Over the weekend I put up a new interlaced 10/15M yagi at abt 50'. The 10M
section
appears to be working very well when compared against my reference
antenna, an A3 sidemounted at 30' on the same tower. On 10M it is
consistently " 2 s units" better than the A3. Unfortunately the 15M
performance is less than stellar and appears on par with the A3. The new
10/15 antenna has about 2 dB more gain than the antenna it replaced. All
elements on the new antenna are insulated from the boom.
After putting the A3 up 4 weeks ago I noticed that it was on par with my
old antenna on 15M, and, at times, superior. I chalked it up to the
different heights but not am not so sure. My 20/40M antenna is a Force 12
204/402 combo that is about 14' above the 10/15 antenna. I never noticed
interaction before but?? It seems that I am missing about 3-6 dB of
forward gain and the F/B of maybe 5 dB is 10-15 dB below the NEC design.
F/S ratio looks to be better than 35 dB on 15M.
Rotating the A3 below the 15M seems to have no effect on signal strength
and just barely any effect on SWR. All the baluns/pigtails are new, so I
can think of these possible culprits:
1) Bad 15M coax up the tower (SWR is good, but see reflected power)
2) Interaction from 40M antenna
3) Poor 15M design (but the 10 works as planned)
4) Bad construction (10 works as planned, measured everything very
carefully...?)
Loss of forward gain could be any/all of the above, and the first 2
causing me problems previously. Loss of F/B could be any of the last
three. I will try new 15M coax and rotate the 10-15 and 20-40 antennas to
be at
right angles this weekend. Any other ideas?
And does anyone have a YO/NEC/etc. model for the Force 12 linear loaded
40M elements that I could get? Might give me the answer I'm looking for.
73
Jeff N5TJ
n5tj@cwix.com
--
FAQ on WWW: http://www.contesting.com/towertalkfaq.html
Submissions: towertalk@contesting.com
Administrative requests: towertalk-REQUEST@contesting.com
Problems: owner-towertalk@contesting.com
Search: http://www.contesting.com/km9p/search.htm
|