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Transmitter left on

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Old 12-07-2005, 12:26 PM
  #1  
oldtyme
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Default Transmitter left on

OK besides the horrible things that could have happened.......they didn't. I have been flying
for over 25 years and finally I did the unspeakable.........I left my Futaba 8UAP transmitter on
with the antenna collapsed for over two hours. I know in older radios this was a no-no because you
could burn out the finals with the antenna down and the power on. Now to decide whether I fried
my transmitter and replace it or send it in for inspection and an expensive repair bill. I'm thinking
about a Futaba 7C if I replace it. I already have a Futaba 9C for my more exotic airplanes (warbirds and twins) so this is more for my sport models. Opinions please!

Thanks,
Andy
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Old 12-07-2005, 12:41 PM
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EyeflyRC
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Default RE: Transmitter left on

I would range check the radio to see if there is any decrease in range. Chances are nothing bad happened and you can continue to enjoy the radio without repair.
Andrew
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Old 12-07-2005, 10:49 PM
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Default RE: Transmitter left on

I've done this maybe 3-4 times on my 9c. the transmitter pack on the back gets warm, but i haven't had any range issues. i would be more worried about the battery then the radio actually.
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Old 12-10-2005, 04:46 PM
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Default RE: Transmitter left on

I done this on my 8UAFS a couple years ago. Was setting up a plane & when done I put it on the charger but forgot to turn the radio off. Sat like this overnight at least 15 hrs. Got out to the field & discovered the battery was completely drained. I've got a Hobbico quick charger mounted on my field box so this is what I used. Quick charged it in about 45 minutes & was up & flying. Still have this radio today & fly half my planes with this radio, the other half I fly with a 9CAP.
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Old 12-10-2005, 06:25 PM
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Geistware
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Default RE: Transmitter left on

I have done it several times and never had a problem.
Like was said above, range check the TX and it it works, then you are OK.
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Old 12-11-2005, 08:21 PM
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oldtyme
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Default RE: Transmitter left on

Guys,

Thanks for all the input.........unfortunately when I charged the battery and did a range
check, I got almost nothing........my wife commented that that was an expensive mistake.
I figure by the time I ship the radio to Futaba and pay shipping and repair costs on this older
radio I'll be into it for a bit, so I went ahead and bought a 9CAP Super/w/receiver and I'll be
darn careful not to do this again.

I've been in this hobby 25+ years and this the first serious hardware mistake I've made so
while it's costing me a bit..................I have a new radio that I will trust.

Thanks again,
Andy
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Old 12-11-2005, 10:20 PM
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Geistware
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Default RE: Transmitter left on

You do know that the module is what gets damaged.
If you have access to another one, then you can send the module to be repaired and keep flying.
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Old 12-12-2005, 12:22 AM
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oldtyme
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Default RE: Transmitter left on

Geistware,

I did not realize that. I am traveling in the past prior to module equiped radios.
I'll try another module in it this week......too late to cancel the order for the new
radio though...........guess I'll have two now............ :O
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Old 12-12-2005, 01:20 AM
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mimhoff
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Default RE: Transmitter left on

I have a related question-- My radio manuals say not to operate the transmitter without having the antenna extended. Seems to make sense to me but I have also been told when doing a range check to do so with the antenna collapsed. A somewhat contradictory situation. Probably the short time you have the radio on while range checking is probably not enough to damage it but feel that it is equivalent to saying it is fine to "peek" directly at the Sun just don't stare at it. So is it OK to range check with the antenna down or are you potentially damaging your transmitter during every range check??
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Old 12-12-2005, 02:27 AM
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Default RE: Transmitter left on

mimhoff,

When I talked to Futaba, they advised me to do the range check with the antenna collapsed. That is the way I have done it for the length of my involvement in the RC hobby with no bad results. I design printed circuit boards for a living so I was talking to one of our engineers the other day about what the problem is. He said that with the antenna collapsed, and the transmitter is generating the energy and it has no where to go that it is just building up heat. In electronics, heat is a killer and we go through some pretty fancy steps to keep heat down in our designs. So I guess the problem with leaving the transmitter on for an extended peroid of time is just the cumulative heat build up.

When in my shop, I always have the antenna extended when setting up a plane.......that's the paranoid in me.

Hope that helps,
Andy
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Old 12-12-2005, 07:58 AM
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Zeeb
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Default RE: Transmitter left on

If you look at some of the information posted on the manufacturers websites, and the support forums here I think you'll find that for range checks or setup you should extend one section of the antenna. Which one is the subject of some controversy. On my Futaba 9C I've always just extended the smallest diameter or top section, but I've seen posts saying it should be the bottom or largest diameter section. The Futaba 9Z is another story as it has the antenna on a gimbal and so the largest diameter, or bottom section should be extended in order for it to work.

