[MRCA] NVIS on 40M

[Radio Station KW1I]

Gene,

Very interesting.  Thanks for the report.  Look forward to more info as you
do more experiments.

Give the reflector a heads-up so we can give you some data points the next
time you are on the air with the NVIS antenna.

Dale
KW1I


----- Original Message -----
From: <ersmar at comcast.net>
To: <mrca at mailman.qth.net>
Sent: Saturday, March 11, 2006 9:55 PM
Subject: [MRCA] NVIS on 40M


> Gents:
>
>      Yesterday and today I spent a few hours constructing the inverted-V
> NVIS antenna I had posted about last year.  You know - the one that is
based
> on the AS-2259?  I'm getting ready for a Ham radio demo next weekend as
part
> of a disaster preparedness public event in a nearby town.  The antenna
works
> (I can count QSOs with upstate NY and Ohio this afternoon) but with some
> caveats.
>
>      I used five surplus fiberglass stacking poles that I bought on that
www
> auction place last year as the center support.  That brings the top of the
> mast to 44 inches x 5 sections = 220 inches or a little over 18 feet above
> ground.  I thought about going higher, but that would require two levels
of
> guying and getting the pole erect is a bit of a gamble, even with the five
> poles and the small amount of wire at the top. Atop this mast I have a 2
> inch PVC pipe cap that I drilled to hold four brass bolts sticking up out
of
> the cap, spaced 90 degrees apart around the top.  I jumpered adjacent
bolts
> together with lugs and wires and connected a five-foot long piece of
RG-8X,
> with PL-259 on the end, to the pairs of lugs, shield to one pair and
center
> wire to the other.  This way I can connect two dipoles or V's to opposite
> lugs on the cap and they will be connected properly to the coax.  I also
> drilled a hole and bolted a hook eye in the center of this cap (for
possible
> tree suspension of the cap and wires, without the poles.)
>
>      I assembled the poles into one length on the ground and ran a length
of
> RG-8X through the poles.  I connected this main coax to the coax pigtail
> inside the cap with a barrel connector.  At the bottom of the poles I
fitted
> a PVC closet flange (Oatey Caspers 43507 at Home Despot) and PVC reducing
> adapter to serve as a base.  (The closet flange is used as a transition
> piece between a new toilet and the waste line underneath it.)  DON'T knock
> out the center of the flange that's marked KNOCKOUT.  I learned the hard
> way.  Simply drill out a 3/4 hole for the coax and connector to pass
> through. Otherwise the flange provides no bottom support for the pole as
the
> pole passes right through to the ground.
>
>      I started with a seventy-foot long dipole wire for 40M.  I split it
in
> the center and connected the centers to two opposite bolts on the PVC cap,
> using solder lugs on the wire ends and wing nuts on the bolts.  I tied the
> dipole ends to lengths of nylon rope (no insulators yet) for guying to
> ground stakes.  I tied
> the center of a lenth of dacron cord to the eye on the cap for guying at
> right angles to the wires.
>
>       After I raised the pole and its attached wires and ropes, I
tightened
> up all guy lines at the army surplus stakes I had driven into my front
yard.
> (Yes, all the neighbors could see me wrestling with this pole!  But they
> should be used to this kind of stuff - they watched me hammer staples for
my
> 160M inverted L's radials into the grass around my yard a few years back.)
> All this set-up took me about twenty minutes including adjusting the guy
> rope tension.
>
>      I checked SWR - my MFJ259 showed a 1.3:1 minimum at 6.7 MHz or so.
> This, with a slightly (I thought) long dipole.  I'm guessing that the
> antenna's proximity to the ground lowered the resonant frequency even more
> than would be expected from the long wires.  Or the lack of insulators at
> the ends of the wires might cause this lowering of resonant frequency.
This
> will require more investigation.  (I plan to use plastic chain as
> insulators - it rolls up really nicely with the rope and wire.)
>
>      I loaded up the antenna with my Kenwood TS-570's autotuner on 7.250
and
> broke into a QSO with a couple of stations in Ohio.  They copied me above
> the SWBC stations on the air in late afternoon.  I next called a station
in
> upstate NY who said I was at par with the SWBC stations.  The antenna took
> full power (appr 85 W as I was operating off a gell cell on the front
porch,
> and its terminal voltage was around 12.5 VDC.)
>
>      I'm not sure I have enough room to install a V for 80M or even for
60M.
> I'll have to measure this out a bit more.  If possible, then my plan would
> be to install a combination 80/60M V in the plane that the dacron ropes
are
> in now.  I'd split the wires into two segements - 60M with extensions for
> 80M - and use a jumper to lengthen the 5.3 MHz wires for operation on 3.9
> MHz.
>
>      As it is, my NVIS antenna occupies a diamond-shaped space on the
ground
> measuring 28 feet across between the rope guy anchors and about 56 feet or
> so between the wire's guy anchors.  At this spacing, the wire ends are
about
> four feet off the ground (I told you they were low.)  I expect the 80/60
> combo wires will be almost twice that length and even closer to earth.
>
>      My next step (after the public demo next weekend) will be to tweak
the
> 40M wire lengths for proper resonance at around 7.25 MHz.  I might even
try
> setting up two sets of guyed fiberglass poles to test out a dipole
> configuration (wires parallel to the ground) at about 18 feet AGL.  Either
> way I expect that, as long as the wires are close to the ground (NVIS,
> remember?), the wire lengths will have to be shorter than would be
> calculated from traditional formulas.
>
>      I'll keep you guys apprised of progress here.  Hopefully I can bring
> this, and the 80/60M wires, to Gilbert in the summer.
>
> 73 de
> Gene Smar  AD3F
> P.S. Anybody see any photos of the 2005 Meet?
>
>
>
>
>
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