HOW TO CONVERT AM
BROADCAST RADIOS TO RECEIVE ONE SIXTY METERS.
If you don't have
a general coverage receiver you can convert an ordinary am wireless. As
most
broadcast sets cover
up to about 1630khz it is possible in most cases to tweak them upto above
1.8mhz.
With a signal generator
and other service equipment the job is easy but I will explain how to do
it with
minimal gear.You
will need two radios, one to be converted and the other to use as a signal
source. Try to
pick a nice sensitive
one for the conversion to one sixty, as am radios can be picked up for
a few dollars
at junk sales these
days it should not be to hard to find a suitable one in fact its often
possible to obtain at
very reasonable
cost a general coverage set that covers the band, but most miss out on
the lower Short
wave portion of
the spectrum. I have not had much luck converting a set from 2.3mhz down
to 1.8mhz.
Back to the instructions,
first tune the signal source set to about 1400khz this will, assuming a
455khzIF
stage as in 99%
of sets put the local oscillator on about 1855khz which can be used as
a local signal in the
set to be converted
identify the local oscillator coil and slug, its usually painted red and
when turned
it changes the stations,
what you want to do is adjust this so all the am stations move down the
dial. Put
the two radios near
each other and tune the to be converted set to the top of its dial ie the
hf end, adjust
the coil until you
come across the carrier from the local osc of the set being used as a signal
source. In
most cases this
can be achieved without to much trouble. The next step is to tune up all
the rf and ant
stages so they peak
on one sixty this can be done by listening to the band noise and and adjusting
for
maximum sensitivity,
for a wide band noise source go near a light dimmer or flouro light and
tune for the
loudest buzz.
Some times one can
not obtain much sensitivity this is usually due to the fact that even with
all the
trimmers fully out
the stages will not resonate high enough in frequency, this is bit of a
problem but often
one can just disconnect
the trimmers and it will peak ok on one sixty, the problem with this is
that the
tuning won’t track
so it will be very deaf on the normal broadcast band but since most people
have plenty
of radios to listen
to it doesn’t matter, you can fiddle with r/c values and the rest but it
all takes time so if
a set is hard to
convert just try another one.
Car radios are very
good but hard to change, the simplest method is to remove all the ferrite
cores from
the inductive tuning
arrangement, this will make it resonate close to 1.8mhz and use the local
osc coil
slug to tune in
the stations.
SSB RECEPTION
Although we use AM
because of the volume and clarity and easy reception with cheap radios,
a lot of the
stations heard will
be on ssb, to hear this just use the local oscillator of another radio
as a bfo, this system
works quite well
on these frequencies, depending on the strength of the signals heard change
the
distance between
the two sets for the best result.
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