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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.
2) Use a minimum of connections to eliminate signal loss.
3) Each antenna "should" be 3 feet from any other since there may be
resonance or loss or signal sucking because of the proximity. Generally, the
reason for a diplexer is there is only one good location for the comm antenna.
4) Splitters cost several Db signal loss.
5) Don't ever, ever use Terra Comm radios.
My installation currently violates all the rules except # 4). I feel
compelled to confess my sins so that others might save themselves from grief,
gnashing of teeth and possible self mutilation whilst trying to get their
radio gear to operate.
I use a separate antenna for each function-
1. Glide slope antenna is in the right stub wing leading edge outside prop
arc,
2. Transponder (blade, extenal, 600 Kt, 14" gnd plane) is in an outer wing
bay,
3. Marker Beacon is a foil strip on belly centerline,
4. ADF is top mounted with a 25" grnd plane in baggage area ceiling,
5. GPS is mounted atop ADF grnd plane,
6. ELT is a VHF foil "Z" in sidewall behind baggage bulkhead, now connected
to COM2,
7. Loran (now unused) is on the other baggage sidewall,
8. COM1 is in the vertical stab,
9. NAV (Loc/Vor) is in horizontal stab (only one "nav" radio), and
10. The ACK ELT is connected to its own whip antenna, also behind the
baggage bulkhead.
I originally started with a COMM splitter/relay Switch but found it
unreliable with the Terra radios. I disconnected it and use the ELT VHF
Antenna for COM2. Recently, SWR tested OK on both these antennae. Terra
radios, in combination with a "weak" antenna will make a dreadful system and
I look forward to a panel replacement such as a Garmin 430.
It is next to impossible to run the antenna leads far enough away from other
wires to eliminate all noise. With Terra radios, my reception can be
somewhat directional (a 90 deg turn might yield greater range). I have
violated the "minimum connections" rule by installing the required GPS Notch
Filters and gender-changing unions in the COMM antenna leads. BTW, Terra
clarity and range are improved by $500 trips to the shop.
I bet Brent has an S-TEC a/p as I do. During altitude hold flights, keying a
transmission results in a gentle dive. One learns to be terse (100 feet per
15.6 words). Similarly, when I installed King radios in my Skymaster (10
watts instead of 5), A/P managed flight entered uncommanded left turns when
the mike was keyed (.5 deg per word). There was a known fix made to a RF
sensitive servo controller and afterward, all was well.
I may as well ramble on to other antenna oddities:
The "fan" marker antenna is too sensitive since I get marker notification
miles wide of any marker.
The transponder antenna was a spike originally buried in the wing outside the
aileron bellcrank, had a nice ground plane and a 2.5 inch square access door
in the lower wing skin. The test equipment couldn't get a reply 6 feet away
since there was too much signal blockage from the carbon spar caps. I
mounted one of those jet plane blade antennas sticking out thru the little
door. The 14" circular ground plane was mocked up and drilled outside the
wing and consisted of several circular 2.5 inch wide strips of aluminum.
These were threaded into the wing and pop riveted together thru the access
door (like building a ship in a bottle). I have never dropped off a radar
screen while the transponder was on.
The Loran never worked while I was flying in WLS primer. It would work on
the ground, but it never received stations in the air. I believe this was
due to static build-up on the primer. If I ran my hand, or a cat, over the
skin (while on the ground), the hair on my arm would stand up. By the time I
had the plane painted, I had moved on to GPS.
Now, if only I could fix my hearing........
Scott Kureger
N92EX
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