High Power (tr)uSDX

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jerryk
 

Posts: 10
Joined: 21 Mar 2023, 18:42

High Power (tr)uSDX

Post by jerryk »

Today, I successfully adapted my (tr)uSDX to an old homebrew project - the "Tiny Linear". This is a 70W amplifier with an LPF from a defunct Icom 746Pro, a 3-inch touch screen, some glue circuitry that I designed - all crammed into the smallest possible cabinet.

I had to make an adapter for the PTT. The PTT output of the (tr)uSDX is a digital I/O signal right out of the processor. It outputs 5V during receive, and is pulled low during transmit.

The Tiny Linear, OTOH presents 12V at its PTT input, and you sink 3mA of current out of it to pull it low and activate the linear.

So I built a two-transistor buffer. Just a pair of 2N3904's. The "input" one pulls low when it sees the +5V on receive from the (tr)uSDX. When the +5V goes away for transmit, the input transistor turns off, allowing 100 microamps to flow into the "output" transistor. The output transistor has a beta of 200 ( I measured, actually it's 212 ), and now wants to sink 20mA out of the Tiny Linear input. Since that input can only source 3mA, the output transistor is then turned on really hard.

Since one can choose the linear's band with the touch screen, the PTT connection is all that's needed.

I had a nice QSO with a local, running 70 watts.

Only real problem is that now we have multiple boxes and wires all over the desk. Not as much visual fun as just using the (tr)uSDX. But it's nice that people can hear me. Last night, I had an almost QSO with an east coast station - he couldn't quite pull me in with 3.9 Watts.
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