Anyone having trouble on 53 Mhz (6 meters?

I have been flying on 53.4 for years and years. Now all of a sudden I am getting bumped all over the place. Had to retire the old AM sets on this frequency and sent my JR receivers and transmit modules to JR to have changed over from 53.4 mhz of the band. They said "can do - no problem"..You gotta love the JR folks. I have heard here and ther that ther is interference on the high end of the six meter band and wonder if anyoneoout there who flys on 6 meters has encountered this. Incidentally, at our field we can fly without any problems on the 50 mhz portion of the band...but forget the 53 mhz end..it just won't work any more... At least I can get the JR radios fixed for that portionof the band. Frank Schwartz AMA123 Ham license W4KFK

Reply to
Frank Schwartz
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Frank,

I'm just getting back into RC after a long absence. I asked around on the boards about six for my radio(s). Some guys reported that they were getting hits when the band opened. I'm not surprised, you know how six meters can be when the band goes long. Some thought it was from repeaters. I went with 72 just to be safe.

Tony AK1O

P.S. AMA123? did you teach Hal deBolt how to fly? :-)

Reply to
Tony Van

| I have been flying on 53.4 for years and years. Now all of a sudden I | am getting bumped all over the place.

Well, if you look at the ARRL band plan at

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you'll see that 53.4 is right in the middle of `Repeater inputs (except as noted; 19 channels)'. Yes, those channels are listed as radio remote control later, but all it takes is somebody nearby trying to hit a repeater and using lots of power to swamp your receiver.

You appear to live in just outside of Nashville, TN. I can't seem to find any repeaters listed online that would have a such a matching input, but I suspect that there is one.

You might want to get a scanner and scan about 100 kHz above and blow your channel. I suspect you'll find somebody talking on a repeater. Most repeaters use FM, and most scanners can do the 50 mHz band, so pretty much any scanner wil do.

As for what to do about it, there's not really much you can do, unless somebody is transmitting right on your frequency (if they are, they're deviating from the band plan and while the FCC won't really care, maybe if you ask nice they'll correct it.) If they're near your frequency, then there's really nothing you can do.

Not many people use 53 mHz anymore for RC for these reasons. I suspect it'll be removed from the band plans for R/C use at some point in the future ...

Reply to
Doug McLaren

In answer to two questions (thanks, gentlemen, for your response)..no I didn't teach Hal DeBolt tofly, but I have taught abouthalf of the flyers in the Nashville TN area over the years. I am 79 years old..been building and flying for 69 years...still building and still flying.... the other thing is that there is an aircraft landing beacon about 1500 feet off the end of our runway. It is on 75 mhz (on my scanner)..plus I hear a very strong signal from the same beacon on

53.6 mhz....the durned thing must be very dirty...I never had problems at this field before on 53.4.....I will check with the FCC in Atlanta and will ask if they can put me in touch with the service man for this beacon...maybe it needs retuning or something..... All of this is trange as Ihave never ever had troubles on this frequency (53.4) and I have flown onthat channel for at least 40 years... now I have a big box of silver seven and EK and Hobby Lobby am receivers on 53.4....no longer useable.... What the heck..I have Futaba and JR on 00 and 07....I just hate to put away those old friends who have served me so well...with nary a glitch....... Frank Schwartz AMA123 W4KFK in Hendersonville (Nashville area) TN
Reply to
Frank Schwartz

| the other thing is that there is an aircraft landing beacon | about 1500 feet off the end of our runway. It is on 75 mhz (on my | scanner)..plus I hear a very strong signal from the same beacon on | 53.6 mhz....the durned thing must be very dirty...

As a ham, you ought to know this already, but ...

75 mHz - 10.7 mHz - 10.7 mHz = 53.6 mHz.

Most FM radios, including the scanner where you probably picked up the signal at 53.6 mHz, have an IF filter with a 10.7 mHz value, and a strong signal will often also show up at 21.4 mHz above or below it's true frequency.

More on that here --

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(Read the section on `Image reception'.)

Ultimately, just because a general purpose scanner shows a signal at a given frequency, that doesn't mean that the signal is actually there.

