I found your questions #1 and #2 interesting. I found people starting on RF asking these kind of questions, and I would like to learn why you think a a higher bitrate (wider modulation bandwidth) would come for free. I am sure you won't be asking the same for a PIC for instance, meaning you probably realize why a PIC with a max clock of, say, 8MHZ cannot simply run at 800MHZ for simple magic. So why you think that would be the case with RF circuits? If you can explain that it may help people with large experience in RF to help newbies better. Besides some of the modulation details many already detailed in this thread, there are many other aspects as to why a circuit doing 100Mbps is more demanding than one at 250Kbps. You say you understand how modulation techniques work; then you may clearly see that a 2.4GHz carrier modulated by a 100Mbps requiring 100Mhz bandwidth, downconverted to 100MHz baseband signal and being processed by an ADC later will require a much faster device than that of a 250Kbps. A 200MSps ADC won't cost you the same as a 500KSps ADC. This can be extended to many other parts of the transmitter/receiver topology, including filters, VCO specs, etc. Cheers, --=20 Ariel Rocholl http://www.rf-explorer.com On Wed, Nov 16, 2011 at 4:35 AM, V G wrote: > I just started looking into RF literally a couple of days ago (never done > anything with it in the past), and I understand that it's a very > complicated topic, but I have a few questions/thoughts: > > I understand how basic analog (AM, FM) and digital (OOK, ASK, FSK, PSK) > modulation techniques work (not the underlying mathematics yet, but > probably enough to build one) and I bet I could make a very simple digita= l > RF transceiver. I have a few questions. > > 1. Forgive me for asking, but what's stopping me from using a 2.4GHz VCO > and sending in a 100Mhz (100Mbit/s) data stream into the input pin and > receiving it on the other end (via FSK)? There just /has/ to be some > gotcha, because it seems simple enough. I know I should be able to send i= n > at least a 1Hz data stream and see it reliably, but where does the data > speed limit come in, other than the effects of nearing carrier wave > frequency? > > 2. Why are all these modules (http://www.hoperf.com/rf_fsk/fsk/) and most > other cheap RF modules only up to 250kbit/s? What's stopping them from > being run at 10Mbit/s? > > 3. My goal here is to build a short range (less than 100m, more like 10m > tops) digital RF transmitter receiver pair from scratch. The fancy > frequency hopping interference detection stuff is not yet a priority. I'd > be happy building a simple channel-selector switch based 2.4 GHz RF pair. > I'm guessing FSK is a good way to go and dropped/corrupted packets > shouldn't be an issue as long as *most* of the data goes through. All I > need it to do is send a PCM stream of audio with minimal latency at > an application throughput of around 3Mbit/s. Maybe things like using > multiple channels at lower bitrate is a possibility, or high bitrate with > error correction stuff (redundancies) packed into the stream. > > 4. Failing the above, my next idea would be a VCO based analog FM > transmitter, which I suppose is pretty hard to mess up. > > 5. I'd like to stick to the 2.4GHz bands (or 900MHz if 2.4GHz isn't > possible) for either option #3 or #4 to keep antenna length short > and propagation properties from preventing the signal from going too far > out of my walls. > > Dove into a huge, dark, lake that is RF, and no idea where I am or what t= o > do, and can't see anything. Just my thoughts. Hoping to get some advice. > -- > http://www.piclist.com PIC/SX FAQ & list archive > View/change your membership options at > http://mailman.mit.edu/mailman/listinfo/piclist > --=20 http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist .