Here is an idea for the variable input pad control:
Since you are probably going to have a rotary switch to select the correct LPF, use a double pole rotary switch.? 1 pole controls the LPF and the other selects the correct input pad.??
Yes, it makes the part count increase, but it is only a few more resistors.
On Wed, Jan 10, 2018 at 10:51 AM, Diver Martin <diver.martin@...> wrote:
The biggest problem to adding an amp to the uBitx is the fact that it's using the IRF510's as the output amplifier, and the output power is not consistent.? I've thought about adding my 50W amplifier to the uBitx, but the issue there is that the amplifier only needs 0.7W drive at 40m, and needs 3W drive at 10m.? The uBitx is putting out 7-10W @ 40m, and under 3W at 10m, so a variable attenuator or something would be needed, or a set of attenuation resistors and switches.
One option might be to reduce the gain (Increase negative feedback) of the output amplifier using R261/R262 which are pretty large at 200 ohms, and increasing the input drive.? I haven't experimented with this yet though, and they'd probably have to be beefier resistors.? All things in due time, my mod PCB project comes first (it's almost done, will hopefully send out a preliminary design email tonight).
On Wed, Jan 10, 2018 at 8:44 AM, Rob N4RMK <N4RMK.tn@...> wrote:
I'm a total novice with electronics, so I'm not sure whether I could effectively make this mod.? I'm just thinking that a 50 watt or 100 watt amp would be an awesome addition to the uBitx.
--
Martin Held - AE7EU
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