tabb

I have a question for you experts out there. My question is concerning the tx being turned on with the antenna in the retracted position. Since I previously was employed in the cell phone /two way radio buisness I do know that it is a big no no to run a tx without terminating the output to a load whether it is a antenna cut to the correct freq or to a proper dead load device. The result of not doing so will rather quickly destroy the integrity of the final output amp, which in time will quit working as a result of thermal break down. Now to the point, when the antenna is in the retracted position is the load the same as if it is fully extended. My thinking is not, but since I am unsure of this I would ask someone who is a vetran of RC who could maybe elaborate on this subject so that I and many other beginners may be informed. Aircraft can become very expensive especially when nosed into the dirt , and I would be disgruntled if it were to happen and it could have been prevented by a simple piece of knowledge.
I would to thank any input in advance

Thanks
Barry [img]i/expressions/face-icon-small-smile.gif[/img]

Bill L

Hey Barry, Check your output and aircraft response with the antenna in down position. You can even check some transmitters/receiver's response with the antenna unscrewed from the transmitter.
You are making this hobby too complicated. Once after testing I hand launched my plane, and then noticed there
was no frequency flag in front of my face, but the plane was flying anyway. You better believe I pulled the antenna out full fast, before the plane got out of range. Just remember to turn on the transmitter. It is in the 72 mhz band, and I think the phones you worked with are in the 400 or 500 mhz range. yes, or no?[img]i/expressions/face-icon-small-confused.gif[/img]

tabb

You are correct as to the freq on the radios/phones they range between the 150 Mhz- 900Mhz freq range. I guess the main point I am getting at is, Should the antenna on the tx always be extended any time the tx is on to prevent premature failure of the output amplifier in the tx due to varying antenna legnth/load level (because the antenna is tuned to 72Mhz by the length it is cut at) I seem to vaguely recall someone saying that they were burning out Tx's because they were not extending the ant. all the way, or like you said am I making a mountain out of a mole hill. I do know that the ant needs to be fully extended for Proper safe flying range.
Thanks
Barry

FHHuber

Yes, it the TX is going to be on for more than a SHORT range check... the antenna should be extended. It is possible to blow the output circuitry by extended operation with the antenna collapsed.

If your TX is plugged into a PC flight sim... you should pull the crystal.

tabb

Hi Fred,
Thanks for the confirmation also thanks for the tip on removing the crystal I did not realize that this could be detrimental to the radio when using a sim. I will need to remember that. Although I use the supplied Tx more than not, I am glad you mentioned it Thanks ! I appreciate all the info that anyone can provide since I am real new to this hobby.
Thanks again
Barry

Bill L

Thanks FHH![img]i/expressions/face-icon-small-smile.gif[/img] I live at least 7 miles from the nearest flying field, and use my transmitter (antenna down) for adjusting every plane after I install radio equipment here at my house. ALSO since it is a computerized radio I work with it on to do elevon or flaperon links at the house. How come the manual said nothing about prolonged activation with the antenna down?[img]i/expressions/face-icon-small-confused.gif[/img] Thanks again for the tip!

Rodney

Tabb and Huber are very correct. It is quite hard on the output stage on your transmitter to run with the antenna colapsed or removed. The energy that would normally be radiated is now dissipated in heat in the output transistor and , at the very least, contribute to an earlier than normal failure of the output stage.

G.F. Reid

My Feedback: (1)

I'll jump on this bandwagon. You should not do prolonged testing with the antenna collapsed.
While it is a necessary test, don't drag it out. Test the system and get the antenna pulled out or shut the system down.
I know it for a fact for two reasons; First, because I worked in the radio repair field before too...and second, becuase I blew the final x-sistor on one of my trannys doing exactly that...prolonged testing trying to isolate an unrelated problem. I know, I know.... I shoulda known better.
What's really scary is that even with the final blown, I could still get antenna-down range checks out to about 15 feet or so. In other words, I never would have found the problem until too late if I hadn't done a good range check at the field.
In my opinion, the only reason so many people get away with it as long as they do is that the output is so small...In the neighborhood of 500~750mw as I recall.

johnybravo

Back in the early 70's the radio manufacturers warned against prolonged transmitter operation with the antennae collapsed or removed. I remember seeing a warning with my old World Engines equipment that this would damage the xformer. For some reason this info has been deleted from the manuals of more modern radios. I think it's a good idea to limit operation to a quick range test as the gentleman above stated to stay on the safe side.

Bill L

I CHECKED WITH HORIZON HOBBY about this, and they said range check, and computer adjustments in my JR could safely be performed with the antenna down. They then advised using a dsc chord. It would hard wire the plane to the transmitter, and no transmission would take place, but the TX would operate on the airplane batteries, and make adjustments in travel, and end admustments.

tabb

I am not sure on this totally, so don't take it as gospel! I think the newer tx may have a load resitor circuit placed in parallel with the output transistor (some times refered to as a balancing resistor). The reason behind this is that the output is redirected to the resistor if the antenna load is lost. It is placed in as a preventive measure to reduce the strain on the finals in the event the tx is turned on with the antena down(range checking ) the antena connection is lost (cold solder joint) etc. It is always a good idea to use proper care in operating your tx according to the manufacturers recomendations. The failsafe circuitry is in place to protect the integrity of the radio, not for carelessness.
Barry

Ladyflyer

My Feedback: (2)

The time spent with the transmitter on and the antenna collapsed should be kept at a minimum. The mismatch causes a rapid heat build up in the final RF stage. Even new transmitters can be damaged from extended operation with a collapsed antenna.
Also the RC operating regulations suggest strongly that operation of the transmitter while not actually controlling a model craft should be kept as brief as possible .

tabb

To all of the modeling Guru's out there . Thanks!!!!!!!!!!
This website is awesome, in that you are able to obtain so many differen't expert opinions on troubles that we may experience is this great hobby. The Do's and Don'ts if you will. For the newcomers like many of us it is a real asset that the information is available, and at that free of charge! Thanks again for all that have responded, you have answered my question.
Barry.[img]i/expressions/face-icon-small-happy.gif[/img]