Frequency Synth Chip for 40Mhz range

[Bob]

Anyone know of a Freq Synthesizer chip that can be used for the ISM band
(40.660-40.70Mhz). We may have an application where we will need to roll
our own TX/RX.

Since this is a low volume product (a few hundred a year) I would prefer
to find a low power off the shelf TX/RX set in this range if anyone
knows of any.

There are dozens of PLL synthersiser IC's that could be used
along with a bunch of extra bits.

You need to give more detail to get sensible answers.

How many frequencys within that band do you need?
FM? Some other modulation scheme?
Do you want to send analog or digital signals?

For a single fixed frequency with a typical varactor diode
FM modulator and superhetrodyne FM receiver it may make
sense to use a couple of crystal oscillators instead
of a synthersiser.

RF takes experiance to get things to work well.

Being a bodger at heart for 40Mhz I'd be considering
buying a load of basic 27Mhz CB radio's, adding
a little board with a couple of crystal oscillators
for TX and RX LO and changing about a dozen
capacitors. Guessing from the retail prices
CB radios must be available wholesale for about 5$
each. Not ideal if you have portable use in mind.

Bob

 

[Hawker]

Anyone know of a Freq Synthesizer chip that can be used for the ISM band
(40.660-40.70Mhz). We may have an application where we will need to roll
our own TX/RX.

Since this is a low volume product (a few hundred a year) I would prefer
to find a low power off the shelf TX/RX set in this range if anyone
knows of any.

Thanx
Hawker

 

[Robert Lacoste]

Well to answer your questions.
I may need about 200 of these so modifying a CB is not practical.
The ISM band is 40.660-40.70MHz so it would be nice if I could select
anything in that range with say, 5Khz steps. It may be possible we want to
jitter the frequency for reasons I can't go into here. Modulation is not
really important. The device just needs to know a carrier is there. We may
want to modulate something (FM probably) just so we can lock onto that and
know we are not getting other interference. What we are interested in is
variance in signal strength in the receiver based on carrier level, not
any actual information. So I need both a transmitter and receiver
solution.

I realize we will probably hire an RF person to do this, but I want to get
an idea what our options are in parts first.

For these frequencies the easiest solution would probably be to use a DDS
chip (Direct Digital Synthesis), that will produce any waveform you want
with tremendous flexibility. Downsides : quite high power consumption when
active (may be 50mA), not very cheap (5$ ?). See www.analog.com/dds

Alternatives would be discrete PLLs, or even fixed frequency oscillator
(quartz based ?), as there are very very few integrated transmitters working
in these frequencies. To go further a close study of your requirements would
be needed (in particular regarding spectral requirements : noise, FCC/CE
approvals, stability, etc).

PS : If you need an external expert to design your product, just ring us !

Friendly,

 

[Hawker]

There are dozens of PLL synthersiser IC's that could be used
along with a bunch of extra bits.

You need to give more detail to get sensible answers.

How many frequencys within that band do you need?
FM? Some other modulation scheme?
Do you want to send analog or digital signals?

For a single fixed frequency with a typical varactor diode
FM modulator and superhetrodyne FM receiver it may make
sense to use a couple of crystal oscillators instead
of a synthersiser.

RF takes experiance to get things to work well.

Being a bodger at heart for 40Mhz I'd be considering
buying a load of basic 27Mhz CB radio's, adding
a little board with a couple of crystal oscillators
for TX and RX LO and changing about a dozen
capacitors. Guessing from the retail prices
CB radios must be available wholesale for about 5$
each. Not ideal if you have portable use in mind.

Bob

Well to answer your questions.
I may need about 200 of these so modifying a CB is not practical.
The ISM band is 40.660-40.70MHz so it would be nice if I could select
anything in that range with say, 5Khz steps. It may be possible we want
to jitter the frequency for reasons I can't go into here. Modulation is
not really important. The device just needs to know a carrier is there.
We may want to modulate something (FM probably) just so we can lock onto
that and know we are not getting other interference. What we are
interested in is variance in signal strength in the receiver based on
carrier level, not any actual information. So I need both a transmitter
and receiver solution.

I realize we will probably hire an RF person to do this, but I want to
get an idea what our options are in parts first.

am I any clearer?

 

[colin]

Anyone know of a Freq Synthesizer chip that can be used for the ISM band
(40.660-40.70Mhz). We may have an application where we will need to roll
our own TX/RX.

Since this is a low volume product (a few hundred a year) I would prefer
to find a low power off the shelf TX/RX set in this range if anyone knows
of any.

Theres quite a lot of chips with PLL and some with VCO as well,
depends if you want one that has both integrated or not,
there are some PLL that have much higher frequency,
ie 1ghz but these things are also able to work with a reference frequency of
up to 100mhz,
therefore you could provide it with a reference frequency of 1ghz from a
frequency multiplied XCO into the vco port
and put a LC vco into thhe ref port. would give you a good resolution.

