On 13 Aug 2002 at 15:46, George, W5YR wrote:
>
> I don't doubt that the final devices can dissipate 100 watts - with
> that optional fan only?? - but if Joe Ham decides to operate with a
> 10:1 SWR on 40 SSB (using his 10-meter dipole) what will he sound
> like? After all, the specs say that he can operate into any SWR . . .
>
> I agree, Lee, that unless TT has done an exceptional design, unlike
> other 12-volt finals, the overall performance must be similar.
> However, there must be limits to the load mismatch for the distortion
> products to remain within limits.
>
Perhaps the IM will not be too bad into mismatched loads. On
the low Z side, the drive to the final in later Ten Tec rigs is
limited by the current delivered to the PA. So, once the PA
hits around 20 amps or so, the drive will back down and keep
the power transistors in their linear region. Note, this is
different than the more common SWR shutdown philosophy.
In this case, the final will still be delivering somewhere around
100 watts, maybe a little more, depending on the reactive
component of the load.
In the case of a high Z load, the ALC detector will sense the
higher than normal RF voltage and back the power down
accordingly, again keeping the transistors in the linear region.
In this case however, the final will not be delivering 100 watts.
It will be somewhat less depending on load Z.
Solid state amplifiers seldom match output impedance to load
impedance as in the case of tube amplifers. As a rule, solid
state amplifiers have much lower output impedance than the
load to which they are attached. That is why for instance in
solid state sound equipment, you will see the highest output
power being delivered into the lowest load impedance. Ten
Tec goes into this in detail in their older manuals. Makes
interesting reading and helps one understand the PA stages a
little better.
The point of all this is, that low transmit IM does not depend
heavily on the PA stage and load being impedance matched,
hence, we may well see good IM numbers over a wide load
impedance range. But, it would still be an interesting
measurement to make. :-)
-73-
-Lee-
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