Jump to content

Recommended Posts

I've noticed some interference from a couple of locations that I have been flying from, and I was wondering if anyone knew what the possible source of interference was. Please see the images below.

To me, it looks like digital data. Since I'm using 2.4GHz, is it possibly a local WiFi on the same channel? Or some sort of other communication?

post-5-1197493304_thumb.jpg

Share this post


Link to post
Share on other sites

From another site. BTW, the interference comes and goes. The lines are visible for usually one video frame, and then disappear, only to reappear at different locations of the video image.

post-5-1197493485_thumb.jpg

Share this post


Link to post
Share on other sites

What channel are you on? If that's channel 3 (2450MHz) it could well be someone (up to several miles away) is prepping a delicious bowl of microwave popcorn, or is nuking his TV-dinner, as most microwaves use that frequency and leak up to several watts in RF at that frequency :blink:

Cheers,

Sander.

Share this post


Link to post
Share on other sites
To me, it looks like digital data. Since I'm using 2.4GHz, is it possibly a local WiFi on the same channel?

Could be business or household WiFi, cordless phones, are any number of other sources. The usual freq hopping that goes on with those digital RF appliances may explain why the interference appears randomly on your video signal.

If you are using an omni Rx antenna then replace it with a patch. Its narrower beamwidth might mask the source. Otherwise, a new flying field, away from all of mankind, is your best bet; Unfortunately, your videos already show you are out in the boonies, so even that idea does not seem to help anymore.

Share this post


Link to post
Share on other sites
I've noticed some interference

Welcome to the club :(

Just be sure it's not from you, mobile phone, bluetooth or even standing too close with your TX :rolleyes:

Terry

Share this post


Link to post
Share on other sites

ssassen: Wow, that's comforting to know that when I cook food, I've got several watts of 2.4Gig blasting into me! :rolleyes: You'd think that would be closely regulated by the government.

Ok, here's more info. The second and third images were flown first (sorry, got them out of order) on channel 1 (2.410GHz) and from the same location. It only appears to be out in the boonies because of the direction I was pointing at the time. I was at the same location as when I made this video:

Right at 34 seconds in the video, you can see the edge of the field (which is where I set up at) and a bunch of houses just behind there. The plane was at pretty good range (0.6 miles or so) when those images were captured. So the houses were much closer to me than the plane was. The receiver setup was the Oracle with a whip and GP patch pointed in the direction of flight (away from the houses).

First image was done later and at a different field. After the experience at the last field, I changed to channel 8 (2.510GHz) and this time flew with the Oracle and two whip antennas. The reason for the two whip antennas is I always do close in flying at this site. I suspect there is some broad spectrum noise at this location though as I've had RC control hits before, so it's not surprising to see stuff on the video as well. Although I used channel 1 at this location many times and don't remember seeing this kind of interference. I will have to remember to switch back to channel 1 for this location. It would appear you have to find the right channel to transmit on at each location.

BTW, I always try to stand as far away from the receiver/antennas as possible, and I have bluetooth disabled on my cell phone.

Edited by twinturbostang

Share this post


Link to post
Share on other sites

I've got another video interference question. Please see image below...

I'm refering to the horizontal lines seen in the image. Sometimes I see high frequency lines when flying but it usually just looks like video noise. This is different though. I changed transmitters (back to my old 600mW 2.4GHz Lawmate), so I'm thinking it's something to do with that, since I didn't see it with my other transmitters. Also, I'm powering the system directly via a 4 cell Ni-MH pack, so it's nothing due to a switching regulator. The problem is, I think I turned one of the pots on the transmitter before I realized it was the wrong one (was trying to change the video level). I know there's a video level pot, audio level (I think), and then something to do with the PLL. So, assuming I goofed, is it possible I accidentally messed with the PLL, and that's causing the lines?? Would a screwed up audio level mess up the video, even if I'm not using the audio? I'm just trying to figure out what I messed up! lol

post-1515-1200966036_thumb.jpg

Edited by twinturbostang

Share this post


Link to post
Share on other sites

Doesn't appear to be a PLL problem to me. If the Microphone has been completely removed, then the first thing I would suspect is mechanical vibration on the Tx.

