Longer antenna longer range? - RC Groups
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Oct 30, 2017, 07:37 AM
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Question

Longer antenna longer range?


This is just a basic question

Lets say that with an x meter antenna I can get about 200m range. Will I get 400m with a 2x meter ant? 600m for 3x meter?

I have a feeling that a 20x meter will definitely NOT improve range, but rather reduce it.

I understand that some increase in power or voltage or something is needed, as the longer the antenna, higher resistance, failing radios...

Please correct me if I am wrong...

Rome
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Oct 30, 2017, 07:52 AM
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Wrong. The antenna length must match the frequency you use. When it is not the optimal length output power, and range, is reduced. There are multiple optimal lengths for a frequency but in RC the most used it 1/4 standing wave length. Google it, you will learn something
Oct 30, 2017, 08:18 AM
Registered User
"Google it, you will learn something " +1
Oct 30, 2017, 09:00 AM
Registered User
Thanks for the feedback
Oct 31, 2017, 02:07 AM
Registered User
This myth could originate from FM days, where antennas were reduced size, to accommodate an average model, using a coil inside the receiver.
The full length antenna should be 2m for 72MHz and 4m for 35 MHz, but the actual receiver antenna was 75-100cm.

Another source could be the coax/collinear design, where many quarter wave resonators are tied together in series to form an antenna. For this design, indeed more length means more gain.
https://i.stack.imgur.com/zkaG4.png
This design can be found inside the 5/7/9 dB whips, each step adding 3 cm to antenna length.

Same for helix, more turns/length, more gain.
Oct 31, 2017, 12:12 PM
S.A.D. member
ivanc's Avatar
Quote:
Originally Posted by renatoa
This myth could originate from FM days, where antennas were reduced size, to accommodate an average model, using a coil inside the receiver.
The full length antenna should be 2m for 72MHz and 4m for 35 MHz, but the actual receiver antenna was 75-100cm.

. . .
I do not know where you get your numbers but they are not correct. The wavelength of 72MHz waves is approximately 4m, so the regular 1/4-wave antenna is approximately 1m long which is the most common length of 72MHz transmitters and receivers. Sure there are some transmitters and receivers with shorter antennas which have impedance matching coils in series with the antenna.

Ivan
Oct 31, 2017, 06:16 PM
Registered User
err...he said "receiver antenna"...pretty sure 72MHz receiver antennas were not 1m long
Oct 31, 2017, 07:00 PM
AndyKunz's Avatar
Quote:
Originally Posted by pressalltheknobs
err...he said "receiver antenna"...pretty sure 72MHz receiver antennas were not 1m long
They were pretty close to that - realizing that the physical length of the antenna may not be exactly the same since the speed of propagation changes per medium. 1m is close enough - you might have to add few tenths.

The surface antennas were about 18" long - 1/8 wave for 75MHz.

Andy
Oct 31, 2017, 07:12 PM
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ivanc's Avatar
Quote:
Originally Posted by pressalltheknobs
err...he said "receiver antenna"...pretty sure 72MHz receiver antennas were not 1m long
Most of my 72MHz receivers had (and I still have some) 1m (39") long antenna. Bergs, the shorter range Hitecs, GWS and some others had shorter antennas and less range that the "standard" 1+ mile for the receivers with the 1m antennas.

This (the 1m long antenna) was an issue on smaller airplanes (40-size and smaller and even on some 60-size airplanes) where running the antenna all the way to the fin would still expose an extra 6-8" of antenna hanging freely from the tail and dragging on the ground while taxiing.

Ivan
Oct 31, 2017, 07:17 PM
Registered User
Looking around I see you are correct. The ones I have seen and used were shorter...possibly they were all surface as Andy suggests.
Oct 31, 2017, 07:29 PM
AndyKunz's Avatar
Or maybe they were Deans base-loaded antennas.

Andy
Nov 01, 2017, 02:49 AM
Registered User
I can't comment much for 72 MHz, but for 35M (8.5m wavelength, 2.14m quarter wave) this was sure an antenna shortening coil in every receiver.

10 years ago were common LR flight up to 10 km done just by lengthening Tx antenna to 4m, using a wire on a GF fishing pole, connected with a croco clamp on the (collapsed) Tx antenna.
At receiver side the antenna was extended to 2m.


Quote:
Originally Posted by ivanc
I do not know where you get your numbers but they are not correct. The wavelength of 72MHz waves is approximately 4m, so the regular 1/4-wave antenna is approximately 1m long which is the most common length of 72MHz transmitters and receivers. Sure there are some transmitters and receivers with shorter antennas which have impedance matching coils in series with the antenna.

Ivan
Nov 01, 2017, 08:07 AM
I miss President Reagan
KMK001's Avatar
Quote:
Originally Posted by AndyKunz
Or maybe they were Deans base-loaded antennas.

Andy
Sure would like to find a supply of those. I still run 75 on boats.


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