Freq Monitor W/ 15 minute recording?

[HobbyCNC]

Hey gang,
How about a personal frequency monitor with the capability to record the last 10 or 15 minutes for playback in case of "trouble?"

Has it been done? If so, where?

If not, what would it take?

I'll assume a solid state recording chip? Kinda like a memo recorder with RF receiving?

Dave Rigotti

[Gary Warner]

Do you want to record the PWM output channels at the receiver or do you want a ground based RF monitor recorder?

Gary
--

[HobbyCNC]

Gary,
Ground based. Something like a RX plugged into a memo recorder. Like to be able to "play back" the last flight. Could be useful to determine if someone "turned on".

I'm sure Radio Shack may have the digital recorder...just need a way to marry the two.

Dave

[Gary Warner]

If a receiver's I.F. output was run into a detector, the audio modulation could be sent to an audio recorder. It would sound like a buzzing sound. It would be in a repeated cycle, where an interruption or disruption might be noticeable. It's hard to say if the information would be useful in "Black Box" fashion.

Since the survivability of electronics in a crash is fairly good, I suggest an on-board recorder of the frame PWM output. Alternatively, I'd consider a "Glitch Detector" (of which several are available) that would report any dropped or ill-timed frames. The glitch detector can bring marginal reception problems to your attention before (with added problems like a 'bad RF' day) they become a problem that trashes out your plane.

I've spent this entire weekend troubleshooting a self-induced RFI problem on a $2000 airplane. As it turns out, we were lucky enough to have a spare 1100 watt identical drive system (motor and controller) and when it was changed out, the range was doubled. Problem identified.

This got me thinking...

In days gone by, I used to have an RF "sniffer". It was a coil of wire (about 1/4" in diameter) on the end of a wand and it was placed near RFI sources and the audio that was sent to the headphones would indicate if the wand was close to the source of interference. Kind of like an RFI microphone, if you will.

Maybe this has nothing to do with what you want to do, but it's just at the front of my mind toady, considering what I've spent this weekend doing.

Anyway, back on topic...

There are some out here (that watch this group) that know where to tap the I.F. on a receiver to get a detectable audio range output of a receiver. Me? No. But, I have a god idea where to look on any given receiver.

Someone here should ask what receiver you intend to use. Based on that, they can direct you to the circuit location to 'tap' the I.F. detected output.

Gary
--

[peter_jensen]

You really want something like this: http://www.ni.com/streaming/rf.htm :)
Or this: http://www.summitekinstruments.com/oasis/streaming.asp
Of course, they're solving it for much larger chunks of spectrum than we're concerned with most of the time, so you could do it a lot cheaper for one channel of 72 MHz R/C.

It won't be long before this will be a practical application of open source software defined radios that could be made accessible to non-SDR hobbyists for reasonable cost.

Back to your original question - I think there are multiple ways of easily getting "almost there". One way would be to take an Eagle Tree flight data recorder and a second receiver and place it nearby. Of course, the coolest way to handle something like this would be to have a network of direction-finders on the field and a nice 3D+color plot of frequency, location, and power. Then you could actually find the guy who drove up with a TX still on in his car :)

-Peter

[AndyOne]

I thought of using a a JR synth receiver but I'm not exactly sure how you could make it look at each frequency in turn. You would monitor the IF to for signal strength, as well as each of the digital inputs to the divider for the channel number. Perhaps it would be easier to use an old fashioned dial-up synth receiver. Then some way of putting it all onto a memory card so it could be down-loaded to a PC.

Any ideas?

Andy.