[ucc] Electronics help: A nice chip to do 36MHz amplification, mixing and filtering
davemr at crossecom.com
Mon Aug 21 11:12:51 WST 2006
If you're not particularly concerned about costs, the line of products from Minicircuits (they're on the web at
http://www.minicircuits.com/) are brilliant for "plug and play RF". They will probably send you a free line catalog, and you can
match up input and output specs, and know that the modules will inter-play quite nicely. I did a quick project for a TAFE lecturer
that down-converted one of the commercial TV audio (FM) "tracks" into the 88-108MHz FM band. Used a PLL to track the TV station
audio carrier, and a VCO and Mixer to beat down to somewhere in the 88-108 band, and a short wire to re-radiate in a room-sized
enviroment. Worked a treat, first time too!
Only problem I had was the Aussie reps are painfully slow, it might be better to get someone in the US to get them for you and feed
them down here direct.
Of course, there are ways to avoid all that. Most decent flying clubs implement a tag/crystal policy. When (as a paid up member)
you go there, they allocate you a channel, and give you _their_ crystal and tag, to ID you on that channel. In theory, no-one else
can legitimately get that channel. Of course, nothing stops someone coming in with their own crystals and clashing with you, except
good club management / security.
Very little can be done about malicious gatecrashers who don't actually have to be on the premises to cause problems, but at least
you've got a much better chance of not getting accidentally crashed by another club member.
Also, it means that you have to have the sort of RF gear that can take their crystals. Many clubs here have a "if you don't have
gear from the following list, you can't play" policy. In fact, most of them are "... can't join". However, the list is pretty
extensive, so you generally don't have to pay much (if anything) to re-kit your RF.
2c worth, GST exempt.
> -----Original Message-----
> From: ucc-bounces at ucc.gu.uwa.edu.au
> [mailto:ucc-bounces at ucc.gu.uwa.edu.au]On Behalf Of Jeremy Nelson
> Sent: Monday, 21 August 2006 11:00
> To: UCC
> Subject: [ucc] Electronics help: A nice chip to do 36MHz amplification,
> mixing and filtering
> This is a question for the electronics knowledgeable. (I haven't emailed
> UCC in a long time, but I'm hoping someone will be doing an radio design
> unit in EE *right now* and be able to answer the question. Or maybe Dav
> or John will know. :)
> Let me start by explaining the problem, and then what I want the answer
> to look like. :)
> I fly RC gliders which, in Australia, means they carrier frequency is
> somewhere between 36.000 and 36.6000 MHz. A couple of weekends ago I had
> a glider crash which I'm fairly sure was dues to interference. (And
> given that there is a history on the field I fly at of this happening it
> would seem likely that interference is the cause.)
> I'd like to take my Spectrum Analyzer (in this case a Bitscope 310- a PC
> based USB Digital Oscilliscope:
> http://www.bitscope.net/store/?a=add&i=product+66&p=2) plug an antenna
> into it and zoom in on the 36 Mhz portion of the frequency. I can sort
> of do that- I can see the 36MHz peak and tell when my transmitter is on,
> but it doesn't have the bandwidth and sensitivity to get any detail. And
> there is a hell of a lot of noise on and below 1kHz that pretty much
> swamps everything.
> So, following from a basic superheterodyne approach it would be kind of
> neat to filter, mix and amplify the signal (not necessarily in that
> order) down to a more user friendly intermediate frequency- say mix from
> 36.3Mhz down to 1MHz and filtering from just below 0.7Mhz to 1.3Mhz to
> give me a nice clean view of the bit of spectrum I care about.
> Now this should be pretty easy- none of the frequencies I'm talking
> about are that are that weird and I know there are chips that can cover
> the (ha! piffling!) 36Mhz bands on their ear. But I'm having difficulty
> tracking down a chip that is in production and available reasonably
> straightforwardly in Australia. I keep finding end of life chips, or
> ridiculously overpowered chips designed to do WiFi and wireless phones.
> And basically I'm pretty clueless when it comes to RF. So is there
> anyone out there who can give a contemptuous snerk, recommend a chip and
> point me at the data sheets to screw the appropriate R, C and L to make
> it work. Or maybe a web page with a design.
> I would like to avoid building my open superhet since there has *got* to
> be chips that do this stuff. Surely. My objective is not to learn RF
> design and spend weeks testing circuits. I just want to look for
> interference at the field and, possibly, fingerprint the interference so
> we can track it back to a source.
> Many thanks!
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