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Sunday, 11 June 2017

Its brick time!

Well,

To compliment the DATV transmitter I made here, I've been building a PA rated at 60W RF out - it will be used at way less than this, but for any kind of TV transmission we need loads of overhead in the PA to avoid nastyness in the output.

The PA is this design here, the PCB from G4DDK.

The module itself is a RA60H1317M1A and I got mine from Anglia Live.

The heatsink feels like a great find, I saw it listed on eBay by JPG Electronics in Chesterfield; as it's just up the road I paid a visit - what a find! Loads of goodies!

Anyhow, here the PA under test:



The TX RF from the Portsdown will come in through the LPF we tested last time; then through the PA and out through the SMA relay. The RX Signal will pass through the BPF also from last time, and to the Receiver we made here.

The relay was one of a number I found some time ago; they are Ducommun latching 12V SMA relays. These need a driver circuit which I made like this:


and that's built on the veroboard you can see at the front of the PA block. The output lines do this when the PTT is grounded and then disconnected:



All I need to decide now is what to set the Bias voltage to on the PA - not sure about that!

Throughout Miss Luna Cat has been supervising from a distance:


Good, egh?

Saturday, 3 June 2017

Filters Filters Filters

Well,

Following on from the success of last time; it was time to make some filters around the 146.5 MHz DATV frequency on the NoV allocated bit of spectrum we have above the 2M band.

I've also built up a kit I have had here for a while, it's a PGA144 from G4DDK.


So at the top we have the PGA144, middle is the LPF and bottom is the BPF. The designs are really quite simple - just ask if you need the details. Here's the spectrum from all three:


The yellow is the PGA144 - it has a 20dB attenuator at the input so the signals are actually 20dB higher than shown - the gain at 145MHz is exactly 20dB.

The purple is the LPF being swept and looks just fine.

The Blue is my BPF which I am very pleased with - it looks great.

So next will be a 60W "brick" amplifier for 146.5 MHz - waiting for the bits but I have to go work in foreign parts for a week or two so will pick this up on my return.

Local conditions.

Wednesday, 31 May 2017

I think its working

Well,

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?

Well,

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.

4M:


2M:


70cm:


23cm:


Looks a bit odd to me, but lets see.

Local conditions.

Sunday, 28 May 2017

Telly - really?

Well,

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?

Well,

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.

Friday, 7 April 2017

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: