RadioBanter - View Single Post

January 28th 05, 07:51 PM

wrote:
It would be quite
simple to weld up some angle-iron to make a mount for this, and keep
the
feed point low to the ground, so I can have a longer whip (higher
efficiency! Yay!) on top of the load coil.....................

I'd ground that angle iron as well as possible. Myself, I tried angle
iron
one time, and it didn't work too well. I did run an extra grounding
strap to
body/frame. But it wasn't enough...I think the problem was from a lack
of
metal area directly underneath the antenna. That seems to be fairly
critical.
When I moved it from that angle iron support behind the back window,
and moved
to the side toolbox, the low band performance was much better. The top
of that
utility bed toolbox is a pretty good platform, and is a few inches
wide, and
naturally, pretty well grounded. Maybe use real wide angle iron??
I think you will find the bandwidth to be fairly narrow. And swaying of
the
antenna vs body of the truck will vary the SWR a lot at that low freq.
If it's
rigid, or guyed some way, it will be more stable. Should be plenty
enough for
SSB bandwidth, but for multiple freq's, I'd add extra taps on the coil,
to allow
you to move around. I have three or four 80m taps on my coil...
BTW, I was thinking about coil length vs wire size, and I may have been
a bit
off. An 80m coil of insulated 14 gauge would probably be about a
foot...
But 16 or 18 gauge would probably be a bit shorter. About wire size...
In the past I had made coils using larger dia wire thinking it really
mattered..
It does make a slight improvement, but I'd say slight...Hardly worth
the extra
weight...I made one using thick 14 gauge, and I can't tell a heck of a
lot of
difference compared to 16 or even 18 gauge. I think my present coil is
16 gauge
wire. That antenna is *light*. About like a fishing rod and reel. Using
thick
wire will make the coil much heavier, and then you have to worry about
it overly
swaying, unless guyed. So I don't use overly thick wire anymore. If I
make a 160
antenna, it will probably be 16 gauge...Maybe even 18...
If you mount the antenna low, it does increase ground loss, but I think
getting
the coil that much higher from the base *should* override the increased
ground
loss. Or as good as I can calculate anyway...I've never actually
mounted one
real low yet to compare..I do have hitches...Maybe I could try an
experimental
antenna on my bumper/bumper hitch...Would give me about a 3 ft longer
base under
the coil, compared to it's current mount on the toolbox.
Yea, vertload is pretty handy...I think probably the "Reg" program I
use the most
out of his vast collection. But I've been running these "plastic
bugcatchers" for
years...Since about 1990 I guess...I like the light weight. I've got a
"real"
80 m bugcatccher coil, and just that coil alone probably weighs 5 times
the total
weight of that 10 ft antenna I have. It's heavy and requires heavy
hardware to
support it. But heavy hardware doesn't "talk" any better than light
hardware..:/
MK

Sage advice.

The mount strap for the fuel tank is mounted directly to the truck
frame, so grounding isn't really going to be that big of an issue. I
have the cab and the sleeper strapped together with 3" strap, the doors
strapped to the cab with 1 1/2" strap, and the sleeper strapped to the
frame with 3" strap. All the "strap" is tinned copper flat braid.

I know ground losses will be greater, but having the antenna longer will
hopefully more than overcome that..

I could, also, tilt it back along the sleeper, but that gets it too
close to the sheet metal, and I'll get coupling losses from that.

I've also changed my mind on using a SS whip on the top. 1" copper pipe
would be better, and easier to guy/stabilize. I can fashion standoffs
from the cab/sleeper junction out of PVC, too, if necessary.

This is going to be fun.. Maybe I should set up a switched cap/inductor
at the feed point so I can force the antenna on to other nearby
frequencies. A wheatstone bridge could take care of the controls...

Thanks for all the pointers.

73 de AI8W, Chris