Ross Kean

I believe that I know the answer to this but I am posting to get some responses from others to show to some doubters in our club.

We have a simple frequency board at our field where the flyer just puts a clothes pin over their frequency before they fly. Anyone going to fly has to make sure that their frequency is open and "pin" it to reserve the space. Works quite well as long as there aren't too many people flying at once. There are, however, a number of individuals at the club who have made their own personalized pins which cover their frequency plus the frequency on either side of theirs (three channels). They maintain that this practice is necessary to prevent frequency "bleed" so others don't interfere with them. I have always maintained that this is not necessary for modern radios and receivers and that this habit comes from the days before narrow-banding. They "smile and nod" but still use these pins. They get quite indignant if anyone wishes to fly at a frequency + or - one from them.

Opinions are like buttholes; everyone has one - so is there an authoritative reference I can point them to which provides an intelligent discussion of frequencies and the need (or lack thereof) to cover multiple frequencies? This isn't usually a big problem but I sometimes get a litle annoyed if MY flying time is more limited than it has to be. (Maybe I don't know what I am talking about and the practice is valid??)

Ross

rmh

Current systems typically work fine -as intended - this practice of using multiple slots says a few things about your fellow flyers
You have flyers with old /bad equipment - or - they fear others have old/ bad equipment.
Maybe the constant smile is caused by gas.

Highflight

My Feedback: (4)

Interference from 2IM or 3IM (Second, or Third Order Intermodulation) IS still possible today even though it really shouldn't be.
The problem was discovered to be prevalent mostly with AM, Single conversion, pre-narrowband receivers. The movement to FM, Dual conversion, narrowband equipment "should" have eradicated the problem, and for the most part has.

However, really GOOD noise rejection takes more parts and costs more to manufacture so while most of todays receivers are pretty much immune to 2/3IM, there are still brand new RX's out there (let's be honest and just say "cheap") that can still be hit.

So your flying buddies are probably over-reacting because they are acting on information that's more than 10 years old. It is rare nowadays that 2/3IM will shoot anyone down. At the same time, there still remains the remote possibility. Personally, I have no problem flying on a channel next too, or in the middle, of adjacent channels because I fly top-notch equipment. It's the guys who buy discount junk that have to be careful. The problem today is going to be found in RECEIVERS that lack proper filtering characteristics, not with transmitters that are properly narrow-banded with most of them transmitting on FM (but even the few AM transmitters out there shouldn't cause a problem if they're properly tuned because, again, it's the receivers that relevant to the issue, not the transmitters).

Lastly, don't confuse 2/3IM with splatter. If someone is using an out-of-tune transmitter no matter what kind it is, then he can shoot ANYBODY down and not necessarily on just the two adjacent frequencies. Splatter is NOT 2/3IM.

In short, ask your buddies if they are using JUNK equipment. And when they indignantly point out their JR, Futaba, Multiplex etc. equipment, then ask them why they are afraid of 2/3IM.

Here's a reference I found a while back that I printed up for our club newlsetter that explains this a little more.
http://www.bergent.net/SC-DC.pdf

Highflight

Rodney

If adjacent channels interfer with anyones receiver, their equipment is either outdated or out of spec. There is no reason for any adjacent channels to be interfering with others unless the errant transmitter is defective (may someone changed transmitter crystals with out haveing a service tech checking it out) or using an old wideband transmitter that has not been gold stickered or they have a defective reciever.

ezflyr

My Feedback: (32)

I'm curious whether your club has a policy regarding this issue? This practice effectively reduces the number of available frequencies that your club can use by 66%, so IMO, it's a significant issue. If there are no legitimate technical concerns, and this is just a couple of nervous-nellie old farts afraid of their own shadows, I'd would get a consensus in the club to ban the practice, and invite nay-sayers to fly elsewhere!

John

Ross Kean

Our club doesn't have a policy per se. Certainly there is nothing in writing. It's just that some people "know" that this is the right way to do it and "if you don't agree, you obviously don't know what you are talking about". You know the drill. Frequency crowding is not a big deal for a regular day's flying. We don't usually have a large number of people out at any given time. Its more of an issue when we have an event of some sort. Just an inconvenience for the most part and those who will have their way are the same ones who generally take the fun out of the hobby. Unnecessary rules and other nonsense.

Ross

Clark L

Ross,

What? are your flying buddies still using "Brown and White"? This problem has been resolved. All transmitters on the 72mhz band built or modified since 1991 are narrow band. This just isn't a problem anymore.

Good luck!

Jean13704

One way to address the issue is to use a scanner to "see" if a transmitter is having any measurable effect on adjunct channels. This should convince anyone. The new Polk transmitter has a built-in scanner and there are two RC scanners on the market that I know of, maybe more. Anyway that you could borrow a scanner on a one-time basis to show all concerned whether or not a given transmitter is affecting more than its own channel?

apteryx

I think nothing beats a good spectrum analyzer "picture" to show the doubters. You can borrow on through the AMA and your frequency co-ordinator ? But doubters are hard to convince about something they can't see and touch. When they crash they will look at you anyway.

Do they maybe have an old ham/electronics buddy they trust ? Maybe you can enlist his/her aid in convincing them.

TLH101

My Feedback: (90)

My flying partner has all his equipment on an adjacent channel to mine, (12 & 13), and we fly together at the same time a lot. We have even crossed our antennas (not touching) to prove the point to some doubters. They thought we were crazy.

Lynx

I wouldn't do that intentionally, but I think you did prove your point =>

Geistware

My Feedback: (16)

Frequency bleed is not a concern. Even "IF" is not a problem.
Tell them to quit hogging the channels or be willing to give up the pin for others.

Ross Kean

I found an interesting article about [link=http://www.repairfaq.org/filipg/RC/F_RC_interf.html#RCINTERF_003]Interference[/link]


I don't know whether this will help them see the light. Some people will never accept anything that does not conform to their current understanding.

Ross

rajul

My Feedback: (58)

Ross, great article. Thanks !

Geistware

My Feedback: (16)

Yep this is a good article and site with valuable information.

smokingcrater

double conversion rx's are good, single conversion rx's are still capable of being hit with interference. at my field the club trainer is on ch 19, all my stuff is on 18. everything flys great, with the exception of my sky scooter with a micro FM single conv rx in it. even then it only gets an occassional glitch when getting close to having the ch 19 tx inbetween mine and the plane. but... as i said, it isn't a 'take over the plane and crash' type interference, just a slitch twitch of a control surface or the motor sputters a little.

4*60

My Feedback: (41)

You are a member of MAAC. MAAC just changed to the no channel separation policy in the last few years . Point them to the MAAC radio spectrum committee pages on the MAAC site.

http://ont.net/frequency/page6.html states that blocking only the frequency in use is the MAAC requirement due to today's narrow band radio equipment.

PS: I needed to do the same as you are doing (convince people), but first I had to manufacture pins blocking the neighbouring frequencies. Now we just tuck our pins in behind the other guys on the neighbouring frequency and we use them all or I now use an ordinary wood clothespin with my freq. and name marked.

Ross Kean

4*60

I also came across the reference from the MAAC website. I think I'll print a copy of this plus the reference I cited above on Interference and bring them along to the next club meeting. Maybe copy this thread as well - except that some will be offended by description of individual behaviors.
Maybe I can edit it a bit...

Ross

Phil Cole

I don't think it's the single conversion aspect of the micro receiver that is the problem in this case. It's more that to make it small and cheap, the whole design of the receiver is compromised.