Comparison of R/C Receiver Range with Various Antenna Configurations
       By Richard Ellis AMYA 9426

    Recently I have been experiencing temporary loss of boat control during sailing.  The “drop outs” usually occur at the farthest point of the course.  Other times I have noticed a control loss when the transmitter antenna was pointing directly at the boat.  When I brought the antenna up to the vertical position, control returned.  The conclusion was that the antenna configuration in the boat was marginal, (well, duh!)

    In order to improve my radio reception I needed some good guidelines to aid in revising the antenna in my boat.  I decided to conduct tests on dry land (my front yard) using the radio equipment out of my boat.  The transmitter was set with the antenna collapsed and held at the waist, with the antenna angled up at a 45 degree angle.  The receiver, servo and battery were set on a card table at one end of the yard.  I attached a Popsicle stick on a regular servo laid down on the table. When the transmitter stick was moved,  I could see the Popsicle wave back and forth from across the yard.

   To test a configuration I stood off from the receiver / antenna and while facing the radio equipment walked away from the receiver until I  could see that the Popsicle stick did not follow my commands.  I then walked back to the receiver, counting steps on the way.  Some tests were repeated to check on the repeatability of the results.  It was found that there were small variations in range each time the antenna wire was reset in the test position, probably due to small variations in the bends of the antenna wire.

  I have a number of radios; the latest was a Futaba Attack two channel on 75 mHz.  The usual radios are 27 mHz Hitec transmitters with various brand receivers.  While running the tests I realized why there were range problems.  The 27 mHz receivers come with a 39 inch segment of antenna wire. I had installed an antenna with 24 inch length horizontally under the deck in the problem boat.  The data showed that the 24 inch antenna cut the range by about half with the 27 mHz radios; see test 1 versus test 10.  The 75 mHz receivers come with 18” antenna wires.  The result of the testing also lead to the following conclusions:

1. Measure your receiver antenna wire length when you get a radio. This will allow you to restore the original length if you happen to cut it.
2. A vertical, straight antenna will give the best range –Test 1, 19
3. A horizontal antenna (typically taped under the boat deck) will lose significant range when it points away from the transmitter – Test 4
3. The best practical installation is to run the antenna under the deck to either the stern or the mast and have the remainder of the wire vertical.  Test 7 and Test 21
4. An antenna taped to a metal mast or wire performs well –Test 24 –26
5. Loops of any size taped under the deck have poor range –Test 5, 22
6. A vertical antenna with coils at base work ok –Test 16 (same as base loaded commercial antennas. Sometimes they are seen on autos where a straight antenna sticks up from a cylindrical unit at the base.
7. An 18” antenna works as well for the 75 mHz receiver as the 39” antenna does for the 27 mHz radios. Higher radio wave frequency has shorter wavelength, which allows the 75 mHz radios to perform well with shorter antennas.

  During testing I would sometimes run out of room trying to step off more than 70 steps, that is, across the road and into the weeds.  So where 70* steps are recorded the range may have been slightly longer.  Later in the testing I decided to trample into the weeds deeper so on tests 24, 25, 26 the actual range was slightly longer than 70 steps.
   As is common with testing done under conditions other than the actual situation, the results may not perfectly reflect the actual case.  This test was done with the transmitter antenna in the fully collapsed position in order that I could see the servo movement within a reasonable distance.  The other variation from real life was performing the testing over ground rather than over water.  Both surfaces reflect radio waves in a similar manner, that is, both are flat surfaces or ground planes.  These test results are inappropriate for simulating model airplane antenna performance.  The only surprising result that this testing revealed was that reception seemed to not be affected much by proximity to metal masts.  The testing was useful to me and reminded me of the basics. Don’t mess around with antenna length. Don’t crumple up wire in the bottom of the boat. Have the antenna stick up in the air.  After revising the antenna in my boat I was able to extend the range from 30 steps to 60 steps. At a regatta after the fix, I did not loss control of the boat. Another excuse for losing goes away! Thanks, Rich