I typically try to get a combination of lowest SWR at my chosen center frequency with the widest SWR curve. Then check impedance on the Smith chart at the center frequency. I'm using a nanoVNA, I don't have a grid dip meter. Impedance in the best case i've gotten is around 200 ohms on the inductive side of the chart (which explains why my body capacitance affects it so much it would seem). VNA was calibrated for the 6-8 mhz range before starting.
I'm tapping the coil when adjusting by jumping from the feed to higher up on the coil. Just to try, I jumped from the antenna side to the coil. not a lot of difference, but I didn't have the Smith up then. I need to leave SWR and Smith on I think to get more information, rather than switching. When I move my hand close, the frequency of the SWR dip drops (as does the SWR). I didn't think to check the Smith when doing that. Right now I wouldn't consider it resonant on 40 LOL. But the calcs say it should be. They assume an effective ground radial system (among other things). My next try will be with a couple of 33 ft radials to see if that helps like several folks have pointed out. Once it stops flooding here that is. Thanks for all the input guys- Happy for any suggestions you have. Andre W4SFZ On Tue, Jun 18, 2024 at 5:11 PM Rick Hiller via BVARC <bvarc@bvarc.org> wrote: > Questions...... > > What do you mean "tuned" to 7.2? > > Are you feeding it at the base of the coil? Have you tried moving the > feed point up the coil? > > What frequency change do you see when moving your hand close? > > Here is where just knowing the SWR is not what you need. What is the feed > impedance when measured at the feed point? Lower than 50 ohms or higher? > Reactive? > > Is the antenna system resonant on 40? How do you know? Do you have a > GDO? > > What are you using to measure SWR? Maybe the analyzer has what you need > as far as measurements required. > > Sounds like you are having fun. GL...Rick W5RH > > ps...just saw Chris's note about the GP. You might want to make a more > lengthy or resonant elevated GP system to see how that affects it. > > > > On Tue, Jun 18, 2024 at 4:39 PM Andre Pollard via BVARC <bvarc@bvarc.org> > wrote: > >> I normally use a 5’x8’ faraday cloth which works fine on 20 and up. I >> made up 16 radials 10 feet long to try that and saw no difference. >> >> >> >> On Jun 18, 2024, at 4:24 PM, wb5itt <wb5...@att.net> wrote: >> >> >> What kind of a ground system do you have? >> >> Chris WB5ITT >> >> >> >> Sent via my Samsung Galaxy S10e, an AT&T 5G Evolution capable >> smartphone..so there! 😂 >> >> >> -------- Original message -------- >> From: Andre Pollard via BVARC <bvarc@bvarc.org> >> Date: 6/18/24 4:19 PM (GMT-06:00) >> To: BRAZOS VALLEY AMATEUR RADIO CLUB <bvarc@bvarc.org> >> Cc: Andre Pollard <apollard...@gmail.com> >> Subject: [BVARC] Antenna help >> >> I need one of our antenna gurus to give me some input- >> >> I have an 18'-4" telescoping antenna I have been using when camping. By >> adjusting length, I can get it to tune at <1.5 SWR on all bands 20M and >> above. So far so good, but when do we ever leave well enough alone. >> >> I'm getting ready to travel for a while, and wanted to extend the range >> down to 40M. So I used the calculators at Coil-Shortened Vertical >> Antenna Calculator (66pacific.com) >> <https://www.66pacific.com/calculators/coil-shortened-vertical-antenna-calculator.aspx> >> to >> determine the necessary coil. It said I need 4.9 mH. I made the coil per >> the calcs one the same site, using a 1.9 inch diameter PVC pipe. I'm >> running it bottom-loaded. >> >> By tapping the coil a couple of turns down, I can get it to tune to 7.2 >> mhz, but the SWR is >6. If I put my hand very close to the coil , the >> frequency shifts (expected), and the SWR drops to 1.2. So I tried adjusting >> the length and tapping different turns, never better than 4 SWR on any >> frequency around 7 mhz. However, if I get my hand near the coil, SWR drops. >> >> Thinking this meant I needed capacitance, I tried a hat to the whip, with >> several different designs and sizes. Changes frequency, but horrible SWR >> still. >> >> Bypassing the coil I can adjust the whip and get great SWR on 14 mhz and >> above. So, I don't think it's a problem with the coax (20 feet of RG8X) or >> nanoVNA. >> >> Google shows up all sorts of sites showing making a coil loaded shortened >> vertical like i'm trying. None mention the issue I'm seeing as a problem. >> >> I'd appreciate any input, I've been 'learning' on this for a couple of >> days now and haven't gotten it to work yet. >> >> Thanks, >> Andre >> W4SFZ >> >> ________________________________________________ >> Brazos Valley Amateur Radio Club >> >> BVARC mailing list >> BVARC@bvarc.org >> http://mail.bvarc.org/mailman/listinfo/bvarc_bvarc.org >> Publicly available archives are available here: >> https://www.mail-archive.com/bvarc@bvarc.org/ >> > > > -- > Rick Hiller W5RH > *e-mail: rickhille...@gmail.com <rickhille...@gmail.com>* > *Cell/VM/Text: 832-474-3713* > *Physical: 9031 Troulon Drive* > * Houston, TX 77036* > ________________________________________________ > Brazos Valley Amateur Radio Club > > BVARC mailing list > BVARC@bvarc.org > http://mail.bvarc.org/mailman/listinfo/bvarc_bvarc.org > Publicly available archives are available here: > https://www.mail-archive.com/bvarc@bvarc.org/ >
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