Hi Carl, Does not appear anyone has answered you, so let me give it a quick shot while between flights in Japan. I'm somewhat confused with your final L network configuration because you mentioned one capacitor, and then a second capacitor without mentioning if you still had the first capacitor in your configuration, etc. You also did not mention what L network configuration you used (see below).
Therefore I started from scratch to see what a 64 foot vertical wire would look like at 7.050 Mhz to see what kind of L network would be required to convert its impedance to a pure 50 ohms resistance. Using EZNEC demo, I approximate a 64 foot vertical wire on 7.050 Mhz has an input impedance of approximately 1274 +j1436 ohms when just using a ground rod with medium soil (because this antenna has such a high input impedance it really does not matter what I use for ground conductivity). Then using an online L network calculator I come up with the following two different L network configurations you could use to match to a 50 ohm resistive source. *L network with inductor between bottom of 64 foot vertical and ground.* L = 10.18 uh C = 59.9 pf *L network with capacitor between bottom of 64 foot vertical and ground.* L = 8.5 uh C = 67.6 pf Not sure what L network configuration you used, but does it sound like I closely replicated what you have based upon one of the above mentioned L network configurations? If not, then please better describe your configuration. Please advise so we can better answer your question, and hopefully I have not messed something up with my quick analysis/approximation. Don (wd8dsb) On Sat, Feb 13, 2016 at 4:53 PM, Carl Braun <carl.br...@lairdtech.com> wrote: > I have revised my question to correct the length of the antenna in question > > > Topbanders > > In the past, I've posted some questions related to making my 80 meter > verticals (64' tall ground mounted) work on different bands. The pair is > spaced at ¼ wl on 80m and then I switch in base loading to resonate the > same pair on 160m which are then effectively spaced at 1/8 wl. Now I want > to make them work on 40m which would have them resonate as ½ or 5/8 wl and > would have an effective spacing at ½ wl. > > So this is what I did...I installed an L network off of the vertical > effectively tuning a 64' stick of aluminum to 7.050. It took me a couple > of tries as the first 1500pF (monster) variable capacitor wouldn't get down > low enough to get me flat. I had another 50-150pF Johnson variable cap > available so I tried that and got the antenna to tune to 46 ohms at j+0. > Inside the shack I see 1.0:1 Vswr from 7.000 to 7.290...wow! > > I measured the cap and it came to 70pf. My cheapie Chinese meter doesn't > register anything on the L scale but I have 7 turns on a 3 ½" inductor. The > full coil is 33 uH at 25 turns so I estimate 8-12 uH of inductance. > > But what have I done? Have I resonated a ½ wl antenna or have I resonated > something else like a 5/8 wl antenna with the added inductance? > > I plan on treating them as ½ wl spaced phased verticals on 40 and feeding > them with equal lengths of ¾ wl feedlines for broadside phasing and then > adding an additional 2/4 wl to get my 180 degree shift for end fire. > > Please share your comments. > > thanks > > Carl de AG6X > > _________________ > Topband Reflector Archives - http://www.contesting.com/_topband > _________________ Topband Reflector Archives - http://www.contesting.com/_topband