On 22 Feb 2005 06:38:53 -0800, wrote:

I'm tracking a high altitude balloon on 2m via a handheld scanner, and
in the past have used the standard rubber-duck antenna that the scanner
came with. However, reception isn't too great at times. What kind of
gain increase could I expect to see if I were to replace the current
rubber-duck antenna with a quarter-wave antenna (designed for 2m and
70cm)?

Thanks in advance for any insight!
Dave

Hi Dave,

Well, I see you got advice, but unrelated to the problem you offered.

The standard rubber duck and a quarterwave are going to have the same
failings: they both have the same response curve in space. Basically
they both are designed to work with transmitters located at right
angles to them. And if you stand in the conventional upright manner
of a biped, then those antennas are going to be vertical with the
favored direction lying along the horizon.

Now, if your balloon is tracking along the curve of the earth's limb,
some several hundred miles out, then this might work admirably (it
doesn't take all that much power to hear this distance when nothing is
in the way). However, as balloons go, they are generally above you
and your antenna is pointed toward them, or nearly so (certainly more
so than at the horizon). This is NOT a favored direction for
communication and antennas when they are small (and a rubber duck, a
quarterwave, or a halfwave easily meet that dismal prospect).

To obtain overhead coverage for communication (and this presumes that
the balloon antenna is also vertical - which means it will suffer from
the same geometry); then you need an antenna that is at least one
wavelength long, or longer (1¼ wavelength would be a nice way to go).

Long antennas have more sensitivity in the direction along their
length.

Now, if your tracking pastime includes all angles from the horizon to
directly above, then you need to consider designs that are more
isotropic (and none of the suggestions offered by everyone, including
me, come anywhere close).

73's
Richard Clark, KB7QHC

Richard Clark wrote:

The standard rubber duck and a quarterwave are going to have the same
failings: they both have the same response curve in space. Basically
they both are designed to work with transmitters located at right
angles to them. And if you stand in the conventional upright manner
of a biped, then those antennas are going to be vertical with the
favored direction lying along the horizon.

Richard,
Thanks for the advise. However, I thought 1/4 wave antennas were more
isotropic than 'most' other antennas... (see link below)

http://www.astrosurf.com/lombry/Radio/dipole-height.gif

What am I missing?

Basically, all I'm trying to do is increase the sensitivity of my
handheld scanner for the 2m range.

Thanks,
Dave

Dave, I have seen you get some good information and some bad
information. The 1/4 wave will give you better results over the short
rubber duck.
There will be not much difference in the pattern between the original
antenna and the 1/4 wave. There will be an improvement in signal level
by about 10 dB. One poster said that you were in trouble because your
antenna was vertical. I am willing to bet you can turn your head and
look upward with the scanner turning upward as well.

Your radio is designed for a 50 Ohm antenna so half or more of the
information given by "Reg Edwards" is bogus as well. I don't think he
tried to mislead you, but may not have experience in real life experiments.
The case of the radio is important only in how it capacitively couples
with your hand or body.
A short vertical has an impedance far below a normal quarter wave. That
means your idea matches better to your radio.
As a sort of ground wire, a 1/4 wavelength long counterpoise, (as
someone said a rat tail) will also help.



Dave wrote:
Richard Clark wrote:


The standard rubber duck and a quarterwave are going to have the same
failings: they both have the same response curve in space. Basically
they both are designed to work with transmitters located at right
angles to them. And if you stand in the conventional upright manner
of a biped, then those antennas are going to be vertical with the
favored direction lying along the horizon.


Richard,
Thanks for the advise. However, I thought 1/4 wave antennas were more
isotropic than 'most' other antennas... (see link below)

http://www.astrosurf.com/lombry/Radio/dipole-height.gif

What am I missing?

Basically, all I'm trying to do is increase the sensitivity of my
handheld scanner for the 2m range.

Thanks,
Dave

On 22 Feb 2005 18:10:53 -0800, "Dave" wrote:
Thanks for the advise. However, I thought 1/4 wave antennas were more
isotropic than 'most' other antennas... (see link below)

http://www.astrosurf.com/lombry/Radio/dipole-height.gif

What am I missing?

Hi Dave,

Umm, those are lobes for a HORIZONTAL dipole --- wrong polarization,
wrong size. Cross polarized signals come with beaucoup loss.

Basically, all I'm trying to do is increase the sensitivity of my
handheld scanner for the 2m range.

