interference with antenna?

[Gasman]

Hi Guys

I`ve noticed quite a few lines in Speclab like this one at 20:52:15 while checking for meteors which I think is interference from household apps like the washer and wondering how to filter them out, maybe the ferrite coils I`ve read about?

Its a screen shot via Teamviewer of my study pc running Speclab!

cheers

Steve

[Al.Grant]

Hi Steve,

I get ones exactly the same as that.  The script I'm using at the moment tends to filter out most of them but some do still get counted.

I was watching my display at the time we had lightening over the UK and was getting the same thing.

A couple of days ago I got this:

Which tied in perfectly with this from:

There were lightening strikes visible local to me  (I'm a little below Derby) and a good number out to the SE.

Not saying all of these are lightening, but think there's a good chance you may not be able to totally limit them.

I've got a current 'noise' problem of my own which I am convinced in from withing the house.  A solid line, on the same freq each day and I see it switching on/off quite clearly (nothing fading in/out).  You can see it very faintly in the first image, often much stronger.  I've narrowed my freq range at the moment so it doesn't get counted as a meteor.

Frustrating though the noise is, just keep reminding yourself .....  at least we are capturing meteors .... and that's pretty cool    

Cheers

    Al

 

[Gasman]

Hi Al

Thanks for that I did wonder as the lines didn't match when any thing switched on although I suppose a neighbours leccy supply could cause that too!

Steve

[Gasman]

Had quite a few lines tonight which seem to indicate interference/bad weather futher afield!

[Al.Grant]

Hi Steve,

I've posted images of some of he interference I see on my detector on my website here:  http://www.ukstargazer.org/meteor/non-meteors-noise/

I'm hoping to get some time in the next few days to try and actively hunt down some of the sources of local noise.  There is a long duration one in particular that I want to try eliminate as it's started to show up on a freq just above where my meteor detections appear.

I know it's local interference as it follows when I retune the FCD dongle, next I want to try rotating the antenna left/right to see if I get any indication of the direction the noise is coming from.

So far I've tried checking things in the house (lighting/heating/microwaves etc) and also watched the screen when my neighbour is in his shed using his lathe and other heavy power tools ... nothing!

Al

[SteveNickolls]

Hi Al,

Some interesting screenshots you have there. I'd agree Screenshot 2 looks like a satellite track. Screenshot 3 is a very bright, regular return when present and that makes me think it's a large-ish object orbiting across the GRAVES radar signal. Even when I've seem a reflected ISS signal its nowhere near as strong or bright as the one in the screenshot.

I've not (yet) seen anything like your screenshot 4. Screenshot 5 shows three signal each 1000Hz apart (1700/2700/3700Hz) and another faint signal below 1600Hz. While I haven't seen a track which switches frequency like that I have seen what I took to be an artefact of SL which I have seen always at 2000Hz on three occasions when I have been 'playing' with Colorgramme while SL is running. At first I wondered if I was getting a direct signal from GRAVEs due to some atmospheric condition but settled on an artefact as turning SL off and back on cleared the track every time. I attach a screen shot of what I have been seeing.

Best of luck trying to track down the 'culprits'.

Cheers,

Steve

[Al.Grant]

Hi Steve,

Thanks for your thoughts, I think tracking down some of these will take a bit of time (and in some cases a bit of luck!).

I should point out that on image 5 the signal at 3700hz only steps down to 2700hz because I dropped my FCD centre freq from 148048Khz to 148049Khz because I wanted to be absolutely sure it was local noise.

If it had been something transmitting on a particular freq then it wouldn't have stayed the same level above where I was tuned.

I know that the object in screenshot 3 has been seen by Phil and the overall characteristics of the detection were a very similar including  times, duration and shape of the trace.

I've changed my SL screen now so it's split.  The left side shows the area around my normal meteor detection freq.  

The right side shows the spectrum all the way up to around 7000hz I'm hoping this will help me in tracking down nearby interference and also give a wider/longer trace for suspected ISS/Satellite tracks

The 3700hz line is still there, far enough away from the detections that it's not a problem, but it will be good practice to try track it down. Especially as there are times I see it much closer to my detection freq.

