Just bought a second hand Field Force 7 outfit and have a question on range testing it. I have a Futaba 6EXA outfit which has the aerial fixed in place with a short stub out of the transmitter. This does a ground range test fine with the aerial down as far as it will go.
The FF7 has an aerial which goes right down into the Tx box so how should I set it for a ground range test? Should I leave the aerial right down or should I pull it out until it clicks in place and then looks like the 6EXA?
Reason for asking is that when it's fully down in the box there isn't a lot of range at all but pulled up in place it's fine. I've flown with the FF7 and never had any problems so I'm guessing it's fine. Just that I like to check them before I fly.
Range test with the aerial right down. Major fault with the old FF7 is that the aerial is only connected to the board via a couple of feet through which the aerial slides up and down - many now dirty and intermittent performance results. IMO FF7 are old, tired and due for a full service check - retune and request aerial and sliders be thoroughly cleaned to ensure good contact. Check gimbals for sign of cracking/failure. Check wiring harnesses for signs of failure at the solder joints where attached to volume controls (pots) 8UA series in particular.
- some instances of people left holding a stick no longer attached to gimbal etc. - NOTE: this material failure applies to all brands of older TX not just FF7.
Quote from Terry Rance's (Service Manager at Macgregor Industries) "Radio Range Testing", article in the RCM&E 10 Sept.97 "It is not necessary to verify the range with the TX aerial fully extended as a check with the TX in the retracted position will give representative results. As a rough approximation the range on the ground with the aerial up will be ten times that obtained with the aerial down although, of course, if the retracted aerial is particularly long or short, this will affect the figure. Since transmissions from other transmitters in the vicinity can affect the result, the test should take place with only the test TX operating. Ideally a clear open field should be used as a test area, but a test along a road or a path will be satisfactory provided that an allowance is made for the localised signal distorting effects of parked cars and other large metal objects. IT TAKES TWO = Two people are needed for the test. One should take the TX with the aerial retracted and operate it as if flying the model, moving a control stick to operate a servo in the model. The other should walk away from the side of the person holding the TX, with the model held at right angles to the direction of walking so that the TX and RX aerials are approximately parallel. With the model at waist height, a range of at least
70 paces should be obtained and cab be verified by observing the servo or control surface on the model. The servo should smoothly follow the TX commands without chattering or hesitation. If the model is held lower, the range obtained will be less and if the model is held higher the range will be more. Pointing the RX aerial at the TX will dramatically reduce the range. TWO DIMENSIONAL = The radio signals are emitted from the side of the TX aerial. Only a very small signal is sent out from the top, along the aerial's axis. Similarly, The RX picks up the strongest signal when it's full length is exposed to the TX. If the RX aerial is held in a straight line and pointed at the TX, only the diameter of the RX wire is available to pick up the signal and the result will be a very short range. For these reasons we recommend that the TX aerial is not pointed at the model and the RX aerial is arranged in two dimensions so that whichever way the model turns, there is always a good length of exposed RX aerial to pick up the signal. Taking the end of the RX aerial to the top of the tail fin is strongly recommended. The ground absorbs radio signals and makes them weaker. As a model moves away from the ground, the available TX signal gets much stronger and because of this the air range might be two or three times the ground range."
The above has proved correct, in practice, for all brands of RC systems over the past 36 years of RC flying.
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