I personally have some major power line interference nearby that even
makes noise on 144MHz. One day I'll go and track it down! (Not that the
power company will do anything!)

- You'll generally find that a horizontally polarised antenna will
receive less local noise than a vertical. Note I am not talking about
close noises sources (say less than 100 yards) but those up to a ground
wave distances away. Also keep in mind that the receiver you are using
may have some of its antenna "internal" in the form of a ferrite etc bar
that might alse be responding to other polarisations. (ie also try
rotating the radio)

- Many noise reduction techniques come out of specialized receiver
design. This of course doesnt help you!. DSP techiques for example
sampling much more than the usual AM/SSB bandwidths to apply digital
filters make a huge difference nowadays.

- It is also conceivable that what you perceive as noise may even be
fundamental overload of the receiver front end with strong signals. ie
the radios selectivity isnt good. There are various ways to combat that.
If the active loop antenna has a tuning adjustment this can make a huge
difference. The main help will be a directive antenna of some variety.

- I should point out that I have heard anecdotal evidence that a magloop
antenna receives less noise but I have never found out why. I dont know
if your active loop antenna is one of these. They would normally have a
manual adjustment for frequency - that I dont see...

- You can use phase addition/subtraction techniques to suppress
interference/noise from a single source. Probably not helpful in your
case but still worth mentioning.

- The active antenna may be helpful if it has a reception/radiation
pattern nulls that can be positioned to point at the noise source.

- Noise blanker and noise limiter circuits are useful if the receiver
has them. If I was into SWL nowadays I'd be using a DSP filter, possibly
by using a PC soundcard.

- If you run a remote antenna (eg an outside dipole) ensure that the
currents in the feedline are balanced. (Use a balun etc) This makes
errant signal pickup along the feedline length less of a problem. (Or
coax transmitting RF if it is connected to a transmitter)

- An RF ground is important for noise reduction. Given your top floor
location though this may be difficult. Not a good idea to use the
power/utility ground as that will be full of noise. Note that a balanced
antenna system removes the need for RF earthing as one side of it "works
against the other" rather than against a ground counterpoise.

- The best noise solution is to tackle the sources.

- Ham radio ops will generally be much weaker than broadcast stations.
An antenna (or 3) tuned for the job may even be a good investment.

Probably not all that helpful, sorry.

Cheers Bob


weatherall wrote:


I've only been involved in shortwave radio for several months, so I'd
be glad to hear any additional advice regarding interference.