A new approach to 13cm

Well,

You may recall back here where I built a 13cm capability. I've decided to go about it a different way.

Instead of sending lots of RF up lossy coax with a fixed station arrangement, I'm going to generate less RF but right next to the antennamabob and make the whole setup portable.

So here we have 13cm take 2:

In here we have the transverter, sequencer, the VLNA, a SMA relay and driver, plus this PA will also fit; but I dont have the PA yet. The wonky board you can see is a FET driver to switch the PA bias supply on during TX; that will be mounted on top of the PA once I have it here.

I've hooked up my XL Microwave power meter to the output of the Transverter via a 40dB attenuator and I am measuring:

about 32.5 dBm so close to 2 watts - exactly on the money of the transverter spec.

The PA needs a 1W drive so I will have to attenuate the TX signal by 3dB to get that correct.

Good, egh?

I'm about there!

Well,

You'll remember last time I started modifying the 13cm PA I had acquired. Well, I think it's about done.

What we have is the modified PA, an Arduino Nano plus some software to monitor:

• PA Temperature
• Forward power
• Reflected power
• Bias current (driver, Left and Right PA MOSFETs separately)

and trip if anything goes out of bonk.

The Amplifier now looks like this:

I've just to wire up the Analogue inputs in this image. There are three "status" LEDs on the front panel; one for "All OK", one for "It's gone horribly wrong" and a final one for "TX". If you connect the serial cable to the Nano then there is a status line repeatedly output giving the details of all the inputs read and their values.

The connector on the main board of the Amp is configured like this:

and it was therefore a fairly simple case of wiring the various pins to the I/O of the Nano and writing some code. I stole a lot of the ideas for the code from Mike G0MJW - but there are quite a few differences between what I have ended up with and what Mike created a few years ago.

The 9V line to the bias and other bits of the board is permanently on; the 28V line is also enabled all the time but switched bu a FET switch under software control. This switch is the same as the one in the sequencer, it's just altered slightly for 28V:

I've stuck the source code here if anyone is interested.

Time now for some testing.....

**UPDATE**

A couple of minor software mods (updated on the link above) during testing and all seems to be OK. I am not entirely convinced about the scaling values used to convert from the ADC readings into the value units, but time will tell.

Here's the whole system - there's an IF cable from there to my IC9100 which is used on 70cm as the rig for the transverter:

**UPDATE 2**

I found that the cheap Chinese sourced FET I was using to switch the 28V line had failed, but my software didn't pick up on this. I've changed the device for a Farnell sourced component and also added an extra digital line to the Arduino to monitor the voltage on the 28V supply to the PA. There's a potential divider added to the FET switch board to provide 3.3V when the 28V line is high, this is in turn connected to pin 9 of the Arduino and the code linked above modified accordingly. There is an additional trip condition when the 28V line is High and we are in RX or the 28V line is Low and we are in TX.

Here you can see the potential divider I have added to the FET switch to monitor the 28V line status:

And here is the finished article:

Finally - All coming together

Well,

There have been many musings recently all building to a 13cm (2.3GHz) system:

1. The Transverter
2. The VLNA
3. The masthead enclosure and switching
4. The antennamabob
5. The sequencer

So now I'm trying to glue it all together!

The case is a bit tall, but it's all I had. I created a very simple PSU based on a 723 voltage regulator and a 2SC5200 as a pass transistor - I have tried to over-rate the power supply (please excuse the terrible layout below):

That plus the transverter and sequencer we played with previously.

The Gubbins basically remains the same as designed:

So, there is a VLNA at the masthead next to the antenna and two co-ax feeds back to the shack - one for TX and one for RX. The TX is 15mm Web-600 and the RX line Westflex 103.

This is all driven from 423 Mhz multi-mode transceiver - I plan to use the IC9100.

Now for the linear amplifier, I picked up one of these for basically scrap metal value:

There is information on modifying the unit for our purposes here.

As ever, the first thing required is to take it to bits, once you get the bottom off this is revealed:

then that board comes out and slung to one side:

then we remove another million screws and get the screen out of the way:

and then the top of those two boards gets slung:

Now we need to lift a cap off the board and connect in where our RF feed will be:

Now for the bias for those lovely MOSFETS....  here's the board with my bodged bias circuit:

I reached out through the UK Microwavers Yahoo! group and have received some very useful information including this:

I've added an Arduino Nano into my enclosure and may have a bash at reading some of those control signals:

And throughout, Florrie the Ham cat has been assisting:

Next, a bit of testing.....

Local conditions.