On 4/21/2012 7:09 PM, christofire wrote:
"Jeff wrote in message
...
For some irrational reason, that probably defies logical
justification, I've decided to setup my PCR1000 receiver as an
internet accessible receiver. There are about 7 programs available to
do this, so I don't expect software to be a problem. The receiver
will eventually be moved to a mountain top repeater site, which
unfortunately does not have much room for an antenna. The receiver
will tune from 0.1 to 1300Mhz. I don't wanna deal with an antenna
tuners or switches.

Is there an antenna or combination of antennas that are suitable for
such a wide tuning range and that is small enough to fit in a limited
rooftop area?

I was thinking of a monstrous vertical biconical dipole for HF, a
diplexer, and a discone for VHF/UHF/etc. For Field Day, I once made a
biconical out of two trash can lids, with holes for the wires around
the perimeter. It worked amazingly well but I never bothered to make
measurements.
http://en.wikipedia.org/wiki/Biconical_antenna

Can anyone suggest something better, smaller, less ugly, or more
practical?


--
Jeff Liebermann
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558


If it's always receiving and you can make an amplifier with high input
impedance throughout the frequency range, then you could use a short dipole
'doublet' - drawing insignificant current from the antenna would make its
very low radiation resistance less of a concern. Its directivity gain would
be almost constant because its radiation pattern comes from its (fixed)
axial symmetry, but a wavelength^2 factor would apply to its effective
aperture area. It probably wouldn't be easy to design a single high-input-Z
amplifier over that frequency range, but there might be scope for dividing
the range and combining the _outputs_ of several amplifiers, each fed by
their own doublet.

Would you need any kind of 'monstrous' antenna if the requirement was always
receiving? I could see that you might want something large to get the
radiation resistance up if you were transmitting from it, but for receiving
a high-Z amplifier becomes easier at lower frequencies. I vaguely recall
that some of the companies that have offered professional 'radiomonitoring'
(i.e. evesdropping) equipment, such as R&S, have used combinations of
different types of element for different parts of the wide frequency band,
but never anything monstrous.

Chris



The only comment I would have is capture area.

tom
K0TAR

"Jeff Liebermann" wrote in message
...

snippage

http://en.wikipedia.org/wiki/Biconical_antenna

Can anyone suggest something better, smaller, less ugly, or more
practical?


--
Jeff Liebermann
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558

Nothing small is going to be broadbanded. Roy, W7EL, a contributor here,
offered his wisdom on antennas and it's been echoed by others, I'm sure.

Small
Broadband Pick any two.
Efficient


Words to live by.

"Sal"

On Sat, 21 Apr 2012 22:59:10 -0700, "Sal" wrote:

Nothing small is going to be broadbanded. Roy, W7EL, a contributor here,
offered his wisdom on antennas and it's been echoed by others, I'm sure.

Small
Broadband Pick any two.
Efficient

Words to live by.
"Sal"

Thats a good rule of thumb. However, this is a receive only antenna,
which does not need to be perfectly matched and can be fairly
inefficient and low gain. Even so, I don't think the radiation
efficiency is going to be that horrible. They're mostly due to
conduction losses (at HF) and dielectric loss (at UHF). For the high
currents required for transmitting, these losses are fairly large for
a short broadband antenna. However, in a high impedance receive only
antenna, the conductivity loses are a much smaller part of the antenna
impedance than in the transmit antenna.

It's much the same in the discone. The antenna VSWR averages about
3:1 over about 6 octaves of frequency. With such a high VSWR, it's
not a suitable transmit antenna. However, for receive, it works
tolerably well.

--
Jeff Liebermann
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558

"Jeff Liebermann" wrote in message
...
On Sat, 21 Apr 2012 22:59:10 -0700, "Sal" wrote:

Nothing small is going to be broadbanded. Roy, W7EL, a contributor here,
offered his wisdom on antennas and it's been echoed by others, I'm sure.

Small
Broadband Pick any two.
Efficient

Words to live by.
"Sal"

Thats a good rule of thumb. However, this is a receive only antenna,
which does not need to be perfectly matched and can be fairly
inefficient and low gain.

Yup. As long as what you're giving up has a worthwhile advantage to
something else, go for it.