Antenas
11-21-2005 | 04:21 PM
#2
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From: Berlin Center,
OH
RE: Antenas
Antennas don't work that way. The length of the antenna is proportional to the frequency (wave form, in height) being eminated from the transmitter. Adding wire to your antenna will not give it better range.
Only if you switched frequencies (IE, went to a different FM frequency such as going from 72 mHz to say, 35 mHz, which you wouldn't), you would theoretically increase your range.
If you cut your antenna wire and make it shorter, you're essentially eliminating the frequencies the receiver was designed to pick up. Although if you switched the transmitter to a higher frequency, say 100 mHz, it would pick the signal up, but at a lesser range.
MPB
Only if you switched frequencies (IE, went to a different FM frequency such as going from 72 mHz to say, 35 mHz, which you wouldn't), you would theoretically increase your range.
If you cut your antenna wire and make it shorter, you're essentially eliminating the frequencies the receiver was designed to pick up. Although if you switched the transmitter to a higher frequency, say 100 mHz, it would pick the signal up, but at a lesser range.
MPB
11-21-2005 | 04:29 PM
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From: Manchester,
NJ
RE: Antenas
You really have to compute antenna length. It's related to the wave length of the received signal. Just adding wire will likely not improve performance unless you happen to stumble on an electrically correct length. I am curious as to why you would want to add any length at all because the typical 72 Mhz receiver with a standard length of approximately 39" (1 meter) will receive a signal beyond the range of visible control of the aircraft. In other words, if your plane is beyond the range of the sight needed to fly it, what's the point of extending the signal reception?
11-22-2005 | 02:54 AM
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From: Southern , CA
RE: Antenas
Thanks for the infor Shagg. So what you are saying is that if I increase the freq. on the transmitter theorectically the range would increase. In addition, you are saying that if I increase the antenas on the plane, this would not increase the range. Correct me if I'm wrong. Thanks!
11-22-2005 | 03:47 AM
#6
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RE: Antenas
Net net is don't go messing with your antenna.
If you need more range, get a receiver with a higher range rating. There are lots with over 1+ mile range ratings.
For my 6-7 channel gliders I use the Hitec Supreme 8
For others I have a variety of Hitec receivers, but the Electron 6 is my favoriate. Small, light and 6 channels.
I have had planes out 3/4 mile and 1000+ high with no problems.
If you need more range, get a receiver with a higher range rating. There are lots with over 1+ mile range ratings.
For my 6-7 channel gliders I use the Hitec Supreme 8
For others I have a variety of Hitec receivers, but the Electron 6 is my favoriate. Small, light and 6 channels.
I have had planes out 3/4 mile and 1000+ high with no problems.
11-22-2005 | 04:07 AM
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From: Christchurch, NEW ZEALAND
RE: Antenas
Technically frequency = speed of light divided by wavelength so for 49MHz this is 6.2m. Now an ideal antenna is a quarter of the wavelength you want to receive so 6.2/4 = 1.55m. Now if you measure your antenna you will probably find that it is not the theoretical quater wavelength length, it will be less. This is because the receiver design uses what is called a base loaded antenna, that is it has other components to "trick" the RX front end into thinking it has the correct length antenna attached. This helps fine tune the sensitivity. In other words the front end of the RX is tuned to a specific frequency and antenna length to give maximum sensitivity changing the length will not improve the range.
As for increasing the frequency to increase the range this won't work. To get greater range you need to decrease the frequency this is why technology such as Bluetooth will only work over a short distance.
So at the end of the day the only way to get a greater range is to either increase your TX power (which is illegal as TX power is stricly controlled under the terms of the radio licence that we use) or get a RX with better sensitivity which involves looking at specs for ranges etc.
Cheers
Vaughan
As for increasing the frequency to increase the range this won't work. To get greater range you need to decrease the frequency this is why technology such as Bluetooth will only work over a short distance.
So at the end of the day the only way to get a greater range is to either increase your TX power (which is illegal as TX power is stricly controlled under the terms of the radio licence that we use) or get a RX with better sensitivity which involves looking at specs for ranges etc.
Cheers
Vaughan
11-22-2005 | 05:43 AM
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From: Yukon,
OK
RE: Antenas
If your afraid of losing control due to out of range problem, or if you have had glitches while you were way up high, oh the size of a popcorn kernal; Ya might just wanna send your TX and RX in to be tuned. Otherwise as everyone has stated, the signal will cover a greater distance than you can possibly see, so dont bother.
11-22-2005 | 06:51 AM
#10
My Feedback: (1)
RE: Antenas
The bottom line here is that the antenna is cut (tuned) to a specific frequency. It is, as said above, based on the wavelength of the operating frequency.
And, you just cannot change the frequency of your receiver. It doesn't work that way either. The receiver is designed with components that operate at a specific frequency and that's that. Changing the crystal, for instance, only works for a very narrow band and won't work for, say 72 MHz down to 49 MHz. They are a totally different design and a different wavelenth (again, as noted above).
