Thank youCharlie wrote:Great troubleshooting, Gina!
If there's anything wrong you can be sure I'll find itI extended my (already extended) cable by about 1.5 m (to about 10 m total) yesterday, and I am now seeing spikes. They are only about 0.5 to 1 degree so I may just live with them. At least I now know how to fix them if I choose to, thanks to your efforts.
Perhaps I should stop following your posts. I never seem to see the problems until you point them out!
I'm a "nit picker" Thank youEvilV wrote:Conrgatulations Gina. You have certainly identified the cause and solved the problem. I see a tiny blip on your temperature graph at around 0830 this morning. Without the screened cable, I have little doubt that would have been another big spike.
I've been thinking about this. My hand-held scope won't run for for the several hours required to record the (rather infrequent) bursts of interference. A simple crystal set type of receiver would convert the rf bursts to something I could record. Either with an ADC or maybe even as audio. If it's sparking it will be wide band and anything will pick it up. Anyway a wide-band receiver should give an idea of what it is. I could record on the computer then look at the result. One thing I will say - my AWS is for measuring weather, not interferenceThe next question is where is the interference coming from?
Can you record it any way? I'm wondering if your digital oscilloscope can preserve the spikes. If so, maybe you could make a directional antenna and gradually track it down by rotating the antenna over time and preserving the spike traces. If all else fails in the detection and recording business, you have a pretty effective ready made unit in your Fine Offset broadband interference detector.
Some kind of coupling transformer and a directional antenna fed into the socket of the F.O. wind input, and you'd be there, I think. The only hard part would be to work out how to make an effective directional antenna without having any idea what frequency you are dealing with. It is probably low frequency sparking or something, so research into the kind of antennas used for lightening detection might be useful. I once made a Direction Finding set up which worked very well, and it was just a high Q loop antenna with a variable capacitor in parallel with it. On the other hand, you can get a pretty good null with a ferrite rod antenna, so, you could wind a coil onto a ferrite rod, couple that into your detector / recorder (F.O.) and rotate the ferrite over time to identify the line that goes through the signal interference source. Unfortunately, it could be in either direction of the bearing you finally get, but nonetheless, it would give you an idea.
http://www.homingin.com/joemoell/80intro.html
It certainly would be interesting, I agree.EvilV wrote:If the amplitude of the interference is enough, I reckon a rotatable ferrite rod with a coil on it, fed into a simple transistor amplifier, might supply enough signal for you to record on the computer, though I have no idea where you would feed it in Gina. My mention of your PWS was simply because you already have ALL of the components for detecting and storing the pulses on there now, ready and working. Supply the signal from the ferrite rod antenna, rotate it a few degrees every twelve hours, keep a record of the times and bearings of the ends of the rods and then spot the nulls in lower amplitude pulses when they happen. Then you would know where the bearing of the interference source. My bet is some switching of a heavy current, or breakdowns on a power line insulator.
It would be interesting to finally solve the cause wouldn't it?
Yes, I agree. Another small spike has occurred around 1800 and now an even bigger (though still much smaller than before) spike at about 2050. This last spike has become of significant size IMO. Tomorrow I'll check that the screen connection is still intact and have a general check. I may then add the LC filters on the input lines though I am puzzled by this last spike. To put things into perspective, I'm posting a 48 hour plot which includes the "standard" spikes when the screen was disconnected.EvilV wrote:I see a tiny blip on your temperature graph at around 0830 this morning. Without the screened cable, I have little doubt that would have been another big spike.
I had forgotten all the broadcast signals. Yes, I'll have to watch they don't overload the circuit. And yes, the interference must be pretty strong. Think I'll try without rf amplification first and I could cut out the audio amp if I use the microphone input. Now that's a lot simplerEvilV wrote:I'm sure that would work fine BUT don't forget you would have a lot of strong broadcast signals. The circuit would feed i the whole of the long wave and medium wave broadcast band signals, so I suspect you wouldn't want too much amplification. Of course whatever it is that is causing the interference is much stronger than that. You might need to put in some kind of attenuator, unless you just used the ferrite rod.
EDIT:
Sorry - you covered the use of just the ferrite rod antenna in your post.
Add a variable C across the coil and we have the jolly old crystal set Yes - that's what it is. I think it would also work if you just connected the coil across the mic input signal and ground. The diode in the crystal set is there to demodulate the audio signal on the Amplitude Modulated RF signal to produce a varying dc voltage that represents the audio signal. If you think of the long signal cable of your FO PWS as the coil in your circuit above, it is quite clear that the PWS didn't need any additional components to pick up the interference pulse and register its amplitude.Gina wrote:I had forgotten all the broadcast signals. Yes, I'll have to watch they don't overload the circuit. And yes, the interference must be pretty strong. Think I'll try without rf amplification first and I could cut out the audio amp if I use the microphone input. Now that's a lot simplerEvilV wrote:I'm sure that would work fine BUT don't forget you would have a lot of strong broadcast signals. The circuit would feed i the whole of the long wave and medium wave broadcast band signals, so I suspect you wouldn't want too much amplification. Of course whatever it is that is causing the interference is much stronger than that. You might need to put in some kind of attenuator, unless you just used the ferrite rod.
EDIT:
Sorry - you covered the use of just the ferrite rod antenna in your post.
but you are obviously a purist engineer, whilst I am back yard bodger....... 
Yes, I'm just testing out the rx and recording setup.EvilV wrote:But if you don't use a directional ferrite rod antenna, how will you be able to work out where it is coming from? Maybe I've misunderstood, and you are just proving the receiving system first.
Yes, I'll do that next. I had a ferrite rod with coils already on it but I dropped it (only on the lawn) and it broke into 3 piecesI thought you would be gradually rotating a ferrite antenna, say 15 degrees every 24 hours and keeping a record of the bearing along the ferrite. That way, you would be able to see when the real nulls were happening and could correlate them with the rod positions. The signal will have a significant drop when the ends of the rod are pointing at the source as opposed to the side on position, and you should be able to pick that up on your data record. The side on will show higher signal strength, but you will get a much sharper null on the ends.
I expect about 60 turns of something around 28 swg wire on a decent ferrite rod (about 4" long would be a good size) will give good coverage of low frequency bands. It is almost certain to be pretty low I think, because it is likely to be sparking of some sort.
I don't think that's the only one I've got - I'll have to have a hunt As I recall, if a ferrite rod gets broken it's no good fixing it back together again.