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I think urban legends are multiplying about antennae and RF transparent
aircraft. Some rules seem to apply to all these aircraft. but others seem to
have happened to one only and the correct explanation was not found and so
was applied to all.
> Less than a quarter wave length is really bad
> from both a VSWR and the radiation pattern stand point. The formula for
> wavelength is: 11803/ FREQ. in MHz. = wavelength in inches. So there being
> only one good location for an internal COMbI antenna (unless you have twin
> verticals) and antennas don't work well close together, it follows that
for
> aircraft with dual transceivers and no good location for a second antenna
> there is a need for a two set switching device of some type.
This may be true if you are transmitting with two transmitters
simultaniously, but we rarely do that. With a splitter you can't.
> LNC2's provide a challenge for anyone that wants all the antennae inside
(for
> speed) and still follow these basic rules:
>
> 1) R58/U is leaky so don't run antenna leads close to any other wires.
You
> can use better (but heavier) lead wires.
There lots of qualities of RG 58. Good stuff doesn't leak, and anyway when
you transmit your airplane is saturated with full strength RF.
> 2) Use a minimum of connections to eliminate signal loss.
might be true, but connectors cost money so save money to be on the safe
side.
> 3) Each antenna "should" be 3 feet from any other since there may be
> resonance or loss or signal sucking because of the proximity.
all Lancair push rods (and even rudder cables) are antenae, they are just
not connected to radios. Rudder cables or elevator push rods would make good
ADF sense antenas if there were any reason to have an ADF.
> Generally, the reason for a diplexer is there is only one good location
for the comm antenna.
There several good locations for com antenae. Lazyness is the greatest
reason for a diplexer (I have a new one for sale for $30)
> 4) Splitters cost several Db signal loss.
Radio experts seem to agree on this. Non experts agree they cost $$.
> 5) Don't ever, ever use Terra Comm radios.
Good recommendation, they were so good that used ones sell for more than
they cost new, now that you can't buy a new one.
N7WB has the following radios that work right, except for the transponders,
which at certain angles from the station blanks. This is rare and probably
is caused by the carbon spar cap. All radio have Grass Valley $10 (for all)
dipole antennae except transponder, GPS, and ELT. SWR is less than 1:1.25 on
all.
Terra 720 com Antenna in vertical fin
Val760 com Antenna behind pilot
AKC ELT dipole behind passenger made of 28 ga. wire (you
don't want bandwidth on this one)
Terra nav VOR antenna in wing ILLS antenna under passenger
floorboard
Terra transponder Supplied antenna mounted under pilot floor board on
5" x 0.015" ground plane
Apollo GPS Antenna on Glare shield (makes for short cable) I had
to cover antenna with black cloth to
Keep the white from reflecting on the
windscreen.
When I first started flying I had trouble transmitting. This was found to be
caused by a cheap intercom that had no RF caps and was unshielded.
Everything worked fine without the intercom. I now have an expensive
intercom (PS1000) and everything still works fine. If I weren't lazy I would
mount a small white blade outside for the transponder.
When I'm high and transmitting to a station 100 miles out the station can't
tell the difference between the VAl (10 watts) and the Terra. This may be
due to the slightly better placement of the Terra antenna.
Bill N7WB
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