On 9 Jul 2006 06:33:19 -0700, "Steve" wrote:


David wrote:
On 8 Jul 2006 20:22:18 -0700, "Steve" wrote:

The last couple of nights I've heard a very faint broadcast station on
4050, but I don't see anything listed for that frequency on the EIBI
schedule. Anyone happen to know what it is? I heard it at around 01:30
or so.

Steve

3rd harmonic 1350?

wh..?

THE ULTIMATE CHALLENGE:
DXING MEDIUM WAVE HARMONICS
By Don Moore
This article was originally published in The Journal of the North
American Shortwave Association.


If you've been reading NASWA very long, you've noticed by now that
shortwave broadcasters aren't the only broadcast stations using the
shortwave bands. On occasion loggings of mediumwave (AM) "harmonics"
creep in. But, although some mediumwave stations broadcast on
shortwave at times, usually when they do they don't even know it! And
that's just part of what makes DXing mediumwave harmonics such a
challenge.


WHAT ARE HARMONICS?
All radio transmitters naturally put out harmonics, which are
multiples of the fundamental frequency. For example, a station on 1400
kHz will transmit harmonics on 2800, 4200, 5600, etc. Twice the
fundamental frequency, e.g. 2800 khz, is called the second harmonic;
three times it, e.g. 4200 khz, is called the third harmonic, etc. The
first harmonic, or one times the fundamental frequency, is the
fundamental itself. Harmonics should not be confused with images,
which are generated internally in a receiver, and are usually received
plus or minus 910 kHz or 1000 kHz of a frequency, depending on the
receiver, or receiver mixing products that cause exceptionally strong
stations to appear where they don't belong. Harmonics are produced at
the transmitter, not the receiver.
Harmonics may seem like a free way for a small AM station to become an
international broadcaster, but AM stations don't want to intentionally
transmit harmonics, as any power that goes into a harmonic frequency
is not being used for their fundamental frequency, which means a less
powerful signal for their main audience. In addition, harmonic
transmissions are prohibited by law as these unintentional broadcasts
on higher frequencies may interfere with other stations which are
licensed to use those frequencies. To prevent these problems, station
engineers suppress harmonics below a maximum level allowed by the FCC
or their nation's equivalent agency, although enforcement may vary
(especially in Third World countries). But, not all stations have
competent technical help watching over the equipment, or even if they
do, mistakes can happen. Sometimes something gets maladjusted or
whatever and suddenly there is maybe fifty or a hundred watts going
into a harmonic instead of half a watt or a watt. Usually the problem
is so small that it won't be noticed until the engineer does a regular
check-up on the transmitter, or someone hears the harmonic and tells
the station about it. In the meantime, it's happy harmonic hunting for
DXers!