Today's Message Index:
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1. 05:45 PM - Finally! A decent radio antenna (Richard Pike)
2. 06:39 PM - Re: Finally! A decent radio antenna (John Hauck)
3. 08:47 PM - Re: Finally! A decent radio antenna (b young)
Message 1
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| Subject: | Finally! A decent radio antenna |
After a year of frustration, finally got good radio reception on the FSII. Before
the crash, the antenna was on the bottom of the fuselage under the seat, and
it had a ground plane, and it worked pretty good.
After the rebuild, decided to try using an old ELT antenna located on the front
of the gap seal/cabin top as the com antenna, but that didn't work. Figured
that an antenna tuned to 121.5 ought to be in the spectrum, but apparently not.
A lot of hash and static, couldn't understand anything or anybody.
Took it to an avionics shop and they replaced the ELT antenna with a Comant style
fiberglass antenna in the same location - no good either, still noisy.
Put a ground plane under the seat and put the antenna on the bottom of the fuselage.
Same results. Tried a different radio - same results. Tried all sorts of
combinations of antennas and radios, - and then got lucky.
Carried the hand held all around the airplane with the engine running and the headset
plugged into it and at the top of the vertical fin found a dead spot that
was free of hash. Several test flights today confirmed that this is a very
quiet spot with great reception in almost all directions - except dead ahead of
the airplane. You can semi-sorta maybe hear whatever the airplane is pointed
at, everything else works fine. We can live with that.
Tried the Icom's rubber duck antenna, the home made whip is twice as good. Here's
how it's made: 24 1/4" long from the end of the BNC connector to the little
rounded curl on it's end. There is a jack-to-jack BNC bulkhead pass-through screwed
into the bracket. The ground plane consists of the front of the vertical
fin, the boom tube, and the stab brace wires and the stab, so you have a ground
plane in front and to the sides, not much in back. Maybe that's why reception
stinks straight ahead? Transmission is good in all directions. Go figure -
The antenna is made by taking a Radio Shack twist-on male BNC connector, part #
278-103 and a length of 1/16" model airplane pushrod steel wire, and combining
them like this: take one end of the steel wire, and taper it on a grinder until
it will fit into the connector until the end just pokes through the end of
the middle terminal connector. Solder it to the connector at that end. Fill the
shank up with epoxy, and after it hardens, cut it to about 25 inches total
length, and trim it to final length while checking an SWR meter. If you don't
have an SWR meter, make it 24 1/4" long total length, ground plane to curly end
tip, it will work. I suggest putting a little curl on the end, or Murphy's Law
says someone will poke it in their eye. Cost? $8. Weight? 2 ounces.
Worth what ya paid for it.
--------
Richard Pike
Kolb MKIII N420P (420ldPoops)
richard (at) bcchapel(dot)org
Kingsport, TN 3TN0
Now faith is the substance of things hoped for, the evidence of things not seen.
Hebrews 11:1
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Message 2
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| Subject: | Finally! A decent radio antenna |
After the rebuild, decided to try using an old ELT antenna located on the
front of the gap seal/cabin top as the com antenna, but that didn't work.
Figured that an antenna tuned to 121.5 ought to be in the spectrum, but
apparently not. A lot of hash and static, couldn't understand anything or
anybody.
--------
Richard Pike
Richard P/Kolbers:
I have used an ELT antenna for my com radio since FS days with good results.
Use a small 6 or 8 inch disc for ground plane under the nose of the FS and
MKIII. Cut the coax to a specific length. Can't remember what it is right
now, but 6 feet pops in my brain housing group.
Transmitting is critical to antenna tuning.
Reception is not, as far as I know. You can lay a piece of wire on the
ground and it will receive.
Didn't some aircraft use a trailing wire antenna to receive UHF or was it
SSB.
Ignition and alternator noise a greatly reduced with a 22,000mf capacitor
between the 12VDC + wire and ground. Getting the antenna as far away with
as much mass between it and the engine helped on my FS and MKIII.
Glad you finally got yours working.
john h
mkIII
Titus, Alabama
Message 3
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| Subject: | Re: Finally! A decent radio antenna |
Didn't some aircraft use a trailing wire antenna to receive UHF or was it
SSB.
generally a trailing wire antenna is used for hf radio communications. the
airlines use hf for comm when over the oceans etc.
boyd
do not archive.
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