CC2500 reference design component question

The Murata coils are fine copper wire wound around a core. This is superior to the multi-layer printed inductors of the same size found at a lower price. The multi layer printed parts do not perform as inductors at 2.4GHz and several harmonic multiples above that and will not work.  If you find inductors of similar wound copper contruction as the murata part you should be fine. Compare the 'self resonate' frequency specification to be sure.

The caps are a little more forgiving.  If you stay with C0G/NPO parts with a similar dielectric, value, similar voltage rating (infers similar contstruction) you should be ok. Often the manufacture's data sheet will have curves that you can compare with the Murata parts.

Thanks for your reply. I've got another question that I'd like to ask:  there is an L_BEAD_102_0402 component in the design, which is an RF LC filter inductor
(inexpensive multi-layer type). What type of a component do I need to use for that? Sorry for being such dumb but I'm quite a beginner in RF designs.

For certification reasons it serves to reduce the RF on the Vdd line and it's potential re-radiation to an acceptable level. On a test board you would likely not miss it provided there was still a path for the DC current to flow. It is best to have it, my point is first order its value is not critical to basic opperation of the board and if you use a substitute you likely will not see a diferrence unless you have a spectrum analyzer to measure the low level re-radiation.

So, select a part that will handle the current (50ma or greater) with a similar Impedance @ Frequency, DC resitance, in the 0402 package and you will be set. The DC resistance is the one to watch, too large will result is a large voltage drop, At 50ma a .1V drop is  E/I = R  .1/.05 = 2 ohms is a good max so stay under 2 ohms while maxing  Impedance @ Frequency.

Hey,

since you are having trouyble with your RF design, you can use an entire module and not worry about any of the components.

Look at this :

http://www.anaren.com/content/File/AIR/A2500R24AGR.cfm\

-Mdani

Hi,

I'm back again with a question concerning the crystal in the reference design. I found that it's a rather exotic one: from NDK, 26.00 MHz, +/-10 ppm, 10 pF, HC49 SMD package. I can't find one even at Digikey, the closest bet is Abracon 26.00 MHz, +/-30 ppm, 18 pF. Can I go with this? Thanks.

All right, it is getting clear by reading DN021 - CC2500 and CC2510 Sensitivity versus Frequency Offset and Crystal Accura.

However, it seems I'm not gonna get those crystals +/- 10 ppm, 10 pF in HC-49/US-SM package on this planet. These specs are only in 4-pin, miniature surface mount package (5x3.2mm). What if I mount these in the place of HC-49/US-SM using a tiny piece of PCB? Can this interfere with the high frequency content? 

I have used a digikey 644-1095-1-ND (NX2520SA-26.000000MHZ-B9) with two 15pf 0402 caps with success. The caps values resulted from testing over a -40C to +80C range without drop outs or start up problems. Keep in mind the caps are in series thus 10pf for your indetified XTAL would be two 20 pf caps minus PCB contribution.

JustGreg said:

using a tiny piece of PCB?

The  HC-49/US-SM is one large package for just a XTAL. I would suggest the dead bug approach. Flip the 4-pin, miniature surface mount package (5x3.2mm) on a speck of expoxy and use 4 fine wires (36 GA) from its pads to the PCB. With a little solder paste in a syringe you can get a clean "shipable" install. Your pcb approach will work for a test unit but may be subject to noise, re-radiation and microphonics, and it sounds like a lot of work for a test piece.

Thank you H Stewart I really appreciate your help. I'd try this from Farnell (as I'm in the EU and the Digikey shipping+customs would cost me $50 ):

http://uk.farnell.com/avx/cx5032sb26000f0fljzz/crystal-sm-cx-96f-26mhz/dp/1368781

H Stewart said:

 I would suggest the dead bug approach. Flip the 4-pin, miniature surface mount package (5x3.2mm) on a speck of expoxy and use 4 fine wires (36 GA) from its pads to the PCB. With a little solder paste in a syringe you can get a clean "shipable" install.

I'm sorry, could you elaborate on this? You mean I'd solder 4 thin wires on the pads of the crystal?Or use epoxy to create a makeshift HC-49. Sorry if I'm dumb.

I also need advice on the double GND pins of the 4-pin package. Since the reference design uses a 2-pin one I don't know what to do with them. Solder it to the closest  ground pad or just leave it floating?