 

"Michael Black" wrote in message news:fs4hu4
That term applies to a filter used after the first mixer to limit
the passband but which doesn't provide ultimate selectivity.

My point was that I wonder if you can get a few KHz of selectivity
up there. Otherwise, we'd surely see it in commercial equipment
and even home made. All the design books decades ago would say the
best design is to put the ultimate selectivity right after the first
mixer of a receiver, yet as receiver design changed to put the first
IF in the 45 to 70MHz range, I've never seen an instance of a narrow
filter right after the first mixer.

I don't know whether it can be done, but the fact that it isn't done
suggests there are limitations.

The filters in a cellphone would be wide enough for FM, and given that
all the cellphones I've seen convert to a lower frequency where there
is another filter, they probably are relatively loose filters up at
45MHz or so.

MIchael VE2BVW

Michael,

I am not up on this, but I believe narrow BW roofing filters are now
being marketed for many rigs. InRad has some, and I am pretty sure
TenTec offers them.

Pete

45-70MHz crystal filters, MQF,lattice,ladder?
 

On Sat, 22 Mar 2008 23:53:51 -0400, "Tio Pedro"
wrote:


"Michael Black" wrote in message news:fs4hu4
That term applies to a filter used after the first mixer to limit
the passband but which doesn't provide ultimate selectivity.

My point was that I wonder if you can get a few KHz of selectivity
up there. Otherwise, we'd surely see it in commercial equipment
and even home made. All the design books decades ago would say the
best design is to put the ultimate selectivity right after the first
mixer of a receiver, yet as receiver design changed to put the first
IF in the 45 to 70MHz range, I've never seen an instance of a narrow
filter right after the first mixer.

I don't know whether it can be done, but the fact that it isn't done
suggests there are limitations.

The filters in a cellphone would be wide enough for FM, and given that
all the cellphones I've seen convert to a lower frequency where there
is another filter, they probably are relatively loose filters up at
45MHz or so.

MIchael VE2BVW

Michael,

I am not up on this, but I believe narrow BW roofing filters are now
being marketed for many rigs. InRad has some, and I am pretty sure
TenTec offers them.

Pete


Pete,
The Ten Tec Transciever filters are at 9 MHz except in the "general
coverage up convert" receivers. in which case they are not narrow at
all.

Note that INRAD offers roofing filters 4-5 KHz wide at VHF frequencies
from 40 to 73 MHz ( see page 13 of their catalog ) with i/o impedances
of 50 ohms : http://www.inrad.net/inrad.php?mode=catalog

Ed, N5EI

45-70MHz crystal filters, MQF,lattice,ladder?
 

"Edward Feustel" wrote in message news: Pete,
The Ten Tec Transciever filters are at 9 MHz except in the "general
coverage up convert" receivers. in which case they are not narrow at
all.

Note that INRAD offers roofing filters 4-5 KHz wide at VHF frequencies
from 40 to 73 MHz ( see page 13 of their catalog ) with i/o impedances
of 50 ohms : http://www.inrad.net/inrad.php?mode=catalog

Ed, N5EI

Thanks Ed, I haven't kept with this at all. The INRAD 4 to 5 kHz BW
roofing filters sound very interesting though. A lot better than the
18-kHz BW 40.455-MHz monolythics I've played with in the past.

Pete