I have a new Icom R-75 and have some newbie antenna questions. I have a
random length wire in the length my attic, and the receiver is located
in the basement.

The R-75 has a two antenna inputs. One coax, and one for a wire with a
ground input. I attached my random wire to the wire antenna input and
it seems to work, but there is a high level of noise on everything,
even WWV stations. Connecting the ground to my house's ground doesn't
make any difference.

I'd think the problem is that I have an antenna that has to snake
around the house, near electrical wires, computers, lights, etc. that
are causing interference.

I think a solution is to connect the random wire to shielded coax and
run that from the attic to the basement and hopefully that will reduce
interference. I think I need to use an impedance matcher to connect the
wire to the coax, like this one:
http://www.shortwavestore.com/sws/pr...5&cat=0&page=1

Does this all sound right, or is there a better way to do this? With
the random wire connected directly to the receiver, I can pick up a
lot, but it's very noisy.

Thanks!

On 28 Dec 2005 09:42:45 -0800, "Ben Sinclair"
wrote:

I think a solution is to connect the random wire to shielded coax and
run that from the attic to the basement and hopefully that will reduce
interference.

Hi Ben,

Sounds like the right answer, short of putting your antenna outside
(with the same shielded coax).

I think I need to use an impedance matcher to connect the
wire to the coax, like this one:
http://www.shortwavestore.com/sws/pr...5&cat=0&page=1

Will do nothing for noise that you haven't already accomplished with
the coax. Further, it says nothing of what's inside, nor offers any
specifications - just marketing snake-oil.

You could also choose to "choke" the end of the coax by using ferrites
in any of several forms. Research W2DU style BalUns on google and pay
attention to the theory of their operation.

Also, obtaining a very cheap ham 3 knob antenna tuner (without meters)
will perform all the matching you could wish for AND it will eliminate
the most common form of desensing for SWL (front end overload from out
of band transmitters - your friendly neighborhood AM station being
most often the culprit).

73's
Richard Clark, KB7QHC

Ben: Welcome to the world of SWL'ing in the new Century...

It sometimes seems the whole world is a huge RF noise generator, and
the more urban your listening location, the worse off you're likely to
be. Too, just wait 'till 'BPL' (broadband over power lines) becomes a
reality...

Known RF noise generators commonly found in the home:

Light Dimmers
Computers
Televisions
Fish Tank Heaters
Electric Blankets
Microwave Ovens
Cell phones

And if you're in a suburban neighborhood, these noise sources can be
coming from any (or all) of your neighbors homes.

If you're attempting to hear the microwatt station from Micronesia,
you'll need a well considered antenna system to improve the signal
(good) - to - noise (bad) ratio.

Generally this means an antenna that is erected as high as possible,
and at right angles to known noise sources.

An antenna tuner attempts to 'transform' the impedance of a random
length wire to 50 ohms; useful in *transmitting* applications, but of
little or no use in reducing electrical noise interference to a
receiver.

A better bet would be a device that captures the same noise as your
main receive antenna, then 'compares' this common noise signal and
cancels it out. Search for the 'Timewave ANC-4 RF Filter', a somewhat
fussy, but very effective "locally generated noise eliminator".

Good Luck.

MW

Thanks for the replies! Yesterday I connected my random wire to the
center of my coax and strung it down to the basement. It seems to work,
but there is still some noise. I don't really have anything to compare
it to though.

I'll research the noise filters and see what I can find. Is the W2DU
balun something I should still consider? The "wire man" has several and
they are fairly inexpensive, so I could at least try one.

I don't know a lot about how propagation works, but does it seem normal
that In the early evening I could hear WWV on 10, but not 2.5, 5, or
any other frequency, then late at night I couldn't even hear it on 10?
This morning it was again coming in loud and clear on 10, but not any
other frequency.

From the NIST WWV FAQ:

"Multiple frequencies are used because shortwave propagation varies
with many factors, including time of year, time of day, geographical
location, solar and geomagnetic activity, weather conditions, and
antenna type and configuration. In general, the lower frequencies of
2.5 and 5 MHz are best during nighttime hours, the higher frequencies
of 15 and 20 MHz are better during daytime hours, and 5 and 10 MHz are
probably the best compromises overall. The 5, 10, and 15 MHz
transmissions are at higher power than the other frequencies."

MW

On 29 Dec 2005 08:17:52 -0800, "Ben Sinclair"
wrote:
I'll research the noise filters and see what I can find.

Hi Ben,

They are nice toys suitable to sources of noise that are not easy to
fix, like a power pole arcing (or a neighbor's electric fence around
the horse pasture). Still, if you simply visit the neighbor and offer
to fix his problem (grass is too high, or a wire is drooping); or call
the utility (it is in their interest to fix their noisy poles); then
you've not only saved money, you don't have that noise anymore.

Is the W2DU balun something I should still consider?

Like I said, research the theory behind it. You don't actually have
to buy anything if you coiled the far end of the coax - research the
properties of a transmission choke. Choking your transmission line
can push your home's contribution of noise down considerably.

I don't know a lot about how propagation works, but does it seem normal
that In the early evening I could hear WWV on 10, but not 2.5, 5, or
any other frequency, then late at night I couldn't even hear it on 10?
This morning it was again coming in loud and clear on 10, but not any
other frequency.

This is one of the hallmarks of listening to WWV, WWVH, or CHU or any
number of time stations or beacons (CHU, located 15 km southwest of
Ottawa, transmits on 3330 kHz, 7335 kHz, and 14670 kHz). They give
you an indication of how well propagation is working from those
points, to you, on those bands at any particular time of day (which is
a significant factor). They are always there, and always at a known
power level. For example, this makes it quite simple to determine
that if you cannot hear WWV at 2.5MHz with 1KW, you are not going to
hear anyone else in Colorado on 2.5MHz unless they have substantially
more power. On the other hand, there is nothing in that region to
listen to anyway given this is an extinct marine band, and the seas
around Fort Collins evaporated millions of years ago.

73's
Richard Clark, KB7QHC