Range of an AM transmitter?

[CoyoteBoy]

I've had an AM transmitter/rx for some time now - a futaba one. I used to
use it for my model car, now I'm putting it in a gas powered boat. My
question is, how far can it go before I hit problems. The manual I had said
300 yards but that seems far further than most people get and I dont
remember using my car more than 50 yards cos you lose sight of it!

Obviously it depends on objects in the way/surrounding, but presuming you
are on a flat lake with nothing around?

JB


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[A.T.]

No easy or exact answer. A receiver that has been used in a car is often
subjected to hard knocks and may have a reduced capability, not the TX.
A two channel bottom end Futaba TX has a lower output than the multi channel
sets - permits more model cars & boats to be used in built up areas. 2SR
(VR) and most 4ch and above maybe >3000ft - 1500 M in the air but not the
cheaper sets for which instruction book suggests for car and boat use only.
These may demonstrate 550ft for a car across a grass lawn and a boat on
water about 850ft. Range tests with 2CR, 2DR & 2ER vary considerably - but
major range variances usually relate to RX used, especially if a 122JE RX
tuned with a 500mm aerial in lieu of the earlier 1000mm aerial. Range also
varies, according to how the RX aerial is routed, full length direct upwards
e.g. in a tube is best, taped to aluminium masts or metal stays is not good,
buried inside around the top of a carbon fibre hull is generally bad news.
Range also varies with cars and boats when you are transmitting at ground
level or on a platform or bank well above the model. (never point the TX
aerial at the model). Testing a boat, the boat is best checked whilst
floating on the water preferably where it will be used and in the case of a
power boat with engine running, whilst tethered or a helper holding the
model..
Range check each time before use to ensure there has been no significant
reduction from earlier tests. [If possible, compare range with a friend who
has similar set up. Swap TX crystals and try each unit again and again with
RX xtals to learn which TX or RX is giving the least range.]
Futaba 2CR, 2DR and 2ER 2ch are cosmetic case changes.Results achieved will
vary as a number of new sets on 27 and 29 MHz recently tested, all with
122JE RX had a variance in range testing between 12 and 25 paces. The
results appeared to relate mainly to each RX. Crystals were interchanged
(within same 27 or 29 band) and individual RX displayed similar range each
time with a different TX. Two older sets held on 75 MHz have a 6 pace
difference in range test, swapping RX xtals highlighted problem RX. The
following is a good guide bearing in mind that the distances recommended
relate to more expensive higher powered multi channel FM systems.
1. refer to "Range Test - Futaba answers. "
http://www.futaba-rc.com/faq/faq-q331.html
refer also to = http://homepages.ihug.co.nz/~atong/ and scroll down to all
the answers available under = "Radio Systems, Accessories, Alterations and
FAQ"
2. Refer to range tests for PCM (also applies to PPM & AM except you do not
see the failsafe actuate) at =
http://www.horizonhobby.com/articles/1079.asp
includes extra articles on PCM Range Testing, Comprehensive Testing, Why
PCM, 7 Simple Steps, What's Good Range?,Variables, Range Testing Stories,
Download Your Own Log.
3. 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 can 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."

regards
Alan T.
Alan's Hobby Web Links
http://homepages.ihug.co.nz/~atong/
=================================================
"CoyoteBoy" <j.buckle@btinternet.com> wrote in message
news:bd1hrv$rhr$1@hercules.btinternet.com...
> I've had an AM transmitter/rx for some time now - a futaba one. I used to
> use it for my model car, now I'm putting it in a gas powered boat. My
> question is, how far can it go before I hit problems. The manual I had
said
> 300 yards but that seems far further than most people get and I dont
> remember using my car more than 50 yards cos you lose sight of it!
>
> Obviously it depends on objects in the way/surrounding, but presuming you
> are on a flat lake with nothing around?
>
> JB
>
>
> ---
> Outgoing mail is certified Virus Free.
> Checked by AVG anti-virus system (http://www.grisoft.com).
> Version: 6.0.490 / Virus Database: 289 - Release Date: 16/06/03
>
>

[Fly Higher]

Don't know about the AM but, I've had an FM set make it a good 1/4 mile in a
sailboat.

F.H.

"CoyoteBoy" <j.buckle@btinternet.com> wrote in message
news:bd1hrv$rhr$1@hercules.btinternet.com...
> I've had an AM transmitter/rx for some time now - a futaba one. I used to
> use it for my model car, now I'm putting it in a gas powered boat. My
> question is, how far can it go before I hit problems. The manual I had
said
> 300 yards but that seems far further than most people get and I dont
> remember using my car more than 50 yards cos you lose sight of it!
>
> Obviously it depends on objects in the way/surrounding, but presuming you
> are on a flat lake with nothing around?
>
> JB
>
>
> ---
> Outgoing mail is certified Virus Free.
> Checked by AVG anti-virus system (http://www.grisoft.com).
> Version: 6.0.490 / Virus Database: 289 - Release Date: 16/06/03
>
>

[Barry]

Far enough for Birkenhead's lake !!!!

"Fly Higher" <someone@somewhere.net> wrote in message
news:6T7Ja.5982$pH3.2034@news2.east.cox.net...
> Don't know about the AM but, I've had an FM set make it a good 1/4 mile in
a
> sailboat.
>
> F.H.
>
> "CoyoteBoy" <j.buckle@btinternet.com> wrote in message
> news:bd1hrv$rhr$1@hercules.btinternet.com...
> > I've had an AM transmitter/rx for some time now - a futaba one. I used
to
> > use it for my model car, now I'm putting it in a gas powered boat. My
> > question is, how far can it go before I hit problems. The manual I had
> said
> > 300 yards but that seems far further than most people get and I dont
> > remember using my car more than 50 yards cos you lose sight of it!
> >
> > Obviously it depends on objects in the way/surrounding, but presuming
you
> > are on a flat lake with nothing around?
> >
> > JB
> >
> >
> > ---
> > Outgoing mail is certified Virus Free.
> > Checked by AVG anti-virus system (http://www.grisoft.com).
> > Version: 6.0.490 / Virus Database: 289 - Release Date: 16/06/03
> >
> >
>
>