Antenna Expertise

[Jeff Leavitt]

Hi!

Sometime back, somewhere, someone posted the optimum ant length for each channel on 72 mHZ in the range we use in the US. (11-60) Anyone have any idea where I could find this info again?

I've heard it said that the rx's we buy, usually come with about a 39" ant. And, that that length is optimized to allow use with crystals in the 11-60 range. Is this an accurate statement?

Is there an appreciable gain to be had by using the exact length for a particular channel?

Also, I've heard it said that the ant on recievers are generally 1/4 wave. True? If that's true, would doubling the length make the ant a 1/2 wave? Generally speaking would the 1/2 wave be better for our RC purposes? Your comments will be much appreciated. Thank You... Jeff Leavitt

[Mr.RC-CAM]

Sometime back, somewhere, someone posted the optimum ant length for each channel on 72 mHZ in the range we use in the US. (11-60) Anyone have any idea where I could find this info again?Just take 2808 and divide it by your operating frequency. For example, 2808 / 72.090Mhz = 38.95 inches.

Is there an appreciable gain to be had by using the exact length for a particular channel?No. On our 72Mhz radios, going to a perfect 1/4 wave length (~39") would not offer any noticeable improvement over the 38" to 42" lengths that are found on most Rx's. On the other worldwide RF bands (27Mhz-53Mhz), some antenna gain could be realized if an accurate 1/4 wave was used AND the Rx's antenna matching circuitry was changed/adjusted to accommodate it. However, these antennas would be a bit long for some models.

Is there an appreciable gain to be had by using the exact length for a particular channel?None that you will ever notice. The biggest impact lies in the installation. How you route the aerial and the localized EMI/RFI issues play a bigger role in range than eeking out another fractional inch of element length.

Also, I've heard it said that the ant on receivers are generally 1/4 wave. True?False, at least in the model R/C domain. Regardless of RF band, they are usually cut to a meter length since that is a practical size to mount on a model. The Rx circuitry is designed to deal with the resulting impedance and its massive RF gain budget sufficiently makes up for the losses due to lower element efficiency (poor resonance).

Generally speaking would the 1/2 wave be better for our RC purposes?You will not notice any improvement and some Rx's will lose RF stability due to the changes in aerial impedance. However, you can safely eek out a couple more dB of gain if you counterpoise the main Rx antenna with another 1/4 wave element that is connected to the Rx's RF ground.

RC-CAM

[Jeff Leavitt]

Mr. Rc Cam

Appreciate the info, thanks a lot... You have helped me quite a bit. I do have one related question that I'd rather not ask on the forum. Would you mind if I emailed you directly? Thanks again Jeff......

[Mr.RC-CAM]

Not a problem. Just PM me.

RC-CAM