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

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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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