yamr6rider

I am building a(n) 1/2(50%) scale RC car and was wanting to include a motorized car stereo antenna that extends when the engine is started, but will that adversely affect the range or function of the antenna if I hook it up to the radio plug end of the antenna?

The sheer scale and projected actual speed of this thing calls for maximum range, so I need to figure out how to make this work without sacrificing the range of the radio.

MikeL

My Feedback: (3)

I'm confused.  Why would your motorized stereo antenna have to have anything at all to do with your receiver antenna?  The two shouldn't have anything to do with each other.

yamr6rider

well, I don't want to have the Rx antenna up in the air like a big whippie antenna, so I wanted to run it through the stereo antenna instead. That way, when it's all shut down, there's no RC antenna sticking up into the air. When you fire it up though, not an RC antenna, but a stereo antenna motors up out of the car. I want to use the stereo antenna AS my RC antenna.

Zor

yamr6rider,

Just make the extended antenna total length the same as the original receiver antenna total length.

There is no such thing as a stereo antenna; there is an antenna for a car stereo receiver.

Zor

yamr6rider

I understand about "car stereo receiver" antennas, but was trying to keep my posts from being unnecessarily wordy. Anyhow, the RC receiver antenna is about 12-14" long, and the "car stereo receiver antenna" is something like 36" long. I know with CB's and such that the length of the antenna can make or break the range and quality of the signal, but don't know how this'll effect an RC radio setup; which was the basis for this thread.

MikeL

My Feedback: (3)

You've got a lot of options that are far better than combining the two antennas.   If you've got to use 75mhz (and why would you have to?) you can mount the antenna someplace inconspicuous on a project that large.  If you go with 2.4ghz, you'd not even have to ask about any of this.

Zor

No problem

36" when fully extended. The anennafo the stereo receiver probably has a length of coaxial transmission line frem the antenns to the stereo receiver.and is not a tuned antenna. It is notresonant.
I am guessing (you did not say) that your model car receiver is operating on the 75 Mhz bandand itsantenna may be mounted with a very short wire from the antenna to the model receiver. Such an anenna is likely tuned (inresonance to that radio band) If so, the resonanceis essential to the receiversensitivity to the transmitted signal. Thus the need to have the exact same total length and mounting setup.

The antenna response (sensitivity of the antennas circuit) definitely affect the range but not the quality of the signal (distortion). You may consider that the receiver for your model may have been designed for close range control of a smaller vehicle. You realize (I can see that) that your 1/2 scale might be used to much farther distances. These distances may exceed the normal range of this radio equipment.
That is for you to verify.

What I wrote in my first response is still valid.

Best of success,

Zor

Zor

My writings responding to this thread is based on my understanding that he wants to use the antenna of a regular car radio instead of the antenna that comes with the radio for model control.

Thus not combining the two antennas.
I do not understand why you are asking "and why would you have to?"

I just wished to clariffy the outlook of my response.

Zor

MikeL

My Feedback: (3)

I'm a big believer in Keep It Simple, Stupid. Combining the two is foolish if there's a mechanism that automatically raises and lowers the antenna. There are better ways to do this, particularly if the project is as large as he says it is. If he can engineer something like that and make it appropriately safe, finding a concealed spot for a 75mhz antenna shouldn't challenge him.

A.T.

If Stereo antenna is connected to a working radio, would keep the RCreceiver antenna well away from it.
Not to get into any debate as to the use of 75Mhz or 2.4 Ghz etc, there are several<dt>considerations if 75MHz is to be used.
Receiver Antenna - Does Length Really Matter?
Antenna - shorten for RC Tanks, Boats & Cars - Easy DIY Modification - </dt><dt>Antenna Design Information & Software </dt><dt>Base loaded receiver aerials - DIY Whip Flywire
Guide to receivers - and solving apparent RX & "Interference" problems"
See also sub Section "Glitches & Jitter in Receiver, Servo & ESC - causes and cures " under
"Receiver - FAQ, Guides & Aids To Best Reception..." at:
Alan's Hobby, Model & RC FAQ Web Links
</dt><dt>Regards
Alan T. </dt>

Zor

MikeL

I am reprinting your original posting below with red comments inserted ____

Original posting below ___
You've got a lot of options that are far better than combining the two antennas. If you've got to use 75mhz (and why would you have to?)"why would you have to quite obviously apply to the use of the75 Mhz band. He has to use that band or a legal radio band .you can mount the antenna someplace inconspicuous on a project that large. If you go with 2.4ghz, you'd not even have to ask about any of this.
End of original posting ___

You now see why I wondered ___you seemed to say that he has other choices than use 75 Mhz.
I did not assume that he would want to buy 2.4 Ghz for his project.

Also I understood that he wants to use the car antenna instead of the antenna that the model receiver comes with and not a combination.

