tag:blogger.com,1999:blog-1142737426092510126.post2962486187270482476..comments2024-03-27T18:30:37.287-05:00Comments on AE5X: SWR problem on bike verticalJohn AE5Xhttp://www.blogger.com/profile/06884676867006975179noreply@blogger.comBlogger9125tag:blogger.com,1999:blog-1142737426092510126.post-88925198617608608952020-04-14T16:43:55.786-05:002020-04-14T16:43:55.786-05:00Hi John,
Indeed! That is yet another advantage. T...Hi John,<br /><br />Indeed! That is yet another advantage. This is a very wideband solution. Great for a trapped vertical or for a screwdriver type. No tinkering required. 73, DonDon, ND6Thttps://www.blogger.com/profile/03134427261152371297noreply@blogger.comtag:blogger.com,1999:blog-1142737426092510126.post-65867199752322468442020-04-14T16:20:25.463-05:002020-04-14T16:20:25.463-05:00Hi Don - I have seen what you describe being used ...Hi Don - I have seen what you describe being used to Z match stages in circuits and would be interested to trying it here but I want to use the antenna on both 17 and 20 meters. Would an autotransformer be broadbanded enough to accommodate both? I tinkered with SimSmith a bit today and think I'll just make an LC match for now. It was a fun learning process and I may try you idea on another John AE5Xhttps://www.blogger.com/profile/06884676867006975179noreply@blogger.comtag:blogger.com,1999:blog-1142737426092510126.post-15822640262488872382020-04-14T16:10:52.355-05:002020-04-14T16:10:52.355-05:00Hi Dave - I was thinking it would be around 35 ohm...Hi Dave - I was thinking it would be around 35 ohms, giving me a 1.4:1 SWR. But now that I think about it, that's for verticals whose radials taper at a 45-degree angle from the radiating element. I was surprised that adding two additional radials did very little in terms of changing the R+j values.<br /><br />73 - JohnJohn AE5Xhttps://www.blogger.com/profile/06884676867006975179noreply@blogger.comtag:blogger.com,1999:blog-1142737426092510126.post-28412138379822983272020-04-14T14:25:39.108-05:002020-04-14T14:25:39.108-05:00One way to lengthen it even more after it's ex...One way to lengthen it even more after it's extended all the way is to put some sort of capacity hat at the top of the mast. Try that first before going the shortening/inductor route.<br /><br />My guess is that 4 to 6 inches more of mast won't be enough to get enough inductive reactance. You're going to need about +j25, and then about -j44 in the capacitive stub. This is assuming David Ryeburn VE7EZM and AF7BZhttps://www.blogger.com/profile/10215002968835286422noreply@blogger.comtag:blogger.com,1999:blog-1142737426092510126.post-52759840910158475342020-04-14T13:08:03.586-05:002020-04-14T13:08:03.586-05:00I guess you found out that the resonant impedance ...I guess you found out that the resonant impedance of a vertical is typically much lower than 50 ohms. I've used a small matching coil to ground at the base of my mobile HF vertical to help deal with this. It's a 'cheat' because it doesn't affect the real radiation resistance of the actual antenna, but it makes the transmitter happy.Dave Newhttps://www.blogger.com/profile/14606866637455669041noreply@blogger.comtag:blogger.com,1999:blog-1142737426092510126.post-78760648549881332042020-04-14T11:21:58.851-05:002020-04-14T11:21:58.851-05:00If I may elaborate on my previous suggestion of an...If I may elaborate on my previous suggestion of an autotransformer:<br />An efficient implementation would be a "fractional UNUN", a trifilar winding of 7 or 8 turns on a type 43 (or similarly high permeability ferrite). The size of the core would be dependent upon the power level. The "one of three" configuration should provide a nearly perfect match for stepping 22 ohms up Don, ND6Thttps://www.blogger.com/profile/03134427261152371297noreply@blogger.comtag:blogger.com,1999:blog-1142737426092510126.post-72926086086919287362020-04-14T10:07:27.429-05:002020-04-14T10:07:27.429-05:00Since it is resonant it might be good to just try ...Since it is resonant it might be good to just try an autotransformer on a small toroid. Simple, small, cheap. <br />73,<br />DonDon, ND6Thttps://www.blogger.com/profile/03134427261152371297noreply@blogger.comtag:blogger.com,1999:blog-1142737426092510126.post-38370325171140351692020-04-13T19:03:49.704-05:002020-04-13T19:03:49.704-05:00Excellent, David - thank you for those suggestions...Excellent, David - thank you for those suggestions. I just happen to know where I can borrow a BNC-T that will make the trial& error easier. I will try lengthening first but only have 4-6 inches of mast left before it's fully extended. If that doesn't do it I'll try the stub/inductor next.<br /><br />Tnx again & 73,<br />JohnJohn AE5Xhttps://www.blogger.com/profile/06884676867006975179noreply@blogger.comtag:blogger.com,1999:blog-1142737426092510126.post-82754251250613919332020-04-13T18:53:24.365-05:002020-04-13T18:53:24.365-05:00You need to get the resistive component higher tha...You need to get the resistive component higher than 22.5 ohms. First try lengthening the antenna a bit and put a capacitor between antenna base and ground. The resistive component will rise a tiny bit, but more important the inductive reactance will rise above 0.4 ohms and that plus the capacitor will make an L network raising the impedance somewhat. Adjust the capacitor for best SWR. You can David Ryeburn VE7EZM and AF7BZhttps://www.blogger.com/profile/10215002968835286422noreply@blogger.com