It's all coming together for me now - after three crashes, I think I can
blame the transmitter!
It started last week with the Rare Bear - It was flying beautifully around
the schoolyard. I took it pretty far out for a long run and then, bam, lost
the radio signal - it rolled upside down and powered in.
Since the Bear was a used, relatively recent plane, I chalked it up to my
inexpierience with a single conversion GWS receiver, and getting it too far
So, I took that plane home and put it on the bench for repairs. This past
weekend, I took my son out to the park with some planes, including a Piper,
run by the same radio. We launched it, and it glitched almost immediately
out of my hand. Another partially-powered dive into Earth, and broke the
motor loose. Trying to determine what the problem was, I kept the plane
powered and watched the servos. They would go wild for bit, all speeds, all
directions, and then quiet down for a little while, even with the radio,
fully extended antenna, right next to the plane.
We were at a new location, so I figured, "interference". Plus, this plane's
been around the block a few times. Maybe it was just its time!
Anyway, I had the Bear repaired by this time. Took it to the tried-and-true
park, launched, and was having a pretty good flight (despite being badly out
of trim from the first crash), with only an occaisional hiccup, when again,
bam, no radio control whatsoever. It fell in from high-altitude, unpowered.
Again, doing problem determination back at the car, servos were going nuts,
prop was twitching. Now I'm thinking, "it's not the planes. It's the
radio". It made no difference if the radio was on or off. It was almost as
if the signal would fade in and out.
This is the Hitec Radio that I had dropped on it's antenna, cracking the
circuit board, and re-soldered back together (I know, I know, but just
listen to the story :^). I did that when it was almost brand-new. It's
been working that way for about a year, nearly daily (I love to fly).
I'd like not to have any more crashes! I can replace the radio, no problem,
but it's curious to me that it would work just fine for so long, and then
start working so badly. Is there anyway to look at its signal and confirm
that it is indeed the source of the problem? I have an O-scope that seems
to be setup to show radio signals, with a co-ax connector on the front.
I'll try hooking it up myself to an antenna and seeing what I get (maybe it
will be obvious?) but if anyone can tell me what I should be looking for, it
would be greatly appreciated!
Anyway, the boy's taken an interest in learning on the buddy port, so I
reckon I'll get another Hitec Laser 4 (my other radio) and we'll fly
together when I get this all straightened out!
What you're looking for is another crack on the PC board, or a fractured
crystal, capacitor, tuning slug, or other component. If you don't want to send
it in for PROPER repair, replace it.
"Seems to be"???
If you ain't sure, don't play with it. A little knowlege is dangerous. AND
On the other hand, I'm glad you're both interested in R/C. Do yourselves a
favor and do it right, not slap-hazardly, makeshift, or shade-tree engineered.
"There's a Hun in the sun!"
If your oscilloscope has high enough bandwidth, you should be able to see
the carrier - however, to do so your scope needs to be at least twice the
sampling frequency of your radio - if you're on 40MHz you'd need a 80MHz
scope, if you're on 72MHz you'd need a 150MHz scope - most standard analogue
scopes are only 10 or 20MHz. If it is good enough, you don't need a direct
connection, just a length of wire connected to the probe.
If the scope isn't an option, you might find your RX is sufficient to
monitor the TX's behaviour while you stress it - standard routine is to heat
up the board with a heat gun, then cool it with a cold spray - or put it in
the freezer, then hit it with the heat gun while you watch your servos to
see if it misbehaves. By combining this with flexing the PCB, you can narrow
the fault to a board crack, or a faulty component.
That said, these kinds of faults can be very hard to identify - I've just
lost 2 planes in a row to what I now conclude must be a faulty RX (or
switch) - both were at full throttle when the radio went off the air,
leading to plane-shattering crashes. The first I though was my fault, the
next was at the hands of a very experienced instructor. Very depressing when
I think I could have saved the second plane if I'd correctly identified the
fault after the first crash .
Sorry to hear about your two planes. Yep - if I'd done a little more
research on the first crash, I might have saved a couple more.
I think I already know the answer - it looks like I have two receivers
telling me the same story (namely, "quit flying us around with THAT radio!")
Actually, in my opinion it really was interference. Let me tell you my
I used to fly all my planes using a Futaba 8UAP transmitter which has
memories for lots of models. For years I flew on channel 51 with no
problems, ever. Then one day I took a couple of park flyers down to my
local schoolyard and found that on both of them the prop would start and
stop spontaneously when I didn't command it, even with the transmitter
on and sitting right next to the plane. This went on over the course of
half an hour. This was clearly interference -- two different planes,
different brands of receivers, both responding the same way at the same
time on the same channel.
