Crystals for 870 MHz

[spuffock]

I need to make a device using rfPIC chips, operating in the 868-870 MHz licence exempt band. Does anyone know of pairs of crystals, in SMD packages, already available, or do I have to get them cut specially?

 

[audioguru]

Crystals don't go higher than about only 50MHz on funamental and maybe to 450MHz if you use them in harmonic mode. A bunch of frequency-doublers or a frequency synthesizer can also be used. You might be able to buy a little crystal controlled oscillator or steal one from a cheap little commercial unit.

 

[spindrah]

RFPic12F675H is the only one with a frequency range from 850-930

Ftransmit = FrfXtal * 32

so the max Crystal you can use is 29.0625

 

[Nigel Goodwin]

I need to make a device using rfPIC chips, operating in the 868-870 MHz licence exempt band. Does anyone know of pairs of crystals, in SMD packages, already available, or do I have to get them cut specially?

You should try reading the rfPIC datasheet, which explains about crystals.

As Audioguru quite rightly says, you can't get crystals above certain values, and certainly no where near 870MHz - and if you could, they wouldn't work on an rfPIC.

Page 50 of the rfPIC12F675 gives the details for crystal calculations, plus a table of suitable values (but for 433MHz) - basically it's 1/32nd of the frequency you want, and is multiplied by an internal PLL to give the desired frequency.

 

[audioguru]

I guess there is one inside my car's keyless entry remote. The pic even has the transmitter buit-in.

 

[Nigel Goodwin]

I guess there is one inside my car's keyless entry remote. The pic even has the transmitter buit-in.

I suppose it depends if it's PIC based or not?.

Most of the ones I've seen have a seperate processor along with a tiny transmitter module in a little metal can (usually a round can).

BTW, have you seen how much it costs to replace one of those keys if you lose it?.

 

[audioguru]

BTW, have you seen how much it costs to replace one of those keys if you lose it?.

Yeah, my son bought a car (hey dad, can I borrow some money to buy this good deal?) that was re-posessed from someone who didn't pay for its lease. The dealer shared the high cost of a remote key for it. I was given a DVD player from the dealer for supplying the money. :lol:

 

[spuffock]

I am sorry for assuming. Of course I've looked at the data sheet, and I had erroneously assumed that anyone replying would have done so too.
Now, given that everyone in this discussion knows what they're on about, I need a pair of crystals, which will give, when multiplied by 32, 1)a frequency in the range 868-870 MHz, and 2) a frequency separated from this by 10.7 MHz, or another common IF frequency that I can get a filter for. It seems probable that I may be able to obtain a kit, consisting of a suitable pair of crystals, an IF filter, and an 869 MHz SAW filter. If anyone knows where such may be obtained, please let me know. Thanks

 

[Nigel Goodwin]

I am sorry for assuming. Of course I've looked at the data sheet, and I had erroneously assumed that anyone replying would have done so too.
Now, given that everyone in this discussion knows what they're on about, I need a pair of crystals, which will give, when multiplied by 32, 1)a frequency in the range 868-870 MHz, and 2) a frequency separated from this by 10.7 MHz, or another common IF frequency that I can get a filter for. It seems probable that I may be able to obtain a kit, consisting of a suitable pair of crystals, an IF filter, and an 869 MHz SAW filter. If anyone knows where such may be obtained, please let me know. Thanks

10.7MHz is the standard IF for VHF/UHF radios, so should be available from any supplier of radio parts.

The crystals, as the datasheet says, may need to be custom made, but this is fairly normal with TX/RX crystals anyway.

What are you actually doing?, trying to design a device for production?, or just build a 'one off' unit for your own use?.

 

[spuffock]

It is hoped to be a large volume production thing, but, sworn to secrecy and all that. Patents are a load of rubbish, you just have to make so many so cheap that no-one else finds it worth the trouble

 

[Nigel Goodwin]

It is hoped to be a large volume production thing, but, sworn to secrecy and all that. Patents are a load of rubbish, you just have to make so many so cheap that no-one else finds it worth the trouble

In that case you need to be getting in touch with suppliers for production quantities, and it's no problem getting custom made crystals because of the volume you'll need to have made.

You don't have your location filled in, so people can't offer suggestions, as they don't know where you are?.

 

[spuffock]

Buying production quantities of components to see if I can get a project to work?

 

[Nigel Goodwin]

Buying production quantities of components to see if I can get a project to work?

Assuming it's a genuine device that you intend to produce in quantity?, a manufacturer would probably supply you free samples for prototyping (as do MicroChip).

Now we know you're in the UK, a simple google for '+crystal +saw +manufacturer' gives a good few examples to look through.

The top offering was https://www.euroquartz.co.uk/.