On Sat, 17 Apr 2021 17:19:57 -0500 Charles Plunk <af4o@twc.com> writes:
> Good point. And that line of site quality is a good thing to narrow
> down
> the area.
>
> Are your referring to the W1TRC dish in the QST article?
Yes, that's the one.
> I built
> mine
> years ago with a prefab circuit board and the dish specified in the
>
> article. I have heard sourcing the dish is more challenging right
> now.
I have a source for a 20" clear plastic reflector. It's made as a
"squirrel guard" made by "Havahart" and it works VERY well for our
purposes. The plastic
is about 1/8" thick and as such it might heavier than aluminum.
Doing some research here 'cuz I'm curious...mine looks like this one:
https://www.duncraft.com/Clear-Plastic-Squirrel-Baffle. I'm pretty sure
it's
the same baffle...just has a different name. I see Amazon has the same
thing
as do other on-line stores.
When I looked for reflectors, I happened to see a squirrel guard at a pet
store. I looked
it up on the web, downloaded the photo, then drew a parabola over it with
a
drawing program. Perfect match!
I found that it's easy to locate the focal
point by pointing the clear plastic dish using a light souce such as
a flashlight. The plastic is just shiny enough to reflect and focus the
light
onto a piece of white paper and can be easliy seen in darkened room when
the
flashlight is ~50 feet away. When used as a ultrasonic reflector, the
greatest output
is when the light source "floods" the surface of the detector, not where
the
light focus is a pin-point. I used a camera tripod to support the dish
while experimenting.
This has turned out to be rather long, but I'll add one more thing. The
20" dish
will exceed the width of most ultrasonic detector module signal lobes,
but that's a good thing.
It will help shield the detector from stray signals.
73,
Charlie, N0TT
> If so, yes it works quite well. In fact, if i do not hear it with
> the
> dish i really begin to question if i am at the right pole. Yes there
> is
> a background hiss but once you hear an arc you will not forget the
> sound.
>
> My recent fix was as high as 25db over S9 due to the proximity of my
>
> doublet to the pole. I heard it easily with the dish once i found
> the
> right pole......This is preliminary and I have more work to do but I
>
> still have some weak arc sound on some bands. Its so weak though I
> think
> natural noise is not allowing me to hear it on some bands. And yes I
> am
> hearing a faint signal in the suspect area with the dish. I need to
>
> match a noise pattern before I request they do more work.
>
> I think though a new nut/washer and moving the ground wire will do
> it. I
> think my issue was decades of crud on the 7200v hardware was making
>
> enough of a carbon trace around the old hardware to arc to that
> ground
> wire stapled to the pole next to those nut/washer.
>
> I am enjoying such quiet noise levels now I may not even mess with
> it. A
> little NB adjustment knocks it right out and most bands I dont hear
> it.
>
> 73
>
> Chuck
> AF4O
>
>
>
> > Yes, good tool, but keep in mind that it will not hear an arc on
> the
> > "other side" of
> > a structure. It has to be line of sight from the arc to the
> receiver or
> > at least close
> > to that.
> >
> > RE the QST article ultrasonic pin-pointer...has anyone built it?
> If so,
> > how
> > sensitive was it....could you hear a very small arc at 50ft? Was
> the
> > circuit quiet...i.e. was there
> > any "hiss" when it wasn't detecting any signal?
> >
> > 73,
> > Charlie, N0TT
> >
> >
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