Best Antenna for Receiving - NEWBIE
 

Hi,

Being a Newbie, in West London, to this hobby of SWL, I am seeking advice on
best antenna to use.

I have ICOM PCR1000 and Yaesu FRG100. At present I use a 25MHz-1300MHz
(TANDY/RADIO SHACK) Discone for the ICOM and a long wire with HOWES ATU on
the FRG. Both rigs used in first floor room so grounding is a problem as I
would nead around 10m cable run to get to a ground rod, at moment connected
to water pipe. The ICOM performs well with the Discone throughout its range,
even on the HF. The longwire is not as long some mentioned on the
websites/books, its around 8m long and slopes east/west direction, cannot
install in any othe direction or increase its length. The FRG performs well
but only seems to receive channels from the East and sometimes from west,
channels North and South seem to be elusive. The broadcast bands work well,
but HF Airband and Datamodes seem to be very weak and noisy.

Since my main interest is Airband and Datamodes I would like to be able to
improve my reception of these.

So I hope answesrs to the following questions will help me in reolving the
problems:
1/ I understand that Longwires can be directional so limit whats
being received, so considering my available space would one of the vertical
wide range give better alround performance with restrictions on direction.

2/ Are Dipoles directional as ?

3/ Do Dipoles need to be mounted horizontally ?

4/ Is it possible to have dipole with both elements parallel to
each other or do they need the traditional arrangement of being opposite
each other.

5/ Can the Dipole be made using wire with the Elements arranged
in an inverted V formation ?

6/ Can Longwire be folded/bent round corners ?

7/ Is it possible to use several long wires in different
directions connected to the rig simulatenously ?

Any help and suggestions in resolving the above will be most appreciated.
Regards
Birderman
West London, UK

On Fri, 26 Aug 2005 09:56:55 +0100, "Birderman"
wrote:

So I hope answesrs to the following questions will help me in reolving the
problems:
1/ I understand that Longwires can be directional

Hi OM,

Your 8 meter "long wire" is long only for frequencies above roughly
20MHz. You neglect to offer how high it is, but in all probability,
it is lower than a quarter wavelength for mid-HF. In this regard (and
being unbalanced) it is probably quite omni-directional.

so considering my available space would one of the vertical
wide range give better alround performance with restrictions on direction.

No.

2/ Are Dipoles directional as ?

As what? the long wire? Same kind of problem of being low to the
ground. You might get some directionality gain from having a balanced
antenna - being able to HEAR the difference is another matter (and
more to the point, you would want to null noise sources which might be
a possibility).

3/ Do Dipoles need to be mounted horizontally ?

All depends on your goals. Otherwise, no, as long as you can make a
right angle connection at the midpoint (or snake the drive line up
through the interior of the lower section - research a "sleeve
dipole").

4/ Is it possible to have dipole with both elements parallel to
each other or do they need the traditional arrangement of being opposite
each other.

This anticipates your question about a V antenna:

5/ Can the Dipole be made using wire with the Elements arranged
in an inverted V formation ?

Yes, such an antenna is so named.

6/ Can Longwire be folded/bent round corners ?

Yes, but as you are putting this to wideband use, such elaborations do
not really contribute to the whole.

7/ Is it possible to use several long wires in different
directions connected to the rig simulatenously ?

Yes. This is called a "fan dipole" and the wires are usually cut for
different bands.

73's
Richard Clark, KB7QHC

Just a few comments..

- When receiving only the important part is to have a good signal to
noise ratio. HF is always pretty noisy and pretty well never below the
receiver noise floor. Antenna design for HF RX needs to consider
reducing noise as well as increasing signal.

- A dipole has a maximum response at right angles to the wire. This ONLY
applies if the dipole is a half wavelength long and is centre fed. (Some
pattern skewing will normally be evident with an end fed dipole in the
direction away from the feedpoint) A piece of wire one wavelength long
will tend to exhibit maximum responses at about 45 degrees to the wire.
ie there will be 4 lobes in the horizontal plane. You see then that it
isnt simple to give a straight answer on this. Whatever frequency you
choose for the particular wire length you will get varying patterns. You
can of course cut the antenna for the band of interest.

- Vertical antennas tend to be noisier than horizontal antennas. (ie
they pick up more local man made noise)

- There is no reason why you cant mount a dipole vertically or even
diagonally. It is important though to have the feed line at right angles
to the wire for some length. The pattern is of course affected by this
orientation. When it is vertical it will tend to radiate equally in all
(horiz) directions. You should also consider the ground as a kind of
lossy reflector.

- You might like to look at a folded dipole antenna. I have heard the
claim that they are less noisy than a single wire dipole. Suggest you
have a look at Mr Cebik's TFDP on http://www.cebik.com/wire/wbfd.html

- Two parallel elements will generally speaking look like a continuation
of the transmission line and not radiate/receive as effectively. It
depends on the spacing though. You can tune the distance apart so that
some gain in a particular direction/directions will occur. I would
suggest you keep away from this for general HF use.

- A right angled dipole (lookup "Inverted V") with the feedpoint at the
highest point is a valid design. I'll admit I havent researched it but
anecdotal comments to me in the past say it works much better than a
dipole with a lower feedpoint but same average height.

- Yes a long wire can be bent. It is surprising (to me) how much it
doesnt affect directivity. (Assuming the bends arent too great!) You may
wish to model this kind of thing (and other antenna designs) using
Eznec/4NEC2 etc. Its all very fascinating.

- A wire in a horizontal V shape will tend to radiate/receive more in
the direction of the open end of the V. Once again though for varying
frequencies/lengths this behaviour will be variable.

- Yes you can connect more than one wire to the RX at one time. There
will of course be interaction depending on their length and usage
frequency. You may get a useful directive pattern or something that is
useless.

- If you want to monitor a specific spot frequency on HF I would suggest
a single quad loop.

- If you really want to fiddle with a sharply tuned low noise antenna
have a look at magnetic loops. They can usually be made to cover a 2:1
(or more) freq range and maybe what you are after for RX only purposes.
The signal strength will be lower than (say) a dipole but the signal to
noise will be much greater. (anecdotal knowledge)

- Make sure your station grounding is good. For noise reduction as well
as safety. You may also want to check your house appliances for noise
creation and suppress them. Keep in mind that at the distance you
currently have to ground that looks like a 1/4 wave on about 7Mhz, 3/4
on 21Mhz etc and thus a high impedence path. ie the noise volts in the
system (at those freqs) wont flow well to ground through this path. In
fact any other noise that exists on the water pipe ground from other
sources may interfere. Whether running a separate piece of braid/wire
will help is an unknown. It depends on a number of variables, but it
cant however hurt to try. Also ensure that power and other boxes
connected (eg a computer for digi modes) are single point earthed and
isolated accordingly. (eg if you are using a soundcard to demodulate
digi signals make sure there is (say) transformer coupling between the
radio and computer)

Hope this is helpful. My suggestion would be a WBFB as big as will fit
in your yard, maybe bending some of it to fit. Also keep the feedpoint
high (ie inverted V construction) Also run a thick braid earth from your
station to a seperate ground stake. Read up on this espcially in the
area of grounding RF rather than just safety issues. Then bond that
stake to your electrical ground as well (ie outside the house)

Cheers Bob W5/VK2YQA East Texas

Birderman wrote:
Hi,

Being a Newbie, in West London, to this hobby of SWL, I am seeking advice on
best antenna to use.