I hope again that this clarifies what was my interpretation of his posting.

Zor

yamr6rider

Ok, to clarify. I am using JRXF631Tx with an JR R700 Rx on 75Mhz(converted to ground freq), I could fab up a new car style stubby antenna, but want the radio antenna that motored up when the engine starts simplybecause I just think it'd beawesome to see.



I don't want my RC system to make the antenna go up. That'll happen automatically from my ignition output once the remote start has the engine running. I think we're on the wrong start here. My 1/2 scale car will be started from the transmitter, so it won't necessarily be right nextto me, and the end idea is for it to be able to start and be driven off of the trailer.

Zor

It would be nice to see .
There is no problems to do that.


I think there is a simple way to do it ( the KISS method).

Where the model car is has nothing to do with the antenna operation.
It is said that when the engine is started the same function will also raise the antenna.
That is understood.

Where a problem may (and I think will) arise is that the receiver in the model originally has a short antenna (quioted as being 18 to 20 inches long) and this receiving antenna is quite certainly tuned (resonate electrically) to the 75 Mhz band.

That part of the setup should not be changed to avoid detuning the antenna.

A KISS solution might be to have the model receiver and its antenna installed so that the raise and lower mechanism do so such that both the receiver and its antennas raise and lower as one unmodified unit.. The leads to the servos can be flexible and their length is not critical within reason.

Of course if this receiver is instrumental in starting the car (starting the engine) it must be able to operate in the retracted position (no shielding).

Just a thought from Zor

yamr6rider

ok, ok, I think I can work on a way to integrate that inside of the antenna shell. I figured they were wave tuned to the freq just like CB antennas. that should mean though that I should be able to exactly double the length and maintain the wavelength. Should take it from a quarter-wave to half-wave, long as the resistance stays consistent.

Zor

Yamr6rider,

I hope your "ok, ok," does not reflect annoyance. I have only beentrying to help.

When you saythat should mean though that I should be able to exactly double the length and maintain the wavelength

The wavelength is determined bythe source of the operating frequency and not by the antenna length.

If you are thinking about the resonance of the antenna system, doubling the antennalength (the length that is seen when extended if extension exist) will not maintain the resonance of theantenna if the antenna system is resonated using internal impedances withinthe receiver.

For example, I have a hand held CB radio, TRG-217, 40 channel, that has an extended antenna of 48 inches fully extended out of the case and a loading coil at 18 inches out of the case. Adding 48 inches at the end of this antenna would simply detune the resonance of the antenna circuit in the center of the CB band.

I think I have pretty well covered this topic.
Some other postings in this thread are well worth going over.

Some pictures of your project would be fascinating to see if you can post some.

Best to you,

Zor

yamr6rider

not annoyed at all, just taking it all in. I forgot about the internal impedance. I'll see if I can figure out how to get it to draw in the length of my RC antenna as it's going up. I have an idea on that, just gotta get on ebay and order a universal power antenna.

Flying Geezer

My Feedback: (14)

Formula for determining the resonant length of the antenna is: meters = 3 X 10 to the 8th power divided by the frequency. You can divide that by 2 for half wave, 4 for quarter wave, etc.

yamr6rider

so, by that equation, my Rx's antenna is a 2-wavelength antenna. is there a specific thing denoting the right calculation of waves, or just maintain increments or 1/4 wave? this is getting more complicated than I wanted..... Think I'll stick with the work off of the standard antenna idea.

Zor

Guys ___follow me ___

Radio waves travel at a speed of 300,000 kilometers per second which can also be written as 300,000,000 meters per second

75 megahertz is 75,000,000 hertz (cycles per second).

Divide the two the answer is 4.00 so each hertz (cycle) is 4 meters long.
A half wave is 2 meters long.
A 1/4 wave is one meter long. and expressed in inches it is 39.37 inches.

That is the length of the waves ___ NOT necessarily the length of the antenna.

However if we provide a whip having a lengthbetween 38 to 42 inches it is convenient to handle physically out of a transmitteror receiver case (box) and is also easy to provide electrical circuits that make the antennas system resonant thus being able to radiate maximum energy out of the transmitter as well as absorbing maximum energy at the receiver.

Hope you now understand that, by that equation,your Rx's antenna is NOT a 2-wavelength antenna.

Zor

yamr6rider

check... not a 2 wave. That'd make it 1/8 wave. ok, ok Too much figuring for me. Standard Rx antenna it is.

carrellh

I would not try to connect the RC antenna to the car stereo antenna in any way. You can still have the car stereo antenna go up and down when the car is started and stopped.

I'd just tape the regular receiver antenna to the inside of the body so it will be hidden. You'll need to do a really good range check before driving the car since you will be dealing with distances beyond what is common for RC cars.