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Thursday, 22 March 2018

13cm Complete


I've received the PA for the 13cm masthead project and added it to the box with a heatsync and suitable input attenuation:

I haven't stuck it down in the photo hence its a bit wonky.

The documentation with the PA suggests that about 5.1V on the monitor pin is close to PA saturation so I have adjusted my input attenuator to give just over 5V from the PA monitor port with CW key down.

With the output connected via these two attenuators:

to my XL Microwave power meter I am reading -2 dbM so that's about 38 dBm or 6.3 watts - it should be closer to 10 Watts.

To check the value of the attenuator at 2320 MHz, I used the spectrum analyser and tracking generator I made back here in zero span at 2320 MHz, and compared the signal with and without the attenuators, I measure a signal of +10.4 dBm without the attenuator and -29.2 dBm with. So that makes the attenuator 39.7 dB - so pretty much on the money.

Local conditions.


I kept finding my TX/RX switching was going into some kind of oscillation on RX. The unit would rapidly switch between TX and RX until I pulled the power. Oddly (and still somewhat a mystery) this only happened when the +ve voltage to the VLNA was connected to the sequencer. No VLNA power, all fine, attach VLNA power, TX/RX oscillation.

There is a VOX feature in the transverter that switches to TRX on detection of RF on the input; changing that to have a long detection time (a jumper on the transverter board) has cured the problem.

I have no idea either.

As SG labs don't seem to link the transverter datasheet on their site anymore, it's included here for reference.

Wednesday, 21 March 2018

A new approach to 13cm


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 transvertersequencer, 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?

Thursday, 8 March 2018

Yet more on 3cm (10 GHz)


Following my efforts last time, I managed to get my hands on a 10GHz power amplifier (of sorts):

 This delivers a huge 1W out on 10368 MHz and requires 50mW drive.

According to the transverter manual, I need a sequencer to work this kind of set up properly:

It seems a little strange to me as the Transverter is put into TX first, then the changeover relay and then the PA. I would have thought the relay, PA then transverter so we generate RF last, but hey-ho.

I did a quick design of a simple sequencer:

And here it is prototyped on the bench:

It was giving me about 500ms delay between the relay and the PA on TX:

and about half of that on TX Off:

So I made the circuit on some veroboard and stuck it to the top of the PA:

I also made a latching relay driver from here and bunged it all in a bigger box.

Now, I configured my XL Microwave power meter to read frequency and power and hooked it to the transverter output and adjusted the TX gain to give me 20dBm out. I then hooked that to the input of the PA.

I'm reading about 27dBm out on TX which is 3dB short of target (so half power!). The PA has a voltage point to measure TX power and the sheet that came with it says 2.7V is 1W out, I'm measuring more like 3.5V at that pin so implying that I am over-driving the PA. It's so difficult at these frequencies to know whats accurate and whats not. When I measure the output of the transverter I have to use a 20dB attenuation - I don't know how accurate that is at 10 GHz for a start! Then there will also be losses in the interconnecting cables; so it's all a bit of a muddle.

So I am suitably confused at the moment!

Here's our lovely Florrie Cat proudly sitting in an empty egg box:

Local conditions.

Thursday, 1 March 2018

Arduino CW Beacon


I was messing about on 10GHz and I wanted to get my FT-817 (the IF drive for the 10GHz transverter) to "beacon". As there is no such function in the radio, I wrote some very simple Arduino code and used a Nano to key the CW line to the radio.

I've put the code here if anyone is interested.

It is the most simple thing in the world.....

The two wires from GND and D2 simply connect directly to the CW key jack on the FT-817.

Local conditions.