Receiving VHF FSK data - Page 1
Forum section: electronics / beginners

author: brendan-petrol
author_rank: Contributor
timestamp: January 29, 2013, 10:04:23 am
content: Hello All,I was wondering if anyone had any advice for receiving FSK data on the VHF band. I've been researching VHF FSK receiver ICs and have come up with this:http://pdf1.alldatasheet.com/datasheet-pdf/view/356681/MOTOROLA/MC3356P.htmlHowever, the datasheet makes no mention of equations to choose the correct values for components for the band I want. It looks like (from that DS) that I just need an antenna on the RF side (is that right?), however I don't know how to pick the components to finish it.I am self taught and haven't got as far as RF yet! From what I've learnt a circuit like this won't work on a solderless breadboard because of the characteristics of the breadboard. However, would something like this work on a stripboard type thing?I hope this makes sense and that I'm not too far out of my league!Brendan

author: ve7xen
author_rank: Super Contributor
timestamp: January 29, 2013, 05:49:22 pm
content: What are you trying to receive? Do you have a source for MC3356 (it's long obsolete)?Seems to be a pretty simple FM receiver with some extra components to help you decode FSK. Without lots of tuning and some external circuitry and wired as in the examples it's basically a 'is the signal above or below the LO' detector. Good enough for some FSK, but useless for other types.

author: Smokey
author_rank: Super Contributor
timestamp: January 29, 2013, 07:19:27 pm
content: If you are in the higher end of VHF, give the SI4432 a look. You can get a Chinese breakout board in the form of the RFM22, but it's just the reference circuit for the SI4432. All they did for documentation was take the SI data sheet and change all the company references and logos. It's pretty funny, but for 12USD I'm not going to complain too much. There are Arduino libraries that handle most of the features. It's pretty amazing what this chip can do. Don't get put off too much by the "fixed" frequency of the RFM22. The chip is software tunable from 240 - 960 MHz. It does pretty well outside the tuned settings, and you can always change the PCB components if you want to re-tune the antenna circuit for some specific band.https://www.sparkfun.com/products/10153Using something like this takes a lot of the black magic out of the RF, which is great for me since I'm not an RF wizard by any means. I'm not sure if you need an embedded solution, but an RTLSDR dongle and GNUradio does a great job at picking out FSK

author: brendan-petrol
author_rank: Contributor
timestamp: January 30, 2013, 01:30:50 am
content: I am trying to receive paging data just above the 2M HAM band. I already have a pager, however I want to trigger some lights when I get a page on a specific capcode.I can get the MC3356 from alibaba quite cheaply! I tried getting a Radiometrix module customised to the right band, however I cannot get it to output valid data. They told me it should work, however when I hooked an audio amplifier circuit up to the audio out on the module I cannot even hear a trace of the FSK data!

author: SeanB
author_rank: Super Contributor
timestamp: January 30, 2013, 04:03:26 pm
content: Why not just get another pager ( or a cheap handheld) and grab the received data from that?

author: madires
author_rank: Super Contributor
timestamp: January 30, 2013, 04:32:59 pm
content: Have a look at the XR2211 (1,65 Euros).

author: brendan-petrol
author_rank: Contributor
timestamp: January 30, 2013, 10:34:58 pm
content: I could get a cheap handheld, and I am looking at doing that in the meantime, however it doesn't exactly lend itself to a compact receiver project. Getting another pager programmed to the same band will be difficult and/or very costly.The XR2211 looks awesome! What sort of RF receiver circuit would I need to put infront of it?

author: ve7xen
author_rank: Super Contributor
timestamp: January 31, 2013, 12:28:56 am
content: You'll need an RF frontend (amp, gain control, filters etc.), local oscillator, and mixer to downconvert to the KHz range this chip operates at. None of this is particularly trivial, and parts that do some of these things easily are disappearing from the market in favour of SDR and dedicated ICs. Some old VHF voice comms and broadcast FM parts might be usable.SI443x or SI446x look to do everything you need in a single chip though, and much easier to use.

author: brendan-petrol
author_rank: Contributor
timestamp: January 31, 2013, 02:10:31 am
content: Ahhh! That seems to be exactly what I am after! That's amazing!I'm looking at this one -http://www.silabs.com/Support%20Documents/TechnicalDocs/Si4362.pdfat the moment, the application example is SO simple! Now I just need to find out if the DS mentions what those inductor and capacitor values should be!Hopefully even I can't stuff that up!