Swan felt the power output should be lowered if the SWR was high in these early solid state transceivers from the 70s.
On Sun, Apr 29, 2018, 8:50 PM Jerry Gaffke via Groups.Io <jgaffke=
[email protected]> wrote:
Ah, where you say "R1", you meant to say "RV1".
Still curious how desirable you have found Swan's ALC to be.
On Sun, Apr 29, 2018 at 05:58 pm, Jerry Gaffke wrote:
Michael,
The Q90 and RV1 you refer to are definitely in the uBitx schematic.
I'm not finding R1 except in the Tandem Match here:??
Is that the R1 you are referring to??
Probably not, as it is not fed with "weak RF from the first amplifier of the transmitter"
An attenuator around RV1 is certainly a good choice for adjusting output power, effective for both CW and SSB.
For SSB, this attenuator could be most anywhere, all the way back to the mike.?
Perhaps an audio AGC circuit or speech compressor between mike and rig?
Have you found Swan's ALC to be a useful feature?
In what way??
Jerry
. . .
?
On Sun, Apr 29, 2018 at 05:32 pm, Michael Shreeve wrote:
Looking at the circuit, I see R1 simply is fed with full RF at the top, but relatively weak RF from the first amplifier in the transmitter. I'll measure the voltage, but its simple, ? the wiper sends however much RF you need on to the rest of the output circuit. If this control could be mounted on the panel of the radio, you would have a transmit power control. But, it might not be good to take it off the board.?
?
This is done, if you look , right at the output of the first rf amplifier Q90 and RV1 passes the rf along to the input of a couple of dc direct coupled 2n3904s . Some sort of RF attenuator after rv1 would do the trick, and control voltage from a bridge swr detector could control that. I'm guessing the Circuit Don uses, or part of it, the AGC, could be modified To control RF when it detects a lot of voltage from a swr bridge. Then you would have what swan calls a "ALC" !
?
Michael Shreeve