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Maxon SM-3010
Conversion into 2 meter
Amateur Radio service

By Joe Loucka  AG4QC

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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.

Table 

N

 

 

 

 

 

 

 

 

 

 
Chip Pin 11 12 13 14 15 16 17 18 19 20  
Address N0 N1 N2 N3 N4 N5 N6 N7 N8 N9  
Diode M O P N A B C D E F  
Weight 1 2 4 8 16 32 64 128 256 512  
                       


Table

A

                   
Chip Pin 23 21 22 24 25 10          
Address A0 A1 A2 A3 A5 A5          
Diode I G H J K L          
Weight 1 2 4 8 16 32          
                       

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:

Table 

N

Chip Pin 11 12 13 14 15 16 17 18 19 20
Address N0 N1 N2 N3 N4 N5 N6 N7 N8 N9
Diode M O P N A B C D E F
Weight 1 2 4 8 16 32 64 128 256 512
  X   X X     X X X  


Table

A

Chip Pin 23 21 22 24 25 10
Address A0 A1 A2 A3 A5 A5
Diode I G H J K L
Weight 1 2 4 8 16 32
  X   X     X

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.

.
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.

.

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:

Table 

N

 

 

 

 

 

 

 

 

 

Chip Pin 11 12 13 14 15 16 17 18 19 20
Address N0 N1 N2 N3 N4 N5 N6 N7 N8 N9
Diode M O P N A B C D E F
Weight 1 2 4 8 16 32 64 128 256 512
        X       X X  


Table

A

         
Chip Pin 23 21 22 24 25 10
Address A0 A1 A2 A3 A5 A5
Diode I G H J K L
Weight 1 2 4 8 16 32
  X   X    X X

Cut the diodes in the SECOND row to correspond to your table. This should allow you to receive the repeater frequency.

Crank up the radio and flip it to channel 1. Hopefully, the transmit red led will be out, meaning the PLL is locked. If it's blinking, then the receiver PLL needs to be tweaked.  This is the top left adjustment below the diode board. You can either remove the board, make a small tweak and put the board back until you get lock. Or build and extender cable and do it the easy way. Or do what I first did and drill a hold in the diode board right over the adjustment location. There is plenty of room and you should be able to mark the location, remove the board and drill the hole without damaging any electronics. All the diode traces are external to that location.

Anyway, with both the transmit and receive frequency in the radio, you should be good to go into the repeater. Well, unless you use CTCSS on the repeater.. But hey, this is the easy part..

Look around and find the little CTCSS board. It's on a board that shares a screw with the diode board you have just been updating.. On there is a 6 position switch.  Use the following table to set your PL..


 

Using the above table.. Lets set the tone for 156.7.. Looking down the table we find  it is 0-1-1-0-1-0  this relates to the switch on the board as:

Notice the switch is backwards..  0 is ON and 1 is OFF. Also switch 6 corresponds to the first bit. and it works backwards from there..  Yeah, I know it's confusing, but it's easer then figuring out which diodes to cut!

One thing to keep in mind is this switch sets the CTCSS for ALL channels. This could be a problem if you access multiple repeaters with different tones. You 'could' mount the switch external and make it available that way.. Or use the extra diode slots on the diode board and switch the tones around that way.. That's certainly doable and maybe some time I'll write something on that.

This completes the transition of the radio. Do the same as all the above for each channel., remembering the channel diodes count from the top down, with the first row the transmit and the second the receive. That makes the bottom row of diodes on  the bottom row of the board the receive for channel 6.

Alignment
This radio works well without any changes to alignment of the front end. But if you have the equipment it's a great idea to align the front end for the new frequency range. You will need some sort of frequency generator. I just used a MFJ 259. Run a cable from the 259 to the antenna input. ( make sure you unplug the mic, as transmitting into your signal generator can be a disaster.)  Set the generator to somewhere around the middle of the frequency you want to use. 146.5 is probably a good place. But it's not critical. Now lets align this baby!..

With the signal injected, use a scope or rf probe to measure the voltage on the trace of the 5 can's.. One trace can work for all the alignment. See picture below. I normally just solder a short wire to the trace so I can then flip the radio over and align the can's.

With the probe on the traces, adjust the cores of the 5 can's that are across the top of the picture below. Adjust them  for the highest signal level. Go back and forth, as there is a little interaction between them.  Also adjust the two coils that are below the last big can. Do not try to align the smaller cans as they should be fine.

The green pot that is to the right of the last big can is the power control. Also, you can tweek the deviation by adjusting  the white pot that is directly below the VCO can you adjusted a few pictures above.

Well, that's about it.. Once you set a few of these up. it takes about 20 min;'s to do a complete radio. I talked about a repeater in this document. But of course it works on simplex also.

If this is a PDF document, drop by our website http://w4fhu.org and get the latest version of this document and much more!

If you have any questions, feel free to drop me a e-mail at joel@cyberbest.com

Joe Loucka  AG4QC

Update on 4/9/2006