(1) Do the video lines change as you move the throttle around and do they go away with the motor off (power-off glide)?

(2) If you sharply rap the Tx's metal sardine can case with the plastic handle of a screwdriver, do you see the video flinch at strong impacts?

Share this post


Link to post
Share on other sites

Well, the lines were visible before I even launched the plane. So I'm guessing it's not a motor vibration issue. Also, there was no microphone to begin with. The white line was never hooked up.

Ok, I just did a test on the bench. I still see the lines. They tend to slowly scan up, then the lines stop in place, then slowly scan down, etc. It's not even connected to the plane, so that rules out ESC, motors, vibration, etc. Just for giggles though, I tapped on the case to see what would happen. I have to tap on it fairly hard before real glitching lines appear. Also, I swapped my 500mW Tx in, and did not see the lines at all. Went back and forth several times and it does appear to be localized to the 600mW Tx. So I'm not sure what else to do now, except start turning pots. I'm not sure if you're familiar with this Tx or not, but the one I had turned by accident before is visible from the outside of the case, just below the channel dip switches. I can open the case and take a picture of where the pot is on the board though. That might give an indication as to what it does.

Edited by twinturbostang

Share this post


Link to post
Share on other sites

It's probably time to turn the pot (if it is related to the PLL then it will nearly always be an adj trimmer cap). Just mark it so that you can restore it back to where it was if things go south.

Share this post


Link to post
Share on other sites
Brian, if you need help tapping your TX, send it over to me ;)

Haha. Keep that hammer away from my transmitter!! :)

Mr. RC-CAM: Ok, I will try to work on it in the next day or two. I will try to post some pictures of the board. Maybe you'll be able to determine which ones adjust and which ones not to. :)

Share this post


Link to post
Share on other sites

Ok, here's what I've got. First pic shows outside of the case, with the channel selector dip switches and the pot below it that I accidentally turned. Second pic is flipping the Tx over and opening the case. The silver pot close to the wire leads is what I have adjusted previously to try and get better image quality.

So... which one does what? And which should I be messing with?

Thanks,

Brian

post-1515-1201059511_thumb.jpg

post-1515-1201059525_thumb.jpg

Share this post


Link to post
Share on other sites
So... which one does what?

Photo on the left shows the PLL's trimmer cap. Photo on the right appears to be the video level pot.

And which should I be messing with?

The PLL adj should involve an accurate frequency counter or spectrum analyzer to tweak it. The video level pot can be adjusted using the procedure summarized here: http://www.rc-cam.com/lawmate.htm

Share this post


Link to post
Share on other sites

The PLL adj determines the accuracy of the transmitting frequency. Each design has its own behavior, so it is hard to say how sensitive yours is to misadjustment. If it is truly messed up already, then playing with it some more is probably not out of the question. Just mark the current position so that you can restore it if need be.

Share this post


Link to post
Share on other sites

Since I don't know where it was originally, I decided to turn it some and see what happens. So far I haven't seen any change in video quality by adjusting it. However, that's with the receiver about 6'-8' away from the transmitter. At long ranges, the story may be different, if it is in fact altering the frequency. BTW, I also noticed that the transmitter is in fact worse than I originally thought in regards to vibrations. If I tap on it, I can get some pretty bad video interruptions. Much worse than what was visible in JMS's test over on rcgroups. That seems to be a separate issue, but is still important to keep in mind nonetheless.

Thanks for your help. I don't have access to any frequency measuring equipment, except for an oscilloscope at work. I will try to test the video levels at some point with that. But as far as adjusting the PLL, I don't know. Will have to figure that out.

Edited by twinturbostang

Share this post


Link to post
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now

×