Ken:
I've not run HF measurements on bricks, but I can tell you that a brick wall
is extremely lossy at 1 GHz and above, by measurement. Their water
(dielectric constant = 80) content is relatively high unless recently baked
and sealed, and depending on the particular clay they were fired from, they
are somewhat conductive. So, placing your antenna close is like putting it
next to a high dielectric RF absorber. Not a good choice.
--
Crazy George
Remove NO and SPAM from return address
"Ken Bessler" wrote in message
...
What effect would a brick wall have on a HF antenna?
I'm talking 1-2" distance from the bricks, folks. The
wire used is 22 ga stranded insulated speaker wire.
Now no lectures about power - I run QRP. :-) The
station is well grounded to a copper baseboard heater
pipe and all components have short runs (12" or less)
of 1/4" braid line going to a common point. From there
it's 1/4" braid (26" long) to the pipe. I can touch any
part of the system while transmitting and see no change
in SWR.
I cut an inverted V 66'7" per leg 133'2" overall. It's fed
with 12' of rg8x coax with a 6 turn 2-5/8" dia coil at the
feedpoint. The apex of the antenna is roughly 25' up. The
ends of the antenna are at chest height. The antenna is bent
around the corner of my building 90 degrees (I'm in a
corner unit). The last 8' of each leg bends again 90 degrees.
The antenna resonates as follows:
============
2.130 2:1 swr
2.715 1:1 swr (flat)
3.620 2:1 swr
============
8.970 2:1 swr
9.210 1.8:1 swr
9.390 2:1 swr
============
12.230 2:1 swr
13.040 1.9:1 swr
13.850 2:1 swr
============
15.930 2:1 swr
============
20.970 2:1 swr
22.745 1.2:1 swr
24.520 2:1 swr
============
If I figure 468/133.1666666667 I get 3.514.393 mhz
for resonance How come the antenna is so far off?
Could it be the height? Not that I'm complaining - I
like the low resonance and my Z11 autotuner will take
this antenna down to 1.8 mhz real easy. Although at
that freq I expect the antenna will radiate a NVIS
signal due to low HAAT.
Any ideas???
72's de Ken KG0WX
|