# Range conundrum



## jebouck (Jan 2, 2008)

This one is so bizarre, that you will think I'm making it up just for controversy. Believe me, I am not! 
At my layout, we get 100 feet of range for all the AirWire/Phoenix P5 commands and functions. 
At a friend’s layout, we get 100 feet as well. 
This includes inside tunnels, behind mountains, etc. 

At a third friend's layout, we get 15 feet or less of range! 
We still get forward, reverse, and stop and go at 100 feet. 
However, all Phoenix functions, except the diesel idle go away. 
We cannot blow horns, ring bells, or use any functions. 

Here is the only difference: 
Mine and layout 2 are raised. 
Layout 3 is on the ground. 

Any comments or input on this one? 

I’m going to post this on other boards, as well. 

John


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## Cougar Rock Rail (Jan 2, 2008)

John! How are you? Is that Phoenix P5 in an RhB loco?  
I'm wondering if it isn't radio frequency interference with the P5 board, and here's why: I'm running DCC and the only sound board I have any problems with is the P5 board in my Heidi loco. Most times it is fine but once in a while it will 'fall off the rails' and start blowing whistles, ringing the bell and making all kinds of sound without responding to regular commands. The 2K2 boards don't do it, nor do the LGB onboard sound boards, which makes me think it's picking up something from local cell phones, wireless home phones etc. Does your friend have a wireless phone in his house or are there overhead power wires? 

Cheers, 
Keith


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## Gary Armitstead (Jan 2, 2008)

I got my new Accu C19 yesterday from Jonathan at EMW and it has Aiwire and Phoenix P5 sound. He was commenting on the range of this set-up. He ran my loco on his railroad, in the backyard, from a location in the front of his house. That distance is in the neighborhood of 100'. He said that cell phone interference, wireless garage door openers, etc. will definitely affect range. He had one customer who had problems with rebar used in patio decks and walls! Lots of things to ijnterfere with the reception.


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## Del Tapparo (Jan 4, 2008)

This an old problem that I first reported several years ago (to the mfgs involved) with the Airwire/2K2 board combination. I don't know who's problem it is, but there is definitely a motor noise issue with the DCC port which triggers the sound board. I've since removed the Airwire and decided I prefer to trigger my sound boards via track magnets anyway. And with an SST board installed, it is not only automatic, but random and much less annoying.


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## Mike Reilley (Jan 2, 2008)

There is a physics phenomenon called multipath…and I believe this has a lot to do with why elevated layouts work well on RC…and ground based ones work less well. 

We all have experienced multipath…while listening to AM radio stations in our car. As we drive away from a distant AM station…the radio signal gets better…then worse….then better…than worse. This is because the AM radio signal that we receive in the car is getting to the car by multiple paths….on might be a direct path, radio station antenna to us….or one might be on bounced path, radio signal bouncing off the ionosphere then to us. Both signals are at the same frequency…because the radio station only transmits one…but, radio signals are waves…like you see on the ocean. When a radio signal goes further (or shorter actually) in its trip to your radio in the car, the direct wave and the bounced wave TOPS shift in placement in space because they travel different distances. 

Now…radio receivers ADD all the signals they receive. If the direct wave and the bounced wave get displaced by exactly a half wave length, one cancels the other because when the radio adds the amplitude of two waves of the same height that are displaced by a half wave length....the positive part of the direct wave is added to the negative part of the bounced wave…and you get zero…no signal. Now, in real life, the direct signal and the bounced signal don’t have the same height…so, you don’t completely LOOSE the signal…but you do hear the volume on the radio go up and down…or static increases…or you lose the station for a while and then it comes back. And..the direct wave signal is NOT always bigger than the bounced wave…the point is that the two signal paths can lead to signal cancelation. The place where that signal cancelation exists is a called a multipath null. 

Now…how does this multipath stuff effect RC? Well, the water in the soil in a yard is like the ionosphere…the water reflects radio waves. So, when you are using an RC system, the signal the engine is receiving comes from a direct path from the transmitter to the engine…AND, a bounced path from the soil to the engine. Now, at 27MHz, the wavelength is like 6’ long…so the half wave length is like 3’…the length of the antenna wire. So…if the signal bounced and the direct signal get shifted 3’, the signals cancel. This is what is happening when engines run on the ground…and is why walking with the engine seems to make control better. If the moisture level in the soil is 18” down…and you’re walking with then engine…then the bounced signal goes 18” down…and then back up…3’…and you get signal cancellation at the engine. That’s simplistic…but it makes the point. 

