>> At 100 watts carrier, that puts the IM at about
>>0.4 watts. Significant? Sure, but not deadly.
>
>Maybe not deadly at HF, but much worse on VHF where the background noise
>levels are so much lower. That's a real issue for HF/VHF rigs because
>the same standards do not apply... I mean OUR standards, not the FCC's.
Ahhh....good point! I had neglected the fact that the 847 operates at
VHF/UHF. You are correct.
>
>The other question is how quickly the IM products go down into the
>noise. It's possible to live with the 3rd and 5th order if the higher-
>order IPs disappear. The real problem is when they hang up there,
>because even IMD at the -70 to -80dB level can cause a lot of trouble to
>other VHF weak-signal operators if it's spreading right across the band.
Yep. Right again, Ian. For weak signal stuff, the IM could kill other
stations. I stand corrected on that one.
>
>>
>>You get what you pay for in rigs.
>
>As far as IMD is concerned, it's "we" - all the rest of us - who get
>what "you" pay for!
Well, since I bought an FT-1000, I think I've done my part to clean up
the neighborhood! :-)
>
>>So if you compared the FT-847
>>to an FT-1000D, you'd probably see a huge difference in IM performance.
>>
>That's certainly true, in that only top-of-the-line rigs use 28V devices
>and power supplies because of the added expense.
Yes. And better devices are used in the more expensive rigs as well.
The nice thing about the 28 V devices is that you can get one that can
provide plenty of power and a decent bias current. So you can bias them
a bit heavier and improve IM products a lot. Sure, efficiency goes down,
but everything is a tradeoff.
>
>Also, several recent QST reviews of HF transceivers seem to suggest that
>the IMD performance of solid-state finals is quite poorly controlled in
>production.
Not at all surprising. Probably very few ham transceiver production
lines use statistical process control to manage all their manufacturing
processes. And again, it's the cost issue. The consumer wants a cheap
product. So corners are cut and the product justs "gets by."
73,
Jon
KE9NA
--------------------------------------------------------------------------
Jon Ogden
jono@enteract.com
www.qsl.net/ke9na
"A life lived in fear is a life half lived."
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