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Maxon SM-3010
Conversion into 2 meter
Amateur Radio service
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The Maxon SM-3010 is a 6 or 8 channel commercial VHF radio available on the surplus market. It's normal used in public service but easily converted to Amateur Radio service.

The following is a quick introduction to it's conversion. PLEASE venture at your own risk!

Things to know:

• Frequency is controlled by a diode matrix input to the MC145152 PLL synthesizer.

• The PLL feedback comes through a MC12017 prescaler in divide by 64 mode.

• The channel step is set to 5khz by the options on the MC145152

• The IF frequency is 21.4 MHz

Knowing the above you can figure out the diode combinations for any frequency.  The diode board looks like this:

Click on any picture for a close up.

If you cut a diode, It's as good as it not being there. If you want to change the frequency at a later date, simply solder the cut back together.

The diode combinations are derived  by doing the following.

Take the frequency you want and divide it by the prescaler  (64). Now divide that by the channel spacing (5000)  This will give you a number in the 200-400 range. Take the WHOLE number and use that to fill table "N". Now take the remainder and multiply that by 64 and that will be used in table "A".

Don't get too excited, we will run through a few examples in a second. Here are the two tables.

Now for example.. We want to use this radio on a repeater on 147.105 MHz  This repeater has the repeater split 600 KHz up. So we transmit on 147.705 MHz

Using the above we come out with:

• 147705000/64=2307890.625  (This is the frequency divided by the prescaler)

• 2307890.625/5000=461.578125 (This is the answer from above divided by the channel spacing)

• So.. 461 is the number used in table "N"

• Taking the complete number 461.578125 and subtract the whole number used in table "N" : 461.578125 - 461=.578125

• Multiple that number by the prescaler.. .578125 * 64 = 37

• So 37 is used in table "A"

Now we need to fill the tables.. The value 461 needs to be represented in table "N" This is a binary representation. The easiest way to do that is use the largest numbers from the table to subtract that value from the number until it's gone.

• Going from right to left, subtract 512 from 461 and it's too big. So that diode needs to stay.

• 256 will fit in 461 with 205 left. So we put a "X" in the table under 256.

• 128 will fit in 205 ( the value left from the above calculation) with 77 remaining. So put a "X" in the table under 128

• 64 will fit in 77 ( the value left from the above calculation) with 13 remaining.. So put a "X" in the table under 64.

• 32 or 16 will NOT fit in 13 ( the value left from the above calculation) so skip these in the table

• 8 will fit in 13 with 5 remaining and so put a "X" in the table under 8.

• 4 will fit in 5 with 1 remaining. Put a "X" in the table under 4.

• 2 will NOT fit in 1, so skip this in the table

• 1 will fit in 1 with nothing remaining. Put a "X" in the table under 1

Now lets fill table "A"  The value needs to be 37

• 32 will fit in 37 with 5 remaining.. Put a "X" in that field in table "A" under 32

• 16 or 8 will not fit in 5, so skip these fields

• 4 will fit in 5 with 1 remaining,  Put a "X" under 4

• 2 will not fit in 1, Skip this field

• 1 will fit in 1, Put a "X" in this field.

This finishes our diode cut list. Your tables should look like this:

To check your work.. Add up all the values in table "N" and it should equal your original whole number..  So, 256+128+64+8+4+1=461 Do the same thing to check your work in table "A".  32+4+1=37.

Now lest see if this is really the frequency we want.  Take the number from table "N" (461) and multiply by 64. 461*64=29504.   Take this number and ADD the value from table "A".  29504+37=29541.  Now multiply the answer by 5000. This should be your frequency.  29541*5000=147705000  If all the above checks out, lets get into the radio and make it work.

You will notice that the two tables have rows for Diodes. If there is a "X" in that field the diode that corresponds to that value needs to be cut. If there is nothing in that row, then that diode needs to stay. (Note: diodes in position D & E are always missing - cut..

Lets take a closer look at the diode board. Click on the picture for a better look.

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Notice there are characters from A-P across the top. and D & E are always missing. There are two rows for each channel. The top row is for transmit frequency and the row beneath it is the corresponding receive frequency. There are 12 rows, to represent 6 channel pairs.

In this case lets set the first channel to transmit on 147.705 as we figured out in the above tables. Because these are used radios, some diodes are already cut. It might be a good idea to soldier all the diode cuts back together and then just cut the ones you want. No matter how you do it. You only want the 9 diodes cut.  For simplicity sake, lets say we have whole diodes, they were either not cut or we soldered them back together.

Now lets cut the diodes..  Find the top most diode under the C ( D & E are as good as cut because that are missing) and cut this lead. Don't cut it too close to the body as someday you might need to solder it back to change frequency. Now cut the rest from the two tables.  The results should be you cut diodes  C, H, I, L, M, N, P ...  That's it for the frequency selection on the transmit side.

Connect a dummy load to the antenna. This radio is rated at 30 watts, but most put out a bit more.  Now flip the channel selector to 1 and push the microphone PTT. If you're lucky, it will transmit. If that's true, continue to the receiver section of this document.
But there is a good chance the PLL will not lock and need to have it's free running frequency adjusted lower. There is no easy way to do this as the adjustment is under the diode board. You have a few choices, you can make a small adjustment and plug the board back in and keep doing that until it locks. Or you can make up a extender 20 pin cable to extend the diode board. Either way you need to adjust the PLL oscillator.

This is what the adjustment portion of the radio looks like.

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The top is the PLL adjust  for the receiver. The one slightly and towards the middle is the transmitter. The one on the left and bottom is the common PLL. I recommend you adjust the common first. If you have a frequency counter, lay the counter probe along side the bottom of the metal can. It will probably read in the 140 MHZ range. Adjust the COM  until it's in the 133 MHz or so range. If you don't have a counter, make slow adjustments and plug the diode board back in and see if you have lock. There is some interaction between the transmit PLL adjustment and the common. So they both might need to be tweaked. You can tell if you are getting close, as the further away you are, the faster the red transmit light blinks. I highly recommend you make a extender cable OR do the receiver part first as you can drill a hole in the diode board as the receiver adjustment is under a part of the board that has no diodes and so can be adjusted while in place. Once you have lock ( and it's not as bad as it sounds) it should lock on all your 2 meter frequencies. The first time I tried this it took me about 4 times to get lock.

Receiver frequency.
The procedure we used to figure out the diodes for the transmit frequency above is the same we use for he frequency for the receiver. The big difference is the IF frequency must be SUBTRACTED from the wanted frequency, as this radio has 'low side' injection.  The IF frequency is 21.4 MHZ.. So lets do the math...

• The above repeater is on 147.105 MHZ  So take the frequency we want to receive at. and subtract the If  frequency:  147010500-21400000=125705000  That's the frequency we want the PLL running at. So we use the same procedure as for the transmit side and get:

• 125705000/64=1964140.625 (Prescaler output)
  1964140.625/5000=392.828125 ( Channel spacing)

• So we have table "N" as 392

• 392.828125-392=.828125

• .828125*64=53

• Put 53 in table "A"

Your table "N and "A" should look like this: