+++++++++++++++++++ ate: Mon, 25 Mar 2002 21:04:14 -0500 From: "Dave" To: "Low Power Amateur Radio Discussion" , rohre at arlut.utexas.edu Subject: [123203] Re: coax as an antenna element re velocity factor I have made all my wire antennas using PVC insulated wire (this is usually because I hang them in trees and want them insulated) I have found that about 2% shorter than calculated length is required and in the case of any Full wave loop I have made then it is usually 4% shorter for resonance. just my 2 cents Dave W1QB ++++++++++++++++++++ Date: Mon, 25 Mar 2002 20:20:35 -0600 From: "Stuart Rohre" To: "Dave" , "Low Power Amateur Radio Discussion" Subject: [123208] Re: coax as an antenna element re velocity factor Glad to see the 2 per cent for dipoles confirmed,and the 4 per cent makes sense for loop, since you are bringing two ends together. 73, Stuart K5KVH ++++++++++++++++++++ Date: Tue, 26 Mar 2002 08:48:35 -0700 From: "Walter AG5P" To: Subject: [123250] Re: coax as an antenna element re velocity factor Hi Dave and all, wow, it is refreshing to read your posting on the variations of lengths from the standard formulas. My findings are very close, for horizontal loops under 30 feet usually 984/fMHz gets within inches of resonance. With a tuner and twin-wire feed it is not an issue. With coax and No tuner and a 75 ohm 1/4 w.coax attached directly to the swr bridge and rig then maybe take off 1 to 2 inches from the wire loop. For horizontal loops over 30 feet, it seems that 995/fMHz is best and it gives the same 1 to 2 inches still need to be trimmed for resonance. Guess it needs saying that these measurements are used in conjunction with non-metallic supports, ie, pvc pipe or trees. Another thing that has proven the horizontal loop for a 'keeper' antenna is make it for one band lower than your normal operating use. That is if you work 40 and up, then put up an 80 meter horiz. loop. Sure they are real estate intensive, but at field day or operating portable there is normally space to put up a loop. One last note, using insulated wire, put another loop under your 'in the air' loop which is about 3% longer than the transmitting loop. Just lay it out on the ground, directly under your transmitting loop.You have to use a tuner with your loop because the counterpoise loop will detune it but oh my, what a difference a little wire makes. 72 / 73 Walter, AG5P +++++++++++++++++++++