Well, there's the rub:
There is no wired ptt.
It's appreciated the manufacturer intented to make it easy to use, but this in turn creates a problem by not providing wired ptt.
The AMP HAS wired ptt and VOX, but the upconverter has no ptt in or out.
You need 100mW to trigger VOX. I'm pretty sure, with 100mW INput the Output on 13cm is more than 100mW. The amp max. drive is 80mW.
Thus , if you use it according to the manual, your options are:
Clean, but stuttering signal. The upconverter stutters because input level is low.
Clean but stuttering signal, because upconverter AND amp stutter, same as above.
Distorted signal without stutter, because you provide enough input power.
No signal at all, because you can not trigger VOX from a too low input level.
There may be a small power range where all is ok. But again, it is not clarified in the manual. Oh, i know , you must insert an attenuator between upconverter and amp. This is not stated in the manual, either. Just put everything together, you will be fine. NOT!
Look at the transponder. If I'd place bets which signals are coming from this brand, i'd win more often than loose.
Yes, i know, there are dirty signals coming from other brands, too. Some users care, some do not, others just don't know because nobody tells them so.
73, Martin