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YAESU FT 102 AM SURGE MODIFICATION
12-08-08 |
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Please note - this surge modification in its
complete and detailed phototutorial form is
Available Here.
And the phototutorial mod can also be seen at this address: http://www.amwindow.org/tech/htm/ft102overshoot/ft102overshoot1.htm Many folks have asked me to come
up with a good AM surge modification for the 102 and so I
listened and have come up with an excellent modification that can be done
in an afternoon or less.
This modification was prompted by
an email from Bill W3DUQ who has also published a mod for the
102 overshoot modification. Bill correctly found that the cause of the
overshoot was the 8 volt AM transmit supply line which was unstable
at initial onset of transmit while it was going from a resting voltage of
0 to the working 8 volts. He correctly
undertstood that a stable 8 volt supply was needed and had to be on in
receive as well as transmit so that there would be no
variation of the voltage at the onset of AM transmit.
Below is my email to Bill with
the new and simplified modification and its explanation.
Hi Bill,
OK, I have it figured out and it
overcomes all the short falls of the initial modification.
Your initial modification had two
very serious drawbacks:
1. - The radio and
board were neither forward or back compatible. By that I mean that the
modified board could not be used in another unmodified 102 and that a modified radio could not
accept a normal unmodified AM-FM board.
2. - Because AM is
also powered up when FM is selected in your modification both forms of
modulation mix and the output on FM is very distorted by the simultaneous AM modulation
components.
Starting with an unmodified radio
and board cut the wire going to pin 1 of P60 (J01) of the AM-FM
unit. Leave enough room (about 2 inches) to solder another lead to it and insulate the
other cut end which carried the old 8 volt supply to pin 1, so it doesn't short out.
Then go to the AF board and pick
up a lead from pin 2 of J15/P38. This is noted to be a 12 Volt, AM line.
It a yellow wire and is energized only when in the AM mode. It is on continuously in
both receive and transmit. It is not on in the FM or any other mode as was the case with your mod.
This line (yellow wire) will be
your new power source for the AM unit but it must first be converted to 8
volts. I recommend using a three terminal 7808L (L is for low power) regulator (cost
is well under a dollar) to bring the 12 volts to 8V. Then connect the 8 volt output line from the regulator to the wire from
pin 1 of P60 and it is done.
This will give you a constant 8
volts at pin 1 of plug 60 - but only in the AM mode and will be activate
in both receive and transmit so there will be no variation when going from receive to
transmit. This power line will not be active on FM or any
other mode so that AM modulation components cannot
interfere with FM functions since AM will not be switched on.
The nice thing with this
simplified modification is that a modified radio and unmodified boards are
both forward and backward compatible. Give it a try. The Modification and phototutorial are available
73 de NC4L
Mal
This surge modification in its complete and
detailed phototutorial form is Available Here
The modification can be done in
an hour - just click on the blue link at the top of this page.
73 de NC4L
Mal
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