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

On 4/21/2012 5:23 PM, Jeff Liebermann wrote:
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?

One thing not to forget is there are relatively inexpensive
duplexers/triplexers/etc. from the likes of Comet and others. Or roll
your own.

I know that doesn't help much on the low end of things but means a
couple discones on the mid and upper will do well.

And yes there will be some small to medium gaps because of the device.

tom
K0TAR

On Sat, 21 Apr 2012 17:33:54 -0500, tom wrote:

On 4/21/2012 5:23 PM, Jeff Liebermann wrote:
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?

One thing not to forget is there are relatively inexpensive
duplexers/triplexers/etc. from the likes of Comet and others. Or roll
your own.

I like to make my own diplexer/triplexer boxes. In this case, only a
diplexer is needed. The Radio Shack discone antenna will (allegedly)
work from 30-1300MHz.
http://www.radioshack.com/graphics/uc/rsk/Support/ProductManuals/2000043_PM_EN.pdf
Below 30MHz is the real problem. Also, none of the commercial
diplexers I could find had a 30MHz cutoff frequency. Looks like I get
to build something.

I know that doesn't help much on the low end of things but means a
couple discones on the mid and upper will do well.

I've compared the performance of discones and biconical antennas.
Biconicals are better because the radiation pattern is towards the
horizon, instead of towards the sky. It also has about 1-2dB more
gain. However, I'm not in the mood for building yet another
mechanical marvel, and will probably use the discone.

And yes there will be some small to medium gaps because of the device.

I can probably ignore the TV bands (54 to 700MHz) but I want most
everything else.

Thanks much.

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

On 4/21/2012 10:23 PM, Jeff Liebermann wrote:

I like to make my own diplexer/triplexer boxes. In this case, only a
diplexer is needed. The Radio Shack discone antenna will (allegedly)
work from 30-1300MHz.
http://www.radioshack.com/graphics/uc/rsk/Support/ProductManuals/2000043_PM_EN.pdf
Below 30MHz is the real problem. Also, none of the commercial
diplexers I could find had a 30MHz cutoff frequency. Looks like I get
to build something.


I have one and have never bothered to check it because I've never
actually used it. It's one of my backup backup antennas.

Time to test it.

tom
K0TAR

On Sat, 21 Apr 2012 20:23:04 -0700, Jeff Liebermann
wrote:

gain. However, I'm not in the mood for building yet another
mechanical marvel, and will probably use the discone.


discones are fine, but like to pick up static.

w.

In message , Helmut Wabnig
writes
On Sat, 21 Apr 2012 20:23:04 -0700, Jeff Liebermann
wrote:

gain. However, I'm not in the mood for building yet another
mechanical marvel, and will probably use the discone.


discones are fine, but like to pick up static.

Any more than any other vertical antenna (or even ANY antenna)?
--
Ian

On Sun, 22 Apr 2012 10:34:23 +0200, Helmut Wabnig [email protected] ---
-.dotat wrote:

On Sat, 21 Apr 2012 20:23:04 -0700, Jeff Liebermann
wrote:

gain. However, I'm not in the mood for building yet another
mechanical marvel, and will probably use the discone.

discones are fine, but like to pick up static.
w.

Static electricity or radio static noise? Static electricity should
not be a problem as the PCR1000 probably has a 100K resistor across
the antenna connector. This is standard on most radios. If not, I
can easily add one to bleed off any excess charge.

At VHF frequencies, any generated radio static should not be a
problem. The building is high enough that it might end up inside a
thunder cloud, where precipitation static might cause trouble.
Besides, there's not enough dielectric material on the discone to
build up much of a charge. If the humidity is low enough and the wind
speed high enough to create arcing, I'll have much bigger problems
than to deal with than a little static noise.

However, there may be another problem. We try to use grounded and low
impedance antennas on mountaintop sites in order to reduce induced
currents from nearby lightning hits. Both my proposed antennas are
ungrounded and/or fairly high impedance. Oh-oh.


--
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
...
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

On Sun, 22 Apr 2012 01:09:26 +0100, "christofire"
wrote:

If it's always receiving and you can make an amplifier with high input
impedance throughout the frequency range,

Good idea. I've done that before with a long wire (about 200ft)
feeding a 3:1 turns ratio torrid xformer. It was a bit lossy at low
frequencies, but that doesn't matter because the atmospheric noise
level is so high, that everything is buried under the noise anyway.

