rva1945

It's common to read that to test your RC system, you have to colapse the antenna and see if you receiver receives the signals at 50-100 ft; but some say that this way the transmitter can get damaged because the full power is not transmitted, instead the power transistor or whatever it is literally melts.

Any light on this dark subject?

Thanks

exeter_acres

My Feedback: (2)

it is ok for a minute or two while doing a range check....

if you were to leave it like that for an extended time...that could burn out the transmitter.....

XJet

As the previous poster said, it is possible to damage the RF section of your transmitter by operating it for extended periods of time with the antenna retracted but it's not common.

Like most people, I've accidentally left one of my transmitters turned on with the antenna down and only discovered this after the (2500mAH) battery was well and truly flat -- that's about 9 hours of continuous operation!

I was very careful to check that this hadn't caused any problems. If' I'd had any doubt I'd have replaced the RF module (it's a Hitec Eclipse so that's only $25).

Josey Wales

My Feedback: (61)

Yep...Leave the antenna down for a few minutes then feel the module..it will feel warm

s3nfo

My Feedback: (14)

Or, put the antenna up for a few minutes then feel the module...it will feel warm. Making RF causes heat whether the antenna's up or down. Leaving the Tx on with the antenna down can burn out the RF section.....after hours and hours of doing it that way.

Josey Wales

My Feedback: (61)

Very true but I have noticed that the module feels significantly wamer when the antenna is down for a long period..(at least it does to me) A few minutes wont hurt anything but if your setting up a new plane you could have the TX on for a long time.

dirtybird

My Feedback: (5)

I think a designer of the RF section would be crazy to design the PA so that would happen. Almost everyone has left his TX on and put it away with the antenna down. I have done it at least twice. I have a field strength meter and can determine that there is no difference at least on my Futaba TX.

Rodney

As an electrical engineer and a ham, I can guarantee that when you run the transmitter with the antenna in any position other than fully extended you will undully heat up the output transistor. Whether damage happens or not depends on how well the unit was designed to dissipate excess heat, some are better than others. Those units with modules rather than crystals seem to heat up faster and hotter due to their compact design in a closed area. Yes, the mean time to failure will be shortened by running with the antenna down, and, in some cases the damage can be catostrophic if done for a long enough time. What is a long enough time? Depends on the design of the heat sink again, most RC units will handle short periods (two to 5 minutes) with no problems. If you are interested in long life for your unit, it is best to minimize the time you operate with the antenna collapsed or partially collapsed.

dirtybird

My Feedback: (5)

As an electrical engineer and a designer of R/C equipment, I can guarantee that if you don't design for that possibility you are in for serious equipment problems. All you have to do is provide sufficient heat sink to keep the temp low enough.
You may be an EE, Rodney, but it sounds to me that you need a little real world experience.

CrashGaalaas

My Feedback: (8)

There are also simple circuits that protect the final amp against high swr just so that they don't burn up. Guess I'm going to have to dive into one of these rc transmitters and see what it really does. But I suspect that as the antenna is collapsed, the swr goes way up. And I anticipate that the power output from the final amp in turn drops way back thus protecting the final amp.

On my ham gear the power drops from 100 watts to about 5 watts as the swr approaches 3:1.

Rodney

Dirtybird, I suspect I probably have many more years in the business than you have, some 45+, most of it in instrumentaion, rf testing, missile design, spacecraft design etc. and, since profit is the bottom line on most RC equipment, the design for best profit is often not for highest reliability. I have examined many RC transmitters and all, repeat all, have been at the low end of the best design for reliability. Most will withstand a substatial amount of abuse but all will suffer some loss of life (lower mean time to failure) if subjected to higher than normal operationg temperature. Mean time to failure roughly is cut in half for every 10 degree Centigrade of increased operation temperature in nearly all electrical equipment. I have also spent many years in failure analysis and life testing of electronics and related equipment. The bottom line to the original question is still "yes, running with the antenna collapsed will shorten the life span of the equipment".

piper_chuck

My Feedback: (12)

I highlighted the key word in what you said. As we all know, when it comes to manufacturing there's often a gap between what should be done and what is done.

