Radio EMI problem...

I'm trying to track down an EMI problem. This is with my solar powered RC plane.
Specifics: I'm using standard 6M RC gear from JR on ch 04, FM on 50.880 Mhz.
I've got two receivers that exhibit exactly the same problem. A JR FM receiver and a berg FM receiver.
Both work fine until I turn on my switching solar maximum power point tracker.
The power tracker runs 6 seperate channels at about 25W each channel. The switcher runs at ~ 150Khz +/- 20Khz
I've filered, shielded and added caps with very little effect.
The receiver is in the tail of the airplane the converter in the front,. There is currently no electrical connection from the receiver to the other electronics on the plane. I'm currently powering the receiver from battries. The only connection is capactive to the carbon fiber airframe.
I'm using an Icom R3 to hunt for the EMI.
The Icom receivers shows the 50.880 signal clear as a bell. When I turn the TX off the icom sees no no difference in background signal with the power converter either on or off.
When I run the Icom receiver tuned to 50.880 near the RC receiver I see a significant reduction in range, but not as much reduction as when I run the power converter.
My first theory is that I am generating IF or image noise that is clobbering the receiver. To test this I set a signal generator out next to the receiver and ran it at 450Khz, 455Khz and 10.7 Mhz with no effect on range. (signal generator is an old digital fluke runing 13dbm into a 2 ft peice of wire)
Any ideas on what I can do to solve this... it is driving me crazy, I've been working on it for more than a month.
Paul (Kl7JG)
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| Specifics: | I'm using standard 6M RC gear from JR on ch 04, FM on 50.880 Mhz. | I've got two receivers that exhibit exactly the same problem.
Speaking of the problem, what is the problem? Jittering? Loss of range? Something else?
| A JR FM receiver and a berg FM receiver.
Note that both of these are single conversion receivers. But they're the good single conversion receivers -- in theory, as good as the dual conversion receives out there, but the duals might still be better for some applications, perhaps yours.
You might want to try a dual conversion receiver -- they might be better able to reject the interference you're seeing.
| The power tracker runs 6 seperate channels at about 25W each channel. | The switcher runs at ~ 150Khz +/- 20Khz
You're probably seeing harmonics of that, somewhere. I'm not sure what this thing is, but switching power supplies are well known for generating interference. ESCs do too, but the capacitors used on them filter it out pretty effectively. | I've filered, shielded and added caps with very little effect.
Ferrite beads around all the wires to it perhaps? The servo wires might also be bringing it into the receiver -- I've seen people putting small chokes in their servo wires, perhaps that would help? (I think it was mentioned in the most recent Model Airplane News.)
| I'm using an Icom R3 to hunt for the EMI. | | The Icom receivers shows the 50.880 signal clear as a bell.
Unfortunately, RC receivers tend to be cheap, and will get birdies and such. Just because there's no interference at 50.880 mhz that doesn't mean that there's nothing to interfere with the RC receiver.
| When I run the Icom receiver tuned to 50.880 near the RC receiver I | see a significant reduction in range, but not as much reduction as | when I run the power converter.
The Icom receiver causes interference by itself?
| My first theory is that I am generating IF or image noise that is | clobbering the receiver. | To test this I set a signal generator out next to the receiver and ran | it at 450Khz, 455Khz and 10.7 Mhz with no effect on range.
I believe that 10.7 mHz is a dual conversion thing, and neither of your receivers is dual conversion. Well, JR does make some, but most of their receivers are not.
| Any ideas on what I can do to solve this... it is driving me crazy, | I've been working on it for more than a month.
Well, if it's a solar plane, it's probably costs enough that $50-$100 more for a receiver is well spent if it makes the problem go away. :)
And you could try 72 mHz equipment ... maybe it would work better? In theory it should work the same, but it's a possibility.
--
Doug McLaren, snipped-for-privacy@frenzy.com
These pills can't be habit-forming; I've been taking them for years!
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Loss of range. (60% reduction),

Who makes a good 6M dual conversion receiver? (See the end for why it gopt to be 6M)

I've got both common mode and normal mode inductive, ferite filters on all leads going to the receiver. The problem still exists with the receiver completly disconnected from the other aircraft wiring. The servo leads are short (6 inches) and filtered.

Not uncommon for two receivers tuned to the same area to have LO image problems.

I'd gladly spend $500 for a receiver if it made the problem go away. 6M receivers are hard to come by, JR, Berg and FMA are the only ones I know of. I had some real bad problems with an FMA a while a go and I'm a bit gun shy.

