Frequency Synth Chip for 40Mhz range

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

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Bob
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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

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Hawker

On 3/22/2007 9:26 AM, The digits of Bob's hands composed the following:

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?

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Hawker

"Hawker" a écrit dans le message de news: snipped-for-privacy@mid.individual.net...

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

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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,

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Robert Lacoste
ALCIOM - The mixed signal experts
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Robert Lacoste

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 =^.^=

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colin

On 3/22/2007 11:15 AM, The digits of Robert Lacoste's hands composed the following:

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

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Hawker

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

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Frank Raffaeli

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Frank Raffaeli

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

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Barry Lennox

"Hawker" a écrit dans le message de news: snipped-for-privacy@mid.individual.net...

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.

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

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Robert Lacoste

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

You can make a cheap (

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Frank Raffaeli

Thanx, looks like a good start,

On 3/22/2007 6:03 PM, The digits of Frank Raffaeli's hands composed the following:

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Hawker

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