Your 2k artefact looks very stable and much like what I see if I ever turn on the 2k signal generator.  But not obviously you wouldn't actually see that unless you had actually switched on the signal generator!

Al

[Gasman]

Hi Al

Wonder if its worth sussing out any other beacons with maybe different frequencies to try?. I only know of the Graves one but there must be plenty of others.

Steve

[Al.Grant]

Hi Al

Wonder if its worth sussing out any other beacons with maybe different frequencies to try?. I only know of the Graves one but there must be plenty of others.

Steve

It needs a CW carrier, so most other radars are out.  I think many used to use the analogue TV transmitters, but the digital ones don't work.

I don't think there are any other options (at least not better ones) other than the Brams HF beacons in Belgium.  The dongle should be OK on that freq but it required a totally different antenna.

I've seen discussions where others have looked for alternatives and not found any (at least not in the UK/EU).  If you look at the RMOB site pretty much everybody is on 49.9Mhz (Brams) or 143.050Mhz (Graves).

Al

[todd8137]

Ferrite rings or clamps might cure this if you winding coils out of coax they are freq Dependent what freq do you use ?

[Gasman]

I did two windings of coax on the antenna just before the connection as per the instructions made by winding around an aerosol can maybe 50mm diameter and the funcube dongle is tuned to a frequency of 143048 kHz for the Graves beacon at Dijon!

cheers

Steve

[SteveNickolls]

Hi Guys,

Can I add another 'what is this?' to signals picked up by SL?

I first noticed the signal at 13.22 UTC this afternoon and which has continued up to now, unfortunately causing SL to count the stronger returns as a meteor trail when the signal is above the THRESHOLD value of 18. The S:N ratio can be above 22 at times. I had a similar issue in September when I thought the signal might have been a Earth-Moon-Earth bounced signal from GRAVES but today the signal has persisted even after the Moon has dropped below the Dijon horizon. In hindsight the signal was too strong, much stronger than the ISS returns I see so I don't now believe it is the Moon at all. However as to what it is I have no clue. Over the afternoon the signal frequency slightly varies between 2178 and 2183Hz on the SL waterfall.

I have not seen the signal since the 12th September and I am hoping it will go away as it makes meteor counting with GRAVES difficult. I could raise the THRESHOLD value to 23 but would rather not have this as a permanent solution.

Can I ask if anyone else picked up this signal today?

Cheers,

Steve

[Gasman]

Hi Steve

Nothing like that today although I didn`t have the laptop switched on at the time you did. My oldish win 7 laptop runs very hot so reluctant to leave it running for any length of time.

The pulses in your screen grab look very regular, can you see them most of the time or just certain times of the day?

It does seem to correspond to the faint constant line I get at 2130 Hz!

regards

Steve

[SteveNickolls]

Hi Steve,

Thanks for your post. I'm kind of sorry you haven't seen anything similar today, although I wouldn't want your counts to be out like mine are :-) I haven't seen this signal since mid-September when it suddenly disappeared later the following morning. I put that down to the Moon going below the horizon and the weather at that time affecting propagation. At the time it really seemed to coincide with the Moon and I found on the Internet- http://dk5ec.de/Graves-Echo-english.pdf a document which in picture 4 showed almost an identical signal return attributed to 'bounce back' off the Moon. The signal however is at times very strong and appears far brighter than the reflected returns of say the ISS which while being a much smaller object is only 260 miles up. The signal I'm getting has the characteristic of fading over irregular periods as do EME signals but the signal was still being received when the Moon went below the Dijon horizon around the time of my earlier post today so I have to rule that out. Interesting that you are getting a persistent signal at 2130Hz, would you say it looks identical? I can confirm I haven't had a signal at that frequency. As I now write the signal appears finally in the last few minutes to have finally disappeared. I'm left thinking it's some product of propagation when the conditions are 'right' (or is that 'wrong'?).

Thanks again for your input Steve-much appreciated. I'm sure this issue with odd signals will run and run.