One of the purposes of the airplane is to set some FAI records, I've built a 1W 6M amplifier and put it on a 4 element 6M yagi so I have positive control. I can't do that on 72Mhz. My higher power rig also limits me to straight FM, not PCM as I drive my 1W transmitter with a trainer cord. This problem is with the normal JR Tx, not my super Tx. As a side note I've put my Super TX on a spectrum analizer and it looks good well within normal Ham tx purity limits.
P.S. Before anyone freaks out wrt this project and the AMA presidents last note about being nice with the FAA, I've been talking with the local FAA FSDO (Flight Standards District Office ) and we have an understanding as to where I can fly this for alttitude attempts how high, notification requirements etc....
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| >Speaking of the problem, what is the problem? Jittering? Loss of | >range? Something else? | | Loss of range. (60% reduction),
Hmm, not good. Any sort of strong RF intereference can desense a receiver, even if it doesn't directly interfere.
How far are you trying to go anyways? I'd think that with good directional antennas, pointed in the right direction, you could do 5 or so miles even with just one watt.
| >You might want to try a dual conversion receiver -- they might be | >better able to reject the interference you're seeing. | Who makes a good 6M dual conversion receiver? (See the end for why it | gopt to be 6M)
| I'd gladly spend $500 for a receiver if it made the problem go away. | 6M receivers are hard to come by, JR, Berg and FMA are the only ones | I know of.
Futaba does too. I've got a few of them. They seem to work fine, though I don't have the challenges that you do.
I don't think there's any shift issues with the 50 mhz equipment, so a Futaba 50 mhz receiver should work fine with your JR transmitter. Were you close, I'd let you try one of them, but you can order one from Tower Hobbies easily enough for under $100.
http://www2.towerhobbies.com/cgi-bin/wti0001p?&I=LXAKL8&P=ML http://www2.towerhobbies.com/cgi-bin/wti0001p?&I=LXAKM4&P=7
You might be able to get some more range by properly tuning the receiver antenna, making it the right length to be a 1/4 wave antenna? Perhaps cracking open the antenna and finding the other lead, turning it into a 1/2 wave dipole? (This all depends on your receiver internals, of course -- there might be a coil inside to make the antenna resonant even though it's less than 1/4 wavelength, especially for 50 mhz. Maybe making a 5/8 wave antenna? (Of course, that would be very long.) Sounds like you know what you're doing, so you can try that.
| I had some real bad problems with an FMA a while a go and I'm a bit | gun shy.
I've had fine luck with FMA receivers, though I've not tried a 50 mhz one.
| >And you could try 72 mHz equipment ... maybe it would work better? In | >theory it should work the same, but it's a possibility. | | One of the purposes of the airplane is to set some FAI records, | I've built a 1W 6M amplifier and put it on a 4 element 6M yagi so I | have positive control. I can't do that on 72Mhz.
Most R/C transmitters transmit at one watt, whatever the band. So why would you need a one watt amplifier? Or was 1W a typo, and the actual figure is higher?
The FCC regulations only permit one watt for R/C control on the ham bands, so I don't see where they let you use more power than the 72 mhz band anyways.
And is there any reason you couldn't use a directional antenna on 72 mhz? I don't think the 72 mhz band would let you make your own transmitter, but I don't think it would prevent you from making your own antennas?
| My higher power rig also limits me to straight FM, not PCM as I | drive my 1W transmitter with a trainer cord.
I'm not sure that's the case. PCM uses the same FM transmission mode as FM (PPM) does, it's just that the signal being sent is different, PCM vs PPM. Your transmitter should happily transmit the PCM signal just like the FM signal.
... though some transmitters do send a PPM signal over the buddy box cord, even when in PCM mode. But this would only be the high end transmitters ... the lower end ones send the same signal as they transmit.
The Futaba 6XAS radio I have definately sends PCM both ways. But the 9C I have doesn't -- or, at least it has the option of not doing so. If your radio has a module, you might be able to pull the PCM signal from the wires going to the module if you need to.
Not that I think PCM will help -- it will have exactly the same range problems as PPM.
--
Doug McLaren, snipped-for-privacy@frenzy.com, AD5RH
`I never entertain wicked thoughts -- but sometimes they entertain me.'
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after reading the complete dialog, the odds are that a harmonic of th
switching frequency gets into the IF of the receiver(s).
if this is true, then dual conversion would not help here since it ha its highest gain part in its second IF which is essentially identica to that in a single conversion receiver (but it would be worth th test).
you will probably wind up having to completely shield the switcher using feed-through capacitors at its inputs and outputs.
secondly, you may want to build a metal can for the receiver to shiel its IF strip which uses non-shielded filters in most receivers. an ground the crystal can. if the switcher is operating with those hig currents it most likely puts out a nice picket fence on the spectru analyzer - if you could buy, borrow or steal a spectrum analyzer tha would save you a whole bunch of time.
you would probably also benefit from a coaxial antena connection an use a 'tuned' (appropiately loaded) dipole-like antenna, as far away a possible from switcher.
where are you located?
peter berg kq6a
-- potifa ----------------------------------------------------------------------- potifar's Profile: http://www.rcgroups.com/forums/member.php?action=getinfo&useridD0 View this thread: http://www.rcgroups.com/forums/showthread.php?threadid $872
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Several comments:
1W Tx...... When an RC manufactuor actually publishes TX watage values it is 500mw or 750mw. I know that 1W is not much more, and may not be worth the effort. My 1W tx delivers 1W 3 inches at the terminals of a 3 el yagi. That is probably a different discussion.
Antennas...and noise source I have room to put a full resonant dipole in the wings, but the wings are covered with solar cells, The wing also has an Al spar that conducts the return current from the cells back to the center, so I'm not sure how well the antenna would work that other conductive noisy components. ~12A of current in each wing The switcher peak to peak ripple current is on the order of 1/2A at the imput to the switcher, I've got a big cap on each of the switcher in0put leads before they leave the foil enclosure. I've already put the switcher in an Al foil enclosure The switcher ripple current is very hard to reduce as power inductors are heavy, I can either increse the Sw freq, or add bigger inductors...
Note to Peter:     The first Rx I tried was one of your Berg rx's I've also tried the JR, both seem to behave identically, the JR is actually more sensitive to the interpherance as it does not try to make sure the signal makes sense it just passes what it receives straight through.....thus I've done most of the troubleshooting with the JR.
I don't have a spectrum analizer I can take to the plane, but the Icom R3 has a spectrum display with 5K,10K,20K,and 100K wide bins that I can use to look at 1Mhz at a time. I've spent some time looking for image problems, but I'm not sure where to look.
Is the Berg Rx IF at 455Khz?
One last note, The plane also has a 900Mhz telmetry radio tranmitting at ~100mw, but turning that on and off has absolutly no detectable effect on the RX range.

