Had a talk with Santosh yesterday  and  asked him my doubt regarding receiver  antenna length.

he explained to an ignorant me that normally the  receiver antenna length on a standard fm receiver is around 1/4th wave length and can be increased  to enhance range but the problem is the practicality of using such a long receiver antenna and that 1 wave lenght should give really good range .

Did a bit of looking around and came across this interesting  calculator for  wavelength calculation :

http://www.csgnetwork.com/freqwavelengthcalc.html

Eg on my FPV plane I use  72.890 mhz  hence the wavelength is 4.116 M , 13.5 feet  antenna  


With this calculator you can find the wavelength of an frequency  including 2.4G those are like in some decimal of  a foot.

Interesting for Annadi's like me  so I thought I will share it.

sai

we all use half wave length antennas for our ham radio opertions,i/4  wave lenghth on the one side of the antenna.(not the full wave length)


santhosh

Sai,
I guess I have discussed Antenna length for your earlier post for increasing Tx power.
Fiddling with Antenna is not straight forward, esp when it comes to Transmitting. What Santosh is talking about is a Folded Diapole antenna , like your TV antenna on the roof, 1/4 wave length on either side. For a unidirectional 'Rod' antenna, its always 1/4 of wavelength. You should not simply change these lengths.

The output gain of of Tx is tied to Antenna design (Diapole/Yagi/uni dir/Cubical Quad/Diamond Quad) which have lengths arrived after wavelength calculations. if you want to increase the gain, move to a higher gain antenna instead of changing the antenna length arbitrarily. You would also need to change the impedance of the matching coil accordingly.  Then you would also need a SWR meter to see if the antenna is properly matched to the final Amp stage (matching coil) and there are no standing wave which may fry your transmitter Amp FETs

Do the changes in  the circuit learning basic antenna design and AMP driver principal. Any simplistic HAM radio book like "ABC of Amateur Radio" by Raj Verma should help you fast.

Ujjwal ,
Thanks for the book ref should help .

I am not planning to arbitarily increase the antenna length .
Just that I thought it is interesting that such a calculator is available on the net  and might get a few other than me interested in understanding more on this subject.

rgds
sai

Quotenormally the  receiver antenna length on a standard fm receiver is around 1/4th wave length

Not valid for RC Rx antennae. Just compare 35, 40 & 72MHz receiver antennae lengths (same brand). You will find them almost - if not exactly - the same.

1/4, 1/2 or full wave antennae are used for "maximum" gain for a particular frequency or band. Normal receivers for RC are designed for the length supplied. This is why they advise that the antenna should never be altered in length.

The same hold true for Tx antennae.

Quote from: ujjwaana on March 27, 2010, 11:32:55 AM
Sai,
Any simplistic HAM radio book like "ABC of Amateur Radio" by Raj Verma should help you fast.

Ujjwal ,
Any Idea if this book is available in Chennai and where can I get it ?

Sai

@ Sai

"ABC of Amateur Radio" will be available at:

Business Promotion Bureau,
8/1 Ritchie Street Mount Road,
Chennai 600002.
Ph: 28410796, 28550491





Sanjay

Thanks Sanjay will check it out.

sai