emcRFspectrum analyzer
I need to test that my project will not interfere with radios in the 27 – 72 MHz band.
I can't afford a spectrum analyser. Nor can I afford to buy all tx/rx pairs in between 27 and 72 MHz (27, 35, 47, 72…) My budget is a maximum of £100.
I was thinking of modifying a radio to have a much larger tuning range, but it would need to be sensitive to very low EMI emissions. I've found AM radios are slightly sensitive to noise but probably not enough.
Does anyone have any suggestions?
Infrared emitters and receivers can be used to transmit/receive data. However, interference with other devices like remote controls might be a problem. If the connection needs to be really reliable, this probably wouldn't be that great of an option. However, you might be able to find a really uncommon wavelength emitter and receiver to limit the amount of interference.
These are pretty common, and very cheap. Packs of 20 emitters for $1 and packs of 100 receivers for $13 can be found on eBay (not including shipping). Lots of electronics stores have them as well.
The application SOUNDS so trivially simple that, if it isn't, there is no way to know due to the "death by 1,000 blows" approach to defining the problem. At 30 cm the way to use RF is to use RF. Any RF equipment that I have ever met would work over that range in free air in the absence of metal. You can buy transceivers and transmitter / receiver pairs. With the stated specs, if it transmits and receives RF it will be suitable. If any RF data transfer solution does not work in this context then it is because the spec is inadequate. Simple RF solutions usually have minimal latency once the data stream is synchronised. All that is required is Sync_phase - delay_until - sync_now. QED. Repeat as needed. Processor helps BUT a cheap no processor solution is easy.
More complex RF systems such as Bluetooth will also work but may have variable latency. This can be overcome by some interactive communications that establishes link parameters OR designed around known performance. BUT simple cheap off the shelf one way RF modules will work well enough. "ASK" transmission is probably fine and gives you something to search for.
This $5 receiver {315 MHz version} or 434 MHz version
plus this $4 transmitter or its up frequency cousin
will together give you a $9 solution if you are happy to talk one way.
Double that for 2 way.
Or
Two of these $7 transceivers - 434 MHz will give you a bidirectional $14 solution. ~ 16mm x 16mm x 4.2mm.
That size is known OK as the spec did not specifiy otherwise when all details were provided.
That cost is known OK as the spec did not specifiy otherwise when all details were provided.
Datasheet
Programming guide
eXCELLENT APPLICATION GUIDE
mORE OF THE SAME - MANUFACTURERS HOME PAGE {PROBABLY}
rfm12 LIBRARY
Two of these give you a WiFi link - over over over kill.
In the absence of any real clues as to why the following are not suitable, the following may be suitable:
IR may work well and easily and cheaply.
Unless you are an IR expert, your reasons for excluding it may well be unsound.
With what you have told us so far, IR would be the candidate solution of choice.
Low cost, easy, low power. ie
Better, cheaper, faster - choose any three!
Tell us what you want and we'll tell you what you need :-)
Electromagnetic "RF LIKE" "near field" coupling may or may not suit better than RF. .
Optical
Acoustic
Capacitive
... GSM ... Iridium ... Inmarsat ... [just joking] :-) .
Pleased explain clearly & completely the environment and relevant constraints. eg:
Potted in concrete, welded in a mumetal drum at the bottom of a shallow shark pond ... :-).
Indoors, outdoors, ... .
There are many "obvious" solutions that may or may be suitable BUT as you do not explain your real need nobody can tell*.
Again: Tell us what you want and we'll tell you what you need :-)
IR sounds good to me, so far.
Best Answer
If my time was worth nothing, or I was doing this as my own fun project, I would design and build my own rf power meter. There are schematics available for this in AARL back-issues.
If this is for work, I would go and rent the tools.
If this isn't for work, and you don't know very much about RF, and you don't have a lot of money - go make friends with amateur ham radio people in your area and butter them up.