On 22 May 2005 22:35:37 -0700, "
wrote:
Hi,
I am a new radio amateur from India (I got my license only a couple of
months back). My callsign is VU3RDD. This is my first experience with
Radio installation, so the questions and the problem I am facing may be
too silly and stupid. Neverthless... here it goes.
Hi Ramakrishnan,
Welcome to the fraternity. What you describe are common enough
problems and part of the "fun" of the hobby. Antennas are the last
frontier (which is to say you have to spend a lot of money to buy one
that works as advertised - and only if you spent far more to obtain a
tower).
I live in an apartment on first floor. My inverted V for 40m and 20m
are on concrete terrace (of the 5 floor apartment). The mast is about
10 ft high. The ends of the dipole are not very symmetrically tied, as
the space constraints do not permit so. One of the ends of the dipole
is facing north and the other end towards west. Not exactly 90 degree
wide, but probably 100 to 120 degrees wide.
This is fine.
The hight of the ends from
the terrace is not the same.
No problem with this either.
I purchased a used rig last week and when
I measured the SWR, it sometimes hits 2:1, and sometimes more (if I
shout at the mic) for both 20m and 40m.
This should really be done in CW mode, not voice mode.
I have afew questions.
1. What are the ways to improve my antenna installation?
By any number of ways, but what you have is in many ways far ahead of
the general Ham. That is, you have an asset with more than adequate
height for the bands you describe.
2. Does the concrete terrace act as ground for the antenna, and is 10
ft mast, just too short a height. The terrace itself is at around 50 ft
from the Ground.
I presume you mean, by mast, that it is 10 feet out from the terrace
which is 50 feet above ground. That is all fine and well, but you say
nothing of the dipole ends. That is, their height above ground. It
shouldn't matter too much, unless they are planted into the ground.
3. I run a low loss RG213 coax from the terrace. Does the loss in the
cable contribute to the high SWR I am seeing?
No, loss if anything will tend to present a lower appearance to a high
SWR situation. For a lossless line, SWR is constant all along its
length (which means you would measure the same SWR anywhere between
the transmitter and the mismatched load).
Any other suggestions or general observations about this setup and hopw
I can improve the antenna setup?
I don't see any discussion of a tuner. You will eventually need one,
if you don't need it already.
I also plan to learn NEC and simulate
this setup (hope it is possible to do it with NEC).
This is ambitious and commendable. As I said, antennas being the last
frontier makes this the last chance of experimentation (other than
getting the hang of using your gear).
73's
Richard Clark, KB7QHC
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