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Base Loaded vs regular Antenna where is the true!

Old 12-21-2005, 12:45 PM
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Felix72
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Default Base Loaded vs regular Antenna where is the true!

Hi, first of all sorry for my english because I'm from Italy.

I have some different base loaded antenna and I'm trying to understand better the way they work, but I need help for you antenna "GURU"!

I have also the following receiver:

Hitec ELECTRON 6, Micro 555, RCD3500 (all double conversion FM) 40 Mhz

Graupner SMC-20DS (double conversion PCM) 40 Mhz

JR R995S (single conversion PCM) 72 Mhz

Antennas:

Quick-uk base loaded antenna 40 Mhz

Deans two piece Mini antenna 72 Mhz (to be used with 36" - 39" antennas)

Revolution base loaded whip antenna 72 Mhz

I want to point out that the considerations I will do are based only on practical analysis with 40 and 72 Mhz, what I need is the theory behind this and considerations with the use of the two bands.

I discovered that most of the standard receiver antennas are 1 meter long (more or less) regardless of the frequency they are supposed to use (40 or 72).

I discovered also that both of my transmitters (Graupner MX-22 and JR PCM-10 aero) have the same antenna length (115 cm) even if the JR is supposed to work on 72 Mhz (I bought it in the USA) and the Graupner is supposed to work on 40 Mhz (I bought it in Europe).

How is it possible ??

I did some test using the Electron 6 FM 40 Mhz (40.735 frequency) with the Revolution antenna (supposed to be used with 72 Mhz) in my Robbe Spirit-PRO.

I got more then 50 meters with the MX-22 on 40.735 frequency and the Tx antenna collapsed, the revolution antenna were placed on a leg of the Spirit, pointing forward.

at 50 meters away I still have no glitch.

I don't know really why, but seems that ther is some strange phenomenon.

What I'm missing??? Do I have to do some other check ?? Any suggestion ??

Perhaps the distance at which we usually fly our helicopters, in conjunction with the power of the transmitter, mask all the problems ??


Any considerations will be appreciated.


Gianluca
Old 12-22-2005, 10:10 AM
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dirtybird
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Default RE: Base Loaded vs regular Antenna where is the true!

All of those antenna should be 1/4 the wavelength of the frequency you are working with. If that is not physically possible or desireable you can load it to make it seem its the correct length. Loading the antenna is accomplished by placing a coil of wire in the proper place to make the antenna seem longer. Just think of it as winding some of the wire of the antenna up and putting it in a coil. You can do this both for the transmitter and the receiver
Old 12-22-2005, 10:17 AM
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Rodney
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Default RE: Base Loaded vs regular Antenna where is the true!

You will find nearly all RC receivers use a form of base loaded antenna. It is not quite as simple as as dirtybird implys but he is close. For proper results, you use a combination of inductance and capacitance in the loading portion of the coil and really requires some measuring equipment to do it with best results. You can find some good info at www.rc-cam.com/ant_exp.htm on how antenna length effects your receiver.

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