If the moisture level is 3” down….then there is a place where the angle of the radio wave from the transmitter to the engine will go through the soil for 18”…be reflected…and then go out of the soil for 18” to the engine…and you got cancelation again. This is why on ground based layouts engines go out of control for a while when you stand off from the engine. The engine might have to move 10’ to shift those direct and bounced signals out of cancelling one another…and to you, it means you have no control during that period. If you’re standing next to the engine…it might only have to move a foot before the signals stop cancelling each other. 

It also explains WHY walking with an engine on the ground, the control is better. In reality, the signal that bounces on the ground moisture is “attenuated”…meaning reduced in strength. The direct signal is NOT. Therefore, when the two signals add at the receiver…the direct signal is strong enough to overcome the strength of the bounced signal…and the radio can see the signal…and life is good. Things work as advertised. 

OK…so why does an elevated layout work better? Even on an elevated layout, the engine receives both the direct path and the bounced signal. Well…the answer is…we hold our transmitters at about the same height as the track…even when the track is way out there. When the train is 100’ away, the angle from our antenna to the train is NOT real different that when it’s 3’ away. That means…the direct path is always getting to the engine strongly and the bounced path is going through a LOT of soil…even if the moisture level is only down a few inches. If the angle the bounced signal hits the soil is a few degrees, it goes through feet and feet of dirt on the way into the moisture level…then bounces (is reflected)….and feet and feet on the way out of the soil That reduces the strength of the bounced signal greatly…and the direct signal dominates…and you maintain control. 

To be complete, yes….there ARE multipath nulls even on an elevated layout…but it turns out that multipath nulls tend to be more concentrated at low elevations. This is why missiles that attack ships are designed to fly just a few feet off the ocean surface….and why fighters and bombers fly very low on strike missions…they’re trying to fly IN the multipath nulls at low altitude of the radars they are trying to get past…or as has the pressed states it….fly under the radar. 

That’s the basics…but have ya ever wondered why folks are switching to Airwire and away from TE, RCS, etc? Cause it “works” better. The answer is in the frequency. Airwire is a 900MHz system. TE/RCS/etc are either 27MHz or 75MHz systems. Well….what makes that important? Simple…wave length. The wavelength on an Airwire system is several inches long. The wavelength on the TE/RCS/etc is several feet long. 

So, why does that matter? Well it means that the time when a moving engine has its direct path signal and it’s bounced path signal exact, say 2” apart (a half wavelength when the signals are canceling)…is VERY short. The engine might only have to move a ½” to get back a signal that the receiver can see. So…you don’t see the effect of multipath. Now think about the 6’ wavelength situation…the TE/RCS/etc frequencies…it means the engine has to move several FEET…maybe yards…before the signal is no longer canceled. These are the time periods that we all bitch about. 

There are other things that impact this too…the most important one being how you deploy the antenna. LSers make two mistakes…all the time. First, they wrap the antenna around some cardboard and they put it in the roof of the tender. Secondly…the point the transmitter AT the engine. 

Let’s talk about number one…wrapping the antenna wire. An antenna that is properly “tuned” should collect at least a half wave length of energy from a transmitter….just plain physics. So…if you want to properly “tune” you antenna…you want it stretch out completely…and they are cut to the length of a half wavelength by the radio maker. When you wrap the antenna around something…you’re trashing the antenna’s performance. 

Second point…aiming the transmitter. Well…it’s NOT just the transmitter…it’s also the receiver antenna. There are two things going on. It turns out (again physics) that the side of an RC antenna transmits/receives the strongest signal….and the ends transmit the weakest signal. This is called the antenna pattern. So…if you “point” the antenna at an engine….like a gun…you are substantially reducing the level of the signal that the engine receives on direct path…AND…guess what…you sending MORE signal though the ground bounce…and it’s reduced in strength by the soil. So pointing is NOT good. 

Last point…why do RC cars work good at 27 and 75 Mhz….and not LS engines. Answer….it’s the old antenna pattern again…and something called polarization (which I’ll stay out of). RC cars have VERTICAL antennas….that are a half wave length long. So…if you hold your transmitter with the antenna UP..and the RC car antenna is UP…you’ve got the best signal path possible….antenna side to antenna side. If LS trains could have vertical antennas…RC control would be a lot better…. 

BUT WAIT….we CAN have vertical antenna in a LS train!!!! How? Use a higher frequency radio….like an Airwire where the half wave length is like 2”….meaning….you can stand the antenna UP inside the tender because its only 2” long. This is a case where bigger is NOT better. 

