Deviation Balance using Astro 25 Tuner on Spectra

[mutantblue]

I am trying to align the deviation balance on a UHF Astro Spectra Plus using Astro 25 Tuner. I've used the tuner on an XTS 2500 before and everything worked fine. With the 2500 and tuner, modulation tones of 60 Hz and 3000 Hz are balanced as advertised. However, when I try to align the Spectra +, I get a modulation frequency of 10 Hz for the low tone and 67 Hz for the high tone. If I actually try to align the radio with these two tones and set the deviation limit accordingly, I get erratic decoding of my P25 signal on some (but not all) repeaters. Radio performance with the default softpot setting of 38 is good, but when I try to align it, the softpot wants to be about 70, and that's when I get the marginal performance.

I know some may say, "if it works, don't fix it" (use the default value and be happy), but I would like to know there is a reliable way to align the radio. With a normal Spectra, it is possible to inject a wide range of modulation frequencies (down to PL frequencies) on the accessory connector. This would allow an alternative method to balancing deviation at 60 Hz and 3 kHz, albeit somewhat outside the tuner application. Unfortunately, the Astro Spectra Plus seems to be different, and this audio input isn't available.

Does anyone have any experience with this problem or have alternative way of performing the balance? Even though this impacts digital performance, my initial motivation was to improve the analog transmit audio characteristics, which seem a little compressed and distorted.

[xmo]

Because it uses such low frequency tones, the Astro Spectra Plus is especially challenging to align.

The service manual, 6881076C20, recommends the use of the Agilent [HP] 8901B modulation analyzer. Specific recommendations are made for the instrument settings.

You may also achieve satisfactory results using a General Dynamics R2670 with firmware 5.04.XXX or newer. This firmware provides for deviation smoothing when observing the bar graphs [expanded] display. Set the analyzer up per the recommended procedure in the XTL5000 service manual 6881096C73.

[mutantblue]

So are the 10 Hz and 67 Hz tones correct? Why is this so much different from the tones used on the XTS 2500?

I was using an HP 8920 to measure the deviation, but could get access to an 8901 if needed.