Scale Antenna's

[Russell Bear]

Harry, Sure do appreciate it. So with this mount is the wire length a concern? Can the RX wire be left the stock length?

 

[hgatjens]

I am afraid I do not know technically how big of a concern it is. We used to leave it stock length and then someone made a big deal about how the overall length wasn't supposed to be changed so we started trimming the receiver antenna. To tell the truth we didn't notice any difference. It worked both ways. But, I am not an expert on the technicalities of it.

 

[Russell Bear]

I am afraid I do not know technically how big of a concern it is. We used to leave it stock length and then someone made a big deal about how the overall length wasn't supposed to be changed so we started trimming the receiver antenna. To tell the truth we didn't notice any difference. It worked both ways. But, I am not an expert on the technicalities of it.

109694[/snapback]

​

Fair enough. Thanks again Harry, I'm sure someone else will chime in on this.

 

[Don Ferrette]

Harry please be VERY cautious when you run that Spectrum unit. There have been numerous range issues with the current ones as they are intended for the r/c car guys. Spectrum is supposed to be releasing a longer range version but as far as I know it is not available yet. I last heard not until late September.

Hi Don, Where did you here this? I talked with Horizon Support this morning and he said he has heard nothing about this.

Thanks

Pete

109138[/snapback]

​

Just a little FYI. Horizon has also being giving refunds on these-

http://p086.ezboard.com/fjimsrcboatdockjim...cID=20085.topic

 

[JimClark]

Paint the Deans one black and you wont see it when running.

jim

 

[Brian Schymik]

Paint the Deans one black and you wont see it when running.jim

111218[/snapback]

​

I have Deans on my scale boat and my old Sport 40. They are nice and short ( 5 inches or so). They work great.

My new sport 40 has the regular long receiver antennae in one of the usual plastic tubes that lies down in the boat flat under the cowl. It has workes fine in practice and will race this weekend.

Brian

 

[Racerdude]

Hi all -

If I'm not mistaken, the Spektrum units run at 2.4 GHz. This would, in fact, make them need a very little antenna (believe it or not, I am a radio engineer for real). They are spread spectrum radios, which tries to help make up for the additional proagation loss suffered at this high frequency. This frequency (and in fact all frequencies as you go higher) become more nd more directional and incurr higher losses going through air. This is why I have not yet been able to talk myself into one of these radios. Something as small as another boat coming between you and the you boat when it is out on the pond could cause major path losses which could have an adverse affect on your communications link. Diffraction at high frequencies is more severe, causing losses when even a small object comes between the transmitter and receiver.

Now, it may be that it is unlikely that this would happen, but it IS possible.

I'm not surprised to her a report of a range problem.

Radios are not like computers...higher "GHz" is NOT better. That is why I run channel 63. I would have run 61, but someone else locally has that channel here.

 

[Racerdude]

Most antennas are 1/4 wave dipoles because 1/4 of the wavelength is about as small as you can go without beginning to seriously affect gain. On the other hand, the longer the antenna, the more gain it has. A 1/4 wave dipole antenna has 3 dB less gain (that is half the gain, 3 dB is always 50% up or down). In other words, the signal you receive with a 1/4 wave dipole antenna will be half the power you will receive with a 1/2 wave dipole.

The name "1/4 Wave Dipole" gives a good hint as top how long it is - One-fourth (1/4) of the wavelength. The wavelength is usually called "Lambda", and it is calculated as follows:

Lambda = c/f

where c is the speed of light in a vacuum (3x10^8 m/s), and f is the frequency (in Hz, NOT kHz, MHz, or GHz) The answer is in meters because it is wavelength - the length of the wave.

So, for example, the wavelength of a 75 MHz signal is :

Lambda of 75 MHz = 300,000,000/75,000,000 = 4 meters

Now, if we take 1/4 of 4 meters, then we would say that an optimum gain 1/4 wave dipole for 75 MHz would be 1 meter long, remarkably about the length of the telescoping antenna that we have attached to our remote control transmitters.

Now the receiver does not use an antenna so big, mostly because at this frequency, we are actually blasting quite a bit of power out of the remote (that's why battery life is short). Of course, if we were to put a transmitter antenna on the receiver (as well as the transmitter), we would most likely increase the range substantially (but it would not be 50%!!!!).

 

[LOU]

I'm using the DX3 and so far so good. Raced 20 heats glitch free and no range problems. This was on the 1/3 oval. I have anywhere from 5 to 6 inches of antenna out of my hulls. So far no regrets but when I read about some peoples problems, It's gotta make you wonder whats going on. I run the Energizer lithum cells in my transmitter.

I have had what seemed like signal loss in some of my testing sessions but then I was right at ground level and may not have been holding the transmitter with the antenna vertical. I also was more then 1500 feet away from the boat.

Got 2 more races this season and one thing is for sure. Impounds suck

 

[hgatjens]

If I'm not mistaken, the Spektrum units run at 2.4 GHz. This would, in fact, make them need a very little antenna (believe it or not, I am a radio engineer for real). They are spread spectrum radios, which tries to help make up for the additional proagation loss suffered at this high frequency. This frequency (and in fact all frequencies as you go higher) become more nd more directional and incurr higher losses going through air. This is why I have not yet been able to talk myself into one of these radios. Something as small as another boat coming between you and the you boat when it is out on the pond could cause major path losses which could have an adverse affect on your communications link. Diffraction at high frequencies is more severe, causing losses when even a small object comes between the transmitter and receiver.

