Operating Practices on 136kHz
Since UK amateurs gained access to the 136kHz band in 1998 it has developed
a character quite different from any other amateur band. Furthermore,
since those first few days there has been an enormous change in operating
practices as stations have slowly improved their stations. It is
hard to believe that stations which were barely audible at this QTH as
they had their first tentative QSOs are now 599+ and able to have QSOs
with relative ease.
The 136kHz band is significantly different from the other amateur bands
in a number of respects.
It is the narrowest band of any, and CW is the norm.
Antennas are almost always very small with respect to wavelength.
A relatively high output power is required to produce the legal limit of
Propagation on 136kHz is mainly groundwave during the day with some skywave
propagation at night. Achievable range depends very much on the transmitting
stations capabilities, with the better equipped stations now achieving
several hundred kilometers in daytime and up to 1000km at night.
At many locations the limiting factor is locally generated electrical noise.
Unfortunately the lf spectrum is rich in all sorts of interference sources:
As well as these local sources, other externals sources include:
TV timebase interference - at multiples of 15.625kHz, none of which fall
in the 136 band. Some TVs are better than others - see my
Switched mode power supplies - as used in TVs, VCRs, computers and all
sorts of domestic appliances. These frequently operate in the 50-100kHz
range with rough harmonics in the 136 band.
Low energy light bulbs or compact fluorescents. These operate in
the lf range and can be heard as rough rasping unstable interference drifting
across the band. Some makes appear worse than others.
QRN from electrical appliances such as drills and motors.
Other digital generated signals and carriers. At this QTH there is
frequently a strong carrier on 137.4kHz which appears to be locally generated.
Electrical storms. Thunder static during the summer can make the
Other atmospheric noise. This is much higher during darkness hours.
Loran. Operating on 100kHz, the Loran navigational chains have residual
radiation extending up to 136kHz and beyond. Although the transmitters
are operating within their specifications this interference causes reception
problems for users of the band. The transmitter at Lessay in France
causes problems especially for amateurs on the south coast of England.
Possible Future Problems
Increasing use is being made of the LF spectrum for various mains
signalling techniques and data transmission. One such system under
development by Norweb has recently been dropped, officially because it
was not financially viable. Interference has already been caused to 136
operation by high speed data carried by telephone networks, being radiated
due to incorrect screening practices. Of current concern is the ADSL
system of carrying internet traffic over normal twisted pair telephone
lines, which is somewhat slowly being introduced. This uses frequencies
up to 1.5MHz. In its design stages potential interfence to amateur
traffic was considered, but at that time 136 didn't exist so was not a
consideration. It is not yet known if there will be serious interference
problems from this system, but in due course it may be wide spread.
Representations have been made by the RSGB EMC committee to the various
It is likely that noise from these type of systems will increase in
time, as the commercial advantages of high speed internet and other data
links seem to outweigh many other considerations.
It should be remembered that the amateur allocation is fairly close to
the long wave broadcasting band and crossmodulation effects from these
high power transmitters must be considered when designing amateur receivers.
There are a number of strong commercial stations very close to the band,
and intermodulation products from these cause problems for some amateurs.
The use of two or more tuned circuits at the front end can do a lot to
mimimise these problems. Unfortunately many commercial modern receivers
have broad band input stages.
Most of the current activity on the band is on conventional CW, although
speed tends to be slower than is normal on the other bands since this aids
copy in noisy conditions. There is also some activity on digital modes,
includin slow CW and various forms of BPSK. Because some stations
are crystal controlled, and also because of very narrow antenna bandwidths,
split frequency operation is often used (not a problem with only 2.1kHz
to tune!). Increasingly more stations however now have full transceive
capability, and there are one or two stations who operate with full break-in
(QSK). In the early days stations used to beacon for long periods
- today the level of activity has made this largely unnecessary, and at
levels of high activity antisocial.
There is activity at most times, but peak activity tends to be during the
daytime at weekends and early to mid morning during the week. Sunday
mornings in particular are usually quite busy with the band sometimes sounding
like one of the HF bands. During the summer the noise level is at
a minimum for a couple of hours after dawn and this period was used to
good effect in 1998. In the winter months noise levels are higher
and it is not until 0900 or so that the noise level starts to drop.
The following countries currently have permits for 136 and have been worked
from the UK: G, EI, ON, PA0, HB9, OH, OK, LX, DL, OZ, I, F, SM.
Several other countries are licensed or shortly will be the band is destined
to become a Europe wide allocation. There is currently much activity
from G, ON and PA0. A few stations in VE1 and the USA currently have experimental
licences and it is hoped in due course they will permit full access to