wrote in message
oups.com...
Looking around at Yagi's the largest selection is obviously for the
amateur bands. How much gain will I loose on airband from a 2M (144Mhz
ish) Yagi? Somehting like this maybe:

http://cgi.ebay.co.uk/ws/eBayISAPI.d...tem=5821390009

Cheers
Kev

The loss will be considerable. Yagis are quite narrow band. For a few
bucks/pounds/euros you can buy some aluminium tubing from a hardware store
and build your own.

If the countryside around you is reasonably flat, it makes sense that you
are having trouble hearing GA aircaft. The top mounted antennas are barely
5ft off the ground, the belly antennas merely 18" off the ground. That's not
a lot of antenna height. Most GA aircraft coms run less than 10W.

Brad.

On Sun, 23 Oct 2005 18:46:51 +1000, "Brad" bradvk2qq AT w6ir.com
said in rec.radio.scanner:

The loss will be considerable. Yagis are quite narrow band. For a few
bucks/pounds/euros you can buy some aluminium tubing from a hardware store
and build your own.

Or look for "broomstick and wire hanger" designs on the web. If you
have a long enough piece of wood for the boom and a few wire hangers
it'll cost you nothing and still work as well. Or you might look into
building a quad - more gain with less antenna.

Hi

I liked the idea of the 'broom stick and coat hanger' antenna, but have
strugled on the practicalties. I went through the design he

http://k7mem.150m.com/Electronic_Not.../yagi_vhf.html

and ended up with a very large (about 48" square) antenna that still
complained it was to short and the elements too thin!

It also doesn't explain the driven element connection details.

Help please

Cheers
Kev

On 24 Oct 2005 04:18:49 -0700, said in
rec.radio.scanner:

I liked the idea of the 'broom stick and coat hanger' antenna, but have
strugled on the practicalties. I went through the design he

http://k7mem.150m.com/Electronic_Not.../yagi_vhf.html

and ended up with a very large (about 48" square) antenna that still
complained it was to short and the elements too thin!

48" square? The antenna is 1" thick at the center (the boom) and
~1/8" thick for the rest (the element thickness). It's about 12' long
and 4' wide at the reflector end. You can shorten the boom by asking
for less gain - the gain is determined by boom length, but you can't
shorten the elements. 1/4 wavelength is fixed by the laws of physics
for any given frequency. (A quad is smaller for the same gain than a
Yagi.)

Try this - it's for 10dbd gain (~10 times the signal strength - signal
doubles for each 3dbs of gain) at the center of the band (122 MHz):

122 MHz, 8 Elements, 10.575 dBd Estimated Gain

Warning: The specified Gain of 10 dBd is too Small. Gain should be
greater than 11.8 dBd.

41.4 Degrees Horizontal Beam Width

44.3 Degrees Vertical Beam Width

N/A Diameter, Non-Metalic Boom with Insulated Elements. N0 Boom
Correction applied.

Electrical Boom Length of 148.9" (12' 4-7/8"). Allow for overhang when
cutting boom to length.

00.125" (0-1/8") Driven Element Diameter.

00.125" (0-1/8") Parasitic Element Diameter.

Cumulative Spacing-Element Name-Element Length

Zero Reflector 47-7/16"
19-3/8" Driven Element 47-1/8"
26-5/8" Director1 44"
44" D2 43-11/16"
64-13/16" D3 43-5/16"
89" D4 42-15/16"
116-1/8" D5 42-9/16"
145-1/8" D6 42-5/16"

It also doesn't explain the driven element connection details.

You can use just about any driven element. The simplest one is to
offset the 2 halves (the elements are all total length, except the
driven element, each half of which is 1" longer than half the total
length. Drive these halves into the boom about 1/4" apart, centered
on the correct mounting point (IOW, 1 piece 1/8" in front of the
12-3/8" point, the other 1/8" behind that point). Connect the cable
center conductor to one half, shield to the other half.

Or you could do this:
http://k7mem.150m.com/Electronic_Notebook/antennas/yagi_vhf_feed.htm

Dress the cable along the boom to the balance point, at which point
you'll mount the mast, and dress the cable down the mast.

It probably won't be too great for transmitting, but it should beat
the pants off the rubber ducky for receiving.

On 24 Oct 2005 04:18:49 -0700, wrotF:

Hi

I liked the idea of the 'broom stick and coat hanger' antenna, but have
strugled on the practicalties. I went through the design he

http://k7mem.150m.com/Electronic_Not.../yagi_vhf.html

and ended up with a very large (about 48" square) antenna that still
complained it was to short and the elements too thin!

It also doesn't explain the driven element connection details.

Help please

Cheers
Kev
Take a look here.
http://k7mem.150m.com/Electronic_Notebook/antennas/yagi_vhf_feed.html#Page_Top