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Friday, 14 October 2016

More 23cm Power Required!


The other night, there were a few of us trying out JT65C on 23cm. I could decode quite a few of the other stations but couldn't be heard. This is no surprise as I was using only 10W out of my IC-9100.

Quite a while ago I bought a 23cm PA module from PE1RKI - now this is a fairly serious bit of kit that I hadn't got round to doing anything with - until today.

I also bought a number of other items to go with the PA including a case, a switch mode PSU and a Ultimate Amplifier Control Board from W1PQL.

I built the control board and here it is just being attached to the rear panel of the amplifier case:

So the first thing in this kit board is a sequencer to handle all the different things we need to switch as part of going from TX ro RX and back again in a linear amp.

There's an ALC output -ve voltage to keep RF at nil from the driving radio, until such time as all the relays have gone clunk. Once that's happened the -ve voltage is removed and the RF allowed to flow.

Secondly there's a sequencer to drive the TX and RX co-ax relays plus turn on the main DC supply to the PA and it's bias. I have taken the advice from W1PQL and switched both the main DC supply and the bias off during RX. The main DC supply is switched by an external FET switch and the bias by an external relay as the current requirements of this amp are too high for the board to switch alone.

Here;s the SMPS I am using or the amp; it delivers 28V (it's a 24V unit with a pot adjustment) plus a separate 12V output. I can't remember the current rating but this amp needs 11 Amps at 28V so there should be more than enough here.

In the image below you can see the bulkhead N-Type connectors for the outside world, the control board, the external FET switch and the N-Type relay on the amp output. There's an SMA relay on the input which you can just see the side of on the far left of the picture. The second image shows the SMA relay much clearer.

Here's a close up of the innards of the amp itself:

Now, the control board would also control a fan based on a thermistor input - however I'm just wiring the fan on permanently in this build. It would also take a feed from a directional coupler and switch the amp off in the event of high SWR on the output - a most excellent idea - however, I don't have a directional coupler that will work at these frequencies so I guess we are going to risk it....

Chopsey AKA Bastard Cat from Hell hasn't helped much today:

Local conditions.

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