RJConnet

I have to agree with dirtybird on this one. If an RC Tx is designed so poorly that it could not handle such a commonly made mistake as letting the battery run down with the antenna collapsed the manufacturer would not last long in this market place. I have been in the hobby for 50 years and have not personally talked to anyone who has ever experienced Tx damage from operating one with the antenna collapsed. [8D][8D]............RJ

Josey Wales

My Feedback: (61)

http://www.rcuniverse.com/forum/m_22...tm.htm#2256596

dirtybird

My Feedback: (5)

Sorry Rodney you lose. I have been in the business more than 50 years.
The experience you quote is Aerospace and everyone knows that is not real world experience. The people you design for in aerospace are highly trained and can be counted on to not mistreat the equipment. Try designing for the average klutz sometime. You will learn some interesting things. One of those things is that normal handeling of the equipment shall not degrade the equipment or you won't be in business very long.

XJet

I'm also an EE with some 35 years experience in RF, telemetry and control systems.

Looking at the schematic for your average RC transmitter there is *no* circuitry designed to limit the current draw of the final RF stage (other than a resistor on the emitter leg -- which is primarily for Class-C efficiency purposes anyway).

We have to remember that the RF power levels involved here are pretty small -- 100mW or so; and also don't forget that these RF modules are very much built to a price. The Hitec ones are just $25.

Those who have pointed out the effect of temperature on the MTTF of a semiconductor are correct -- increasing the operating temp signifcantly reduces the operational lfiespan and chances of failure.

I guess it's fair to say that running with the antenna down *does* increase the dissipation of the RF output stage but whether the temperature rise is sufficient to push it into failure is dependent on other factors such as the duration of the abuse, the ambient temperature, etc.

Remember that even if the transistor is well heat-sunk, it's inside a plastic box with little or no ventilation. Given enough time, it will still reach an elevated operating temperature regardless of the size and mass of the sink involved.

Based on my own observations -- its' pretty likely that you'd get away with it quite a few times but *eventually* (perhaps sooner than later in some cases), the increased heat caused by the high SWR *will* cause premature failure of the output transistor. I'm talking here of antenna-down operation in excess of 30 minutes at a time.

Rodney

Xjet, very good reponse, you said it better than I did. Yes, people get by with running with the antenna down for long periods but not everyone is that lucky. I've seen two failures that were most probably due to excessive operation with the antenna down but impossible to prove that was the cause.

dirtybird

My Feedback: (5)

You cannot design for all possible extremes. It would cost too much. If some klutz increases the battery size by three times,( I read where they are putting Lipoly's in there)puts it in a metal box energised, and puts the case in the hot sun you probably will be in trouble. But I don't think that was the question here.
You can make a product fool proof but you can't make it idiot proof.

wgbrown1

So unless we are all EE's then we're a klutz?

tlrascal

My Feedback: (56)

Rodney wins. I know of instances where there were heat sinks offered as an aftermarket item for final output transistors. Remember the World Engines radios? The temperature will be much higher if the transmitter is operated with the antennae collapsed and I have witnessed ocassions where the transistor was finally fried. Think not? Remove the case and expose the output transistor and operate it for 10 minutes with the antennae collapsed and put your finger on the transistor and lets see how long you can hold it there. Immediate blister is what you'll get.

dirtybird

My Feedback: (5)

From 1970 to 1975 I was the repair rep for Kraft, Logictrol, and Royal Products. Just a support my hobby on the side business. I repaired hundreds of radios during that period. I never saw a burned out PA. Mostly broken crystals and out of tune IF's. There were a lot of bad servos but they were too cheap to replace.
The input to the final is low enough that that you are not likely to burn anything out no matter what the condition. You don't need special protective circuits. All you need to do is pick components that are adaquate. We are not talking about a KW power amp here.
Most people that are not technical trained are klutz's when it comes to electronics. I have met a few EE's that are.
I know nothing about the field of music and just because I can operate a mean CD player I don't figure that makes me a music expert.