On 03/20/2014 09:12 PM, Jeff Liebermann wrote:
On Thu, 20 Mar 2014 00:06:50 -0700, Jon Danniken
wrote:

Hi all, I'm cooking up a discone antenna for receiving,

I don't want to discourage you, but if you're building something from
scratch, may I suggest you build an antenna that works better than a
discone. There was a discussion in this newsgroups recently that
drifted over to discones. To illustrate some of the problems, I ran
simulations of a Diamond D-130 discone (without the low frequency
vertical section) to illustrate how the antenna pattern is less than
ideal at the higher frequencies. See:
http://802.11junk.com/jeffl/antennas/Discone/index.html
An animated slide show is at:
http://802.11junk.com/jeffl/antennas/Discone/slides/discone-animated.html
The frequency is shown in the upper left. The gain in the lower
right. Note that the gain is still there, but at higher frequencies
is mostly pointing almost straight up.

Thanks Jeff, I had not considered a biconical, but it looks interesting.
The discone I am building is of a "spoke" variety, with the cone built
separate from the disk, so it would be simple to duplicate another cone
and invert it on top of the other cone.

Unless you're interested in listening to satellites and aircraft, I
recommend a biconcial instead. It's very much like the common "fan
dipole" used for multiband HF operation without requiring traps.

I do like aircraft, although I am starting to think that I might be
better off with a dedicated airband antenna (looking at j-poles right
now) along with a wideband antenna for general scanning.

Speaking of multiple antennas, I know that some antennas use multiple
elements tuned to different bands, but can you connect two antennas to
the same feedline? Like, say, a discone/biconical and a j-pole?

Unfortunately, my only biconical model that might be suitable seems to
have a problem. (I don't recall where I found the model). There are
some nasty nulls at several frequencies between 50 to 1000 MHz that
need to be fixed. I'll play with it some more when I have time.
http://802.11junk.com/jeffl/antennas/biconical/
I set the characteristic impedance to 75 ohms, which seems to work the
best. However, anything between 50 and 200 ohms should work. For 75
ohms, a 1:1 broadband balun (i.e. a transformer) is necessary. I'll
create an animated GIF file for the patterns at various frequencies
when I have more time.

I'll look forward to that, thanks!

Jon