Colin =^.^=

 

[Hawker]

For these frequencies the easiest solution would probably be to use a DDS
chip (Direct Digital Synthesis), that will produce any waveform you want
with tremendous flexibility. Downsides : quite high power consumption when
active (may be 50mA), not very cheap (5$ ?). See www.analog.com/dds

Alternatives would be discrete PLLs, or even fixed frequency oscillator
(quartz based ?), as there are very very few integrated transmitters working
in these frequencies. To go further a close study of your requirements would
be needed (in particular regarding spectral requirements : noise, FCC/CE
approvals, stability, etc).

PS : If you need an external expert to design your product, just ring us !

Friendly,

thanx, That is very helpful. I don't really have a grasp on the number
of bits I need though. It seems like if it is two few I would get to
many harmonics on the output, but perhaps not.
I also need to figure out the receiver.

I also appreciate your offer for help. Unfortunately my client insists
that all contracts and supplier and US so he can say "designed and build
in the US". I do digital design for this client and he wanted me to do
this project. I told him I was not an RF engineer but he seems to want
us to do the work anyway. I'm trying to act more as a project manager
than engineer and doing some preliminary some leg work.

Hawker

 

[Frank Raffaeli]

Anyone know of a Freq Synthesizer chip that can be used for the ISM band
(40.660-40.70Mhz). We may have an application where we will need to roll
our own TX/RX.

Since this is a low volume product (a few hundred a year) I would prefer
to find a low power off the shelf TX/RX set in this range if anyone
knows of any.

Thanx
Hawker

Here's something I had in the archives. I might even have a PCB
somewhere.

http://www.aomwireless.com/sed/synth_39.pdf

Frank Raffaeli
http://www.aomwireless.com/

 

[Barry Lennox]

Anyone know of a Freq Synthesizer chip that can be used for the ISM band
(40.660-40.70Mhz). We may have an application where we will need to roll
our own TX/RX.

Since this is a low volume product (a few hundred a year) I would prefer
to find a low power off the shelf TX/RX set in this range if anyone
knows of any.

Motorola had a whole lot of them in the p/n range MC145162 to 70. The
max freq varied, but was between 60 and 185 MHz.

AFAIK, they dropped the range several years ago, but they are still on
the market, and it should be possible to get the small number you
require.

Barry

 

[Robert Lacoste]

thanx, That is very helpful. I don't really have a grasp on the number of
bits I need though. It seems like if it is two few I would get to many
harmonics on the output, but perhaps not.
I also need to figure out the receiver.

In a DDS-based design the number of bits is probably not a bit issue for
this application, as it has links with the frequency resolution (linked to
the DDS phase registers bit length, but you will have at least a 1Hz
resolution with the worse DDS) and with harmonic content on the output
(linked to the DDS DAC resolution). Harmonics are quite easy to filter, but
the most difficult aspect of DDS are spurious signals in the output, which
are linked to all of the parameters... You will find simulation tools on the
AD web site, but you will have to carefully check it with the exact
frequency and modulation parameters of your application, as well as with FCC
regulations. Often you will find that you have both to select a particular
main crystal frequency in order to "move" the spurious far enough from your
carrier, and to add good pass band filters to remove them.

I also appreciate your offer for help. Unfortunately my client insists
that all contracts and supplier and US so he can say "designed and build
in the US". I do digital design for this client and he wanted me to do
this project. I told him I was not an RF engineer but he seems to want us
to do the work anyway. I'm trying to act more as a project manager than
engineer and doing some preliminary some leg work.

US guys often want to do things alone, like in I... (no, I will not say it,
as I don't want this thread to go be jeopardized

Friendly,
Robert
www.alciom.com

 

[Frank Raffaeli]

thanx, That is very helpful. I don't really have a grasp on the number
of bits I need though. It seems like if it is two few I would get to
many harmonics on the output, but perhaps not.
I also need to figure out the receiver.

I also appreciate your offer for help. Unfortunately my client insists
that all contracts and supplier and US so he can say "designed and build
in the US". I do digital design for this client and he wanted me to do
this project. I told him I was not an RF engineer but he seems to want
us to do the work anyway. I'm trying to act more as a project manager
than engineer and doing some preliminary some leg work.

Hawker

I wasn't aware this band was used in the U.S.

You can make a cheap (<$14, in low volume) high performance TX-RX up
to about 70 MHz with an amp, ADC, FPGA, a micro-controller, and a
switch. No pesky analog mixers, modulators or demodulators necessary.
You don't need an RF guy ... 40 MHz is D.C. ;-)

Frank Raffaeli
http://www.aomwreless.com/

 

[Hawker]

Thanx, looks like a good start,