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Sunday, 28 May 2017

Telly - really?


I've started to play with Digital Television and the broadcasting thereof. The fist part of the puzzle was to construct a means of receiving my own signals so I chose the Minitiouner from the BATC of which I am a member.

I bought the PCBs and the bits and bobs from the BATC shop and have built the project:

The transmit side of things will be from the well publicised BATC project the Portsdown

There is quite a bit to this project, hardware wise, but initially we need a Raspberry Pi and some software to run something they call "Ugle Mode" whereby you can send a picture across the shack.

Well, it works:

So its time to progress the hardware some more and move forward with the transmitter side of the project.

Interesting start, egh?

Monday, 15 May 2017

A tracking what?


As part of the fiddling I've been doing on 13cm, I've been using the new to me (read old) spectrum analyser I have. It covers from about 9KHz up to 22GHz.

You may also recall not so long ago, that I made a signal generator that covered up to 4.4 GHz.

As this spectrum analyser has a 1st IF output socket, it struck me that I could probably make some kind of tracking generator to go with it. Actually the IF output will be doing the tracking, all I need is a signal and a mixer.

Some experimentation allowed me to discover that on the low range, the Spectrum Analyser has an IF output of 3910 MHz plus the tuned frequency.

I've made myself a simple Arduino Nano and AD4351 combination:

The source code for the above is here. I've not done anything clever at all, just used the Analogue Devices software I showed here to calculate the required registry values and then hard coded them into the Nano.

That gives me the 3910 MHz signal required. We then subtract that from the IF output from the Spectrum Analyser using a simple and small Mini Circuits mixer:

Then I've added a low cost return loss bridge from ebay:

Whilst it's not lab grade, in this example you can clearly see the resonant frequency of the antenna that's connected as the Device Under Test:

The difference between the trace with the DUT socket open (the thicker line) and the other trace is the return loss at the specific frequency.

You can see that the open circuit sweep is nowhere near flat - so there are all sorts of issues with this setup, but as a basic antenna analyser up to about 3GHz this works just fine.

All the while, Florrie the ham cat has been sitting on my rotator manual which I am consulting as the display bulb has died:

Local conditions.