I'm in San Diego, specifically in Solana beach. Troubleshooting this problem is complicated by the fact that I can only trouble shoot when it is sunny. We've had a lot of costal low clouds in June...
Note to Peter I belive I have your personal E-Mail, if it has not changed in the last 2 years I'll send you an E-Mail and try to set up a phone conversation.
Paul KL7JG
On Tue, 6 Jul 2004 02:40:11 -0500, potifar

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<SNIP>
Just a thought, are you sure it is being caused by radiated emissions from the switcher? Is the RX powered from the output of the switcher, if it is then it could be conducted emissions getting into the RX that way. To test this you could try powering the RX from a seperate battery pack while the switcher is running. Like someone else said you could try making a shielded box for the switcher.
Thinking about it the third harmonic of the switching frequency is almost bang on the IF frequency (455kHz).
Thats about all I can think of at the moment, I know your pain I had to track down a similar problem with a product at work a while back, noise from a switching power supply getting into the RX of a radio, I fixed that and then had problems on transmit :)
Best of luck Vaughan
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wrote:

This subject attracted my interest, and am sorry it's about run dry. I do have two 50.920 MHz dual conversion receivers, made by HiTec or RCD, with Futaba J servo sockets. They are marked FM/HFD-08RD, whatever that means. I had them in different planes some time ago, and at present am not using them. I also still have the transmit module and the rubber duck for 6 meters, so I can run any sort of test you might like me to try. Or will lend/sell you one of these receivers if you prefer.
What piques my curiosity though is - why do you need a 25 watt switching power supply on board. I've fitted out planes with ATV transmitter and mini video camera, but don't need anything more than battery power here. Just curious, but willing to help if I can.
Olin McDaniel, W4PFZ, AMA 30932, Leader Member To reply by email, please remove "abcd" from Return address ----------------------------------------------------- "Ignorance is treatable, Stupidity is incurable. Sometimes the difference is hardly distinguishable, however."
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