>Rich says;
>
>>However, with RF-derived bias switching, the tubes rapidly switch in and
>> out >of linear bias during normal speech when the relays are in the transmit
>>position
>
>Do I understand from that comment that the majority of these bias schemes
>actually try to switch to follow the RF envelope, rather than 'hang' for a
>few tens to hundreds of milliseconds after the RF disappears?
? The problem is a bit more complex than hang time. In humanoid
speech, nothing happens on a precise time schedule. Even if the
soft-syllable hang time problem could be ameliorated, another problem
occurs at the beginning of words as the bias transistions between receive
(cutoff/non-linear) and transmit (linear). It is fascinating to listen
to the signal (produced by an RF-actuated bias switching amplifier) with
two receivers connected to stereo earphones. Tune one ear on freq. and
tune the other ear up or down c. 4kHz in order to hear only the splatter.
Whilst hearing soft syllables and the beginnings of syllables in the
on-freq. ear, one hears bursts spitting sounds in the splatter-ear. .
> If that's the
>case, I can understand why they are so bad for splatter. Given even a
>hundred milliseconds hang time, it should be OK for splatter (provided the
>attack is fast enough), but without.......................Rich is too kind
>in his comments.
>
The bottom-line is that there should not be a situation where the bias
can be in the non-linear/Rx mode when the RF relays are in the Tx mode.
The fix to make the bias follow the relays.
- cheers, Peter.
Rich...
R. L. Measures, 805-386-3734, AG6K, www.vcnet.com/measures
--
FAQ on WWW: http://www.contesting.com/ampfaq.html
Submissions: amps@contesting.com
Administrative requests: amps-REQUEST@contesting.com
Problems: owner-amps@contesting.com
Search: http://www.contesting.com/km9p/search.htm
|