However, the receiver in your plane works via a similar principal, and it is quite possible that it's seeing the 75 mHz signal at 53.6 mHz too (just like your scanner), and that's helping to swamp your relatively weak transmitter signal. Unfortunately, if this is the case, there's nothing that the beacon operator can do (or has to do) to fix your problem -- the problem would be in your receiver.

| I will check with the FCC in Atlanta and will ask if they can put me | in touch with the service man for this beacon...maybe it needs | retuning or something

Hopefully you haven't already done so. They'd probably laugh at you once you explained it to them. :)

Contact the local ham group. I'll bet they could help you figure out what the source of the problem is (though you may have already done so) and suggest how to fix it. Changing channels (within the 53 mHz band) might be all you need to do.

Reply to
Doug McLaren

There are a few choices Frank. Go to the 72 mhz band or try to find a receiver that has a tighter front end that wont let the 75 mhz freq thru the mixer. (if that is what is causing the inteference.) I think changing the xtal to 10.7 below the input would do it but that is a major circuit change that would probably null the FCC type acceptance rules. We fly off to the side of the ILS just inside the ADF/marker a mile away and I dont think anyone is getting hit. Too bad you cant jack an earphone into the receiver detector and listen to the signal.

Reply to
jim breeyear

| There are a few choices Frank. Go to the 72 mhz band or try to find a | receiver that has a tighter front end that wont let the 75 mhz freq thru | the mixer. (if that is what is causing the inteference.) I think | changing the xtal to 10.7 below the input would do it but that is a | major circuit change that would probably null the FCC type acceptance | rules.

Three things there --

1) This is a receiver -- type acceptance is not an issue. You only have to worry about that if you modify a transmitter.

2) This is the ham band -- again, type acceptance is not an issue.

3) Almost everything uses that 10.7 mHz stage. If you replace that, you'll need to replace the main crystal, and maybe some other stuff too.

Actually, changing to a different channel might be all he needs. 53.1 mHz would get you a lot further from any 53.6 mHz noise the receiver might be generating internally.

| We fly off to the side of the ILS just inside the ADF/marker a | mile away and I dont think anyone is getting hit. Too bad you cant jack | an earphone into the receiver detector and listen to the signal.

Actually, he emailed me directly and I suggested exactly that. I don't know if he'll do it, but it's an idea. There's a chance of ruining the receiver, but he probably knows his way around a soldering iron so the odds are small. And if the receiver isn't usable as it, what do you have to lose?

Basically, you'd open the receiver up, with power, and the transmitter on, and take a high impedance headseat on your neck (not on your ears! This could be very loud!) and hook one wire to the negative terminal on the battery, and start touching other contacts on the circuit board until you can hear the audio signal. Once found, solder a wire to it and pull it out of the receiver, and close it up.

(Disclaimer: I haven't tried this, but it sounds easy enough in theory ...)

Once done, you can hear the signal on the receiver, and so you set your transmitter up at your field, and take your receiver with a battery and your headphone, and start walking around where you lose the signal, and see what the signal sounds like. If it sounds like the beacon, then you'll know what that is. If it sounds like something else, who knows ...

Reply to
Doug McLaren

Let's not forget that six meter ham repeaters are placed interstitially amongst the R/C frequencies. Those have been known to make 53 MHz operation nearly impossible in some metro areas.

I utilize 50 MHz. I have not had a single glitch that could be attributed to in band interference or out of band interference. Multipath, which is common to all radio frequencies does occur upon occasion.

NI

Reply to
Not impressed

| Let's not forget that six meter ham repeaters are placed | interstitially amongst the R/C frequencies. Those have been | known to make 53 MHz operation nearly impossible in some | metro areas.

I already mentioned that ...

| I utilize 50 MHz. I have not had a single glitch that could | be attributed to in band interference or out of band | interference.

I use 50 mHz some too, and haven't had any problems with it either. Or with 72 mHz either, though I might have had a problem with channel

40 in the 72 mHz band last friday (still not sure what happened ...)

| Multipath, which is common to all radio frequencies does occur upon | occasion.

I wouldn't expect multipath interfence to be a large problem with R/C gear, at least not under normal conditions. (Is your flying field surrounded by tall metal buildings?) I'd expect intermod or poor image frequency rejection to be larger concerns.

The best discussion of the various forms of interference we run into that I recall seeing is the one that Berg made --

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Granted, it's purpose really isn't to explain interference but to say how his single conversion receivers are as good as or better than the competitor's dual conversion receivers, but he does a good job of covering interference types as well. And this stuff applies to the other R/C bands other than 72 mHz as well.