And that ends my explanation of multipath effects on LS engines…. 

Be advised that there are a LOT of other aspects to this….like FM vs AM…digital vs analog…polarization…laws/regulations that get into the LS RC discussion. I don’t feel they are as significant as the basic physics issues of multipath and frequency …but others will argue otherwise. What’s above is just my personal opinion…having been a radio/radar electronics engineer 30 years ago. 

Hope this isn’t as clear as mud….


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## Mike Reilley (Jan 2, 2008)

OK...for the rest of the physics lesson as applied to John's problem. 

As I noted in my first post, multipath exists on all frequencies. This means that even 900MHz units suffer from multipath...just less than lower frequency systems. All systems have more acute multipath issues when the receiver is near the ground. 

In my first explanation, I spoke about "cancellation" of signals. Well, that's really too simple. What really happens is that the signal to noise ratio decreases from multipath...and when the S/N gets to zero...you have a cancelled signal. Well, receivers only receive when the signal to noise ratio is above some floor value. Now...to get above that floor value...you need MORE signal...or less NOISE. 

I've explained that high frequency receivers sitting low to the ground have the benefit of a better signal to noise ratio over time (meaning as the train moves) because the multipath nulls are much shorter than those that exist on lower frequency radios. That means...the signal gets to the engine more often...and when it doesn't, it's for much shorter periods of time aslong as the engine is moving. 

Well...that discussion is all about the signal...and NOT about the noise. So what happens to noise when the receiver is down close to the ground. Well...if it's self generated, as in case of motor noise...the noise level the receiver sees goes up...way up. That's because the noise is a signal...in fact, the noise that brushes on motors make is like something called white noise...a signal at all frequencies. So...motors are signal jammers...pure and simple. 

When you have a noise generator that moves with the receiver...and is just above the ground...that noise signal is reflected off the moisture in the ground...or from steel in concrete...or iron in the dirt... and the part of that noise signal that is within the frequency band the receiver is tuned for...is received...and decreases the S/N ratio. 

If the resultant S/N ratio goes below the receiver S/N level floor...the receiver cannot pick out the true signal. The point is that in some locations, the reflections can be very intense (like on wet ground)...or not intense (like on pure silica sand). This explains why the system works in some places and not others where both are on the ground...and why it geneally works whenever it's elevated. 

When it's elevated...the signal from the TX is higher because there is less S/N loss from multipath...AND, the noise signal has further to travel to BOUNCE off the ground. The direct path signal from the motor/noise generator is still there...but the better TX signal overcomes it. 

OK...now here's where I'd experiment to improve the situation. I've NOT done this...just talking as a radio/radar engineer. 

Things that need to paid attention to/messed with are: 

a. Is the receiver antenna vertical? If not, make it so. This improves signal reception...and might minimize the received direct path noise from the motor...because the motor wires are horizontal (this is that polarization thing I don't want to add into the discussion and confuse everyone by). 

b. Is the receiver antenna mounted as high as possible (and vertical) in the tender? The higher it is mounted, the less TX signal loss suffered from multipath. 

c. How high is the antenna from the track? Remember that the wave length of 900MHz systems is small...so moving the antenna up just parts of an inch can dramatically reduce multipath losses (i.e. increase signal strength). And ya know what else...if you're dealing with a self geneated noise situation (motor noise)...moving the antenna up or down parts of an inch could dramatically diminish the motor noise reflected off the ground. The noise that interfers is in the same band with the signal..so if you can get that in-band noise out of phase (in the cancelled position)...the transmitted noise signal will be cancelled by the reflected noise signal. (Technically, you can actually tune the antenna height to your ground based railroad as long as the moisture level stays about the same....but...I said technically...and this may NOT be feasible in the real world...but my guess is that there is a cherry spot that you can find where it works best overall.) 

d. Put caps or chokes on the motor leads to suppress as much motor noise as you can locally. If you haven't and it runs OK on the elevated layouts...and it doesn't on the ground layouts...you can help yourself a lot. In fact...motor leads should always be filtered...caps or chokes...don't matter. When you do this...you are reducing the noise level...meaning the denominator or S/N gets smaller...which increases the S/N above the receivers floor S/N ratio. THIS IS IMPORTANT. 

e. Last...check your antenna location. You want it away from metal. If there's a brake wheel...it interfers (but...a brake wheel COULD be a good antenna too...if is the right length). If there's a metal hatch...it interferes. If the tender is metal..woof...you've put the antenna in a metal can (put a portable radio that is playing loudly inside your dishwasher...and see if you can still hear it when you close the door -- you won't). The point here is that you can improve the S/N ratio that the receiver sees by repositioning the antenna wire....play with that...but try to keep it vertical.