Not trying be trouble here. Just trying to understand. But if a small boat getting in the way of my transmitter causes signal loss, then how does my 2.4ghz wireless phone work at home when it is in a different room?

Also, based upon your formula an antenna for a Spektrum should be 4.875 inches which comes clost to how they are setup?

Help me understand

 

[Don Ferrette]

If I'm not mistaken, the Spektrum units run at 2.4 GHz. This would, in fact, make them need a very little antenna (believe it or not, I am a radio engineer for real). They are spread spectrum radios, which tries to help make up for the additional proagation loss suffered at this high frequency. This frequency (and in fact all frequencies as you go higher) become more nd more directional and incurr higher losses going through air. This is why I have not yet been able to talk myself into one of these radios. Something as small as another boat coming between you and the you boat when it is out on the pond could cause major path losses which could have an adverse affect on your communications link. Diffraction at high frequencies is more severe, causing losses when even a small object comes between the transmitter and receiver.

Not trying be trouble here. Just trying to understand. But if a small boat getting in the way of my transmitter causes signal loss, then how does my 2.4ghz wireless phone work at home when it is in a different room?

Also, based upon your formula an antenna for a Spektrum should be 4.875 inches which comes clost to how they are setup?

Help me understand

111385[/snapback]

​

How far can you get that 2.4gig phone away from it's base? I returned a 2.4 set once because my old 900 set kicked it's tail range wise & that was before I ever knew about this Spektrum DSM stuff. :blink:

 

[T.S.Davis]

  Of course, if we were to put a transmitter antenna on the receiver (as well as the transmitter), we would most likely increase the range substantially (but it would not be 50%!!!!).

111370[/snapback]

​

So then can we deduce that the original length of a RX wire attached to a piece of piano wire would make for better reception/range?

 

[Racerdude]

Not trying be trouble here. Just trying to understand. But if a small boat getting in the way of my transmitter causes signal loss, then how does my 2.4ghz wireless phone work at home when it is in a different room?

Also, based upon your formula an antenna for a Spektrum should be 4.875 inches which comes clost to how they are setup?

==============================================

First, your 2.4 GHz phone may not work at these distances. If the separation between your boat and you is not greater than the normal separation between you and your phone, then a 2.4 GHz controller may be just fine for you. The really difficult thing is when the boat is separated from the remote by a significant distance (let's say 150 yards, for example), and something (a tree branch or another boat) blocks you temporarily from your boat. I would wager your home phone would fail where the remote/receiver setup on your boat fails.

The wavelength of the spektrum unit's frequency is very close to the 4.875 inches you mentioned.

There is one more thing to remember - the spektrum unit uses spread spectrum digital (patents developed by my company) modulation which definitely increases the range over an analog signal at the same frequency. But there is a HUGE difference between 75 MHz and 2.4 GHz. The losses at these two frequencies is different, and I am not sure if the Spektrum unit has enough "whiz-bang" communications stuff inside to overcome this natural law of physics. Maybe it does!

It seems to me that the best answer is digital (PCM) at 75MHz.

Does that help?

Jay

 

[Racerdude]

  Of course, if we were to put a transmitter antenna on the receiver (as well as the transmitter), we would most likely increase the range substantially (but it would not be 50%!!!!).

111370[/snapback]

​

So then can we deduce that the original length of a RX wire attached to a piece of piano wire would make for better reception/range?

111423[/snapback]

​

===========================================

Actually, there could be a piece of truth in the piano wire theory, considering the following:

Antennas do more than just act as amplifiers (remember one of my previous posts was talking about "gain" of different wavelength antennas?), they also have characteristics that act like filters. In other words, a particular antenna may do well at amplifying a particular frequency, but attenuate other frequencies (like a band-pass filter). All of this is dependent on the length of the antenna. So, a long piano wire would do a reasonable job at amplifying a signal if it is cut to 1/4, 1/2, or 1 wavelength. Beyond that or in between that, the antenna would be "tuned" for different frequencies, which could have an adverse effect on the frequency you want to be received.

Does that help?

Thanks

Jay

 

[Racerdude]

111385[/snapback]

​

How far can you get that 2.4gig phone away from it's base? I returned a 2.4 set once because my old 900 set kicked it's tail range wise & that was before I ever knew about this Spektrum DSM stuff. :blink:

111392[/snapback]

​

EXACTLY. That is a great example. I ALWAYS buy the 900 MHz phones instead of the 2.4 GHZ phones exactly for this reason. Now, a very well-designed 2.4 GHz phone (or in our case, a 2.4 GHz radio control unit) CAN (theoretically) have a greater range than a badly designed 900 MHz phone (radio control unit) - BUT NOT BECAUSE of the frequency. Let me explain (although it seems you already got it) -

 

We are talking really about 4 combinations:

 

1 - 75 MHz Digital

2 - 75 Mhz Analog

3 - 2.4 GHz Digital

4 - 2.4 GHz Analog (? don't know if this one exists! I hope NOT!)

 

If we were to compare 2.4 GHz digital (spread spectrum) to 900 MHz analog, I would expect most phones to have about the same range. However, comparing to 75 MHz analog, I would expect the 75 MHz analog to have a better range, although they may in some radios be close to each other.

 

Now if we compare 75 Mhz DIGITAL (PCM) to 2.4 GHz digital (spread spectrum), I would expect the 75 MHz digital to have a much longer range.

 

Whenever we run the test you described - 2 frequencies against each other, IF they use the same modulation technique, the lower frequency win have a longer range in every case. Laws of physics.

 

Thanks for the good example Don!

 

Jay