Here is the quick skinny on Motorola dual radio setups (as I have owned them):
-Motorola Syntor X9000 - Works with the HHCH or the Systems9000 (A9 style) head
-Motorola Spectra using the HHCH with an interface box
-Motorola ASTRO Spectra using the HHCH and the interface box
-Motorola ASTRO Spectra using the W7 or W9 head in the HHR option, second radio is RX only
-Motorola XTL5000 in the W3 setup WITH the correct flashport option. This is/was a time of order option and field upgrades were not offered.
-Motorola XTL5000 was planned for dual radio with the orginal O9 head, but was scuttled due to an engineering snafu and the APX was in the design phase
All the above require TWO radios. The APX radio is the only current true dual band out there, and can use the O2, O3, O5, O7 and O9 heads. The O3 head for the XTL and the APX is the SAME head, so by looking at the head, the only way to tell which radio its connected to is the color of the softkeys.
I do have it on good authority that a federal agency did have dual radio W7 or W9 ASTRO Spectra's, but wasn't able to comment further. I cannot devluge on how I know, but its confirmed.
There is a reference for the HHR setup for the XTL series, but I've never seen the full setup unlike the ASTRO Spectra.
Out of all of those, the ASTRO Spectra was the only radio line that did not require special firmware or software to work, just really expensive cables and being able to order the parts. In the non-hacked factory ordered radios, both the ASTRO Spectra and XTL's used slightly modified boards to compensate for electrical draw, and some antenna connection options.
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