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## Terl (Jan 2, 2008)

Mike 

Great explanation. I will save this post for future reference. 

Terl


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## Stan Cedarleaf (Jan 2, 2008)

Like I said on the Airwire forum..... It's all black magic..... /DesktopModules/NTForums/themes/mls/emoticons/blush.gif Yup. smoke and mirrors.... Goodness, did I mention smoke.... /DesktopModules/NTForums/themes/mls/emoticons/w00t.gif 

I know that's a "smart aleck" answer but after installing, programming and trying to run many units, not one will operate the same, have the same range or the same response. Most all are satisfactory, but none the same. It's still a very good system and recommended for full control of the great Phoenix P5 and 2k2 systems. Most all installs will blow the doors off.. 

 Mike's wonderful explanations are superbly written.... But............. Remember, they're just toys....


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## Mike Reilley (Jan 2, 2008)

Posted By Stan Cedarleaf on 04/17/2008 10:13 PM 
Remember, they're just toys.... 


That is the truth...and the BEST advice to remember...and toys are meant to play with. So...play with the antenna location....play with the height...etc...and if you overcome your issues...you'll be able to play more. There's more art here than science...and it's HARD to screw things up bad.


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## K27_463 (Jan 2, 2008)

Ahhhh Mike, i am going to need to debate you on some of this stuff. But I do not type well enough to do it here...maybe we can find a good face to face place in the next few weeks, preferably with a cool one in hand. I am a big believer in multipath too, but If I remember my RF engineering textbooks well enough, multipath is a big issue over distance, such as why your tv has ghost images reflected from the mountains,(hence your AM radio example-but Am radio is an amplitude mod signal and so very much more affected by anything arriving out of phase) but not so big deal over short distances like we are talking about-mere feet or inches in most cases.Over short distance, there is simply not enough time to get the signal "wrong" enough. There re a lot more factors at play in addition, and they all end up making a complex equation. Need to find out the signal modulation used by Airwire. In an FM environment, the receiver will be "captured" by the best/strongest wave (capture ratio spec is one of he most important in receiver tuners) available, and will attempt to reject other stuff as hash. All things else being considered however, a shorter wavelength is a good thing. The problem is theory does not translate well in to the real working world. I had many a good result way back in teh early mid 90'2s with horizontal antenna, or a tuned length which was then tripled , and wound around wood dowel etc. This was when I was using commercial radio gear, boat throttles- whatever I could find. RCS was just starting so to speak, Murrays realroad throttles also used regular radios, and the only freqs available that I could afford were the toy stuff at 27mhz. Airwire was no where to be found of course, even cordless phones were not yet at 900 . ( took me way too long to write this) 
Jonathan


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## Mike Reilley (Jan 2, 2008)

Yo Jonathan...we'll talk and drink at the NGRC...maybe at Duncan's if you're signed up. Sounds like a good talk.


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## Torby (Jan 2, 2008)

Having a degree in Electronics, I have to agree with Stan. RF is smoke and mirrors


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## Madstang (Jan 4, 2008)

Maybe this was mentioned in Mikes response..but one of my cheracter flaws is being able to completely read a long anything.....that being said quick and dirty..I have to ask...did you try changing frequencies...I agree with changing anteanna locations. 

I find that when I press a function button on the Airwire, sometimes it doesn't respond quickly...untill I hold the hand held straight up...NOT with my arem fully extended, just pointing the handheld up in the air above any objects that may or may not be in the way....then no problem...at all! 

At the train show this last Feb...to prove a point to a fellow club member that it was his hand held that was the problem and NOT the board I was able to control HIS board from completely accross the exibit floor...which was greater then 100' and the layout was on the floor. 

There are variables, with ANY system that when you are using a public frequency..900 mhz, that come into play..as stated above...microwaves, cell phones, portable phones...anything that uses the frequency that we use with our systems. At your friends house , OR neighbors you have no clue or control who is using or uses what at ANY given time. 

All you have to do is problem solve any given situation at any given time and pass it on when you find that variable out. 


Really guys on my layout I have NO problems with my Airwire...I have a layout on the ground and mounted on my fence. 

