The net IMD improvement of raising the 440's supplied V to c. 16v (the
max allowed), and raising the zero-signal collector current (ZSCC) in the
driver to 250mA and final to 400mA -- was not scientifically measured by
me since I no longer possess the needed test equipment. Instead, I
relied on signal reports on the air. The observed result was good. My
guess is that increasing Kenwood's recommended 200mA to 400mA of ZSCC on
the 15,000mA final transistors was the most important factor.
>I would be interested in this information too. With the current batch of
>transceivers its getting hard to find a model with good transmitter IMD. In
>fact the IMD figures seems to be getting worst.
>
>The older model radios like the IC765, FT1000D, JRC 545 all have superb 3rd
>order IMD figures all over -35db. Likewise the 5th order IMD numbers are
>very good. Looking at the recent ARRL reviews there is very little
>difference between the cheapest radios and the top range models. We may have
>to collect these older cleaner radios if you want a clean drive signal.
>
>Considering the noise levels on the bands I wonder what the minimum
>acceptable 3rd order IMD would be?. The ARRL references its measurement to
>PEP and most of the commercial gear is reference to 1 of two tones. This
>would make -36 db the minmum, such transceiver are rare in the ham radio
>market.
>
>The VHF contest operators seem to pursue the best close and far out IMD
>performance which is quite stringent. Of coarse not everyone is so
>considerate in this regard. HF is no different most people who seem to
>splatter don't care. Although these days i frequently only seem to hear bad
>signals with those stations running IC706's into amplifiers, the distortion
>is quite easily detected. The other bad splattering stations are well beyond
>help and seem to be beyond help or wanting to accept "constructive
>criticism" The attitude that "i payed 10 grand and dont splatter" seems to
>predominate with these recalcitrant stations.
>
>Craig
>VK3HE
>
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>
- Rich..., 805.386.3734, www.vcnet.com/measures.
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