On my vertical dipole for an airband VHF handheld, I want to run the RG8 coax and pawsey stub inside a carbon fiber boom to the airframe. Would the shielding effect of the carbon fiber give any problems or (hopefully) bennifits? The bennifit of cable protection and neatness is why I would like to run it inside.
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Carbon Fiber.Will it affect my Pawsey stub ? r boom
- Thread starter cableguy
- Start date
The coax, feed line, shouldn't be affected at all if run through, or is covered by carbon fiber. I'm not sure what you mean by a 'Pawsey stub', so am only guessing about that. If it's what I think it is, it shouldn't be affected.
- 'Doc
- 'Doc
The only positive affect i can think of would be if by moving the antenna it is in a more favorable position (previous position was shielded by more metal) other than that the carbon fiber should not have any negative or positive affect to my knowledge. I should add that this can inversely be a negative affect, if the new location is more shielded (there is more of a metal shield beyond the carbon fiber), it is whats between the carbon fiber and the air which matters and will affect it, if the carbon fiber is the last thing before air you should be doing pretty good.
Thank you all for the feedback (no pun) To answer the first question,the airframe is the frame of the parachute plane it is going on. The pawsey stub is a quarter wave length piece of coax added to the feedline at the antenna. The reason for the carbon fiber is that I didn't want the boom made of metal and the hollow hockeystick shaft was strong and light and all I had to work with. I read that aircraft with a carbon fiber skin creats a faraday effect when the antenna is inside the fuselage.This antenna will be in free air but the stub and feed line will be inside the carbon shaft for the length of the stub plus a few inches. then the feedline will be tie-wraped to the metal frame for about 4 feet to the radio. The antenna will be front and center of the airframe to keep it away from the strobe light and engine. I'll try the Swr meter with cable inside and again with cable outside.
Just got back from the install and did an SWR check and trim. Had to mount horizontal as the pilot was not pleased with the configuration of the verticle mount. Trimmed down to an SWR of 1.3:1 and stopped there since I told the pilot 1.5:1 is good and he said thats good enough. Still had 3/8 inch left to go to target lenght on both elements for 122.7 MHz.(middle of band). Did not test with feedline outside of carbon boom. I was happy. Owner was happy. His buddy with same plane has horizontal mount whip and they mostly talk to each other so good enough for now. I'll make his buddy the same antenna and mount it horizontal as well so at least they are polarized the same. That was my first 2 meter antenna and was pleased with the 1.3:1. I was trimming 1/8" at a time and was getting better each time. Would have liked to see if I could have got better. They normally use 123.2 MHz so the longer lenght makes it worse. Thanks again folks for your input. Jim.
Yes robb I copied Dean Scotts inverted vee design. Cessna uses a similar one eccept the center wire from the feedline is not cut but contiues back into the stub and the outer braid of the feed goes to the ground element and the outer braid of the stub goes to the antenna element.Then the outer braids of both are connected at the end of the stub and grounded to the airframe. With 1.3:1 SWR think Dean is on the mark. I ommited the SO239 from his plans and went with direct element to feedline. Also I used 5/16 "x 3/32" aluminum elements(blades) to hopefully gain bandwidth. Forgot to do an SWR reading on each end of the band. Just a novice but I'll remember next time. Thanks again Jim.