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Wednesday, 31 May 2017

I think its working


Following from my musings last time on the BATC Portsdown project; I think mine is now up and running.

I've been working on a box for the project and the various bits and bobs are now inside:

So, following the suggested test setup I've configured the transmitter to TX on 1255 MHz using 2000KS (thats the symbol rate) and my newly invented DATV receiver from here sees this:

So I conclude it's working. Now to try and stream some video and then think about external amplifiers and filters!

I've decided to initially aim at 146.5Mhz in the NoV only allocation above 2M as my first target frequency.

I've set the Portsdown to tx on 146.5MHz, 7/8FEC with a symbol rate of 333KS. The output close up looks like this:

Checking on the harmonic content we see this:

So I made a LPF (needed!) and now the output looks like this:

In reality the LPF looks like this:

It is a standard 3 inductor design with 22pf at each "end" and 43pf in the middle two locations. The inductors are 3 turns open wound on a 6mm drill bit.

I've hooked up the BATC supplied EasyCap USB device to the Portsdown and I have coupled up my AntennaCam and we can see this on the MiniTiouner receiver we made here:

So, the next thing I need is a TestCard for TX; enter another great use of a Rasperry Pi. I've installed the software called TCANIM from here. I've followed the instructions to the letter but I cant seem to get a video signal out of the Pi AV socket....

Local conditions.

Tuesday, 30 May 2017

Portsdown where?


As part of the project I mentioned last time, I've started to construct the hardware for the BATC Portsdown project.

The fist board I have tackled has been the LO filter. This goes post the AD4135 LO which uses the same development board as we used on the 4.4 GHz signal generator.

This is extreme, extreme soldering! I've invested in a flux pen of decent quality from Farnell and that's made my life much easier. Previously I was using some cheap eBay sourced flux which was a load of dingos kidneys.

Here's the results of my days soldering:

There's basically a 2 bit input thats status determines which of the three on board filters are in line (or bypassed on 23cm). I've tested this and can see three filters, not too sure about their shape though.





Looks a bit odd to me, but lets see.

Local conditions.

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.