MARATRAC RF Power Output Alignment Table

[w1ksz]

How can I relate the Alignment points in the RF Power Output table to frequency ?

I need to adjust the Power Output in the 144 - 148 MHz range.

Thanks, Dick, W1KSZ

[kcbooboo]

The alignment frequencies will show up when you press F6 in the PA Alignment service screen, but they're roughly 1-2 MHz apart. Take the standard range of 146-174 MHz and divide that by 16 and you'll have the approximate frequencies.

There's a list of them inside the programming software (I don't recall if they're 2-byte or 8-byte values). The radio's firmware also calculates what they should be by using a base frequency and a step size, as the radio needs to know which tuning values to use for a given TX frequency.

Basically, the radio isn't supposed to work below 146 MHz. Some will, some won't. There are several solutions, just as there are for MaxTrac and Radius radios. As they use the same logic board, you might want to review info about those radios.

Bob M.

[w1ksz]

When I read the Code Plug, it says the range is 144 - 174, so I am thinking it should work.

[kcbooboo]

The various tuning frequencies are all 8-byte double-precision numbers. I've extracted them here. Even though the code plug says 144-174, the rest of the radio and the software seem to be consistent and cover 146-174.

29.600
30.005
30.500
30.950
31.400
31.850
32.300
32.750
33.200
33.650
34.100
34.550
35.000
35.450
35.900
36.350

36.000
36.400
36.800
37.200
37.600
38.000
38.400
38.800
39.200
39.600
40.000
40.400
40.800
41.200
41.600
42.000

42.000
42.535
43.070
43.605
44.140
44.675
45.210
45.745
46.280
46.815
47.350
47.885
48.420
48.955
49.490
50.025

136.000
137.735
139.470
141.205
142.940
144.675
146.410
148.145
149.880
151.615
153.350
155.085
156.820
158.555
160.290
162.025

146.000
147.875
149.750
151.625
153.500
155.375
157.250
159.125
161.000
162.875
164.750
166.625
168.500
170.375
172.250
174.125

402.590
404.420
406.250
408.080
409.910
411.740
413.570
415.400
417.230
419.060
420.890
422.720
424.550
426.380
428.210
430.040

440.000
442.005
444.010
446.015
448.020
450.025
452.030
455.005
455.005
458.045
460.050
462.055
464.060
466.065
468.070
470.075

470.000
472.005
474.010
476.015
478.020
480.025
482.030
485.040
485.040
488.045
490.050
492.055
494.060
496.065
498.070
500.075

494.000
495.735
497.470
499.205
500.940
502.675
504.410
506.145
507.880
509.615
511.350
513.085
514.820
516.555
518.290
520.025

Bob M.

[motorola_otaku]

Do the highband radios have the power trim pot on the PA driver board? I used that to get a lowband radio's TX power on 52 MHz from 150 watts down to a more prudent 80.

[w1ksz]

I appreciate that list of frequencies used in the Alignment table, It tells me why the
radio power output jumps up below 146 MHz.

NOW, how can I change that table to extend the range down to 144 MHz ?? That might
solve the problem, it's worth a try.

Thanks, Dick, W1KSZ

[kcbooboo]

M_O: All MaraTracs have the power trim pot on the board between the exciter and the PA. It's only got a limited range. The TX power should be set on the bench using RSS with the trim pot set mid-way, then the pot can be tweaked slightly when the radio is installed in the vehicle using a thru-line wattmeter.

khz: You can change the table with a hex editor, however the radio still knows what the various starting frequencies and increments should be used when deciding which tuning value to use for a given TX frequency, so unless you change that as well (it's in the firmware PROM/EPROM and covered by a checksum), you won't get anywhere.

It might be easier to blank/initialize the radio to a VHF Range-1 unit, which will cover 136-154 MHz properly. The hardware will go down to 144 but probably not much lower. At least the tuning values will handle the 144-146 area the way you want.

As the MaraTrac and MaxTrac are so similar, it might be worthwhile to read some MaxTrac articles on these subjects. Titles like "Manual Power Control" (both MaxTrac and MaraTrac varieties) and "MaxTrac Secrets" come to mind.

Bob M.

[w1ksz]

Your paragraph two tells me I cannot do what I want. I know about the Manual Power Mod, having done it in the past of Maxtracs, but I was hoping
not to have to bugger the radio.

One other alternative is to leave the radio alone, and only program in repeaters that are above 146 MHz.

Thanks for all the replies,

73, Dick, W1KSZ

[kcbooboo]

Changing a VHF Range-2 to a VHF Range-1 isn't such a big deal. If you really need the entire 2 meter band, this is an accepted practice and it works well. You will be limited to 144-154 approximately. There's an article about doing this for a MaxTrac for APRS use.

The alignment frequencies in the software, and the various base and step sizes in the firmware, seem to be "cast in stone" and used by a lot of radios of the MaxTrac era (late 1980s to mid 1990s). If you managed to bugger the firmware and software, that would be great for just that one radio. Any time you moved to a different radio, you'd have to go through the same modifications. It really isn't practical.

Bob M.

[w1ksz]

I did a search on MAXTRAC APRS and got 38 hits. None of which had anything to do with moving the MAXTRAC ??

73, Dick, W1KSZ

[Will]

Dick,

Did you adjust the Drive Limit pot on the PA to limit the TX output?