Cheers,

Steve

[Gasman]

Hi again Steve

This is the mysterious line at about 2130Hz, seems to be always on screen??

cheers

Steve

[Al.Grant]

Hi again Steve

This is the mysterious line at about 2130Hz, seems to be always on screen??

cheers

Steve

Steve,

Very similar to the lines I see,  just a different freq.  

For a quick test you could try to retune your dongle to 143049K.  If it's local electrical noise then it should follow you, staying the same distance above the tuned freq.

Here's how it looked on my screen:  http://www.ukstargazer.org/wp-content/uploads/capt1409281135.jpg  ( link rather than full screenshot)

If you then tune back to 143048K is will jump back up.   Whilst I know these unwanted lines are annoying, it doesn't look like it's impacting on your meteor count which would obviously mess things up.

If you do find that it's an external transmission then you could leave your dongle tuned to 143049K, the meteor detection will still work it just means that any audible pings will be heard at a 1khz tone rather than 2khz.

I also found that closing down the bandpass filter helped in excluding some unwanted signals.  

Quick and easy to just change by dragging the edges of that blue filter range on the freq scale and narrow it down a bit close to the actual meteor detection freq.  Was very useful for me when my noise line at 3700hz starged get included in the meteor count!

I was hoping to get some time to look at the source of my noise, but not really had a chance yet

Al 

[Gasman]

Yes you're right Al it does move with the frequency adjusted so thats local electrical noise then !!! I`ll try some of those ferrite coils and see if it will filter out. As you say its a bit annoying but doesn`t affect the counts.

Steve

[Al.Grant]

Steve,

Yeah, looks like noise then if it's following your centre freq.

It may be worth a quick go plugging your dongle into a different usb port.  If using a rear port then try a front one etc.  I've read that ports next to each other can show different noise characteristics, so I gave this a try.

Although I have my dongle on a usb extension lead to move it away from the PC, yesterday when I moved the cable from the rear to a port on the front my 3700hz noise line has almost totally gone.

I still see it sometimes but it's far weaker, that said I now see occasional but different noise lines show on the display.  But they are all much weaker than I was seeing on the rear port, so it's a big improvement.

Al

[Cath]

Are you guys using any sort of band-pass filter on your front ends (between antenna and input to your SDR dongle) ?

[Gasman]

Hi Cath

Im still learning at this part of the EM spectrum and the various filter options have never really occurred to me before. My other hat is in stellar spectroscopy where too much tinkering with the received image can remove (or even worse add ) data so I would assume that filtering radio signals can be a bit iffy too, or maybe not??.

cheers

Steve

[Cath]

Hi Steve

The USB dongles your using have a very limited dynamic range due to them using 8-bit ADC's to sample the incoming RF across the entire RF range the dongles cover, their RF front ends are totally wide band. This is a problem because what you're doing is feeding everything that comes from your antennas directly into the dongles RF front end, that will undoubtedly include strong out-of-band RF carriers that will cause intermodulation and overload in your RF front ends. The end result of all this can be several things, but one of the effects will be seeing carriers within your interested frequency range that aren't really there but are the result of the intermodulation and/or overload.

To try to eliminate/reduce these problems (which will most certainly be there for you with those 8-bit SDR front ends) you need to provide some basic RF filtering to reduce all the out-of-band RF carriers/interference leaving just the ones you want (143MHz). The best way to do that without causing much more than about 1dB (2 at most) loss is to use a 2-pole helical filter, although as you apparently currently have no filtering at all even a simple 2 or 3 pole direct-coupled band-pass filter would no doubt help a lot.

An example of a simple direct-coupled bandpass filter.

Anyway, just letting you know Steve, thought it might interest you to know what problems you face with those wideband RF SDR's without the proper RF filtering.

[wxsatuser]

You could try a shorted quarter wave stub or an open half-wave coxial stub.
This will pass the design frequency and attenuate other frequencies to some degree.

It will not attenuate odd harmonics.

You will need a coxial T connector and a piece of the same coax your using.

The length of a quarter wave would be approx 524.5mm x the velocity factor of the cable.

[Gasman]

Thanks for the info guys, most helpful

Steve