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FT-102 AM Net Fix by Mal, NC4L




 
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Author Topic: FT-102 AM Net Fix by Mal, NC4L  (Read 2562 times)
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« on: December 22, 2012, 01:33:49 PM »

FT-102 AM Net Fix

by Mal, NC4L


The FT-102 has about an 800 cycle offset between transmit and receive on AM. The modifications and procedure below will make the two frequencies the same or "net" the radio.

On the Local Board remove R113 and replace with a 10k trimpot. Only connect the wiper and one side of the trimpot, as all you need are two terminals. I just cut the other terminal with a clipper. Then place the remaining two leads of the trimpot into the holes that resistor 113 was taken from. But be sure that one of those remaining leads is the wiper arm. The trimpot is a somewhat technically difficult replacement as the holes that are there are not the correct spacing for some trimpots. So you may have to push some of the components to clear some room for the trimpot. In this, instance, smaller is definitely better.

Next, on the AF board (PB-2344) go to the green capacitor (TC02 - for frequency adjustment for FM-AM). It is next to the similar looking red capacitor (TC03 - frequency adjustment for CW). Turn the slot on the green cap so that it is halfway between start and 180 degrees. You will note that there is a small arrow indicator to the control. Adjust that arrow so that it faces the front of the set (1/2 of the total capacitance). You may need a magnifying glass to see the point of the arrow.

Next go to the green capacitor of the AF board (TC02) and adjust it for the exact frequency. The green cap only allows about +/- 200 cycles of deviation and the 102 ordinarily comes with 500 to 800 cycle differences between transmit and receive on AM, so TC02 does not have enough leeway to net the frequency in by itself. Therefore, the variable pot on the local board pulls the VCO of the 19 MHz local oscillator into to the proper range so that the green cap on the AF board can do its job.

Think of it this way - the local board replacement resistor with the trimpot is only a coarse control to get you in the ball park - then use the green cap on the AF board as the fine control. This will result in the most stable frequency and still maintain the normal alignment procedure as in the manual.

If you do not have a fairly good frequency counter you can listen in another receiver but you will only be able to net things in by about +/- 30 cycles which is absolutely fine on AM but not as good as +/- 5 cycles with a counter.

The FT-102 is a great rig for AM, FM, CW and SSB. The mods above will make it a much better performer on AM, especially when using it with a linear amplifier. If you are interested in more information and other modifications on the FT-102, please visit my Web page at www.members.aol.com/NC4LMAL. And if you run into trouble, contact me for assistance at NC4LMal@aol.com.
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