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.

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. The hight of the ends from
the terrace is not the same. 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.

I have afew questions.

1. What are the ways to improve my antenna installation?

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.

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?

Any other suggestions or general observations about this setup and hopw
I can improve the antenna setup? I also plan to learn NEC and simulate
this setup (hope it is possible to do it with NEC).

Thanks

73
Ramakrishnan, VU3RDD

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

Hi Richard,

Richard Clark wrote:
Welcome to the fraternity. What you describe are common enough
problems and part of the "fun" of the hobby. Antennas are the last

Thanks. I hope to spend a lot of time, on learning and working on
antennas.

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.

One end of the dipole is at about 4 ft above the terrace (which is 50
ft
from ground) and the other at about 6 ft from terrace.

I don't see any discussion of a tuner. You will eventually need one,
if you don't need it already.

I don't have a tuner yet. It's directly connected to an antenna.

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).

Thanks Richard for the kind and encouraging words.

What could be the possibl;e reasons for the high SWR I am seeing?

73
Ramakrishnan, vu3rdd

wrote in message
ups.com...
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.

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. The hight of the ends from
the terrace is not the same. 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.

I have afew questions.

1. What are the ways to improve my antenna installation?

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.

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?

Any other suggestions or general observations about this setup and hopw
I can improve the antenna setup? I also plan to learn NEC and simulate
this setup (hope it is possible to do it with NEC).

Thanks

73
Ramakrishnan, VU3RDD


Have you checked the SWR at different points in the bands? If you have what
differences have you measured. The antenna might just need tuned.. without
knowing how the difference between the top and bottom of the band it's hard
to say if anything else is affecting it.

Adair

Hi Adair,

I will try doing that. The said SWR is at around middle of 20m and 40 m
bands.

ramakrishnan

On 22 May 2005 23:47:27 -0700, "
wrote:

I don't have a tuner yet. It's directly connected to an antenna.

resolves:

What could be the possibl;e reasons for the high SWR I am seeing?

Hi Ramakrishnan,

The why of your question is simple: the antenna is not tuned to the
frequency you are applying. An alternative is that the set's built-in
SWR meter is hardly a precision instrument - another reason for an
external tuner (with a larger readable SWR meter).

But back to the antenna not being tuned. Again, this is the thrill of
"the last frontier." There are MANY variables that contribute to
tuning and it takes only one variable to be off, and so is the tune.
You should count it as great luck to have been so close to tune with
your first try.

Tune through all frequencies that are available to you, and build a
chart of SWR vs. Frequency. Then make a change in the antenna. This
can include
* changing the angle of the V
* changing the length of either leg of the V
* raising or lowering either/both leg(s) of the V
* raising or lowering the feedpoint of the V
and for each variation taking readings for new charts of SWR vs.
Frequency. Note the trends as they will reveal where your design
focus should be heading.

I would point out, however, that antennas intended for even harmonics
(40M/20M) usually portend disaster. I suggest you research the net
for "fan dipole." That you do not report any such disaster suggests
that due to what you DO report (unequal length dipole legs) suggests
that you have is what is called an OCF (off-center feed) dipole. This
makes yet another variable that tends to throw a spanner in the gears
of tuning. In this regard, you need to research the net for the topic
of "feedpoint choke" or "W2DU style BalUns."

Well, as you can see the discussion has barely warmed up and you have
the prospects of starting a journal dedicated to all the variations of
a simple design. One maxim to observe:
"No one ever builds ONE antenna."
You may as well get used to the idea that nothing is permanent, even
if you get it right. Plan on being flexible so that doing things
repeatedly does not become a chore. If you note all the variations
listed above, it should suggest that at a minimum you should invest in
pulleys. ;-)

73's
Richard Clark, KB7QHC

Thanks Richard for the new frontiers!! :-) I am learning a lot.

Mine is a center fed dipole with a 1:1 balun which feeds both 40m and
20m dipoles. The ends are at unequal heights because I couldn't find a
convenient way to tie the ends in the terrace.

My next experiment is to measure SWR at dofferent frequencies. To make
things simple, is there some kind of input signal suggested? Shouting
can easily come down afew decibels, after going up and down the stairs
adjusting the dipole angle and lengths. :-) I don't have a CW key yet.
:-( So what's the other option?

73
Ramakrishnan, vu3rdd

One more question:

While measuring the SWR, the needle fluctuates, as the voice is
modulated. Is the "value of SWR" the highest it hits? What's the
convention?

73
Ramakrishnan, vu3rdd

wrote:
What could be the possibl;e reasons for the high SWR I am seeing?

2:1 is NOT a high SWR and is tolerated well by most
transceivers. The reason that the SWR is not 1:1 is
that the feedpoint impedance of the antenna is
something other than 50 ohms.
--
73, Cecil http://www.qsl.net/w5dxp

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Richard Clark wrote:

" wrote:
What could be the possibl;e reasons for the high SWR I am seeing?

The why of your question is simple: the antenna is not tuned to the
frequency you are applying.

There's no guarantee that a tuned antenna is going to have
a feedpoint impedance of 50 ohms. Between 0.1WL and 0.33WL
in height, the same resonant dipole can have a feedpoint
impedance variation between ~20 ohms and ~100 ohms. A resonant
dipole in free space will have an SWR of ~1.5:1 using RG-213.

The reason that the SWR for any antenna is not 1:1 is that
the load (the feedpoint impedance of the antenna) is not equal
to Z0 (the characteristic impedance) of the feedline.
--
73, Cecil http://www.qsl.net/w5dxp

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