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Monday, 26 December 2016

Sequencing Secrets


I've been thinking some more about the 13cm project I have on the go, more importantly how I am going to arrange all the bits together.

Firstly we have a 13cm VLNA from G4DDK. I've started the build of this project - this is extreme soldering! the bits are very tiny indeed.

Here's where I am at with the project, unfortunately the last chip cap has made a bid for freedom and is in the carpet somewhere. Here partially built:

and here, almost complete all bar the input components:

Now, I also have the transverter from back here plus a ex telecoms PA that I will start to modify later.

I've started to draw the setup, to save on relays, switching and the associated losses, I will run separate feeds to the antenna (or masthead) for TX and RX. Also, due to the complexities associated with bias-T at these frequencies I will also feed power by cable.

I think it needs to look something like this:

So the thing labelled "gubbins" in the diagram above is actually a sequencer. Having built my 23cm amp back here utilised a ultimate amp control board from W6PQL, that included a sequencer and I had the schematic. So I drew this using non SMD components:

In reality it looks like this once built:

Looking at the top of C1 with a 'scope and grounding the D1 PTT line, we see this:

and as the voltage in C1 rises so the difference between the inverting and non-inverting inputs of the four op-amps swap in sequence as the voltage climbs to the power rail. Here you can see the output state change of the Event 1 op-amp in blue against C1 in yellow:

Event 2 happens later and then event 3 and 4. You can also see that they revert back in the opposite order as the voltage in D1 falls when the ground is removed from D1 and the capacitor discharges through D2 & D3.

Here's the timne delay from PTT to Event 1:

Those in the know tell me that these coax relays can bounce, so a delay of 200ms or more may be needed from thr relay power being initialised to any RF heading that way.

More to come!

Local conditions.

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