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Modified R/X?

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Derek27/06/2009 06:48:53
28 forum posts
Has anyone tried to modify the Ar700 or any of the multi aerial R/X, in as much as lengthening the aerials similar to the AR9300 so that they protrude outside the fuz, if this works why are we spending £130plus on these so called carbon friendly R/X?
Some one told me that the aerials unlike 35 mgs are not tuned by the length of aerial, true or false?
ken anderson.27/06/2009 07:56:26
8424 forum posts
772 photos
hello derek-TIMBO is your man for this dept...........wait paitently..............all will be revealed.....fear not..............
       ken anderson.......
Klippy27/06/2009 08:01:12
750 forum posts
13 photos
Hi Derek, I think you'll find they very definitely tuned, and at 2.4gigs even 1mm will affect the tuning. Try the Wireless internet people, they have suitable small diameter coax that you can use. It may work, obviuosly proper range checks are required.
Tim Mackey27/06/2009 11:25:59
20919 forum posts
304 photos
15 articles
I agree with Tony - I wouldnt mess with it TBH - apart from anything, if it were to cause a problem, and your model crashed, ............?
Frank Skilbeck28/06/2009 09:01:22
4430 forum posts
101 photos
Note the aerial on these carbon friendly RX's is connected to the Rx via coax it's only the end which is the aerial and the length of this is important, you'd need to make sure you have obtained the correct coax/aerial lead for the job. Not sure if the circuit is also different to cater for the additional coax, not worth the risk especially as the AR6250 is available for around £50, and compare to the overal cost of a carbon plane.................
Brian Parker28/06/2009 20:17:48
538 forum posts
"Antennae no longer tuned for 2.4GHz"????
When I was a lad the same characteristics/properties of antennae applied to all radio frequencies.
 The mode of propagation determines the form of antenna. As our 2.4GHz systems are propagated primarily point -to -point the mode is by free space waves.
Insert a carbon wing or a fuselage in the line of sight and we no longer have free space conditions.
 Use of remote multi- antennae using co-axial feeders...
   a) As frequency increases, the losses in coax increases per unit length.
   b)The coax screens the inner conductor. But  at high frequency, current does not penetrate it flows over the outer skin of the conductor and return current flows over the inner skin of the braid (skin effect) and it is also screened by the outer surface of the braid. The electro/magnetic wave curves, it is not linear.
   c)The receiver needs to see a resonate antenna. The antenna input impedance is seen as a pure resistance only when the antenna is resonant.
  d) Alter the length of the coax and the impedance will not match, degrading delivery of signal.
 All the above needs to be considered before altering the coax length or the receiver will be 'deaf' to some degree.
Basically don't alter the length.
ps. Before I'm accused of re-writing the reference books again, these are just simplified notes.

Edited By Brian Parker on 28/06/2009 20:19:41

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