Pietenpol-List: Question for Mark Roberts about fuselage

[matronics]

Original Posted By: John Fay
Well, the discussion wasn't intended to get whacky. From the start, this is whatI had in mind. It's the "j pole" antenna I built over 20 years ago for a verysimilar frequency and it worked really well, in some very non favorable conditions(laying on the dash of a big metal van). I was using a handheld radiovery similar to the aircraft handhelds (it was even an ICOM).I didn't know a thing about antennas when I built it, just followed the directions.I don't know if it'll work in a airplane, but I can't see why it won't. The dimensionsare for about 144 mhz (which has a wavelength of 6.8 feet) and we wantto make it for about 122 mhz (which has a wavelength of 8.0 feet). The entire length of the antenna should be 3/4 of a wavelength, but it's not. I think that's because of the particular 300 ohm brown flat lead TV antenna stuffused or something. So....I'm going to make one using the theoretical measurements and one just scaled upby the percentage difference between 6.8 to 8 feet and see which one works best.It's basically a free antenna, so there's no harm in this. Takes about anhour to make at the most.Here's the article:http://www.harfordemcomm.org/files/twinlead.pdfReplace the numbers in figure 1. with these for the theoretically correct antenna: 72" overall length1 1/2" from the end, 22 1/2" from there to the notch 1/4" notch 47 3/4"remaining.I haven't figured out the other dimensions because I'm not home and don't havea calculator and too lazy to use one online. I won't be able to get to this fora week or two at best, AND I lost my radio charger so I don't even have a radioto check it out on right now! However, 6.8 to 8 is what, about 12 to 15 percent increase? Whatever it is, justincrease the measurements in the article by that. Antennas are just plainlinear I think. There's not a huge difference anyway and this antenna isn't superpicky.If someone has a little time and wants to play around and see if it works beforeI get to it, that would be great. If this does work as well as a vertical,there's no reason we can't make a zillion of them during Brodhead. Honestly, I never even "tuned" it for my ham radio. I just made it exactly likethis article and used it. Always had good reports and it worked better thanmy magnetic mount 1/2 wave whip, which is essentially the same thing as mostof us are using now.Cheers,ToolsRead this topic online here:http://forums.matronics.com/viewtopic.p ... ______Date: Fri, 23 Mar 2012 12:44:44 -0500Subject: Pietenpol-List: Question for Mark Roberts about fuselage

[matronics]

Original Posted By: "Cuy, Michael D. (GRC-RXD0)[ASRC AEROSPACE CORP]"
I can't give a definitive yea or nay on the "dashboard" J-pole design... buildit, test it, tune it, test it again... who knows. The theory behind the J-poleis sound as you can adjust the J-leg to achieve proper tuning and the largerelement (usually 1/2 wave) should provide better gain over the normal 1/4 waveverticals, but I don't think it's the best suited design for an airplane. Theyare also sensitive to surrounding metal objects, so that needs to be considered...and you will likely need a balun to provide the proper impedance... buthey, tinker away! If it doesn't work as well as you would like, just add morepower! [Laughing]Let us know how it works out.--------Mark ChouinardWings, Center Section and Empannage framed up - Working on FuselageRead this topic online here:http://forums.matronics.com/viewtopic.p ... __________

[matronics]

Original Posted By: Mark Roberts
Subject: Re: Pietenpol-List: Question for Mark Roberts about fuselage