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

In article .com,
wrote:

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.

Snip

As I posted in the other thread if you disconnect the antenna from the
coax then you need to put a 50 ohm resistor across the end otherwise the
coax will behave as an antenna. You sure will pick up stations if you
don't terminate it.

With the far end not grounded or terminated from the radio the outer
shield will pick up passing EM wave energy. That energy races up and
down the coax shield where the current induces a complementary voltage
on the center conductor. The result is a differential voltage at the
radio end and yes it works pretty darn good.

When you choke the coax you prevent the RF current on the outer shield.
It should be more effective to just terminate the far end with 50 ohms
than using a number of chokes space along the coax.

--
Telamon
Ventura, California

I first tried grounding each end but found the diagram in
http://www.members.aol.com/WA1ION/nrants.pdf to
be much more effective in reducing QRM in my location.
Putting the coax 18" underground helped a lot also.

I tried the choke presented in
http://www.dxing.info/equipment/coax_leadin_bryant.pdf
to be nearly as effective with each end of my coax grounded.

With both ends isolated from ground and the adition of the
inductance in/on/with the coax it completely removed all the
noise from our home. This is before I connect an antenna.

I had wondered about the QRN versus signal I was receiving
on the 20' run of wire from the ground mounted 9:1 transformer.
I wanted to mount the transformer 20' up where the horizontal
wire ended. I tried coax first and while it was better then having
the 9:1 on the ground, it wasn't "perfect". Since I had the triax I
decided to try it. I tried this once before but got rushed due to rain
movng in. This time I made sure to connect both ends as discribed.
I suspect the "magic" is the 1:1 isolation transformer that connects
the inner conductors of the triax to the coax that carries the signal
to
the house.

IF I could arrange for for my ~70' wire antenna to be a perfect 1:1
match to my 50 Ohm coax across the 100KHz through `30MHz I
suspect I would have less noise. The way cobbled this mess is the
result of trial and error. I am not offering it as the best, or even a
preferable setup. But for me, in this location it gives me the quitest,

as in reducing man made noise, conditions I have yet managed to
achieve. It was more then a bit of a hasssle to get permission from
the electrical instector and our insurance homeoffice to allow a "non
conforming" isnstallation. A strict following of the NEC would require
all grounds to be bonded. I didn't go to all this trouble just for the
fun of
being odd.

Several years ago someone in this group made the suggestion of
using a cathode follower at the wire to coax interface to force a 50
Ohm match. One of these days I plan on trying that now that I have
a usefull supply of Nuvistors and a diagram that I suspect will work.

I would prefer to live in a quiter (RF) location. But I can't retire
yet,
so I must live reasonably close to where I work. I am half afraid that
by the time I retire "broadband over powerline" will have made HF
useless.

For very weak signal HF reception, designers go to great lengths
to prevent any current flowing on the outside of the braid. It will be
coupled via inductance. Our astronomy friend's lab had 1:1 low loss
RF isolation transformers at the antenna, before the grounding bulk
head, and at the receiver. She demonstrated the increase in noise
when any of these where removed by just jumpering across from the
incoming braid to the outgoing braid. She also demonstrated that
audio isolation transformers were also a "must have". She used
balanced antennae so had to use a transformer to match the balanced
antenna to coax. She experimented with twinax but found it to produce
more complications then it was worth.

I was concerned about the loss and Ms C pointed out that HF reception
is almost always limited by the backgroudn RF noise. And that if you
get an increase in noise when you connect the antenna, you are almost
certain to have enough RF. Most "decent" radios have at least a ~30dB
lower noise floor then the atmospheric/comsic noise. So a few DB loss
is well worth the 10dB to 20dB reduction in interference a "proper"
installation can achieve.

(This is why a single passive transformer "power divider/coupler/
hybrid" will not impact 99% of our reception. Even with the additional
~3.25dB loss, the real world noise still dominates reception.)

Most of us don't need anywhere near this level of complexity.
The standard "Doty" "L" antenna is likely to be all that 90%
of us would need. The "nrants.pdf" will help 90% of the rest.
Few of us will have coax long enough for the issues addressed
in the "coax_leadin_bryant.pdf" to be a major concern. My system
may be viewed as overly complex, and of "flawed design", but it
is the best I can do right here and right now.

Terry

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I used 1:1 transformers at the antennas (random wire) and at the
receivers (two receiving locations in the house), similar to the
diagram @br
pre wrap=""a href="http://www.anarc.org/naswa/badx/antennas/"http://www.anarc.org/naswa/badx/antennas//a

I did this before seeing the above diagram. There is no direct ground at the antennas or at the receivers in my setup. Knocked out 99.9 % of the junk. Repeated this on an active antenna after the "shack box" to keep the downlead separated from the station receivers. This worked great as well. I am mostly interested in NDB DX but this worked good for SW as well in my situation. YMMV!



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