182 lines
8.3 KiB
Plaintext
182 lines
8.3 KiB
Plaintext
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HOW TO MODIFY YOUR ICOM R7100 TO PROVIDE AN OUTPUT DIRECTLY FROM THE
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DISCRIMINATOR - WRITTEN BY TIM JACKSON tim@pixie.co.za
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This is an involved operation and should NOT be attempted by anyone who
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does not feel at home with fine electronics work. It is very easy to do
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serious damage to your radio if you don't know what you're doing.
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Please read through this document in its entirety before attempting to
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carry out the modification.
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It is almost essential that you print this out in order to have it handy
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while carrying out the modification. The diagram at the end of the
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article will be of great use.
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Right, let's get down to the nitty gritty.
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You are going to need just one electronic component - a capacitor of a
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value of between 220n and 10u. It can be either polar or non-polar. In
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addition, you will need a length of screened audio cable, any type
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should work but the smaller it is the better. You will need some form of
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connector to put on the one end of the screened lead - a minijack socket
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or phono connector would be good.
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Of course you'll also need a few basic electronics tools such as a
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screwdriver, soldering iron, sidecutters etc.
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With the front panel of the radio towards you, as you would have it for
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normal use, locate the four retaining screws on top of the top cover.
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These are located near each corner. Remove these four screws.
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Do not remove the three screws located around the speaker grille.
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On each side of the radio are two further retaining screws (a total of
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four). Remove these.
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The top cover may now be lifted off the radio taking care to observe the
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speaker cable. The speaker is fixed to the inside of the top cover.
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There is a connector in the speaker cable which should be unplugged to
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free the top cover completely.
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Looking down on the receiver, locate the converter unit. This is the PCB
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closest to the external antenna connector at the left rear of the
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receiver.
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Now locate the coaxial connecter at the extreme left rear of the
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converter unit PCB (see diagram). The cable connected at this point
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bends over and travels downwards into the bottom half of the receiver.
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Disconnect this cable by pulling directly upwards. The connector is
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farily delicate so do not use too much force.
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Now comes the part that requires great care. Take it slowly and do it
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properly.
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The entire top chassis has to be detached in order to reach the main
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unit PCB beneath.
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There are four screws that need to be removed to accomplish this. Two of
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these are located on the rear panel of the receiver.
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Looking at the radio from the rear now, you will see a row of connectors
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for such things as external speaker etc. Just next to each end of this
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row of connectors are the two screws you need to remove. Remove them.
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The remaining two screws are on the top of the unit. Position the radio
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as you had it before (normal operating position).
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Looking down on the radio, you should see four screws near the front.
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Two of these go through the top of the plasic front panel and two of
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them go through the metal chassis (see diagram). Remove the two screws
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that go through the metal chassis.
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Now CAREFULLY lift the top chassis and swing it clear of the radio. Note
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that there are many wires linking the top chassis to the bottom. Take
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care not to strain these. there should be enough slack (just) to allow
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you to swing the top part out and away from the bottom and lower it onto
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the surface you're working on.
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Now you should have a clear view of the main unit PCB. This is where you
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will be making a connection.
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In order to locate the point on the PCB where you will connect the
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screened cable you will need a ruler or tape measure.
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The connection point is approximately half way from the back to the
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front and approximately one quarter of the way from left to right. This
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is just to give you a general idea of where to look. (see diagram)
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Now, using your ruler, measure inwards 55mm (2 1/8") from the left edge
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of the radio towards the right. Imagine a line running through this
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point from the front of the radio to the back.
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Now, measure 120mm (4 3/4") from the rear towards the front along the
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imaginery line.
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At this spot on the PCB (see diagram) you should see a wire link marked
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"W100". This point (the wire link) is output of the discriminator.
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Connect one side of the capacitor to this wire link. If the cap is a
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polar type then the positive lead goes to the wire link.
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Connect the remaining lead of the cap to the centre conductor of your
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screened cable.
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The screen of the screened lead can be soldered to the casing of the
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nearest metal can. There is a suitable can approximately 10mm (3/8") to
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the rear of the wire link (see diagram). Take care not to overheat the
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can while doing this. You should be able to get the solder to flow
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nicely onto the can within two or three seocnds.
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Exactly how you terminate the other end of the screened lead is up to
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you but I would suggest that you extend it through a suitably drilled
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hole in the rear panel of the radio and then terminate it on an in-line
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mini jack socket or phono connector.
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That's it! Well, almost. Now you have to reverse the whole process in
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order to close up the radio again.
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Be extremely careful not to strain any of the wires and take care to
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ensure none are pinched between metal chassis parts as you close up the
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radio.
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Don't forget to reconnect the coaxial lead at the left rear of the radio
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once the top chassis is back in place.
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The new output you have created is basically just "raw audio". It is the
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point in the circuit before audio filtering, volume and squelch control.
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This means that it is a fixed level output unaffected by the position of
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the volume and/or squelch controls.
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Be aware that while short circuiting this output shouldn't cause any
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harm at all, it will deprive the radio of an audio output thus muting
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the internal loudspeaker. The impedance of this output is around 10k
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which is perfect for driving the circuit supplied with the software
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PD.EXE (a pager transmission decoding utility) but may require buffering
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if you plan to use it for other purposes.
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Anyone requiring further assistance is free to Email me at
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tim@pixie.co.za. I'll do my best to help.
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This diagram shows the relative location of various key points within
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the receiver. Be aware that the points shown are all inside the radio
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and that some are visible only once the upper chassis has been removed.
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---------------------------------------------------------
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|X - coaxial cable connector |
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| X - metal can |
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| X - wire link (W100) |
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| X --- chassis screws --- X |
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| X --- front panel screws --- X |
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---------------------------------------------------------
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- - ------------
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Vol Sqlch Tuning
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