Jedi MTS2000 - Front End Realignment - improved sensitivity

[g8tzl2004]

A recently acquired UHF MTS2000 was noticeably deafer than some of my other MTS2000's although it was still within manufacturers specs.

I had previously read about "big" variations in sensitivity between identical MTS2000 radios.

Anyway, I decided to realign the front end. The original settings looked very sensible with a gradual increase in softpot values, as follows:

30, 44, 53, 58, 69, 77, 83

I very carefully realigned the front end. This resulted in a good improvement in sensitivity - the radio is now more or less equal to my other MTS2000 BUT the softpot values do NOT follow a "linear" increasing pattern. Values are as follows

19, 26, 62, 68, 58, 77, 88

Does Motorola actually carefully align the front end in the factory , or do they just input "expected" values and then pass it if its within specs??

Front end alignment is reasonably "broad" - I double checked each softpot value by checking where the sensitivity started to noticeably drop on each side of the peak, as well as where the squelch closed on each side. The "middle" softpot value of the two "extremes" was more or less was in line with my original softpot value for maximum sensitivity.

[tvsjr]

The radios are aligned during manufacturing. That said, components do drift as they age, with temperature, etc. In a perfect world, gear should be PMed yearly with a full alignment. I can complete a complete alignment of an ASTRO25 radio in 15-20 minutes (ugh, let's not talk about APX). And I don't have AutoTune

*Any* radio purchased from an unknown source like eBay should be aligned before being placed into service.

[g8tzl2004]

If you use a Motorola service monitor or SINAD meter can you see the change in sensitivity for each individual unit change in the front end sofpot value??

MTS2000 front end tuning is very broad - you can quickly find an approximate peak BUT to find the absolute individual peak value is not that easy - there does not appear to be much difference between individual softpot values around the peak...but maybe a service monitor CAN actually see that very slight difference?

I've never come across auto tune with any of my Motorola stuff, but when I ran auto tune on an Icom UHF radio, I got different values each time I ran auto tune..but no real noticeable difference in sensitivity. The Icom's front end was even broader than my MTS2000's.

[tvsjr]

No, it's hard to find the peak. Typically, I find the peak signal value, then find the point that the signal begins to decline, then average. So let's say I had a maximum RSSI of 79 and that value shows up with softpot values from 40 to 50... I would typically enter 45.

[d119]

No, it's hard to find the peak. Typically, I find the peak signal value, then find the point that the signal begins to decline, then average. So let's say I had a maximum RSSI of 79 and that value shows up with softpot values from 40 to 50... I would typically enter 45.

This is the same procedure I use when aligning a radio. It's a more or less "safe bet". I too have seen plenty of these radios that needed to be gone through after having been in service for so many years.

[g8tzl2004]

I checked out the front end alignment on another MTS2000.

The original settings were as follows:

34, 49, 59, 64, 75, 84, 91

The new settings after very careful alignment are as follows:

23, 33, 67, 68, 71, 92, 94

I also plotted the softpot values on a graph - frequency on X axis and softpot value on Y axis. I found that for BOTH MTS2000's, the original factory settings were basically is a straight line - both lines were parallel but one MTS2000 had slightly higher values.

My own settings both followed a "zig zag" pattern and were also very similar - almost a parallel zig zag. If you plotted the "line of best fit" through the zig zag plot , it approximates to the original Motorola "straight line" factory settings.

My conclusion is that Motorola are applying default settings in the factory - maybe they measure for one mid value and then apply proportional default values for all other settings - giving a straight line!!!! Infact, I think the specified front end alignment routine for later UHF radios such as the GM1550 is to only measure one mid point front end value and to then apply default settings!!