David_Moen

Last weekend out at thie field, I had my daughter take my TX for a walk to do the range check. I didn't look to see where she was when I yelled for her to turn the radio on, and when she did, my servos started going nuts! I was a little freaked out about that so I paced off the dostasnce to where she was, it was 95 feet - the check was sone with the antenna on my 9C full collapsed. We walked the TX closer to the airplane, and the jittering stopped when we were about 70 feet away. There was no problem at all at any reasonable distance with the antenna up, so I flew the plane without incident for the day. Is this anything I should be concerned with?

Kaoma

My Feedback: (4)

The antenna MUST be UP at any time. The FM stands for Frequency Modulation and if you put the Tx on a Spectrum Analizer you will see that your "band" has peaks and valleys (highs and lows). With the antenna collapsed (shorter wave length) you allow only the "lows" to pass. To allow the "highs" to pass as well the antenna must be 1/4 length of the spectrum wave (extended).
Hope it helped.

Lynx

70 feet with the antenna collapsed doesn't sound too bad.

N1EDM

My Feedback: (2)

Also, was she facing towards the plane, or away from it. If she shielded the transmitter with her body (i.e., walking away from the plane with the tx in front of her), that further reduces the signal. It's called 'body fade' and is a technique used by hams when they go 'fox hunting'.

If you were getting that kind of range with her shielding the tx, you were in pretty good shape.

Regards,

Bob

fossil

My Feedback: (25)

I don't know if the 9C is the same as the Futaba 8U but futaba recomends that you have the first large section of your antenna extended for your range checks. It also recomends that you have at least that much extended anytime your radio is on for more than a few seconds or it will damage the radio. Here are two links to the Futaba web site Faq concerning your issues. They have a lot of good info.
fossil


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

http://www.futabarc.com/faq/faq-q331.html

Rodney

I do not know where Kaoma got his info but hope you all ignore it. He would benefit from dragging out a text book or two and doing a little reading. The only part that was correct is that you should not run your transmitter with the antenna collapsed for more than a minute or two else the heat build up due to the higher standing wave ration (SWR) will cause the output stage to heat up excessivly and possibly do some damage to the output stage.

Mac_Man_UK

Now then now then !.....


What you have to do is temper that information with what the power output is on your system. Here in the UK , we run lower power out than you guys across on the US ( 100mW ).

I transmit with antenna collapsed for a substantial time when bench testing JR Transmitters

We do a range test with Antenna collapsed ( ALL the way down ) and IF I DONT get at least 70 paces ( btw I am 6ft tall ) the as far as I am concerned that transmitter does NOT go out of the door !

If the transmitter has been specced correctly , then the risk of damage is minimal with a collapsed antenna. Transmit current is tuned for a minimum with min antenna.

David_Moen

I'm always carefull to only turn the TX on with the antenna collapsed for a a few seconds wile range checking. While setting up in the shop etc., I always extend it fully then push the top sections down into the bottom peice of the antenna. This way the entire antenna is outside the body of the TX, but I'm not going to bust it off by accident.

Thanks for your input guys, I won't worry about this anymore.

Kaoma

My Feedback: (4)

FYI:

Electronics/HS (radio), Communication-Satellite Communications/College, "WABC" and "Hard Copy Show" Communication BoomTruck, RF Eng. & Field Opperations for a national Communication Co. to name only a few...

Now, what are your credentials???

MY Tx radio test as soon as I bought it: (JR 8103 FM Air)
-NiMH 1850 AA pack fully charged
-Tx radio turnd ON with antenna collapsed
-placed radio in the microwave (isolation box-microwave OFF) for one hr.
-took radio to work and hooked it up to the HPSpectrum Analizer

The Tx radio was right on the dot reading 72.490 (Ch. 35) outputing 675 mW.

Any Futaba owners dare to do this???

The antenna must be UP for the wavelenght reasons ant NOT because you would risk to fry the Tx. On the other hand the telescopic antennas are the worst type anyway.
Here is my .02

(there is so much ignorane about the RF that I gave-up explaining. If you see any guys at the field flying in barefoot...I was the one who told them...)

GRANT ED

Kaoma, I think what Rodney is saying is that having the antenna collapsed does not make it act like a high pass filter. It just makes it less efficient therefore having less range.

JPMacG

My Feedback: (2)

Rodney is absolutely correct.

Toucan

My Feedback: (1)

We all have been posting on DO's and Don't's I guess and not talking of the problem what fellow friend is asking about. According to me you are fine with 70 feet antenna collapsed totally.

Now to be sure you should keep the model 3 feet above the ground and walk away from your model with TX not facing the RX. That would clear you where you are...

I hope that helps.....