Mar - Rcsoaring.com

features an extended length antenna.
We’re going to go back to the time before
the AR500 when the JR /Spektrum
systems used only the 32-mm antennas.
This experiment differs from the 72-Mhz
experiment in that I figured I would rather
not take a chance on the theory of a CF
fuselage completely blocking the RF
signal on 2.4. I suspected that maybe
some of that RF might actually penetrate
the fuselage, and with that in mind, we
pressed forward with making our own
extended antenna. But wait... why extend
the antenna
We needed to extend the antenna for a
couple of reasons. The first was that by
simply placing the Rx inside the fuselage,
there was not enough antenna to poke
out the skin of the plane to receive signal.
Despite a sailplane being very narrow,
the antenna needs to be 32-mm long.
Also, it’s a pain in the buns to get the
Rx in a place where you can even poke
the antennas out. Lastly, where I wanted
to place the Rx inside the plane would
result in the antennas poking out right
where I grip the plane for the launch... not
good! So, I needed to extend the antenna
length. After some careful figuring, I
settled on making each antenna another
40-mm longer.
I started with taking some twin
conductor shielded wire and removing
one conductor from the length. The
remaining conductor was then spliced
on to the original Rx antenna right as it
exits the casing. So, now we have 40-
mm of shielded wire with another 32-mm
of normal antenna at the far end. The
shielding is not grounded or connected
to anything... just wrapped around the
wire. With the Rx on a table in the open,
it performed a perfect range check. This
is good, because by theory, it should not
work. People tell me that the shielding
must be GROUNDED for it to work.
Well, guess what It works and it ain’t
grounded. Remember that all we’re trying
to do is to block the RF by the shielded
portion of the antenna wire. Grounded or
not, the shielding worked.
Now we go to the Rx being inside that
cozy CF fuselage. The Rx is a JR R921
9-channel unit, using a single remote
satellite Rx. Both main and satellite
Rx are given the extended antenna
treatment and range checked. No
problem. Now we do the same range
check with the Rx’s installed in the plane
and antennas sticking out like whiskers.
No difference! It works! We then perform
a complete 360 range check, and the
result is fabulous... no problems. We then
gritted our teeth and made a full power
winch launch. I figure if we’re going to
pile in a plane, let’s do it right! I was not
disappointed, as the plane made like it
was always done this way, quite happy
to range out some 3500-ft away on that
first flight with the new antennas. As for
the fuselage leaking RF through the skin
Yup, there is some leakage as proven
by a range check done with a stock Rx
stuck inside the fuselage. The Rx got
about 1/3 range before losing signal. As
long as there is some range achieved,
there is RF getting through.
I proceeded to make this a big deal and
made postings of the experiment on RC
Groups. The flak I took was amazing!
Engineers, electronics experts, naysayers
and skeptics piled on personal
messages and responses that said I
must be a liar about this, and that it’s
all made up. Amazingly, some people
actually defended me as they had seen
the plane fly at a very large contest event
not two weeks after I made the change. I
can’t tell you how many people wanted to
see what I did inside that bird, but I finally
just left the canopy off so that anyone
could look inside.
By the way, some people using the
whisker approach just don’t seem to get
it. You only need to have the bare 32-mm
of wire exposed outside the CF skin of
a plane. I have seen a number of plane
using the Futaba systems with very long
whiskers hanging out. And I mean like 4
to 5 inches of whisker! It’s weird enough
to see 32-mm of wire out there, but 4 to
5 inches is like cat whiskers compared to
my short “stubble” growth.
Section 3 – the daring stuff
32 R/C Soaring Digest