开云体育

So - with the help of the Tiny Linear - I made my very first QSO with the Softrock. Being mindful of its sensitivity to ground loops, I installed an optocoupler at the PTT output of the AtTiny. I superglued it to the top of the board, fed it with a 1.2K resistor, and soldered a cable with an RCA jack to it.

Worked fine. The Tiny Linear took the Softrock's 2W and magically transformed it to 25W - which people can actually hear :).

I haven't heard of The Tiny Linear. Do you have a link to it?

Dave
W2IJL

I was going to say and ask the same thing. The Tiny Linear sounds interesting.

Dave
KB9GPM

It's my home project. It started out as a set of items:
1. A Chinese linear amplifier kit. Here's a link:
2. An HFsignals.com "Raduino" card, with an Arduino Nano and a 2.8" touch screen
3. A switchable LPF from a defunct Icom IC746pro transceiver
4. A very simple "glue" board that I designed to interface the Raduino to the LPF - to choose the filter
5. Custom software that I made by - basically - stripping out all the excess transceiver stuff out of the HFsignals software.

I modified the Chinese linear by upgrading it to a BLF278 that I had laying around. I also changed the power feed to a
ferrite choke/transformer and eliminated the primary center tap on the output transformer. And took one turn off the
secondary to lighten the load...and raised the drain supply voltage from 12V to 32V. I mounted the linear RF board on a heat sink the same size as the board and packaged the whole thing in a really small box ( hence the "Tiny" moniker ). And mounted a fan on the back.

The Tiny Linear produced 150W when driven by my Elecraft K2 outputting 5W. Unfortunately, the heatsink was really not adequate for that power level, and I fried the BLF278 :(. A new PA transistor got it back online, and doing 25-30W driven by the Softrock - it's just coasting.

If one wanted to build one, I can supply the software. I also have a Gerber for the glue board - which isn't quite there, but enough of it is there to be useful. The main thing - this particular LPF requires +12V drive to each relay that you activate. This is somewhat harder than pulling a relay pin low. I wound up with each relay being driven by a PNP TO-220 pass transistor - two resistors and a snubber diode. In an ideal world, I should have been able to do it with a TO-92 transistor - 2n3906 maybe - but the combination of experimentation and fumble fingers fried some of those - I got tired of it and stuck in big transistors :).

Most of us as a rule do not have LPFs from defunct HF transceivers laying around, and there are Chinese kits for that too. I bought an assembled one, but their QC was lacking. I had to do a bit of reverse engineering to get it working right. Basically, they had stuck in wrong parts. The 5-pole Chebyshev tables at the back of the ARRL handbook were invaluable. One advantage of the Chinese LPF kit is that relays are activated by GROUNDING them - much easier. I could have eliminated my whole forest of transistors with a single ULN2003. Well, there might be positive drive ICs out there....I didn't look THAT hard.

I had a spare Raduino card because I had bought an upgraded one for my Ubitx transceiver from W0EB. The upgraded Raduino has a Teensy 4.1 CPU card, which absolutely runs rings around the Arduino Nano. But the Nano was powerful enough to switch the LPFs from the touch screen, display the drain current of the chip on a bar graph, and display a "TX" annunciator. When I build the 600W linear that I'm kitting up, I will definitely use an upgraded Raduino - it will have enough horsepower to do automatic LPF switching by measuring the incoming frequency.

- Jerry KF6VB