If the balloon is overhead (or off of overhead by ±15°) you are 10dB
down at best, or sitting in a deep null (deaf city). To compare that
30° cone of silence: Hold your hand directly overhead, spread out
your fingers and thumb, the distance between little finger and thumb
tips spans 13 to 15 degrees (half that cone).

Is your balloon in that cone? Worst possible place for a short
vertical antenna to hear; and for a balloon with a short vertical, you
are in the worst place for it to shout down to you. This is a deadly
combination that puts your normal signal at -20dB (or worse).

A KW linear may overcome this sensitivity problem however.

73's
Richard Clark, KB7QHC

Richard Clark wrote:
On 22 Feb 2005 18:10:53 -0800, "Dave" wrote:
Thanks for the advise. However, I thought 1/4 wave antennas were
more
isotropic than 'most' other antennas... (see link below)

http://www.astrosurf.com/lombry/Radio/dipole-height.gif

What am I missing?

Hi Dave,

Umm, those are lobes for a HORIZONTAL dipole --- wrong polarization,
wrong size. Cross polarized signals come with beaucoup loss.

Are there any online sources that show vertical whip antenna take-off
angles vs. antenna length (as a function of wavelength)?

If the balloon is overhead (or off of overhead by =B115=B0) you are
10dB
down at best, or sitting in a deep null (deaf city). To compare that
30=B0 cone of silence: Hold your hand directly overhead, spread out
your fingers and thumb, the distance between little finger and thumb
tips spans 13 to 15 degrees (half that cone).

Is your balloon in that cone? Worst possible place for a short
vertical antenna to hear; and for a balloon with a short vertical,
you
are in the worst place for it to shout down to you. This is a deadly
combination that puts your normal signal at -20dB (or worse).

I don't know about "deadly"... atleast not in this scenario. :-)

Keeping the transmitter and reciever constant, what would you recommend
for the transmitting and receiving antennas in this case?

Thanks,
Dave

On 23 Feb 2005 08:11:47 -0800, "Dave" wrote:

Are there any online sources that show vertical whip antenna take-off
angles vs. antenna length (as a function of wavelength)?

Hi Dave,

Go to:
http://www.eznec.com/
and research to your heart's content with the simple designs (or make
your own).

Keeping the transmitter and reciever constant, what would you recommend
for the transmitting and receiving antennas in this case?

Inverted F comes to mind, but is not the total solution. Then there
is the quadrifilar helix antenna.
Visit:
http://home.iag.net/~w2du/Reflection...lixAntenna.pdf

73's
Richard Clark, KB7QHC

Richard Clark wrote:
On 23 Feb 2005 08:11:47 -0800, "Dave" wrote:

Are there any online sources that show vertical whip antenna
take-off
angles vs. antenna length (as a function of wavelength)?

Hi Dave,

Go to:
http://www.eznec.com/
and research to your heart's content with the simple designs (or make
your own).

Done and done... nice program! I'm hoping I entered the correct values
for everything. Do the patterns listed below look correct? I assumed
things like wire diameter (I used 2mm) didn't affect the output
significantly... although I did notice some things like the number of
segments did affect the output if I decreased them (I used 10 for these
cases).

(filename = length in wavelengths):

http://www.geocities.com/achilles03/eighth.gif
http://www.geocities.com/achilles03/quarter.gif
http://www.geocities.com/achilles03/half.gif
http://www.geocities.com/achilles03/5eighths.gif
http://www.geocities.com/achilles03/1wave.gif
http://www.geocities.com/achilles03/1point25wave.gif
http://www.geocities.com/achilles03/2.gif

Do those look correct?

Thanks in advance!
Dave

On 23 Feb 2005 09:53:05 -0800, "Dave" wrote:

Done and done... nice program! I'm hoping I entered the correct values
for everything. Do the patterns listed below look correct?

Hi Dave,

Yes, however, you will notice there is still a cone of silence above
any of these even if the preferred angle is now higher towards a
balloon.

I assumed
things like wire diameter (I used 2mm) didn't affect the output
significantly... although I did notice some things like the number of
segments did affect the output if I decreased them (I used 10 for these
cases).

Not so much that any change will fill in the cone.


73's
Richard Clark, KB7QHC

Dave wrote:
Are there any online sources that show vertical whip antenna take-off
angles vs. antenna length (as a function of wavelength)?

There's a free demo version of an antenna analysis program,
EZNEC, at http://www.eznec.com It will answer your questions.
--
73, Cecil http://www.qsl.net/w5dxp

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