A quarter wave at 110MHz is 27" in air, but only 17" in coaxial cable because the waves travel slower in the coax.
This kind of balun is called a Roberts Balun, or a folded balun. There's not a lot of literature describing how it works, and there's some question about whether the stub should be 17" or 27", but it's normally made 17. And that works. It even passes enough GS signal, and that's about 330MHz.
New VOR antennas have a transformer-type balun molded into the base.
Can I save my Narco Antenna?
Moderators: GAHorn, Karl Towle, Bruce Fenstermacher
Re: Can I save my Narco Antenna?
Isn't it wonderful, the amazing amount of shared knowlege which exists in our group?DaveF wrote:A quarter wave at 110MHz is 27" in air, but only 17" in coaxial cable because the waves travel slower in the coax.
This kind of balun is called a Roberts Balun, or a folded balun. There's not a lot of literature describing how it works, and there's some question about whether the stub should be 17" or 27", but it's normally made 17. And that works. It even passes enough GS signal, and that's about 330MHz.
New VOR antennas have a transformer-type balun molded into the base.
I love it!
(Now if someone could only explain why the metallic taste in my mouth after I said that antennas are not "dark majic".)
'53 B-model N146YS SN:25713
50th Anniversary of Flight Model. Winner-Best Original 170B, 100th Anniversary of Flight Convention.
An originality nut (mostly) for the right reasons.
50th Anniversary of Flight Model. Winner-Best Original 170B, 100th Anniversary of Flight Convention.
An originality nut (mostly) for the right reasons.
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- Posts: 27
- Joined: Sat Dec 04, 2010 4:26 am
Re: Can I save my Narco Antenna?
Yes, I made a 26" one. Yes, it lays on the headliner behind me.
I bet the short one would work just fine. If I ever have need to take the antenna off, I'll put on a short one and check it out.
I bet the short one would work just fine. If I ever have need to take the antenna off, I'll put on a short one and check it out.
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Paul "Pablo" Britton
Paul "Pablo" Britton
Re: Can I save my Narco Antenna?
I asked about this because of erroneous CDI indications. I had the nav radio and VOR indicator removed and bench tested first and both tested good. All wiring and connections are just a few years old and were not suspected bad. The only piece of the puzzle left was the balun. I made a new one with RG400 and simply duplicated the 17 inch loop that was removed. A ground test yesterday and flight test today revealed a successful repair. Sure was cheaper than a new GI106 indicator!!
Richard Dach
49' A Model N9007A
SN 18762
49' A Model N9007A
SN 18762