*Some interesting questions came to mind for you antenna experts out there: *
*If you're trying to take the SWR minimum to a lower frequency, is it better to lengthen the antenna, or add more inductance? My whips were full out, so I tapped off two more coil turns to drop the SWR minimum 160 kHz to get the minimum SWR on 3910 kHz (SWR minimum was 1.4). (RH) Lengthen the antenna -- this keeps the radiation resistance higher* *There was a lot of inductance on the antenna from those coils. Where is the extra capacitive reactance coming from to cancel out the inductive reactance at SWR minimum? **(RH) **You moved frequency lower and the antenna length stayed the same. So, an increase in capacitive reactance Xc occurred, hence more inductive reactance Xl required to cancel the Xc.* *The Buddipole kit for 80 meters has a Balun with settings of 1:1, 2:1, 4:1. I had no clue or instructions what to set it to, but found another Buddipole user's website who recommended the 4:1 setting for 80 meters. Well, it worked, but in general, how do you know what setting to use? **(RH) **The feed Z of a short 80 meter antenna is quite low. Possibly 12 ohms or so. Using the 4:1 transforms the 12 ohms to 48 ohms, which more closely matches the 50 ohm coax Z. Use the ratio that brings your antenna feed Z close to 50 ohms. Trial and error is the simplest, but using an antenna analyzer is probably quicker. You want to try toe close to resonance, as that is where the SWR is lowest......it might not be 1:1 but it IS lowest at resonance. SWR is determined by the load and its' match to the feedline.* *W5RH made these orange comments...* *Looking forward to your comments, and see you this weekend at Field Day!* *73 de Bill, KG5FQX* On Wed, Jun 22, 2016 at 10:31 PM, Bill Dillon via BVARC <bvarc@bvarc.org> wrote: > I was thrilled to take part in tonight's Rag Chew Net, and made my first > HF contact (with my rig) with Roy, W5TKZ, at a whopping distance of 9 > miles. He noted my signal was weak. > > However, after our net, I stumbled across members of the 3916 Net, and had > a strong signal report from a station in Florida -- I guess the band was > opening up! > > I used a Buddipole with special large coils and extended whips (my radio > is a Yaesu 857D). Antenna analyzer showed the SWR dip was *really* > narrow, and it took a while to tune it to 3910. And I'm sure most of my RF > energy was going straight up. At some point I'll have to get an antenna > tuner and maybe a proper half-wave 80-meter dipole antenna. > > Some interesting questions came to mind for you antenna experts out there: > > > If you're trying to take the SWR minimum to a lower frequency, is it > better to lengthen the antenna, or add more inductance? My whips were full > out, so I tapped off two more coil turns to drop the SWR minimum 160 kHz to > get the minimum SWR on 3910 kHz (SWR minimum was 1.4). > > There was a lot of inductance on the antenna from those coils. Where is > the extra capacitive reactance coming from to cancel out the inductive > reactance at SWR minimum? > > The Buddipole kit for 80 meters has a Balun with settings of 1:1, 2:1, > 4:1. I had no clue or instructions what to set it to, but found another > Buddipole user's website who recommended the 4:1 setting for 80 meters. > Well, it worked, but in general, how do you know what setting to use? > > Looking forward to your comments, and see you this weekend at Field Day! > > 73 de Bill, KG5FQX > > > > _______________________________________________ > BVARC mailing list > BVARC@bvarc.org > http://mail.bvarc.org/mailman/listinfo/bvarc_bvarc.org > >
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