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.

A doublet may not work at a commercial mountain top site. Doublets
require twinlead or ladder line down to the radio. The feed line will
need to either go through about 3 meters of pipe, or through a coax
bulkhead feedthrough. I could probably install the balun before it
enters the pipe or building, but that might not be practical.

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.

I don't have much in the way of expectations in the way of antenna
gain. If it receives anything, I'm happy.

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.

Do I really need an amplifier just to do an impedance downconversion?
I would think a 3:1 xformer would be adequate.

Actually, it's quite easy to build a high input impedance RF
amplifier. I've done it many times. A source follower will do the
trick. So will a grounded gate amplifier. Better yet, a dual gate
MOSFET amplifier or some kind of cascode amplifier derangement. All
of them can be configured for a high input impedance and 50 ohms
output.

However, performance may not be so wonderful. It's a tradeoff between
gain, noise figure, and bandwidth. There's no easy way to make an
amplifier that is ideal for all three. Pick any two. Actually, it's
worse because blocking, overload, and dynamic range are also a factor.
Putting a broadband amplifier on a mountain top full of broadcast
stations and commercial radios is not a great idea. I'll probably end
up with a transformer followed by an attenuator.

Would you need any kind of 'monstrous' antenna if the requirement was always
receiving?

Well, no... but bigger does tend to be better. I could probably use a
base loaded whip, tolerate the mismatch losses, and live with the
general loss of gain at the low end of HF. The site has an 80ft
tower, where I think (not sure) I can install two outriggers, egg
insulators, and build some kind of vertical wire antenna. Various
configurations are possible, but the monstrosity I was considering is
an HF biconical.
http://www.google.com/patents?id=LJ9pAAAAEBAJ
What I like about it is that it's 75 ohms over at least one octave of
bandwidth. However, as each element approaches 1/2 wave at some
frequencies, the impedance goes sky high. The trick is to put those
frequencies in areas where I don't care to listen.

I could also fit a "fan" type dipole antenna or a wire simulation of a
"bow-tie" antenna. However, what I was hoping for was some manner of
fairly short antenna (about 3-6 meters), with a fixed LC network that
yields a fair approximation of 50 ohms. 2-30MHz, without tuning. I've
been playing with such a matching network in 4NEC2, but getting
nowhere. Surely, such a thing exists.

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.

True, but for there reasons I previously mumbled, I don't think an RF
amp on an RF polluted mountain top is a great idea. Besides,
additional RF gain at the low end of the HF spectrum is useless
because of the high atmospheric noise levels. All the gain does is
lower the receiver dynamic range.

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.

Yes, but I suspect they also used antenna tuners to deal with the
mismatch. I could do the same thing, but don't have an easy way to
control the antenna tuner, especially since the receiver doesn't have
the concept of "bands".

Thanks much.

--
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
...

snip

... However, what I was hoping for was some manner of
fairly short antenna (about 3-6 meters), with a fixed LC network that
yields a fair approximation of 50 ohms. 2-30MHz, without tuning. I've
been playing with such a matching network in 4NEC2, but getting
nowhere. Surely, such a thing exists.

I can address that but, alas, not with encouragement.

When I was working, my domain included Navy shipboard antennas, including
broadbanded HF transmit antennas, fed by banks of four or eight couplers
through 50-ohm Heliax. (Yes, I know your application is receive-only.
Please stick around.)

When a ship had the usual three antennas, they covered the range of 2-6,
4-12 and 10-30. At each one's feed point, a fixed, passive matching network
using two, three or four reactive components brought the antenna inside the
3:1 circle on a Smith chart. (We didn't adjust them, we just periodically
inspected and tested them. Why, Ye-es-s-s, we usually found loose, missing
or corroded hardware on the mast. Why do you think we climbed up there?)

I mention this because the Navy tried to get better by doing HF transmit
using only two broadbanded antennas (2-9 and 8-30) but had to relax the spec
to a 4:1 SWR. It worked on a few ships, but the radiomen often encountered
freqs that were difficult or impossible to tune, so they'd revert to a whip
antenna with a base coupler, like the Harris RF-601.

A good passive matching network for 2-30 seems unlikely. The Navy would
have bought them by now if "surely such a thing exists."

"Sal"