It might help the new listener to do some rather simple tests.
Disconnect the antenna from your receiver and tune from the minimum
to maximum freq, noting any birdies or signals you receive.
Many(most?) receivers leak RF from the IF strip that can be received
weakly. Many receivers use 455KHZ so check 455KHZ, and the 2nd
(910KHz),
and the 3rd(1365) harmonics. Pay close attention to any MW or SW
stations you recieve. This test is best done with a 50 Ohm dummy load
on the anntena port, but it is still usefull to know what leaks you
have.
Many of these birdies will be below the noise floor when an antenna is
connected. But they are usefull to now about because they could
interferr
with a very weak signal and can be used as a quick check if you suspect

your receiver of having a problem.

Now connect your coaxial feedline, but disconnect the antenna.
Repeat the search. I will bet that many will be surpised to
find they can receive several MW outlets and oftenmore then a few
SW signals. This is a weak point for RFI to enter your system.

I found that the braid+foil coax had less ingress. Most braid and
foil coax is 75 ohm, but Belden does offer several 50 ohm versions.
I am using Belden 7807A. But I could detect no difference when using
Belden 1258AM 75 Ohm CATV cable.

John Doty's suggestion of placing the coax feedline underground
can help a lot. (http://www.anarc.org/naswa/badx/antennas/)
As can a 1:1 RF transformer before the coax enter the home.
(http://www.members.aol.com/WA1ION/nrants.pdf).
John Brynt's work on feedline ingress is very informative.
(www.dxing.info/equipment/coax_leadin_bryant.pdf) I found that
adding a ferrite torroid with ~20 turns of RG174 at each end helped
reduce the ingress a "lot". To the one MW station I receive with
no antenna.

My reasoning is that the best way to improve your RF signal is
to reduce the invading noise as much as posible. Beyond a reasonable
point, adding more wire doesn't help very much and may well hurt.
A longer wire picks up more signal and more noise. By optimising
our RF signal reception and minimising our RF noise pickup can
greatly improve our stions noise floor. And that set the lower
limit on what we can recieve.

"dxAce" mentioned that he has his 9:1 transformer elevated and
feed with his coax. In an RF quite location this is a very good
and workable option. And it worked much better then an unshielded
wire.

In "http://members.aol.com/DXerCapeCod/z_transformers.pdf",
John Bryant shows 4 basic ways to use a transformer.
I am using a variation on Circuit A. In between T-storms I think
it makes a big difference.

At the very least, users of the "Doty" system may wish to rethink
the inclusion of an unshielded vertical element. I suspect if more
ham and SWLS knew about Triax much more research would have been
made using this "odd" cable.

I have been given a ~150 spool of used, but good 75 Ohm Triax.
When time permits I plan on doing an feed line using Triax from
head to entry point. I suspect that the most gain will be in the
critical first few feet.

With coax, my standard QRM noise source, a noisy wall wort, would
add noise to the recieved signal when it was brought within a foot
or so of the coax. With Triax I could place the noise source against
the Triax with NO increase in noise. With the antenna disconnected
from the coax no increase in noise was noted. I think the noise is
travelling up the shield and getting into the antenna. Ferrite RFI
split beads helped reduce the ingress on the coax slightly. If one
could get enough ferrite it might choke the noise off completly. I
decided to test something else before scrounging up 50 more beads.

The next few weeks(months) will be spent building an outboard
IF/synch detector with SSB/CW capability. Furtehr antenna
experimentation will likely have to wait untill the fall.

Terry