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Correct length for antenna (JR FM)

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Old 04-08-2002, 03:52 PM
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jpmorgan
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Default Correct length for antenna (JR FM)

Can anybody tell me the correct length? channel 15...
Also does the wire have to be the same gauge? I have a smaller gauge wire now I would like to use.
Thanks for your support.
Perry
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Old 04-08-2002, 04:11 PM
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Winger_BC
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Default Antenna length

Your receiver antenna length is not going to matter very much as long as you are in the ballpark. 2 different receivers I have on 22, and 38 I measured are both 39 inches. Of major importance is in antenna lengths on your transmitter. That one must be to spec for the frequency your transmitter is tuned to otherwise some of the rf power will be fed-back to the output transistor. Depending on the mismatch length the transistor will run hotter than normal and could eventually destroy itself. Not having the tx antenna out full will give you less rf power being broadcasted therefore less range. Nevertheless I always measure my receiver antenna and scratch the number on it's case. In case of a mishap and 1/2 the antenna go missing I can always add the proper section back to its original. Wire thickness on the receiver antenna does not matter as long as it can take the physical abuse of flight and hangar rash.
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Old 04-08-2002, 05:25 PM
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jpmorgan
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Default Thanks

Winger,
Thank you very much.
I now have a better wealth of information that I otherwise didn't know.
Great answers.
Perry
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Old 04-09-2002, 05:36 PM
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Dansy
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Default Correct length for antenna (JR FM)

The JR receiver antenna are all of the exact same size......inlike Futaba....

Daniel D.
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Old 04-09-2002, 08:08 PM
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Crash_N_Burn
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Default Correct length for antenna (JR FM)



I just learned something...dansy is correct...

....I just bought a new JR 8103 on 53MHz and measured the receive antenna's length last night ---- 39"!

I would have thought it would be much longer at this lower frequency.

Range would still be lowered I would think with less than a 1/x wavelength receive antenna. I guess we fly so close it doesn't matter. The receiver is probably in saturation all the time anyway.

Thanks for the tip, guys!

-dave-
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Old 04-10-2002, 12:52 AM
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fiery
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Default receiver antenna length

In Australia the main R/C aircraft frequency is 36 Mhz. A couple of spots on 40 Mhz are available but that frequency is shared with pagers etc so not many choose to use it. 29Mhz is also available but is mostly used by R/C buggies.

The standard antenna length here seems to be 39 inches as well.

????

I wonder if that is optimal on 36 Mhz? Any opinions?

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Old 04-10-2002, 01:14 AM
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Default Correct length for antenna (JR FM)

Just tried my rusty antenna math and this is what I came up with......

....39" is a 1/4 wavelength on 72MHz. Which would be optimum.

Lesser/greater frequencies, i.e., 36/50/53/75 MHz would be less than optimum with less than unity (1:1) gain.

I would hazard a guess that (if my figures are correct!) if you took two identical transmitters and receivers, one pair at 36 MHz and one pair at 72MHz, the 72MHz pair would have more range. How much more, I don't know.

Any others?
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