Bubba


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## itsmcgee (Jan 4, 2008)

Thanks for taking the time to share the info Mike.


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## Trains (Jan 2, 2008)

I had my A/W for about three years with no problems. I can run my trains from about 100 feet away. Sounds are about fifty feet.


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## jebouck (Jan 2, 2008)

Sometimes you lay awake at night pondering different things. 
Last night this was one of those things. 
And then I remembered this: 

Two years ago, one of our club members introduced us to RC/Bat for the first time. 
On this particular layout (#3) he only had about 2 feet of range with his RCS!. He had to put the transmitter right down next to the loco! 
It works fine elsewhere. 

2 feet of range! 

Numerous discussions were held with TOC, among them the track was the antenna, etc etc. 
I responded with something about insulators on the track. (This is a track powered layout with enough wiring underground to put the space shuttle to shame!). 

Apparently this poor guy lives under a black cloud!. 

Jonathan Bliesner and Mike Reilly have responded to my other posts on other fora with responses. 
Batt/RC is not an exact science! 
You have air planes, boats, cars, and trains. All RC controlled with various means of transmitting and receiving. 
Trains, being their environment, are the hardest to pin down as to the "quirks." 



RCS got 2 feet of range. 
Airwire 15 feet. 
Haven't tried an onboard Aristo te. I have one. I might just install it and see what happens. 
Haven't tried Loco Link--No one around here has one.


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## jebouck (Jan 2, 2008)

Oh, I forgot to add: 
With the Airwire, we can stop, go, forward and reverse on this particular layout--#3. 
It's the Phoenix P5 that won't respond after 15 feet. 

The RCS wouldnt respond to any command. 
j


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## Stan Cedarleaf (Jan 2, 2008)

Hmmmmmmmmmmmmmmmmmmm.... John.... How close to Three Mile Island are you????? /DesktopModules/NTForums/themes/mls/emoticons/tongue.gif


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## Bill Swindell (Jan 2, 2008)

If the same engine works fine on the other layouts, you have serious radio interference problems in this one location. I suggest you find out what is causing the interference and have that fixed.


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## Torby (Jan 2, 2008)

There really ARE black clouds, RF wise. 

"Our" house in Eldorado Township was in one. All radio stations faded out save 1. Go 1/4 mile and any direction, and you could get lots of radio stations. TV? Only 1 station worked. 

I'd wonder if there was some interferance reducing your range. At my shop in Macomb, TE frequency 5 would not work at all, but any of the others were fine.


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## Road Foreman (Jan 2, 2008)

Mike, 

You are correct on the antennas.. If you need to shorten them, you will want to install 1 from E Cubed R/C.. They have antennas for 27 & 75 MHz that are very small.. 

BulletBob


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## jebouck (Jan 2, 2008)

Posted By Cougar Rock Rail on 04/17/2008 9:12 AM
John! How are you? Is that Phoenix P5 in an RhB loco? " border=0> 


Cheers, 
Keith




Not yet Keith! 
I am just finishing up all my 'Merican stuff and then I will do my RhB 
locos. There's plenty of room in a -III for all the stuff, including the batteries! But I need to figure out how to light the cars, since they are full of people! 
I'm doin' fine, (so far). Thank you for asking. 
Jb


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## DKRickman (Mar 25, 2008)

A couple ideas here... 

At least for steam locomotives, wouldn't the stack be an ideal location for an antenna? it's vertical, and likely the highest point on the locomotive. 

Also, how hard would it be to put the motor, and possibly the electronice as well, in some sort of Faraday cage? I would think that it could be made relatively easily with window screen, and ought to completely block RF signals from getting in or out. Right?


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## Del Tapparo (Jan 4, 2008)

Or one could just eliminate radios all together and use on-board controls.


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## jebouck (Jan 2, 2008)

Problem was solved with the installation of motor chokes. 
Range is fine now on layout #3. 
jb


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## Paul Burch (Jan 2, 2008)

John, 
Just curious. What chokes did you use and how close to the motors did you install them? 
Just to toss something else in,my new Aristo GP40 with their new motor is one of the best I have for range,especially the function commands. Didn't even install the Airwire supplied RFI components. Must be a very high quality motor.


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## jebouck (Jan 2, 2008)

Paul, 
I used the AW chokes and put them right on the motor terminals, one on each side, poked them out of the motor block and fastened them together. Then secured them tightly to the top of the block. The don't touch anything and allow for complete block movement. 

I went ahead and did my two USA s-4's while I was at it, just in case. 

j


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