My progress with a QRO1 23cm amplifier has been largely successful. I have generated over 400W with about 6w drive and somewhere near 20A drain current at 50V. I burned out my 250W dummy load whilst doing this test.

I have lots to do still, like put the whole thing in a box for instance. Metering of power supply and sequencing of antenna switching major circuit construction jobs to do. Perhaps even high SWR lockout might be considered.

To enable monitoring of both transmitted power and return loss (reflected power) some form of directional coupler is required. Many commercial options are available but either they are expensive or dubious Chinese eBay lumps that are rather bigger than needed and only couple in one direction.

So, I made one.

I’m pleased with it. I can adjust the coupling from between -40db and -30db by careful adjustment of the lines. Return loss is approaching -20db and through loss too small for me to measure (<0.2db)

Not bad for an on-the-fly making it up as I go along design.

  1. QRO – one of many “Q” codes used by us geeky radio nutters. Literally means “shall I increase power” – “I will increase power” and is generally considered in most contexts to mean “I am running high power” – In my case I’m looking to generate 400W which is the legal limit. In theory, hypothetically speaking, I could probably get about 700W out of the amplifier I’m currently building. This is enough power to heat your dinner to a temperature that will kill pathogenic food poisoning bacteria in 2-3 minutes, depending on how big your dinner is. This is one reason why it is a good idea to put my antennas on top of a really big mast, then the inverse square law applies and only the crows that are daft enough to sit on my antennas will get cooked. All humans will remain unharmed. There are safety rules designed by ICNIRP by which my license insists I abide by.

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