I've also found the comments on IMD interesting. A couple of months ago I
had the opportunity to measure the HF TX IMD on a TS-2000 for myself, and I
found the results to be in line with most of the other radios on the market
with 12V PAs. VHF performance is quite stinky, I'll grant you, but I
measured -29dB (below PEP) on HF as a worst case, and that was on 160m. The
other HF bands were -30dB or better. In a few cases, much better. This is
consistent with what the ARRL measured (OK, they measured -27dB on 160m).
Granted it's nowhere near as clean as a TS-830 or a radio with 28V finals,
and it's not as good as we'd like, but is it really any worse than the
current crop of HF rigs out there? I've seen it singled out several times
for poor IMD performance, and yet it's right in line with other current
offerings (FT-920, FT-1000MP, IC-746 Pro, Jupiter, Omni 6+, etc. etc.). On
HF anyway. VHF is another matter, but let's compare apples to apples.
I regret that I didn't measure IMD at reduced power levels - it just didn't
occur to me when I was set up to do the tests.
Can anything be done (by non-PA designers like me) to improve the IMD
performance of 12V PAs? Is there any benefit to bumping the supply voltage
to 14 or 14.5V? (No, I didn't think to try that while doing the measurements
either.)
73,
Doug, K4DSP
>
> This thread has got me interested. What should be the minimum acceptable
> IMD spec for a transceiver? An amplifier, I think, will either pass
> through the transceiver's IMD or make it worse.
>
> I quickly scanned through the ARRL web site (members only section) and
> found the IMD test charts for the FT1000MP and the TS2000. The TS2000
> readings are both tabulated and graphed, while the FT1000MP results appear
> to be only in graph format.
>
> If I have read the charts correctly then the FT1000MP has better IMD
> numbers than the TS2000 on 160, 80, and 30 meters. They have the same IMD
> performance on 17 meters. The TS2000 has better IMD on 40, 20,
> 15, 12, and
> 10 meters.
>
> The worst reading for the TS2000 is -27 dB on 160 meters, and the FT1000MP
> worst case is -28 dB on 12 meters.
>
> Assuming, for sake of argument, that -30 dB should be the minimum IMD
> allowed, then the TS2000 does not meet specs only on 160 meters and the
> FT1000MP does not meet specs on 20, 15, 12, and 10 meters.
>
> Does IMD performance vary from model to model? Is poor IMD acceptable on
> certain bands more than others (I doubt it)?
> Will reducing the drive improve IMD significantly?
>
> How do the IMD results show themselves in the real world, how far out will
> the splatter be objectionable? Splatter is bad, but splatter at 10 KHz is
> worse than splatter at 5 Khz.
>
> --
> Zyg AF4MP
> Roswell GA USA
>
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