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Sunday, 11 June 2017

Its brick time!


To compliment the DATV transmitter I made here, I've been building a PA rated at 60W RF out - it will be used at way less than this, but for any kind of TV transmission we need loads of overhead in the PA to avoid nastyness in the output.

The PA is this design here, the PCB from G4DDK.

The module itself is a RA60H1317M1A and I got mine from Anglia Live.

The heatsink feels like a great find, I saw it listed on eBay by JPG Electronics in Chesterfield; as it's just up the road I paid a visit - what a find! Loads of goodies!

Anyhow, here the PA under test:

The TX RF from the Portsdown will come in through the LPF we tested last time; then through the PA and out through the SMA relay. The RX Signal will pass through the BPF also from last time, and to the Receiver we made here.

The relay was one of a number I found some time ago; they are Ducommun latching 12V SMA relays. These need a driver circuit which I made like this:

and that's built on the veroboard you can see at the front of the PA block. The output lines do this when the PTT is grounded and then disconnected:

All I need to decide now is what to set the Bias voltage to on the PA - not sure about that!

Throughout Miss Luna Cat has been supervising from a distance:

Good, egh?

Saturday, 3 June 2017

Filters Filters Filters


Following on from the success of last time; it was time to make some filters around the 146.5 MHz DATV frequency on the NoV allocated bit of spectrum we have above the 2M band.

I've also built up a kit I have had here for a while, it's a PGA144 from G4DDK.

So at the top we have the PGA144, middle is the LPF and bottom is the BPF. The designs are really quite simple - just ask if you need the details. Here's the spectrum from all three:

The yellow is the PGA144 - it has a 20dB attenuator at the input so the signals are actually 20dB higher than shown - the gain at 145MHz is exactly 20dB.

The purple is the LPF being swept and looks just fine.

The Blue is my BPF which I am very pleased with - it looks great.

So next will be a 60W "brick" amplifier for 146.5 MHz - waiting for the bits but I have to go work in foreign parts for a week or two so will pick this up on my return.

Local conditions.