Without actually listening to the signal, as received by the receiver, we're really just guessing about what's going on.

It wouldn't surprise me if any 53 mHz receivers out there just aren't very good. After all, I don't think anybody makes them anymore, and back when they were made, the technology existed to make them good at rejecting interfence, or to make them reasonably small, but I don't think they could do both at the same time. (Small, good or cheap -- pick any two!) Today, things have improved, but it's still the same set of tradeoffs ...

Reply to
Doug McLaren

Receiver design is old hat and is not the least bit as demanding as rocket science. There is nothing new under the sun, except technology to make them cheaper.

R&S Systems made 72 MHz receivers the size of chewing gum packs that were fantastic then and today.

Multipath gave my Kraft Series 82 FM receiver some difficulty whenever I flew over the power lines at the end of our field. A little bit of a down elevator glitch, otherwise, it was okay. I know this is what caused the multipath because I had no problem before the power lines were installed.

NI

Reply to
Not impressed

There have been wierd cases in our area where improperly adjusted repeaters(transmitters, and any are subject) were putting out additional signals due to mixing products in the final amplifiers of the transmitter. Certain conditions have to exist. Occasionally the local pager system nearby the ham repeater will cause the repeater to transmit burps and tones. Being able to hear the rogue signals enabled them to be located. Siting transmitters properly is a big job. I dont know much about receiver design but having a good selective input circuit ahead of the mixer is a plus to minimize out of band signals. If it cant get thru the "front end" then it wont get to the mixer. However rogue signals in the band pass will cause problems.

Reply to
jim breeyear

| Receiver design is old hat and is not the least bit as demanding as | rocket science.

Even rocket science isn't that complicated -- we certainly had rockets centuries before we had radios, and we got the modern liquid fuel rockets not too long after the radio was invented.

`Rocket science' is quite the misnomer -- at their basic level, rockets are VERY simple.

| There is nothing new under the sun,

That is definately not true, especially when talking about electronics. Granted, with radios most changes are evolutionary rather than revolutionary, but things are definately improving.

Modern R/C receivers seem to not change the RF part of the design too much (though that's changing too), but the parts after have certainly changed a lot with the introduction of DSPs and microprocessors.

| except technology to make them cheaper.

... and smaller, and better.

Ultimately, you want your receivers to be small, to reject interference well (and get adequate range) and to be cheap. If you're willing to make it larger, you can get better interefence rejection by adding better or more filters. And by spending more money, you might be able to make it smaller again. But ultimately it's a number of tradeoffs, and most receivers that we use are not that great at rejecting the various forms of interference they may receive. They're good enough most of the time, but signals on certain other frequencies can cause them problems.

At the other end of the spectrum, consider the typical ham 2 m repeater. Thanks to the awesome duplexers (filters) they have, they can transmit at 1000 watts only 600 kHz away from the signal that they're receiving on, on the same antenna, and yet the receiver is still incredibly sensitive. Of course, they're physically quite large, and not really cheap. (Small, cheap, good -- pick any two. In this case, they pick `good' twice and nothing else.)

| R&S Systems made 72 MHz receivers the size of chewing gum | packs that were fantastic then and today.

Actually, as time goes on, the RF spectrum gets more and more noisy. What worked back then may very well not work as well today. Or if it does work, it may just be because it's in a bit of spectrum that's still lightly used (and the 53 mHz band certainly qualifies.)

I don't know anything specially about R&S's receivers, but if they're more than 15 years old, they're probably not even narrow band, and so they'll be totally unsutiable for use today at all.

| Multipath gave my Kraft Series 82 FM receiver some difficulty | whenever I flew over the power lines at the end of our field. A | little bit of a down elevator glitch, otherwise, it was okay. I know | this is what caused the multipath because I had no problem before | the power lines were installed.

Multipath again? Again, it's only one of many sorts of interference, and it's rarely a big problem for us.

Yes, a power line could re-radiate a signal back to cause multipath interfence, but it would be very weak. A large metal building, fairly close, would be required to create a multipath signal that's strong enough to really interfere with our radios. We almost always have direct line of sight to our planes, so any multipath signals are usually much weaker then the primary signal and rarely cause problems.

Power lines can and do create interference of other sorts, however.

Reply to
Doug McLaren

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