To ground or not; attic antenna: any suggestions?
- I was wondering if anyone has any advise re grounding the receiver.
I've read conflicting reports. One writer (H. Helms) advises against
it, says it will worsen reception. My unit is on the 2nd floor, and if
I ground it I will have to run at least 25+ feet of wire to the
outside. I can't use my cold water pipe, seems builders in my area now
use plastic to connect water to the house.
My other question is re attic antennas. Because of the absence of
trees in my yard, an outside antenna isn't feasable, and my wife
refuses to let me plant a telephone pole for this purpose. An attic
antenna seems my best bet. With all the products out there, are there
any which seem to work better than others?
- Hi Octavio,
I won't claim to be an expert on grounding although I have some theoretical
knowledge and practical experience. Grounding at radio frequencies is
something of a 'black art', the higher the frequency, the blacker it gets!
Grounding for direct or power line frequency alternating current is a
different matter - that's generally known as the safety ground and is pretty
straight forward. Grounding at audio frequencies lies somewhere between the
two in complexity and 'art'.
Your DX-394 has a dc ground connection from the chassis to the power line
neutral via R401 (1.8 MegOhms) to bleed off static electricity. The neutral
is connected to the power line ground conductors at the power panel and the
panel is connected to a ground rod. The high resistance makes this a poor RF
ground and, indeed, the receiver's power transformer has a shield between
the primary and secondary windings to make it difficult for RF conduction
between the power line and the radio.
Assuming your house wiring carries a separate ground conductor, you could
experiment by running a (heavy) conductor from the chassis screw to the
power outlet ground conductor (the U-ground in this part of the world). This
would provide the 'safety' ground that is not required of this appliance by
code and will have some kind of RF ground effect. What the effect will be is
quite unpredictable because the dozens of feet of wiring from the outlet to
the earth ground will have inductance and increasing reactance with
increasing frequency. So the radio will be sitting above earth ground but is
probably closer to it with, than without. You may experience an increased
signal strength but also increased interference strength from household
appliances and power line noise. The key question is whether the
signal-to-noise ratio is better one way or the other.
Your cold water pipe, if it is metallic down to the outside connection, may
also provide a better RF ground than none at all and you may have different
results at different frequencies when using it alone, the power line ground
alone, or the two together. Experiment! All those conductors may provide a
counterpoise for the antenna that could be beneficial or might act as an
antenna extension because of the reactance. An antenna tuner could also have
a marked effect on reception quality and its settings could be quite
different depending on the selection of ground.
As to attic antennas, again no expert. For lots of antenna advice, I'd
recommend you join, browse and post on the incredibly rich collection at
http://groups.yahoo.com/group/Shortwave-SWL-Antenna/ . In general, I'd say
just get as much wire as you can running in whatever direction without
doubling back on itself, and as high as possible. If the leadin to the radio
is well removed from the house wiring, no need for shielded coaxial cable,
but if you have a computer or CRT display that is causing interference, then
use the co-ax feedline and a balun at the feed point of the antenna.
73, Tom VE3MEO
----- Original Message -----
From: "Octavio" <odlr@...>
Sent: Sunday, April 03, 2005 5:35 PM
Subject: [RADIOSHACKDX394] To ground or not; attic antenna: any suggestions?
> I was wondering if anyone has any advise re grounding the receiver.
> I've read conflicting reports. One writer (H. Helms) advises against
> it, says it will worsen reception. My unit is on the 2nd floor, and if
> I ground it I will have to run at least 25+ feet of wire to the
> outside. I can't use my cold water pipe, seems builders in my area now
> use plastic to connect water to the house.
> My other question is re attic antennas. Because of the absence of
> trees in my yard, an outside antenna isn't feasable, and my wife
> refuses to let me plant a telephone pole for this purpose. An attic
> antenna seems my best bet. With all the products out there, are there
> any which seem to work better than others?
> Trim all but the core of this message when replying to keep replies from
> mushrooming in size.
> For archives of prior messages, files, links, photos, user survey, members
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