[Towertalk] 80M sloper on Trylon tower

[EUGENE SMAR]

TT:

     This afternoon I hung a sloper wire off the side of my 64-foot Trylon
tower with pretty respectable results.  If you will recall (TT archives
Jan-Mar 2002), I had shunt fed the tower on 80M with a pair of parallel
wires up one face of the tower, about 6 inches away from the steel.  That
worked ok but was very narrowbanded.  I removed the wires before I strung
the sloper.  (I kept the other two shunt feed wires for 160M.)

     After a bit of experimentation (read that:  much up-and-down on the
tower) I ended up with a wire about 67 feet long (surprise, surprise) at
about a 50 degree angle from horizontal, sloping to the northeast. I tapped
the coax shield to the tower at the 53-foot point above ground; the sloper
wire and the coax center conductor are within a few inches of that point.
I measured the feedpoint impedance at the wire end with my MFJ analyzer sans
BCB filter (more on this in a minute) and found it to be 100 + j0 Ohms.
That seemed strange to me, and I suspect that I need to retake this
measurement with the filter on the MFJ, but there it is.  SWR measured 1.6:1
at 3.640 MHz - not bad.

     I'm feeding the wire with RG-58 (cuz that's what I had in the garage
this afternoon.)  The shield is clamped to the tower at the 53-foot level
with a Harger 213T clamp.  I suppose I could use a quarter-WL of RG-59 as an
impedance transformer (100 Ohms X 50 Ohms = 5000 Ohms^2, a good match for 75
Ohm cable), but that will have to wait until I feel like doing it.

     Inside the shack the wire loaded well from 3.5 up to 4 MHz. Running
100W on SSB I received S9+25 dB reports from Canada's Maritime provinces;
these folks were likewise coming in S9+.  I did not A/B compare the sloper
with my 160M inverted L which loads well on 80M, too.   I had to remove the
L so I could string the sloper.  I'll reinstall the L after I reorient the
sloper to the east.  That way the L won't have to run over and across the
sloper wire.  At that time I'll pay attention to any directivity the sloper
displays and report on it here.

     I had originally wanted to put up an inverted-feed elevated ground
plane antenna a la N4KG, but I can't stretch out more straight radials
within the confines of my property.  When I have a bit more time, I will
throw a second sloper wire off the tower and in amongst the trees as the
second radial (didn't want to mess with tree climbing again) and report to
you-all.

     Once I finish and install my HB 6M Yagi, I'm going to need an antenna
switch with more ports at the tower base (my IC-746 has 6M off the HF
antenna ports).  Ain't towers fun?

73 de
Gene Smar  AD3F
BTW:  The capacitive loading of the tower is provided by a Bencher Skyhawk
w/ all parasitics shorted to the boom, D40 rotatable dipole and GP-15 V/UHF
vertical.  I haven't checked the effect of the sloper on these antennas'
SWRs yet.