I'm no engineer, but I've been around various radio installations for quite a few years and the common thing about them seems to be that transmitting with no load from an antenna is not recommended... YMMV
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Old 12-12-2005, 08:18 PM
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Default RE: Transmitter left on

first of all, i'm a ham radio operator and it kills me to know what the SWR is doing when the tx is transmitting with the antenna down...

that said, the 9c manual makes NO mention of any dangers of doing this, and of course instructs you to do a range check with it collapsed. (doesn't specify fully or only one section, but I would have to assume they imply fully collapsed)
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Old 12-13-2005, 12:59 AM
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mimhoff
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Default RE: Transmitter left on

Thanks for your comments. It would seem that powering on the Tx for short periods of time with the antenna collapsed will not hurt the transmitter but for a long time period of time it will. I guess I wish the manufacturers would be more specific in their documentation.

One last question --- if anybody knows -- Does the damage done by leaving antenna down always result in a complete failure or will it some times cause a reduction of power like 50%? I would almost rather have it completely fail than partially fail at least I wouldn't accidentally fly with less than enough Tx power.
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Old 12-13-2005, 10:10 AM
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Default RE: Transmitter left on

Well I'm not going to go dig through the manual looking for mention of where the antenna should be for setup/range check etc. I'll take your word for it. But, here's what the FAQ on Futaba's website says about it and is one of the problems I mentioned about determining what section to extend. It does say there's a 5 to 10 minute time frame with the antenna collapsed before damage might occur, but I'd just rather not take the chance.


"When I am using my radio for programming, setup within my house, experimenting, etc, is there anything special I should do?

With ANY transmitter (modulared or non-modular), you should ALWAYS extend your antenna to at least the bottom or first segment when turning the radio on. If you leave the radio on with the antenna collapsed for more than 5 or 10 minutes, the internal components will be unnecessarily exposed to incorrect matching of the output circuit to the antenna. This may shorten the life or even immediately damage the output circuitry of the transmitter"


And here's the link;

http://www.futabarc.com/faq/faq-9c-q516.html

As for mimhof's question about how electronics fail. While there are a few obvious answers like smoke coming from the unit, if you could successfully predict when, where and how a failure will happen you ought to spend your time picking lottery numbers...

There's just no way to predict how they will fail under normal use, or even how much slight abuse they'll take before failing.
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Old 12-13-2005, 11:22 AM
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Default RE: Transmitter left on

Zeeb,

I enjoyed your comment about smoke coming out of the unit............but with mine, it was really hot. Geistware and Smokingcrater.........would it be safe to assume that if I replaced the module that the transmitter would again be OK? Or would there be some other parts of the "base unit" that
would have been affected. I might, in some future time frame, want to entertain bringing this unit
back up to snuff.

Thanks,
Andy
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Old 12-13-2005, 11:47 AM
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Default RE: Transmitter left on

A couple things should be happening here:
1) The transmitter should have high SWR protection to prevent damage to the finals
2) The transmitter should fold back its power in the face of increased SWR.

These are design criteria I would expect in any modern solid state transmitter. Whether or not they are in modern RC transmitters, I don't know.

I do know that I have inadvertently left my 8uafs on with antenna down more than once and it still works fine.

Maybe I'll have to disect / reverse engineer one of these sometime to see what really is going on.

73,
Larry KBØR
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Old 12-20-2005, 11:22 AM
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Default RE: Transmitter left on

OK so if Futaba could weigh in here..........my range is definitely gone.........if I replaced the module would I be able to salvage this radio just by doing that? I really liked this radio and if just buying a $50 module would fix it, I would do that..........please respond........I want to trust this radio if I do that.

Thanks in advance,
Andy
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Old 12-20-2005, 03:51 PM
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Default RE: Transmitter left on

As far as I'm aware, RC transmitters don't have any protection against the effects of the high SWR produced by an impedance mismatch through operating with the antenna retracted -- with new modules costing $25 it's just not economic to do so.

And yes, all the RF componentry likely to be damaged by running your transmitter for extended periods with the antenna down are found in the module so *if* this is the cause of your short-range, replacing the module ought to fix the problem.

Note that although it's not a legal option for US users, others elsewhere in the world can simply pop a Hitec module in their Futaba transmitter and save themselves $25. We're using the Hitec modules down here (in NZ) and they work 100%.
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Old 12-21-2005, 10:13 AM
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Default RE: Transmitter left on


ORIGINAL: rcandy

OK so if Futaba could weigh in here..........my range is definitely gone.........if I replaced the module would I be able to salvage this radio just by doing that? I really liked this radio and if just buying a $50 module would fix it, I would do that..........please respond........I want to trust this radio if I do that.

Thanks in advance,
Andy
Andy,

If you want an answer from Futaba, I suspect that you'll need to post this question on the manufacturer's direct support area. Occasionally BAX (the Futaba guy) will answer questions here, but if you will post it on the Futaba forum he or Krysta will usually get you an answer within a day.
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