Ft-991 (pre-A samples at least) has trouble tuning some multitrap verticals for all the expected bands, this may explain why
On Sat, Apr 11, 2020, 7:57 PM Mark Goldberg <[email protected]> wrote: > On Sat, Apr 11, 2020 at 6:09 PM Bob McGraw K4TAX <[email protected]> > wrote: > > > My 6M yagi shows a 5.3:1 SWR as indicated on my K3S on 28.3MHz with the > > ATU in Bypass mode. When the KAT3A ATU in the radio resolves a match, > > the indicated SWR indicated is 1.1:1 on the radio. > > > > Using the same antenna but using my KAT500 ATU the best SWR resolved is > > 1.6:1 as indicated on the radio. > > > > Now my antenna analyzer on 28.3 MHz with my 6M yagi connected shows and > > SWR of 7.5:1, a Z value of 16.6 ohms, and R value of 7.3 ohms and the X > > value of 14.7. > > > > That same antenna on the analyzer at 50.2MHz shows the SWR at 1.2:1, Z > > at 39.9, R at 40.0 and Z at 0.0 > > > > My conclusion: although the SWR values may be indicating acceptable > > values, the 6 meter Yagi operated on 10 meters would make a very lousy > > antenna. You'd be much better off to use an 80 meter dipole or better > > yet, just a 10 meter dipole. > > > > In addition, a Yagi operated at a non resonant frequency, especially below > it's design frequency is likely to not act like a Yagi at all. The pattern > depends on the elements being close to resonance. More wire / aluminum is > usually better. A physically short antenna may be tunable but it won't be > efficient. Much of the power will be dissipated in the tuner or balun or > feedline as losses. A physically short antenna + tuner + high power often > results in smoke somewhere! I use a 300 foot horizontal look and it can be > tuned from 80 to 6 meters. Who knows what the pattern is at high > frequencies but I can make contacts! > > So, a tuner is a good idea, but it won't solve every problem. Because it is > easy to understand, Hams use SWR, but in actuality the same number for SWR > results from an infinite number of impedances ( R and X), not all of which > can be handled by the tuner the same way. ARRL has done some comparison > testing with tuners with various impedances, I believe. I don't know if the > losses have been measured, but you can take two different impedances that > result in an SWR of 4:1 and only some can be tuned, depending on the tuner. > > 73, > > Mark > W7MLG > ______________________________________________________________ > Elecraft mailing list > Home: http://mailman.qth.net/mailman/listinfo/elecraft > Help: http://mailman.qth.net/mmfaq.htm > Post: mailto:[email protected] > > This list hosted by: http://www.qsl.net > Please help support this email list: http://www.qsl.net/donate.html > Message delivered to [email protected] > ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:[email protected] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html Message delivered to [email protected]