Also keep in mind that the same thing applies to the transmitter. It was designed for a specific frequency (band... say 72 to 73 MHz aircraft band with 50 channels within that band, each a specific operating frequency).
And, you just cannot change the frequency of your receiver. It doesn't work that way either. The receiver is designed with components that operate at a specific frequency and that's that. Changing the crystal, for instance, only works for a very narrow band and won't work for, say 72 MHz down to 49 MHz. They are a totally different design and a different wavelenth (again, as noted above).
Also keep in mind that the same thing applies to the transmitter. It was designed for a specific frequency (band... say 72 to 73 MHz aircraft band with 50 channels within that band, each a specific operating frequency).
11-22-2005 | 09:44 AM
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From: Springtown,
TX
RE: Antenas
ORIGINAL: Vogan
Technically frequency = speed of light divided by wavelength so for 49MHz this is 6.2m. Now an ideal antenna is a quarter of the wavelength you want to receive so 6.2/4 = 1.55m. Now if you measure your antenna you will probably find that it is not the theoretical quater wavelength length, it will be less. This is because the receiver design uses what is called a base loaded antenna, that is it has other components to "trick" the RX front end into thinking it has the correct length antenna attached. This helps fine tune the sensitivity. In other words the front end of the RX is tuned to a specific frequency and antenna length to give maximum sensitivity changing the length will not improve the range.
As for increasing the frequency to increase the range this won't work. To get greater range you need to decrease the frequency this is why technology such as Bluetooth will only work over a short distance.
So at the end of the day the only way to get a greater range is to either increase your TX power (which is illegal as TX power is stricly controlled under the terms of the radio licence that we use) or get a RX with better sensitivity which involves looking at specs for ranges etc.
Cheers
Vaughan
Technically frequency = speed of light divided by wavelength so for 49MHz this is 6.2m. Now an ideal antenna is a quarter of the wavelength you want to receive so 6.2/4 = 1.55m. Now if you measure your antenna you will probably find that it is not the theoretical quater wavelength length, it will be less. This is because the receiver design uses what is called a base loaded antenna, that is it has other components to "trick" the RX front end into thinking it has the correct length antenna attached. This helps fine tune the sensitivity. In other words the front end of the RX is tuned to a specific frequency and antenna length to give maximum sensitivity changing the length will not improve the range.
As for increasing the frequency to increase the range this won't work. To get greater range you need to decrease the frequency this is why technology such as Bluetooth will only work over a short distance.
So at the end of the day the only way to get a greater range is to either increase your TX power (which is illegal as TX power is stricly controlled under the terms of the radio licence that we use) or get a RX with better sensitivity which involves looking at specs for ranges etc.
Cheers
Vaughan
11-22-2005 | 02:06 PM
#12
Senior Member
RE: Antenas
I frequently see the mistaken comment that the antennas of our RC equipment is cut to a frequency. WRONG WRONG WRONG . The antenna on most RC units, regardless of frequency is 39 to 41 inches (roughly 1 meter) and then the circuitry inside the receiver is tuned by adjustment of L and C to best receive the freqency of interest. Adding or reducing length will usually have undesireable effects, most often reduced range and definatelly poorer selectivity. Unless you have the test equipment necessary to measure these effects, you will be wise to not try to change the length. If you want more info on this, you may want to check out MrRC-Cam's web site as he has done some experimenting in changing antenna lengths along with the results, some good, most bad.
11-22-2005 | 02:25 PM
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From: Springtown,
TX
RE: Antenas
I think it's obvious that they aren't cut to the exact length of the frequency--there is no way for the manufacturer to know exactly what frequency is going to be used at the time of production. However, the antenna is cut to a length that would be optimal for the intended frequency range of the receiver--so that no matter what crystal is installed, range shouldn't be an issue. Bottom line--don't mess with the length of the antenna. There is no need.
11-22-2005 | 02:59 PM
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From: Christchurch, NEW ZEALAND
RE: Antenas
The length will be a compromise for the entire range of the RX. I guess this is why Futaba split the band on thier RX's, they are able to tune the front end a little better for a high band or low band and get that little bit extra performance out of the RX. As Rodney said, with the corect gear and know how you could accurately tune your RX for the frequency that you use.
11-23-2005 | 11:02 AM
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From: Tucson,
AZ
RE: Antenas
If I am flying a small 3 channel bi plane, is is safe to put the antenna out towards the wing tip. If I take the antenna towards the tail I have 8 inches hanging off the back?
11-23-2005 | 01:25 PM
#16
Senior Member
RE: Antenas
Jswanson, no problem. You can run the antenna in any direction you want with no change in performance. The main thing is that you get a reasonably straight run; i.e. no doubling back. I've often seen them set up in a dogleg fashion with no detectable degradation. By dogleg, I mean that they have a change in direction somewhere along there length but usually less than a 90 degree turn, such as to the fin leading edge then out to the stabalizer tip. On my combat planes I run the antenna down the length of the wing, all inside next to the spar.
