Interference Receiver/Detector with direction finding

[Gina]

I decided to move this topic out of the "Lost Sensor Contact!!" thread as it's got so far away from the original topic.

To summarise - I was getting large spikes in my temperature data which were reduced almost to extinction by screening the cable from the wind sensors (on top of 6.3m mast). It was concluded that the cable was picking up bursts of RF interference. Interest was expressed in trying to find where this interference was coming from so I made up a pair of simple receivers using ferrite rod aerials at right angles as a radio direction finder (RDF).

First attempt assumed the interference was quite strong and "crystal set" receiver circuits were built. This sort of receiver picked up some interference using a long wire but nothing was at all with the ferrite rod aerials. With nothing received indoors, a short test was performed with the receiver outdoors and still nothing. Tests were carried out with an audio amplifier plus speakers and recorded on HD on the PC. I also tried my hand-held oscilloscope but that didn't show anything either - not too surprising as the maximum sensitivity is 50mV per div. Anything less than 10mV would not be visible.

I'm now thinking of adding RF amplifiers before the detector stage.

Here's a copy of the post from the other thread:-

I grabbed a little time to knock up a dual receiver using two ferrite rod aerials and the LW coils. The circuit does not have a tuning capacitor, with the coils connected directly to point-contact diodes feeding the two (stereo) microphone inputs, and a 680K load resistor in each channel. The circuit is built on strip board with the ferrite rods attached to the board with sticky pads, one each side, at right angles.

RDF.png

RDF.JPG

[andrewinpopayan]

Do you play on VLF as well? with pings, screechers and tweeters, all sorts of noise from the earths interaction with solar radiation.

[Gina]

Do you play on VLF as well? with pings, screechers and tweeters, all sorts of noise from the earths interaction with solar radiation.

I haven't yet, but I don't rule it out for the future. There are so many things that would be of interest but time is limited and the 'ol brain isn't what it was though I have no intention of vegetating

Regarding the "dual crystal set", I have it set up in the sun lounge at a height of about 6ft where it can get clear reception a little over 180 degrees towards the south. Meanwhile the weather station has so far shown no little spikes so nothing yet to look for in the audio recording. I have other priorities ATM but expect to add RF amplification when I have time.

[DrMD]

Gina, I was so concentrating on temperature being your problem, and temp was not really a problem for me, I was over looking that I do have a very similar problem with spikes. My outside humidity sensor does not work when I hook up the wind direction indicator, but on occasion it does kick in and give me spikes.
Now just seconds before the transmitter transmits, voltage is applied to the various sensors. The rest of the time I can only assume most if not all is off to save battery power.( although there is a thing or 2 I question there).
Anyways these spikes maybe cause by to short a time for the sensors to settle after the voltage is applied.

[Gina]

Gina, I was so concentrating on temperature being your problem, and temp was not really a problem for me, I was over looking that I do have a very similar problem with spikes. My outside humidity sensor does not work when I hook up the wind direction indicator, but on occasion it does kick in and give me spikes.
Now just seconds before the transmitter transmits, voltage is applied to the various sensors. The rest of the time I can only assume most if not all is off to save battery power.( although there is a thing or 2 I question there).
Anyways these spikes maybe cause by to short a time for the sensors settle after the voltage is applied.

It seems possible that you may have a faulty unit. It could be that you are picking up interference. Do you have an extended cable between your wind vane unit and the transmitter unit?

Are you saying that your outside humidity is OK if the wind sensors are not connected but fails when they are? If so I think it most likely that there is a whisker of solder bridging circuit tracks - or it could be an internal fault in the chip.

[Gina]

Regarding the "dual crystal set", I have it set up in the sun lounge at a height of about 6ft where it can get clear reception a little over 180 degrees towards the south. Meanwhile the weather station has so far shown no little spikes so nothing yet to look for in the audio recording. I have other priorities ATM but expect to add RF amplification when I have time.

Well, there were two small spikes in the temperature plot during a 21 hour recording today but not a sign of anything in a plot of the audio recording. So that's proved that the current receiver doesn't work! I have stopped recording until I can add an RF amp section.

[Charlie]

Hi Gina! No posts here for a bit... have you given up on this one?
What about coupling to the sensor cable rather than trying a seperate antenna? Also there is no guarantee the modulation (if any) is in the audio band, so your sound card may not do the trick, although I would expect to see something!

[Gina]

Hi Gina! No posts here for a bit... have you given up on this one?

No not entirely, just temporarily. I've had other things to do lately and this has gone on hold.

What about coupling to the sensor cable rather than trying a seperate antenna? Also there is no guarantee the modulation (if any) is in the audio band, so your sound card may not do the trick, although I would expect to see something!

I have been thinking of running a wire from the cable screen to one of the receivers. I also agree that the pulse of interference might not record very well. I now have a Stevenson screen large enough to take more than just the transmitter unit so there are more possibilities - electronic circuits will not need sealing in a weatherproof box.

[Gina]

I have not seen any signs of interference spikes in the temperature plot for several weeks now - apart from a couple about a week ago. So this project is suspended indefinitely - unless or until the interference reappears.

[Gina]

Having not seen any sign of spikes whatsoever for several months, they're back!! The screen of the wind sensor cable is still connected to battery -ve and I've changed nothing recently.

24hrs-Temperature.png

[Super-T]

Gina. What's the time interval of the spikes? We regularly get sudden spikes in temperature of 2 or 3 degrees and you can feel it when a front goes through. You weren't having thunderstorms passing?
It looks like you have a sample rate of around 10 minutes or so....is this right?

[Gina]

I guess it could be thunderstorms though we haven't heard any. They were forecast though. The spikes have gone again now. Yes, my update interval is 10 mins.

[Gina]

Back again!!

[geoffw]

Back again!!

Oh Dear!