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Richard Pike
Joined: 09 Jan 2006
Posts: 1671
Location: Blountville, Tennessee
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 Posted: Sat Mar 10, 2012 5:44 pm Post subject: Finally! A decent radio antenna |
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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.
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_________________
Richard Pike
Kolb MKIII N420P (420ldPoops)
Kingsport, TN 3TN0
Forgiving is tough, being forgiven is wonderful, and God's grace really is amazing. |
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John Hauck
Joined: 09 Jan 2006
Posts: 4639
Location: Titus, Alabama (hauck's holler)
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| Posted: Sat Mar 10, 2012 6:39 pm Post subject: Finally! A decent radio antenna |
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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
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John Hauck
MKIII/912ULS
hauck's holler
Titus, Alabama |
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byoungplumbing(at)gmail.c
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| Posted: Sat Mar 10, 2012 8:47 pm Post subject: Finally! A decent radio antenna |
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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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Thom Riddle
Joined: 10 Jan 2006
Posts: 1597
Location: Buffalo, NY, USA (9G0)
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| Posted: Sun Mar 11, 2012 4:09 am Post subject: Re: Finally! A decent radio antenna |
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The antenna on my Slingshot is on the tail boom and has given trouble-free service with good transmit and reception. It is mounted on a hat shaped piece of aluminum, roughly 5"x5" riveted to the top of the boom tube with coax run through boom tube. It has room between the hat and boom tube to get to the connections. Seems that getting it behind the engine is indeed a good idea. I don't have detail photo, but this shot shows its location.
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Thom Riddle
Buffalo, NY (9G0)
Don't worry about old age... it doesn't last very long.
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Richard Pike
Joined: 09 Jan 2006
Posts: 1671
Location: Blountville, Tennessee
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| Posted: Sun Mar 11, 2012 4:17 am Post subject: Re: Finally! A decent radio antenna |
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Roger that John, it seemed to me that an ELT antenna would be right on the money. In hindsight, it was the location. I am sure that if we still had the ELT antenna in place of my home made whip it would do just fine. Unfortunately it didn't come back from the avionics shop.
We have a noise filter installed, it is a multi stage capacitor setup designed for cars that make electrical noise and mess up the stereo. It goes into the power line for the radio, it helped a little, but not much.
The antenna is now directly opposite the magneto end of the engine, almost exactly in line with the crankshaft. I am guessing that the mag is making the electrical racket and having the antenna right where the engine blocks it off is why it works at that spot.
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Richard Pike
Kolb MKIII N420P (420ldPoops)
Kingsport, TN 3TN0
Forgiving is tough, being forgiven is wonderful, and God's grace really is amazing. |
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jbhart(at)onlyinternet.ne
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| Posted: Sun Mar 11, 2012 5:41 am Post subject: Finally! A decent radio antenna |
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At 05:17 AM 3/11/12 -0700, you wrote:
Richard,
Initially, I experienced a lot of engine radio noise. Found that the
unshielded magneto kill switch wire was radiating like crazy. Rather than
replace it with a shielded wire, I mounted the kill switch back on the engine.
With that move good things happened. To activate the switch I use some
woven fish line. Saved a little weight. No condenser was used on the
voltage regulator output.
Jack B. Hart FF004
Winchester, IN
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John Hauck
Joined: 09 Jan 2006
Posts: 4639
Location: Titus, Alabama (hauck's holler)
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| Posted: Sun Mar 11, 2012 5:41 am Post subject: Finally! A decent radio antenna |
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I am guessing that the mag is making the electrical racket and having the
antenna right where the engine blocks it off is why it works at that spot.
--------
Richard Pike
Richard P/Kolbers:
Ignition noise and alternator noise are different and change with engine
rpm. Pretty easy to distinguish between the two.
Forgot to mention last night, I had more problems eliminating RF noise with
the 447 two stroke than the 912 4 stroke. Back in the 1980's it was a sin
to fly with resistor spark plugs because the spark plug wire caps had
internal resistors. However, I discovered the 447 flew great with Bosch
resistor plugs and cut down on ignition noise. Cannot remember the number,
but it was the equivalent of the NGK. In fact, they were Bosch Platinum. I
went that route after the fine wire NGK plug came apart and put me down on
Grand Island, NY, in 1988. Never fouled a Bosch Platinum.
In order to use the Bosch Platinum plugs I also had to run Bosch spark plug
wires. A mid-1970's Volvo wire set by Bosch came with metal caps and
internal resistors. I was able to get two sets of wires out of one Volvo
set. If one flew a lot, the caps wore out, usually stress cracking the
metal caps.
The above set up with the large capacitor did a good job of quieting the
447, in addition to locating the antenna under the nose pod.
I started using the ELT, a Pointer, antennas on the FS because they could be
purchased for $15.00 in the 80's.
john h
mkIII
Titus, Alabama
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John Hauck
MKIII/912ULS
hauck's holler
Titus, Alabama |
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