Shortly thereafter I went to a fly-in at one of my local clubs and
encountered the same problem. Strong interference on channel 51. The
interference was causing problems on all of my planes, both with single
conversion and with dual conversion receivers, so I can only assume that
it was either right on my frequency or on an adjacent frequency and so
strong that it was swamping the receivers. I searched up and down the
flightline for a transmitter that was inadvertently turned on or set to
the wrong channel, but found nothing. I went home flightless but
At this point I decided that somebody or something new was on or near my
chosen channel and that it was time to move. So I bought a new Futaba
9CAP transmitter on channel 49 and new crystals for all my receivers.
All seemed well for a while until a couple of months ago when I crashed
my 50" electric Gypsy Moth while flying at the local club. I can't
prove it, but I do believe it was interference -- the plane suddenly
started doing rolls that I didn't command. I got control back briefly
and was bringing it back to land when it went crazy again and dove in.
I couldn't find any problems in the transmitter or receiver after the
Frustrated, I ordered a handheld scanner (Icom ICR5) and programmed it
to scan channel 48, 49, 50 and the frequencies in between. I took the
scanner down to the same schoolyard where I started my story, together
with the same two park flyers. I immediately found a strong signal
between channels 49 and 50 -- strong enough to max out the signal
strength meter on the scanner. The signal seemed to come in bursts
lasting two or three seconds. It consisted of tones only, no voice.
Interestingly the park flyers didn't seem to respond much to this signal
on channel 49-and-a-half, even with their single conversion receivers,
so I took a chance and flew them. I was able to get four flights in
The point of my story is that there is RF interference out there and it
is becoming more common. I also know that schoolyards are common
locations for cell phone antennas. I know that cell phones operate in a
completely different band, but once you have a tower for a cell phone
antenna, it seems like a natural step to add an antenna for some other
service to the same tower. And maybe that other service can cause
trouble for us R/C users.
Paradise Valley, Arizona
| Frustrated, I ordered a handheld scanner (Icom ICR5)
Nice -- wouldn't mind one of those at all :) Alas, the scanners I have
are technically capable of receiving 72mhz, but it's locked out :\
| and programmed it
| to scan channel 48, 49, 50 and the frequencies in between. I took the
| scanner down to the same schoolyard where I started my story, together
| with the same two park flyers. I immediately found a strong signal
| between channels 49 and 50 -- strong enough to max out the signal
| strength meter on the scanner. The signal seemed to come in bursts
| lasting two or three seconds. It consisted of tones only, no voice.
Well, you do know that we share the 72mhz band with pagers, right?
This certainly sounds like a pager ...
With a Yagi antenna and maybe an antenuator, you could probably find
the tower that's causing the inferference. [ read on ]
Of course, what you really need to check is if this pager signal is
staying within it's allocated bandwidth or not. If you were able to
narrow down exactly which tower it came from (with the Yagi I
mentioned earlier. Your local ham club may be able to help.) you might
be able to give them a call and ask them to verify it -- I don't know
how friendly they'd be to that, but it's worth a try.
You're right - there is definitely more RF flying about these days - while
most of the new services (cellphones, WiFi) are well away from RC
frequencies, I imagine that high-powered point-to-point links using highly
directional antennas (as you might find between two cell towers) would
disturb any RX that came into its path.
Russ - it's awfully hard to second guess the experiences of others, if
we were not there to see it. But, in all the questionable situations
that I've either seen, or had happen to me in a state of inattention,
almost all come down to a switch failure in the plane. It looks like
you might be suspecting that yourself. It's a damn shame about the
poor quality these manufacturers supply in their switches, in my
opinion they are definitely the weakest link in the chain. Just my
opinion, though, but others keep on having to learn it for themselves
too. Good luck in working it out.
To reply by email, please remove "abcd" from Return address
"Ignorance is treatable, Stupidity is incurable. Sometimes
the difference is hardly distinguishable, however."
If you fly in an area as risky as that, you might take a look at the Polk's
Hobbies "Tracker II" radio. It not only has a scanner built into it, but
it's synthesized as well so you can first check the frequency you want to
use to make sure it's clear, and then select that frequency on the radio
(and of course also on the accompanying synthesized receiver) and go fly.
To manage the kind of interference problems you're having, the Tracker is a
pretty good deal at $275 for a fully SYNTHESIZED 8-channel computerized TX
with SCANNER (all built in.. no add-on modules needed) and at that price,
includes the "Seeker", their synthesized receiver.